Methylnaltrexone Bromide – Uses, Dosage, Side Effects, Interaction

Last updated: February 8, 2026Reviewed date: February 8, 2026Reading time: 64 min read

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Methylnaltrexone is a methyl derivative of noroxymorphone with selective, opioid-receptor antagonistic activity. Methylnaltrexone is a member of phenanthrenes. Methylnaltrexone displaces opioids from peripheral opioid receptors in the gastrointestinal tract, the bladder, and the skin, resulting in decreases in opioid-related constipation, urinary retention, and pruritis, respectively. Methylnaltrexone does not cross the blood-brain barrier and does not affect the centrally-mediated analgesic effect of opioids. Methylnaltrexone Bromide is the...

Key Takeaways

This article explains Mechanism of action in simple medical language.
This article explains Indications in simple medical language.
This article explains Contraindications in simple medical language.
This article explains Dosage in simple medical language.

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Written byDr. Harun Ar Rashid, MD - Arthritis, Bones, Joints Pain, Trauma, and Internal Medicine Specialist

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Definition

Methylnaltrexone is a methyl derivative of noroxymorphone with selective, opioid-receptor antagonistic activity. Methylnaltrexone is a member of phenanthrenes. Methylnaltrexone displaces opioids from peripheral opioid receptors in the gastrointestinal tract, the bladder, and the skin, resulting in decreases in opioid-related constipation, urinary retention, and pruritis, respectively. Methylnaltrexone does not cross the blood-brain barrier and does not affect the centrally-mediated analgesic effect of opioids.

Methylnaltrexone Bromide is the bromide salt form of methylnaltrexone, a methyl derivative of noroxymorphone with selective, peripherally-acting mu-opioid receptor antagonistic activity. Methylnaltrexone displaces opioids from peripheral opioid receptors in the gastrointestinal tract, the bladder, and the skin, thereby reversing the opioid-related peripheral side effects, such as constipation, urinary retention, and pruritis, respectively. Unlike naltrexone and due to the presence of a positively charged nitrogen atom in methylnaltrexone, this agent does not cross the blood-brain barrier and does not affect the centrally-mediated analgesic effect of opioids.

Methylnaltrexone is a methyl derivative of noroxymorphone with selective, opioid-receptor antagonistic activity. Methylnaltrexone displaces opioids from peripheral opioid receptors in the gastrointestinal tract, the bladder, and the skin, resulting in decreases in opioid-related constipation, urinary retention, and pruritis, respectively. Methylnaltrexone does not cross the blood-brain barrier and does not affect the centrally-mediated analgesic effect of opioids.

Mechanism of action

Methylnaltrexone is a peripherally-acting μ-opioid antagonist that acts on the gastrointestinal tract and inhibits an opioid-induced decrease in gastric motility and transit time. Because methylnaltrexone is a quaternary derivative of naltrexone, it produces its gastrointestinal effects without producing analgesic effects or withdrawal symptoms as it does not cross the blood-brain barrier.

Use of opioids induces slowing of gastrointestinal motility and transit. Following remifentanil administration, the methylnaltrexone and placebo groups showed no change in pupillary constriction while the naloxone group showed a marked change over the time interval tested.

Methylnaltrexone is a peripheral-acting mu-opioid receptor antagonist and does not cross the blood-brain barrier.^[rx] Methylnaltrexone has restricted access through the blood-brain barrier because it is a quaternary amine, which carries a positive charge when in a solution and more has polarity with lower lipid solubility than a lot of the opioid agonists used for pain treatment.^[rx] The peripheral action of methylnaltrexone makes it effective for decreasing the constipating effects of opioids, without interfering with the analgesic effects (of opioids) on the central nervous system.^[rx] This is the primary characteristic that makes methylnaltrexone behave differently than naltrexone.^[10]

Furthermore, as methylnaltrexone cannot cross the blood–brain barrier, it does not reverse the pain-killing properties of opioid agonists or cause withdrawal symptoms, but since a small portion of analgesia comes from the peripheral opioid receptors, it can increase pain from inflammatory conditions such as arthritis.

Indications

Treatment of opioid-induced constipation in advanced-illness patients who are receiving palliative care when the response to usual laxative therapy has not been sufficient.
For the treatment of opioid-induced constipation in adult patients with chronic non-cancer pain or advanced illness who are receiving palliative care, when the response to laxative therapy has not been sufficient.

Use in Cancer

Methylnaltrexone bromide is approved to treat:

Constipation is caused by the use of opioids. It is used in adults with pain caused by cancer or treatment for cancer or by another advanced disease.

Contraindications

cancer of the stomach or intestines
stomach or intestinal ulcer
blockage of the stomach or intestine
liver problems
excessive diarrhea
chronic diarrhea
an enlargement of the intestine with stopped bowel function called megacolon
chronic kidney disease stage 3A (moderate)
chronic kidney disease stage 3B (moderate)
chronic kidney disease stage 4 (severe)
chronic kidney disease stage 5 (failure)
Child-Pugh class C liver impairment

Dosage

Strengths: 12 mg/0.6 mL; 150 mg; 8 mg/0.4 mL

Constipation – Drug-Induced

Opioid-Induced Constipation in Patients with Chronic Non-Cancer Pain:

Oral: 450 mg orally once a day in the morning
Parenteral: 12 mg subcutaneously once a day
Prior to initiation, discontinue all maintenance laxative therapy; laxatives can be used as needed for suboptimal response after 3 days.
Patients should be within close proximity to a bathroom once this drug is administered.
Re-evaluate the continued need for this drug when the opioid regimen is changed to avoid adverse reactions.

Opioid-Induced Constipation in Patients with Advanced Illness:
Parenteral: Weight-based dosing: Administer subcutaneously every other day as needed, but no more frequently than 1 dose in a 24-hour period:

Less than 38 kg: 0.15 mg/kg
38 kg to less than 62 kg: 8 mg (0.4 mL)
62 kg to 114 kg: 12 mg subcutaneously (0.6 mL)
More than 114 kg: 0.15 mg/kg subcutaneously
To determine injection volume for patients whose weight is less than 38 kg or more than 114 kg: multiply patient weight (kg) by 0.0075 and round up to the nearest 0.1 mL

Renal Dose Adjustments

Moderate to severe renal impairment (CrCl less than 60 mL/min):

Chronic Non-Cancer Pain:

Oral: 150 mg orally once a day in the morning
Parenteral: 6 mg subcutaneously once a day

Advanced Illness:
Parenteral: weight-based dosing:

Less than 38 kg: 0.075 mg/kg subcutaneously every other day
38 to less than 62 kg: 4 mg subcutaneously every other day
62 to 114 kg: 6 mg subcutaneously every other day
Greater than 114 kg: 0.075 mg/kg subcutaneously every other day
To determine injection volume for patients whose weight is less than 38 kg or more than 114 kg: multiply patient weight (kg) by 0.0075 and round up to the nearest 0.1 mL

Liver Dose Adjustments

Moderate to severe hepatic impairment (Child-Pugh Class B or C):

Chronic Non-Cancer Pain: Oral: 150 mg orally once a day in the morning

Severe hepatic impairment: Chronic Non-Cancer Pain or Advanced illness:

Parenteral: Weight-based dosing:
Less than 38 kg: 0.075 mg/kg subcutaneously every other day
38 to less than 62 kg: 4 mg subcutaneously every other day
62 to 114 kg: 6 mg subcutaneously every other day
Greater than 114 kg: 0.075 mg/kg subcutaneously every other day
To determine injection volume for patients whose weight is less than 38 kg or more than 114 kg: multiply patient weight (kg) by 0.0075 and round up to the nearest 0.1 mL

General:

If treatment with opioid pain medication is discontinued, this drug should be discontinued; if the opioid regimen is changed, re-evaluate the continued need of this drug.
In clinical trials in patients with advanced illness, this drug was administered concomitantly with a laxative regimen.
In patients with chronic non-cancer pain, all maintenance laxative therapy should be discontinued prior to initiating therapy; laxatives can be used as needed after 3 days.
This drug has been shown to be efficacious in patients who have taken opioids for at least 4 weeks; sustained exposure to opioids prior to starting this drug may increase the patient’s sensitivity to this drug

Patient advice:

Patients should be instructed to be within close proximity to toilet facilities once this drug is taken.
Patients should be instructed to seek medical attention promptly if unusually severe, persistent, or worsening abdominal pain or diarrhea develops.
Patients should understand that symptoms of opioid withdrawal such as sweating, chills, anxiety, irritability, and yawning may occur.
Patients should speak to health care professionals if they become pregnant, intend to become pregnant, or are breastfeeding.

