Trihexyphenidyl; Uses, Dosage, Side Effects, Drug Interactions

Trihexyphenidyl is only found in individuals that have used or taken this drug. It is one of the centrally acting muscarinic antagonists used for the treatment of parkinsonian disorders and drug-induced extrapyramidal movement disorders and as an antispasmodic. Trihexyphenidyl is a selective M1 muscarinic acetylcholine receptor antagonist. It is able to discriminate between the M1 (cortical or neuronal) and the peripheral muscarinic subtypes (cardiac and glandular). Trihexyphenidyl partially blocks cholinergic activity in the CNS, which is responsible for the symptoms of Parkinson’s disease. It is also thought to increase the availability of dopamine, a brain chemical that is critical in the initiation and smooth control of voluntary muscle movement.

Trihexyphenidyl also is known as benzhexol is an antiparkinsonian agent of the antimuscarinic class. It has been in clinical use for decades. One of the centrally acting muscarinic antagonists used for the treatment of parkinsonian disorders and drug-induced extrapyramidal movement disorders and as an antispasmodic.

Mechanism of Action of Trihexyphenidyl

Trihexyphenidyl is a selective M1 muscarinic acetylcholine receptor antagonist. It is able to discriminate between the M1 (cortical or neuronal) and the peripheral muscarinic subtypes (cardiac and glandular). Trihexyphenidyl partially blocks cholinergic activity in the CNS, which is responsible for the symptoms of Parkinson’s disease. It is also thought to increase the availability of dopamine, a brain chemical that is critical in the initiation and smooth control of voluntary muscle movement.

Indications of Trihexyphenidyl

• Cerebral Spasticity
• Extrapyramidal Reaction
• Parkinson’s Disease
• Extrapyramidal symptoms caused by butyrophenones
• Extrapyramidal symptoms caused by dibenzoxazepines
• Extrapyramidal symptoms caused by phenothiazines
• Extrapyramidal symptoms caused by thioxanthenes
• Parkinsonism post-encephalitic
• Arteriosclerotic Parkinsonism
• Extrapyramidal disorders
• Idiopathic Parkinsonism

Contra-Indications of Trihexyphenidyl

• Hypersensitivity to trihexyphenidyl
• Narrow-angle glaucoma
• Ileus
• Caution; People with obstructive diseases of the urogenital tract, people with a known history of seizures and those with potentially dangerous tachycardia
• People under 18 yrs. of age should not be treated due to a lack of clinical experience.
• People should allow a period to adjust to the dose when first starting trihexyphenidyl and when the dose has been increased or added to a regimen with other drugs because acute somnolence and accumulated fatigue can make it particularly dangerous to operate an automobile, heavy machinery etc.

Dosage of Trihexyphenidyl

Strengths: 2 mg; 5 mg; 2 mg/5 mL

Extrapyramidal Reaction

• 4 to 10 mg orally each day. The total daily dose is best tolerated when administered in 2 or three equally separated doses.

Parkinson’s Disease

• Initial: 1 mg/day; increase by 2 mg increments at intervals of 3 to 5 days
• Usual dose: 6 to 10 mg/day in 3 to 4 divided doses; doses of 12 to 15 mg/day may be required

Pediatric Cerebral Spasticity

Children 2 to 17 years old Dystonia in cerebral palsy

• Initial: 0.1 to 0.2 mg/kg/day in three divided doses for 1 week; increase by 0.05 to 0.3 mg/kg/day in three divided doses for the second week; thereafter, titrate up weekly by 0.05 to 0.5 mg/kg/day in three divided doses as clinically tolerated
• Maximum dose: 0.75 mg/kg/day

Side Effects of Trihexyphenidyl

The most common

• nausea, vomiting, stomach pain, indigestion, constipation, diarrhea;
• fever, flu symptoms, cough, sore throat, sneezing, runny nose;
• nervousness, depression, sleep problems (insomnia);
• a headache, dizziness, drowsiness, memory problems, unusual thoughts;
• rash, hair loss, bruising;
• weakness, tremors, problems with balance or walking;
• swelling in your hands or feet;
• vision problems, ringing in your ears; or
• changes in appetite, weight gain.

More common

• Black, tarry stools
• bleeding gums
• bloating or swelling of the face, arms, hands, lower legs, or feet
• blood in the urine or stools
• confusion
• a cough or hoarseness
• crying
• dementia
• depersonalization
• diarrhea
• difficult or labored breathing
• dysphoria
• euphoria
• fever or chills

Less common

• Abnormal dreams
• absence of or decrease in body movement
• anxiety
• bloody nose
• bloody or cloudy urine
• blurred vision
• burning, crawling, itching, numbness, prickling, “pins and needles”, or tingling feelings
• change in personality
• change in walking and balance
• changes in patterns and rhythms of speech
• chest pain
• lack of appetite
• lack of coordination
• large, flat, blue or purplish patches in the skin
• leg cramps
• lip smacking or puckering
• loss of bladder control

Drug Interactions of Trihexyphenidyl

Trihexyphenidyl may interact with following drug, supplements, & may change the efficacy of drug

• antihistamines (e.g,. cetirizine, doxylamine, diphenhydramine, hydroxyzine,loratadine)
• antiseizure medications (e.g., clobazam, ethosuximide, felbamate, levetiracetam, phenobarbital, phenytoin, primidone, topiramate, valproic acid, zonisamide)
• aripiprazole
• “azole” antifungals (e.g., itraconazole, ketoconazole, voriconazole)
• benzodiazepines (e.g., alprazolam, diazepam, lorazepam)
• beta-adrenergic blockers (e.g., atenolol, propranolol, sotalol)
• calcium channel blockers (