Side Effects

The Most Common

vomiting
sweating
chills
anxiety
yawning
headache
abdominal pain and swelling
muscle spasms
runny nose
severe diarrhea
severe abdominal pain

More Common

severe or ongoing diarrhea;
extreme dizziness, or feeling like you might pass out;
bloody or tarry stools, coughing up blood or vomit that looks like coffee grounds;
nausea or vomiting that are new or worsening symptoms; or
symptoms of opioid medicine withdrawal–anxiety, sweating, chills, yawning, stomach pain, diarrhea.
stomach pain, gas, bloating;
mild nausea or diarrhea;
headache, muscle spasms;
dizziness, tremors, feeling anxious;
runny nose; or
chills, sweating, or hot flashes.
Chills
diarrhea
fear or nervousness
increased sweating
severe abdominal or stomach pain
severe or persistent diarrhea
yawning

Rare

Full or bloated feeling
headache
muscle spasms
pressure in the stomach
runny nose
swelling of the abdominal or stomach area
vomiting

Drug Interactions

DRUG	INTERACTION
Abacavir	Abacavir may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Aceclofenac	Aceclofenac may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Acemetacin	Acemetacin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Acetaminophen	Acetaminophen may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Acetazolamide	Acetazolamide may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Acetylsalicylic acid	Acetylsalicylic acid may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Aclidinium	Methylnaltrexone may decrease the excretion rate of Aclidinium which could result in a higher serum level.
Acrivastine	Methylnaltrexone may decrease the excretion rate of Acrivastine which could result in a higher serum level.
Acyclovir	Acyclovir may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Adefovir dipivoxil	Adefovir dipivoxil may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Albutrepenonacog	Methylnaltrexone may decrease the excretion rate of Albutrepenonacog alfa which could result in a higher serum level.
Alclofenac	Alclofenac may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Aldesleukin	Aldesleukin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Alfentanil	The therapeutic efficacy of Alfentanil can be decreased when used in combination with Methylnaltrexone.
Allopurinol	Allopurinol may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Almasilate	Methylnaltrexone may decrease the excretion rate of Almasilate which could result in a higher serum level.
Almotriptan	Almotriptan may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Alogliptin	Alogliptin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Alprazolam	Alprazolam may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Alvimopan	Alvimopan may increase the opioid antagonism activities of Methylnaltrexone.
Amantadine	Amantadine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Amikacin	Methylnaltrexone may decrease the excretion rate of Amikacin which could result in a higher serum level.
Amiloride	Amiloride may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Aminophenazone	Aminophenazone may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Amitriptyline	Amitriptyline may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ammonium chloride	Ammonium chloride may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Amoxicillin	Amoxicillin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Amphetamine	Amphetamine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Amphotericin B	Amphotericin B may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ampicillin	Ampicillin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Amrinone	Amrinone may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ancestim	Methylnaltrexone may decrease the excretion rate of Ancestim which could result in a higher serum level.
Antihemophilic	Methylnaltrexone may decrease the excretion rate of Antihemophilic factor (recombinant), PEGylated which could result in a higher serum level.
Antipyrine	Antipyrine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Antithrombin III human	Methylnaltrexone may decrease the excretion rate of Antithrombin III human which could result in a higher serum level.
Antrafenine	Antrafenine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Apalutamide	Methylnaltrexone may decrease the excretion rate of Apalutamide which could result in a higher serum level.
Apremilast	Apremilast may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Arformoterol	Arformoterol may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Arsenic trioxide	Arsenic trioxide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Atazanavir	Atazanavir may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Atomoxetine	Atomoxetine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Auranofin	Auranofin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Aurothioglucose	Methylnaltrexone may decrease the excretion rate of Aurothioglucose which could result in a higher serum level.
Azacitidine	Azacitidine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Azathioprine	Azathioprine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Azelaic acid	Azelaic acid may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Aztreonam	Aztreonam may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Bacitracin	Bacitracin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Baclofen	Baclofen may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Balsalazide	Balsalazide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Baricitinib	Methylnaltrexone may decrease the excretion rate of Baricitinib which could result in a higher serum level.
Bendroflumethiazide	Bendroflumethiazide may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Benorilate	Benorilate may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Benoxaprofen	Benoxaprofen may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Benserazide	Methylnaltrexone may decrease the excretion rate of Benserazide which could result in a higher serum level.
Benzatropine	Benzatropine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Benzhydrocodone	The therapeutic efficacy of Benzhydrocodone can be decreased when used in combination with Methylnaltrexone.
Benznidazole	Methylnaltrexone may decrease the excretion rate of Benznidazole which could result in a higher serum level.
Benzthiazide	Benzthiazide may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Benzydamine	Benzydamine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Bepotastine	Bepotastine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Bicisate	Methylnaltrexone may decrease the excretion rate of Bicisate which could result in a higher serum level.
Bismuth subgallate	Methylnaltrexone may decrease the excretion rate of Bismuth subgallate which could result in a higher serum level.
Bisoprolol	Bisoprolol may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Bisoxatin	Methylnaltrexone may decrease the excretion rate of Bisoxatin which could result in a higher serum level.
Bleomycin	Bleomycin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Brivaracetam	Brivaracetam may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Bromazepam	Bromazepam may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Bromotheophylline	Bromotheophylline may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Budesonide	Budesonide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Bumadizone	Bumadizone may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Bumetanide	Bumetanide may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Buprenorphine	Buprenorphine may increase the opioid antagonism activities of Methylnaltrexone.
Bupropion	Bupropion may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Buspirone	Buspirone may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Butabarbital	Butabarbital may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Butorphanol	Butorphanol may increase the opioid antagonism activities of Methylnaltrexone.
Canagliflozin	Methylnaltrexone may decrease the excretion rate of Canagliflozin which could result in a higher serum level.
Canrenoic acid	Canrenoic acid may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Capecitabine	Capecitabine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Capreomycin	Methylnaltrexone may decrease the excretion rate of Capreomycin which could result in a higher serum level.
Carbamazepine	Methylnaltrexone may decrease the excretion rate of Carbamazepine which could result in a higher serum level.
Carbidopa	Carbidopa may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Carboplatin	Carboplatin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Carmustine	Carmustine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Carprofen	Carprofen may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cefaclor	Cefaclor may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cefadroxil	Cefadroxil may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cefalotin	Cefalotin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cefamandole	Cefamandole may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cefapirin	Cefapirin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cefazolin	Cefazolin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cefdinir	Cefdinir may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cefditoren	Cefditoren may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cefepime	Cefepime may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cefmenoxime	Cefmenoxime may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cefmetazole	Cefmetazole may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cefonicid	Cefonicid may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cefoperazone	Cefoperazone may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.

Ceforanide	Ceforanide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cefotaxime	Cefotaxime may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cefotetan	Cefotetan may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cefotiam	Cefotiam may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cefoxitin	Cefoxitin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cefpiramide	Cefpiramide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cefpirome	Cefpirome may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cefpodoxime	Cefpodoxime may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cefprozil	Cefprozil may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cefradine	Cefradine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ceftaroline	Ceftaroline fosamil may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ceftazidime	Ceftazidime may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ceftibuten	Ceftibuten may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ceftizoxime	Ceftizoxime may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ceftobiprole	Ceftobiprole may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ceftolozane	Methylnaltrexone may decrease the excretion rate of Ceftolozane which could result in a higher serum level.
Ceftriaxone	Ceftriaxone may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cefuroxime	Cefuroxime may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Celecoxib	Celecoxib may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cephalexin	Cephalexin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cephaloglycin	Cephaloglycin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Certolizumab	Methylnaltrexone may decrease the excretion rate of Certolizumab pegol which could result in a higher serum level.
Cetirizine	Cetirizine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cevimeline	Cevimeline may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Chloral hydrate	Chloral hydrate may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Chloroquine	Chloroquine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Chlorothiazide	Chlorothiazide may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Chlorpromazine	Chlorpromazine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Chlorpropamide	Chlorpropamide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Chlorthalidone	Chlorthalidone may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Chlorzoxazone	Chlorzoxazone may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Choline C 11	Methylnaltrexone may decrease the excretion rate of Choline C 11 which could result in a higher serum level.
Choline magnesium	Choline magnesium trisalicylate may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Choline salicylate	Methylnaltrexone may decrease the excretion rate of Choline salicylate which could result in a higher serum level.
Chondroitin sulfate	Methylnaltrexone may decrease the excretion rate of Chondroitin sulfate which could result in a higher serum level.
Chromic chloride	Methylnaltrexone may decrease the excretion rate of Chromic chloride which could result in a higher serum level.
Chromic nitrate	Methylnaltrexone may decrease the excretion rate of Chromic nitrate which could result in a higher serum level.
Chromium	Methylnaltrexone may decrease the excretion rate of Chromium which could result in a higher serum level.
Chromium gluconate	Methylnaltrexone may decrease the excretion rate of Chromium gluconate which could result in a higher serum level.
Chromium nicotinate	Methylnaltrexone may decrease the excretion rate of Chromium nicotinate which could result in a higher serum level.
Chromous sulfate	Methylnaltrexone may decrease the excretion rate of Chromous sulfate which could result in a higher serum level.
Cidofovir	Cidofovir may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cilostazol	Cilostazol may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cimetidine	Cimetidine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ciprofloxacin	Ciprofloxacin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cisplatin	Methylnaltrexone may decrease the excretion rate of Cisplatin which could result in a higher serum level.
Clevidipine	Clevidipine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Clobazam	Clobazam may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Clofarabine	Clofarabine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Clomipramine	Clomipramine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Clonazepam	Clonazepam may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Clorazepic acid	Clorazepic acid may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Clove oil	Methylnaltrexone may decrease the excretion rate of Clove oil which could result in a higher serum level.
Clozapine	Clozapine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Codeine	The therapeutic efficacy of Codeine can be decreased when used in combination with Methylnaltrexone.
Colchicine	Colchicine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Colistimethate	Colistimethate may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Colistin	Methylnaltrexone may decrease the excretion rate of Colistin which could result in a higher serum level.
Conivaptan	Conivaptan may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Conjugated estrogens	Conjugated estrogens may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Corifollitropin alfa	Methylnaltrexone may decrease the excretion rate of Corifollitropin alfa which could result in a higher serum level.
Cyanocobalamin	Cyanocobalamin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cyclopenthiazide	Cyclopenthiazide may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Cyclosporine	Cyclosporine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Cyclothiazide	Cyclothiazide may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Dabigatran etexilate	Dabigatran etexilate may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Dacarbazine	Dacarbazine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Dalfampridine	Dalfampridine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Daptomycin	Daptomycin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Deferiprone	Methylnaltrexone may decrease the excretion rate of Deferiprone which could result in a higher serum level.
Delafloxacin	Methylnaltrexone may decrease the excretion rate of Delafloxacin which could result in a higher serum level.
Desipramine	Desipramine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Desmopressin	Desmopressin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Desvenlafaxine	Desvenlafaxine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Deutetrabenazine	Methylnaltrexone may decrease the excretion rate of Deutetrabenazine which could result in a higher serum level.
Dexibuprofen	Dexibuprofen may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Dexketoprofen	Dexketoprofen may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Dexmedetomidine	Dexmedetomidine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Dexpanthenol	Methylnaltrexone may decrease the excretion rate of Dexpanthenol which could result in a higher serum level.
Dexrazoxane	Dexrazoxane may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Dextran	Methylnaltrexone may decrease the excretion rate of Dextran which could result in a higher serum level.
Dextropropoxyphene	The therapeutic efficacy of Dextropropoxyphene can be decreased when used in combination with Methylnaltrexone.
Dezocine	Dezocine may increase the opioid antagonism activities of Methylnaltrexone.
Diamorphine	The therapeutic efficacy of Diamorphine can be decreased when used in combination with Methylnaltrexone.
Diatrizoate	Diatrizoate may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Diazepam	Diazepam may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Dichlorobenzyl alcohol	Methylnaltrexone may decrease the excretion rate of Dichlorobenzyl alcohol which could result in a higher serum level.
Diclofenac	Diclofenac may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Diclofenamide	Diclofenamide may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Dicyclomine	Dicyclomine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Didanosine	Didanosine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Dienogest	Methylnaltrexone may decrease the excretion rate of Dienogest which could result in a higher serum level.
Diflunisal	Diflunisal may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Difluocortolone	Methylnaltrexone may decrease the excretion rate of Difluocortolone which could result in a higher serum level.
Digoxin	Methylnaltrexone may decrease the excretion rate of Digoxin which could result in a higher serum level.
Dihydrocodeine	The therapeutic efficacy of Dihydrocodeine can be decreased when used in combination with Methylnaltrexone.
Dihydrostreptomycin	Dihydrostreptomycin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Dimercaprol	Dimercaprol may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Dimethyl sulfoxide	Dimethyl sulfoxide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Diphenoxylate	The therapeutic efficacy of Diphenoxylate can be decreased when used in combination with Methylnaltrexone.

Disopyramide	Disopyramide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
DL-Methylephedrine	Methylnaltrexone may decrease the excretion rate of DL-Methylephedrine which could result in a higher serum level.
Dobutamine	Dobutamine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Dopamine	Dopamine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Doripenem	Doripenem may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Doxacurium	Doxacurium may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Doxepin	Doxepin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Doxycycline	Doxycycline may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Drospirenone	Drospirenone may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Droxidopa	Droxidopa may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Duloxetine	Duloxetine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Dyphylline	Dyphylline may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Edoxaban	Methylnaltrexone may decrease the excretion rate of Edoxaban which could result in a higher serum level.
Edrophonium	Edrophonium may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Eluxadoline	Eluxadoline may increase the opioid antagonism activities of Methylnaltrexone.
Enalaprilat	Methylnaltrexone may decrease the excretion rate of Enalaprilat which could result in a higher serum level.
Enzalutamide	Methylnaltrexone may decrease the excretion rate of Enzalutamide which could result in a higher serum level.
Eplerenone	Eplerenone may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Epoprostenol	Epoprostenol may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ertapenem	Ertapenem may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Estazolam	Estazolam may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Estradiol	Estradiol may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Estradiol acetate	Methylnaltrexone may decrease the excretion rate of Estradiol acetate which could result in a higher serum level.
Estradiol cypionate	Methylnaltrexone may decrease the excretion rate of Estradiol cypionate which could result in a higher serum level.
Estradiol dienanthate	Methylnaltrexone may decrease the excretion rate of Estradiol dienanthate which could result in a higher serum level.
Estradiol valerate	Methylnaltrexone may decrease the excretion rate of Estradiol valerate which could result in a higher serum level.
Estrone sulfate	Estrone sulfate may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Eszopiclone	Eszopiclone may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Etacrynic acid	Etacrynic acid may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Etafedrine	Methylnaltrexone may decrease the excretion rate of Etafedrine which could result in a higher serum level.
Ethambutol	Ethambutol may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Etodolac	Etodolac may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Etomidate	Etomidate may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Etonogestrel	Etonogestrel may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Etoricoxib	Etoricoxib may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Eucalyptus oil	Methylnaltrexone may decrease the excretion rate of Eucalyptus oil which could result in a higher serum level.
Ezogabine	Ezogabine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Fenbufen	Fenbufen may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Fenofibrate	Fenofibrate may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Fenofibric acid	Methylnaltrexone may decrease the excretion rate of Fenofibric acid which could result in a higher serum level.
Fenoldopam	Fenoldopam may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Fenoprofen	Fenoprofen may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Fentanyl	The therapeutic efficacy of Fentanyl can be decreased when used in combination with Methylnaltrexone.
Fesoterodine	Fesoterodine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Finerenone	Finerenone may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Flavoxate	Flavoxate may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Floctafenine	Floctafenine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Florbetaben (18F)	Methylnaltrexone may decrease the excretion rate of Florbetaben (18F) which could result in a higher serum level.
Florbetapir (18F)	Methylnaltrexone may decrease the excretion rate of Florbetapir (18F) which could result in a higher serum level.
Floxuridine	Floxuridine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Fluconazole	Fluconazole may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Flucytosine	Flucytosine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Fludeoxyglucose (18F)	Methylnaltrexone may decrease the excretion rate of Fludeoxyglucose (18F) which could result in a higher serum level.
Flumazenil	Flumazenil may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Fluocinolone acetonide	Fluocinolone acetonide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Flurazepam	Flurazepam may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Flurbiprofen	Flurbiprofen may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Flutamide	Flutamide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Fluvoxamine	Fluvoxamine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Folic acid	Folic acid may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Fomepizole	Fomepizole may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Fondaparinux	Fondaparinux may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Formestane	Methylnaltrexone may decrease the excretion rate of Formestane which could result in a higher serum level.
Foscarnet	Foscarnet may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Fosfomycin	Fosfomycin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Fosinopril	Fosinopril may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Framycetin	Framycetin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Furosemide	Furosemide may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Gabapentin enacar	Methylnaltrexone may decrease the excretion rate of Gabapentin enacarbil which could result in a higher serum level.
Gadobenic acid	Gadobenic acid may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Gadodiamide	Gadodiamide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Gadofosveset trisodium	Gadofosveset trisodium may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Gadopentetic acid	Gadopentetic acid may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Gadoteric acid	Methylnaltrexone may decrease the excretion rate of Gadoteric acid which could result in a higher serum level.
Gadoteridol	Gadoteridol may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ganciclovir	Ganciclovir may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Gemcitabine	Gemcitabine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Gemfibrozil	Gemfibrozil may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Gentamicin	Methylnaltrexone may decrease the excretion rate of Gentamicin which could result in a higher serum level.
Gimeracil	Methylnaltrexone may decrease the excretion rate of Gimeracil which could result in a higher serum level.
Givosiran	Givosiran may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Glipizide	Glipizide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Glycerol phenylbutyrate	Methylnaltrexone may decrease the excretion rate of Glycerol phenylbutyrate which could result in a higher serum level.
Golodirsen	Methylnaltrexone may decrease the excretion rate of Golodirsen which could result in a higher serum level.
Goserelin	Goserelin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Guanethidine	Guanethidine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Guanfacine	Guanfacine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Haloperidol	Haloperidol may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Hydralazine	Hydralazine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Hydrochlorothiazide	Hydrochlorothiazide may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Hydrocodone	The therapeutic efficacy of Hydrocodone can be decreased when used in combination with Methylnaltrexone.
Hydroflumethiazide	Hydroflumethiazide may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Hydromorphone	The therapeutic efficacy of Hydromorphone can be decreased when used in combination with Methylnaltrexone.
Hydroxocobalamin	Hydroxocobalamin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Hydroxyethyl Starch	Methylnaltrexone may decrease the excretion rate of Hydroxyethyl Starch which could result in a higher serum level.
Ibuprofen	Ibuprofen may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ibutilide	Ibutilide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Icatibant	Icatibant may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Icosapent	Icosapent may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Idarucizumab	Methylnaltrexone may decrease the excretion rate of Idarucizumab which could result in a higher serum level.

Idebenone	Methylnaltrexone may decrease the excretion rate of Idebenone which could result in a higher serum level.
Ifosfamide	Ifosfamide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Imipramine	Imipramine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Indapamide	Indapamide may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Indigotindisulfonic	Methylnaltrexone may decrease the excretion rate of Indigotindisulfonic acid which could result in a higher serum level.
Indomethacin	Indomethacin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Inosine pranobex	Methylnaltrexone may decrease the excretion rate of Inosine pranobex which could result in a higher serum level.
Inositol	Methylnaltrexone may decrease the excretion rate of Inositol which could result in a higher serum level.
Inotersen	Inotersen may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Iobenguane sulfate	Methylnaltrexone may decrease the excretion rate of Iobenguane sulfate I-123 which could result in a higher serum level.
Iodixanol	Iodixanol may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ioflupane I-123	Methylnaltrexone may decrease the excretion rate of Ioflupane I-123 which could result in a higher serum level.
Iopromide	Methylnaltrexone may decrease the excretion rate of Iopromide which could result in a higher serum level.
Iothalamic acid	Methylnaltrexone may decrease the excretion rate of Iothalamic acid which could result in a higher serum level.
Ioversol	Methylnaltrexone may decrease the excretion rate of Ioversol which could result in a higher serum level.
Ioxilan	Methylnaltrexone may decrease the excretion rate of Ioxilan which could result in a higher serum level.
Ipecac	Methylnaltrexone may decrease the excretion rate of Ipecac which could result in a higher serum level.
Ipilimumab	Ipilimumab may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Isoniazid	Isoniazid may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Isosorbide	Isosorbide may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Isosorbide mononi	Isosorbide mononitrate may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Isosulfan blue	Methylnaltrexone may decrease the excretion rate of Isosulfan blue which could result in a higher serum level.
Isotretinoin	Isotretinoin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Isoxicam	Isoxicam may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Isradipine	Isradipine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ixazomib	Methylnaltrexone may decrease the excretion rate of Ixazomib which could result in a higher serum level.
Kanamycin	Methylnaltrexone may decrease the excretion rate of Kanamycin which could result in a higher serum level.
Ketamine	Ketamine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ketazolam	Ketazolam may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ketoprofen	Ketoprofen may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ketorolac	Ketorolac may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Labetalol	Labetalol may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Lamivudine	Lamivudine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Lamotrigine	Lamotrigine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Latamoxef	Latamoxef may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ledipasvir	Methylnaltrexone may decrease the excretion rate of Ledipasvir which could result in a higher serum level.
Lenalidomide	Lenalidomide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Lesinurad	Methylnaltrexone may decrease the excretion rate of Lesinurad which could result in a higher serum level.
Leuprolide	Leuprolide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Levacetylmethadol	The therapeutic efficacy of Levacetylmethadol can be decreased when used in combination with Methylnaltrexone.
Levallorphan	Levallorphan may increase the opioid antagonism activities of Methylnaltrexone.
Levobupivacaine	Levobupivacaine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Levocarnitine	Levocarnitine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Levocetirizine	Levocetirizine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Levofloxacin	Levofloxacin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Levomilnacipran	Methylnaltrexone may decrease the excretion rate of Levomilnacipran which could result in a higher serum level.
Levorphanol	The therapeutic efficacy of Levorphanol can be decreased when used in combination with Methylnaltrexone.
Levosalbutamol	Methylnaltrexone may decrease the excretion rate of Levosalbutamol which could result in a higher serum level.
Liothyronine	Liothyronine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Lisinopril	Lisinopril may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Lithium carbonate	Methylnaltrexone may decrease the excretion rate of Lithium carbonate which could result in a higher serum level.
Lithium citrate	Lithium citrate may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Lixisenatide	Methylnaltrexone may decrease the excretion rate of Lixisenatide which could result in a higher serum level.
Lofexidine	Lofexidine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Lopinavir	Lopinavir may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Loracarbef	Loracarbef may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Lorazepam	Lorazepam may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Lorcaserin	Lorcaserin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Lornoxicam	Lornoxicam may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Lorpiprazole	Methylnaltrexone may decrease the excretion rate of Lorpiprazole which could result in a higher serum level.
Loxoprofen	Loxoprofen may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Lubiprostone	Lubiprostone may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Lumiracoxib	Lumiracoxib may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Macitentan	Methylnaltrexone may decrease the excretion rate of Macitentan which could result in a higher serum level.
Magnesium carbonate	Methylnaltrexone may decrease the excretion rate of Magnesium carbonate which could result in a higher serum level.
Magnesium chloride	Methylnaltrexone may decrease the excretion rate of Magnesium chloride which could result in a higher serum level.
Magnesium hydroxide	Methylnaltrexone may decrease the excretion rate of Magnesium hydroxide which could result in a higher serum level.
Magnesium trisilicate	Methylnaltrexone may decrease the excretion rate of Magnesium trisilicate which could result in a higher serum level.
Mangafodipir	Mangafodipir may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Mannitol	Mannitol may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Maprotiline	Maprotiline may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Mecamylamine	Mecamylamine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Meclofenamic acid	Meclofenamic acid may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Medroxyprogesterone	Medroxyprogesterone acetate may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Mefenamic acid	Mefenamic acid may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Megestrol acetate	Megestrol acetate may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Meloxicam	Meloxicam may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Memantine	Memantine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Meperidine	The therapeutic efficacy of Meperidine can be decreased when used in combination with Methylnaltrexone.
Mepivacaine	Mepivacaine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Meropenem	Meropenem may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Mesalazine	Mesalazine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Metamfetamine	Metamfetamine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Metamizole	Metamizole may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Metaxalone	Metaxalone may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Metformin	Metformin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Methadone	The therapeutic efficacy of Methadone can be decreased when used in combination with Methylnaltrexone.
Methazolamide	Methazolamide may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Methimazole	Methimazole may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Methotrexate	Methotrexate may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Methoxsalen	Methoxsalen may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Methyldopa	Methyldopa may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Methylene blue	Methylnaltrexone may decrease the excretion rate of Methylene blue which could result in a higher serum level.
Methyltestosterone	Methyltestosterone may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Meticrane	Meticrane may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Metoclopramide	Metoclopramide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Metolazone	Metolazone may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Metoprolol	Metoprolol may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Metyrapone	Metyrapone may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Midazolam	Midazolam may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.

Migalastat	Migalastat may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Milnacipran	Milnacipran may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Milrinone	Milrinone may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Mirabegron	Methylnaltrexone may decrease the excretion rate of Mirabegron which could result in a higher serum level.
Morphine	The therapeutic efficacy of Morphine can be decreased when used in combination with Methylnaltrexone.
Moxisylyte	Methylnaltrexone may decrease the excretion rate of Moxisylyte which could result in a higher serum level.
Muzolimine	Muzolimine may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Mycophenolate mofetil	Mycophenolate mofetil may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Mycophenolic acid	Mycophenolic acid may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
N-acetyltyrosine	Methylnaltrexone may decrease the excretion rate of N-acetyltyrosine which could result in a higher serum level.
Nabumetone	Nabumetone may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Nadolol	Nadolol may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Nalbuphine	Nalbuphine may increase the opioid antagonism activities of Methylnaltrexone.
Naldemedine	Naldemedine may increase the opioid antagonism activities of Methylnaltrexone.
Nalmefene	Nalmefene may increase the opioid antagonism activities of Methylnaltrexone.
Naloxegol	Naloxegol may increase the opioid antagonism activities of Methylnaltrexone.
Naloxone	Naloxone may increase the opioid antagonism activities of Methylnaltrexone.
Naltrexone	Naltrexone may increase the opioid antagonism activities of Methylnaltrexone.
Naproxen	Naproxen may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Nateglinide	Nateglinide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Nedaplatin	Methylnaltrexone may decrease the excretion rate of Nedaplatin which could result in a higher serum level.
Nedocromil	Nedocromil may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Nefazodone	Nefazodone may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Neomycin	Methylnaltrexone may decrease the excretion rate of Neomycin which could result in a higher serum level.
Netilmicin	Methylnaltrexone may decrease the excretion rate of Netilmicin which could result in a higher serum level.
Nicorandil	Methylnaltrexone may decrease the excretion rate of Nicorandil which could result in a higher serum level.
Nifedipine	Nifedipine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Nilutamide	Nilutamide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Nimesulide	Nimesulide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Nisoldipine	Nisoldipine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Nitric Oxide	Nitric Oxide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Nitrofurantoin	Nitrofurantoin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Nitroprusside	Nitroprusside may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Normethadone	The therapeutic efficacy of Normethadone can be decreased when used in combination with Methylnaltrexone.
Octinoxate	Methylnaltrexone may decrease the excretion rate of Octinoxate which could result in a higher serum level.
Oliceridine	The therapeutic efficacy of Oliceridine can be decreased when used in combination with Methylnaltrexone.
Olsalazine	Olsalazine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Opium	The therapeutic efficacy of Opium can be decreased when used in combination with Methylnaltrexone.
Oseltamivir	Oseltamivir may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Oxacillin	Oxacillin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Oxaprozin	Oxaprozin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Oxazepam	Oxazepam may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Oxybenzone	Oxybenzone may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Oxycodone	The therapeutic efficacy of Oxycodone can be decreased when used in combination with Methylnaltrexone.
Oxymorphone	The therapeutic efficacy of Oxymorphone can be decreased when used in combination with Methylnaltrexone.
Oxyphenbutazone	Oxyphenbutazone may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Oxyquinoline	Methylnaltrexone may decrease the excretion rate of Oxyquinoline which could result in a higher serum level.
Paliperidone	Paliperidone may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Palonosetron	Palonosetron may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Pamidronic acid	Pamidronic acid may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Pantoprazole	Pantoprazole may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Parecoxib	Parecoxib may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Paromomycin	Paromomycin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Patent Blue	Methylnaltrexone may decrease the excretion rate of Patent Blue which could result in a higher serum level.
Pegaptanib	Pegaptanib may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Peginesatide	Methylnaltrexone may decrease the excretion rate of Peginesatide which could result in a higher serum level.
Pemetrexed	Methylnaltrexone may decrease the excretion rate of Pemetrexed which could result in a higher serum level.
Penbutolol	Penbutolol may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Pentaerythritol t	Pentaerythritol tetranitrate may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Pentamidine	Pentamidine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Pentastarch	Methylnaltrexone may decrease the excretion rate of Pentastarch which could result in a higher serum level.
Pentazocine	Pentazocine may increase the opioid antagonism activities of Methylnaltrexone.
Pentetic acid	Methylnaltrexone may decrease the excretion rate of Pentetic acid which could result in a higher serum level.
Pentobarbital	Pentobarbital may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Pentostatin	Methylnaltrexone may decrease the excretion rate of Pentostatin which could result in a higher serum level.
Pentoxifylline	Pentoxifylline may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Perindopril	Perindopril may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Permethrin	Permethrin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Phenazopyridine	Phenazopyridine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Phenelzine	Phenelzine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Phentolamine	Phentolamine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Phenylbutazone	Phenylbutazone may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Pholcodine	Methylnaltrexone may decrease the excretion rate of Pholcodine which could result in a higher serum level.
Phosphoric acid	Methylnaltrexone may decrease the excretion rate of Phosphoric acid which could result in a higher serum level.
Phylloquinone	Phylloquinone may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Picosulfuric acid	Methylnaltrexone may decrease the excretion rate of Picosulfuric acid which could result in a higher serum level.
Pindolol	Pindolol may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Piperacillin	Piperacillin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Piracetam	Methylnaltrexone may decrease the excretion rate of Piracetam which could result in a higher serum level.
Piretanide	Piretanide may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Piritramide	The therapeutic efficacy of Piritramide can be decreased when used in combination with Methylnaltrexone.
Piroxicam	Piroxicam may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Pitolisant	Methylnaltrexone may decrease the excretion rate of Pitolisant which could result in a higher serum level.
Plazomicin	Methylnaltrexone may decrease the excretion rate of Plazomicin which could result in a higher serum level.
Plerixafor	Methylnaltrexone may decrease the excretion rate of Plerixafor which could result in a higher serum level.
Polythiazide	Polythiazide may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Pomalidomide	Methylnaltrexone may decrease the excretion rate of Pomalidomide which could result in a higher serum level.
Potassium	Potassium may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Potassium acetate	Methylnaltrexone may decrease the excretion rate of Potassium acetate which could result in a higher serum level.
Potassium bic	Methylnaltrexone may decrease the excretion rate of Potassium bicarbonate which could result in a higher serum level.
Potassium cation	Potassium cation may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Potassium chloride	Potassium chloride may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Potassium citrate	Potassium citrate may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Potassium nitrate	Methylnaltrexone may decrease the excretion rate of Potassium nitrate which could result in a higher serum level.
Potassium perchlorate	Methylnaltrexone may decrease the excretion rate of Potassium perchlorate which could result in a higher serum level.
Potassium sulfate	Methylnaltrexone may decrease the excretion rate of Potassium sulfate which could result in a higher serum level.
Pralatrexate	Methylnaltrexone may decrease the excretion rate of Pralatrexate which could result in a higher serum level.
Pralidoxime	Pralidoxime may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Pramipexole	Pramipexole may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Prasugrel	Prasugrel may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.

Prednisone	Prednisone may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Pregabalin	Pregabalin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Probenecid	Probenecid may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Procainamide	Methylnaltrexone may decrease the excretion rate of Procainamide which could result in a higher serum level.
Procaine benzylp	Methylnaltrexone may decrease the excretion rate of Procaine benzylpenicillin which could result in a higher serum level.
Promethazine	Promethazine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Propantheline	Propantheline may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Propiverine	Methylnaltrexone may decrease the excretion rate of Propiverine which could result in a higher serum level.
Propranolol	Propranolol may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Prucalopride	Prucalopride may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Pyrantel	Methylnaltrexone may decrease the excretion rate of Pyrantel which could result in a higher serum level.
Pyrazinamide	Pyrazinamide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Pyridoxine	Pyridoxine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Quetiapine	Quetiapine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Quinethazone	Quinethazone may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Quinidine	Methylnaltrexone may decrease the excretion rate of Quinidine which could result in a higher serum level.
Rabeprazole	Rabeprazole may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ramelteon	Ramelteon may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ranitidine	Ranitidine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ranolazine	Ranolazine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Rasagiline	Rasagiline may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Remifentanil	The therapeutic efficacy of Remifentanil can be decreased when used in combination with Methylnaltrexone.
Reserpine	Reserpine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Resorcinol	Methylnaltrexone may decrease the excretion rate of Resorcinol which could result in a higher serum level.
Ribavirin	Ribavirin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ribostamycin	Methylnaltrexone may decrease the excretion rate of Ribostamycin which could result in a higher serum level.
Rivaroxaban	Rivaroxaban may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Rizatriptan	Rizatriptan may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Rofecoxib	Rofecoxib may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Roflumilast	Roflumilast may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ropivacaine	Ropivacaine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Rosiglitazone	Rosiglitazone may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ruxolitinib	Methylnaltrexone may decrease the excretion rate of Ruxolitinib which could result in a higher serum level.
Sacubitril	Methylnaltrexone may decrease the excretion rate of Sacubitril which could result in a higher serum level.
Salbutamol	Salbutamol may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Salicylamide	Salicylamide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Salicylic acid	Salicylic acid may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Salmon calcitonin	Salmon calcitonin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Salsalate	Salsalate may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Samidorphan	Samidorphan may increase the opioid antagonism activities of Methylnaltrexone.
Saxagliptin	Saxagliptin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Secobarbital	Secobarbital may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Selenious acid	Methylnaltrexone may decrease the excretion rate of Selenious acid which could result in a higher serum level.
Selenium	Methylnaltrexone may decrease the excretion rate of Selenium which could result in a higher serum level.
Sibutramine	Sibutramine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Sitagliptin	Sitagliptin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Sodium acetate	Methylnaltrexone may decrease the excretion rate of Sodium acetate which could result in a higher serum level.
Sodium aurothi	Methylnaltrexone may decrease the excretion rate of Sodium aurothiomalate which could result in a higher serum level.
Sodium fluoride	Methylnaltrexone may decrease the excretion rate of Sodium fluoride which could result in a higher serum level.
Sodium sulfate	Methylnaltrexone may decrease the excretion rate of Sodium sulfate which could result in a higher serum level.
Sofosbuvir	Methylnaltrexone may decrease the excretion rate of Sofosbuvir which could result in a higher serum level.
Solriamfetol	Methylnaltrexone may decrease the excretion rate of Solriamfetol which could result in a higher serum level.
Sorafenib	Sorafenib may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Sorbitol	Sorbitol may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Spironolactone	Spironolactone may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Stiripentol	Methylnaltrexone may decrease the excretion rate of Stiripentol which could result in a higher serum level.
Streptomycin	Methylnaltrexone may decrease the excretion rate of Streptomycin which could result in a higher serum level.
Strontium chloride	Methylnaltrexone may decrease the excretion rate of Strontium chloride which could result in a higher serum level.
Sucralfate	Sucralfate may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Sufentanil	The therapeutic efficacy of Sufentanil can be decreased when used in combination with Methylnaltrexone.
Sulbactam	Methylnaltrexone may decrease the excretion rate of Sulbactam which could result in a higher serum level.
Sulfadiazine	Sulfadiazine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Sulfamethoxazole	Sulfamethoxazole may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Sulfasalazine	Sulfasalazine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Sulindac	Sulindac may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Sumatriptan	Sumatriptan may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
S Estrogens, A	Methylnaltrexone may decrease the excretion rate of Synthetic Conjugated Estrogens, A which could result in a higher serum level.
S Estrogens, B	Methylnaltrexone may decrease the excretion rate of Synthetic Conjugated Estrogens, B which could result in a higher serum level.
Tacrolimus	Tacrolimus may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Tadalafil	Tadalafil may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Tamsulosin	Tamsulosin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Tapentadol	The therapeutic efficacy of Tapentadol can be decreased when used in combination with Methylnaltrexone.
Tasimelteon	Methylnaltrexone may decrease the excretion rate of Tasimelteon which could result in a higher serum level.
Technetium Tc-99m	Methylnaltrexone may decrease the excretion rate of Technetium Tc-99m exametazime which could result in a higher serum level.
T mebrofenin	Methylnaltrexone may decrease the excretion rate of Technetium Tc-99m mebrofenin which could result in a higher serum level.
Techn oxidronate	Methylnaltrexone may decrease the excretion rate of Technetium Tc-99m oxidronate which could result in a higher serum level.
Tech pyrophosphate	Methylnaltrexone may decrease the excretion rate of Technetium Tc-99m pyrophosphate which could result in a higher serum level.
Teduglutide	Methylnaltrexone may decrease the excretion rate of Teduglutide which could result in a higher serum level.
Tegafur	Methylnaltrexone may decrease the excretion rate of Tegafur which could result in a higher serum level.
Telavancin	Telavancin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Temazepam	Temazepam may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Temozolomide	Temozolomide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Tenofovir alafenamide	The serum concentration of Tenofovir alafenamide can be increased when it is combined with Methylnaltrexone.
Tenofovir disoproxil	Tenofovir disoproxil may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Tenoxicam	Tenoxicam may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Terbutaline	Terbutaline may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Testolactone	Testolactone may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Testosterone	Testosterone may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Testosterone cypi	Methylnaltrexone may decrease the excretion rate of Testosterone cypionate which could result in a higher serum level.
Testosterone en	Methylnaltrexone may decrease the excretion rate of Testosterone enanthate which could result in a higher serum level.
Testosterone prop	Testosterone propionate may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Testosterone undec	Methylnaltrexone may decrease the excretion rate of Testosterone undecanoate which could result in a higher serum level.
Tetracycline	Tetracycline may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Tetradecyl hydrogen	Methylnaltrexone may decrease the excretion rate of Tetradecyl hydrogen sulfate (ester) which could result in a higher serum level.
Thiabendazole	Thiabendazole may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Thiethylperazine	Thiethylperazine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Tiaprofenic acid	Tiaprofenic acid may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Ticlopidine	Ticlopidine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Tiludronic acid	Tiludronic acid may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Timolol	Timolol may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.

Tinidazole	Tinidazole may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Tiopronin	Methylnaltrexone may decrease the excretion rate of Tiopronin which could result in a higher serum level.
Tiotropium	Tiotropium may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Tirofiban	Tirofiban may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Tixocortol	Methylnaltrexone may decrease the excretion rate of Tixocortol which could result in a higher serum level.
Tobramycin	Methylnaltrexone may decrease the excretion rate of Tobramycin which could result in a higher serum level.
Tocopherol	Methylnaltrexone may decrease the excretion rate of Tocopherol which could result in a higher serum level.
Tolazamide	Tolazamide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Tolbutamide	Tolbutamide may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Tolcapone	Tolcapone may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Tolfenamic acid	Tolfenamic acid may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Tolmetin	Tolmetin may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Tolterodine	Tolterodine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Tolvaptan	Tolvaptan may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Topiramate	Topiramate may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Topotecan	Topotecan may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Torasemide	Torasemide may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Tositumomab	Tositumomab may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Tramadol	The therapeutic efficacy of Tramadol can be decreased when used in combination with Methylnaltrexone.
Trametinib	Methylnaltrexone may decrease the excretion rate of Trametinib which could result in a higher serum level.
Triamterene	Triamterene may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Triazolam	Triazolam may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Trichlormethiazide	Trichlormethiazide may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.
Triethylenetetramine	Methylnaltrexone may decrease the excretion rate of Triethylenetetramine which could result in a higher serum level.
Trifluridine	Trifluridine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Trimebutine	Methylnaltrexone may decrease the excretion rate of Trimebutine which could result in a higher serum level.
Trimethoprim	Trimethoprim may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Trimetrexate	Trimetrexate may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Tropisetron	Methylnaltrexone may decrease the excretion rate of Tropisetron which could result in a higher serum level.
Vaborbactam	Methylnaltrexone may decrease the excretion rate of Vaborbactam which could result in a higher serum level.
Valaciclovir	Valaciclovir may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Valbenazine	Methylnaltrexone may decrease the excretion rate of Valbenazine which could result in a higher serum level.
Valdecoxib	Valdecoxib may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Valganciclovir	Valganciclovir may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Vancomycin	Methylnaltrexone may decrease the excretion rate of Vancomycin which could result in a higher serum level.
Varenicline	Varenicline may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Venlafaxine	Venlafaxine may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Verapamil	Verapamil may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Vilanterol	Methylnaltrexone may decrease the excretion rate of Vilanterol which could result in a higher serum level.
Viloxazine	Methylnaltrexone may decrease the excretion rate of Viloxazine which could result in a higher serum level.
Vortioxetine	Methylnaltrexone may decrease the excretion rate of Vortioxetine which could result in a higher serum level.
Warfarin	Methylnaltrexone may decrease the excretion rate of Warfarin which could result in a higher serum level.
Zaleplon	Zaleplon may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Zanamivir	Zanamivir may decrease the excretion rate of Methylnaltrexone which could result in a higher serum level.
Zonisamide	Zonisamide may increase the excretion rate of Methylnaltrexone which could result in a lower serum level and potentially a reduction in efficacy.

Pregnancy and Lactation

AU TGA pregnancy category: B1
US FDA pregnancy category: C

Pregnancy

The limited available data with RELISTOR in pregnant women are not sufficient to inform a drug-associated risk for major birth defects and miscarriages. There are clinical considerations when RELISTOR is used by pregnant women. In animal reproduction studies, no effects on embryofetal development were observed with the administration of intravenous methylnaltrexone bromide during organogenesis in rats and rabbits at doses up to 20 times and 26 times, respectively, the subcutaneous maximum recommended human dose (MRHD) of 12 mg RELISTOR injection per day. The intravenous doses in rats and rabbits are about 0.5 times and 0.7 times, respectively, an oral MRHD of 450 mg/day. Advise pregnant women of the potential risk to a fetus. The estimated background risk of major birth defects and miscarriage for the indicated population is unknown. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2 to 4% and 15 to 20%, respectively.

Lactation

No information is available on the use of methylnaltrexone during breastfeeding. The manufacturer recommends against breastfeeding in mothers taking methylnaltrexone. Based on pharmacokinetic data, the oral absorption of methylnaltrexone appears to be very low. Observe breastfed infants who have been exposed to opioids during pregnancy or postpartum for signs of opioid withdrawal, especially diarrhea.

How should this medicine be used?

Methylnaltrexone comes as a tablet to take by mouth. It is usually taken once a day with water, at least 30 minutes before the first meal of the day. Take methylnaltrexone at around the same time every day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take methylnaltrexone exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

Methylnaltrexone is to be taken by people who are taking opioid (narcotic) medications. Talk to your doctor if you change how much or how often you take your opioid medication. If you stop taking opioid medications, you should stop taking methylnaltrexone as well.

You should stop taking other laxative medications when you start taking methylnaltrexone. However, be sure to let your doctor know if methylnaltrexone does not work for you after taking it for 3 days. Your doctor may tell you to take other laxative medication(s).

Your doctor or pharmacist will give you the manufacturer’s patient information sheet (Medication Guide) when you begin treatment with methylnaltrexone and each time you refill your prescription. Read the information carefully and ask your doctor or pharmacist if you have any questions. You can also visit the Food and Drug Administration (FDA) website (http://www.fda.gov/Drugs/DrugSafety/ucm085729.htm) to obtain the Medication Guide.

Other uses for this medicine

This medication may be prescribed for other uses; ask your doctor or pharmacist for more information.

What special precautions should I follow?

Before taking methylnaltrexone,

tell your doctor and pharmacist if you are allergic to methylnaltrexone, any other medications, or any of the ingredients in methylnaltrexone tablets. Ask your pharmacist or check the Medication Guide for a list of the ingredients.
tell your doctor and pharmacist what prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention any of the following: alvimopan (Entereg), naldemedine (Symproic), naloxegol (Movantik), naloxone (Evzio, Narcan, in Bunavail, Suboxone, Zubsolv), or naltrexone (Vivitrol, in Contrave, Embeda). Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
tell your doctor if you have or have ever had a gastrointestinal obstruction (a blockage in your bowel). Your doctor will probably tell you not to take methylnaltrexone.
tell your doctor if you have or have ever had stomach or bowel problems including stomach ulcer (sores in the lining of the stomach), cancer of the stomach or bowel, Crohn’s disease (a condition in which the body attacks the lining of the digestive tract, causing pain, diarrhea, weight loss, and fever), diverticulitis (small pouches in the lining of the large intestine that can become inflamed), Ogilvie’s syndrome (a condition in which there is a bulge in the bowel), or kidney or liver disease.
tell your doctor if you are pregnant or plan to become pregnant. If you become pregnant while taking methylnaltrexone, call your doctor. If you take methylnaltrexone during your pregnancy, your baby may experience opioid withdrawal symptoms.
tell your doctor if you are breastfeeding. Do not breastfeed while you are taking methylnaltrexone.
you should know that most people have a bowel movement within a few minutes to a few hours after taking methylnaltrexone. Make sure that you are close to a bathroom when you take this medication.

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Safety note: This is not a prescription or diagnosis. For severe symptoms, pregnancy danger signs, children with serious illness, chest pain, breathing difficulty, stroke-like weakness, or major injury, seek urgent care.

Which doctor may help?

Start with a registered doctor or the nearest qualified health center.

What to tell the doctor

Write when the problem started and how it changed.
Bring old prescriptions, investigation reports, and current medicines.
Write allergies, pregnancy status, diabetes, kidney/liver disease, and major past illnesses.
Bring one family member if the patient is weak, elderly, confused, or a child.

Questions to ask

What is the most likely cause of my symptoms?
Which danger signs mean I should go to hospital quickly?
Which tests are necessary now, and which can wait?
How should I take medicines safely and what side effects should I watch for?
When should I come for follow-up?

Tests to discuss

Vital signs: temperature, pulse, blood pressure, oxygen saturation
Basic physical examination by a clinician
CBC, urine test, blood sugar, or imaging only when clinically needed

Avoid these mistakes

Do not use antibiotics, steroid tablets/injections, or strong painkillers without proper medical advice.
Do not hide pregnancy, kidney disease, ulcer, allergy, or blood thinner use.
Do not delay emergency care when danger signs are present.

Medicine safety and first-aid guide

This section is for patient education only. It does not replace a doctor, pharmacist, or emergency care.

Safe first steps

Avoid heavy lifting, sudden bending, and prolonged bed rest.
Use comfortable posture and gentle movement as tolerated.
Discuss physiotherapy, X-ray, or MRI only when clinically needed.

OTC medicine safety

For mild back pain, pain-relief medicine may be discussed with a doctor or pharmacist.
Avoid repeated painkiller use if you have kidney disease, stomach ulcer, uncontrolled blood pressure, or are taking blood thinners.

Avoid these mistakes

Do not start antibiotics without a proper medical decision.
Do not use steroid tablets or injections casually for quick relief.
Do not delay emergency care because of home remedies.

Get urgent help if

Back pain with leg weakness, numbness around private area, loss of urine/stool control, fever, cancer history, or major injury needs urgent care.

Medicine names, dose, and timing must be decided by a qualified clinician or pharmacist after checking age, pregnancy, allergy, other diseases, and current medicines.

For rural patients and family caregivers

Patient health record and symptom diary

Write your symptoms, medicines already taken, test results, and questions before visiting a doctor. This note stays on your device unless you print or copy it.

Doctor to discuss: Medicine doctor / pediatrician for children / qualified clinician

Tests to discuss with doctor

Temperature chart and hydration assessment
CBC with platelet count if fever persists or dengue/other infection is possible
Urine test, malaria/dengue tests, chest evaluation, or blood culture only when clinically indicated

Questions to ask

What is the most likely cause of my symptoms?
Which warning signs mean I should go to emergency care?
Which tests are really needed now?
Which medicines are safe for my age, pregnancy status, allergy, kidney/liver/stomach condition, and current medicines?
Do I need antibiotics, or is this more likely viral?

Emergency warning signs such as chest pain, severe breathing difficulty, sudden weakness, confusion, severe dehydration, major injury, or loss of bladder/bowel control need urgent medical care. Do not wait for online information.

Go to emergency care if you notice:

Severe or rapidly worsening symptoms
Breathing difficulty, chest pain, fainting, confusion, severe weakness, major injury, or severe dehydration

Doctor / service to discuss: Qualified healthcare provider; specialist depends on symptoms and examination.

Step 1
Check danger signs first

If danger signs are present, seek emergency care and do not wait for online information.
Step 2
Record the symptom story

Write when symptoms started, severity, medicines already taken, allergies, pregnancy status, and test results.
Step 3
Visit a qualified clinician

A doctor, nurse, or qualified healthcare provider can examine you and decide which tests or treatment are needed.
Step 4
Do only useful tests

Do tests after clinical assessment. Avoid unnecessary tests, random antibiotics, or repeated medicines without diagnosis.
Step 5
Follow up and return early if worse

If symptoms worsen, new warning signs appear, or treatment is not helping, return for review quickly.

Rural patient practical tips

Take a written symptom diary and all previous prescriptions/test reports.
Do not hide medicines already taken, even herbal or over-the-counter medicines.
Ask which warning signs mean urgent referral to hospital.

This roadmap is for education. A real diagnosis and treatment plan requires history, examination, and clinical judgment.

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Article Summary

Key Takeaways

RX Patient Tools

Mechanism of action

Indications

Use in Cancer

Contraindications

Dosage?

Constipation – Drug-Induced

Renal? Dose Adjustments

Liver Dose Adjustments

Side Effects

The Most Common

More Common

Rare

Drug Interactions

Pregnancy and Lactation

Pregnancy

Lactation

How should this medicine be used?

Other uses for this medicine

What special precautions should I follow?

Before taking methylnaltrexone,

Related medical topics

Related Articles

Prepare before seeing a doctor

Which doctor may help?

What to tell the doctor

Questions to ask

Tests to discuss

Avoid these mistakes

Medicine safety and first-aid guide

Safe first steps

OTC medicine safety

Avoid these mistakes

Get urgent help if

Patient health record and symptom diary

Care roadmap for: Methylnaltrexone Bromide – Uses, Dosage, Side Effects, Interaction

Check danger signs first

Record the symptom story

Visit a qualified clinician

Do only useful tests

Follow up and return early if worse

Explore related RX articles

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Dosage

Renal Dose Adjustments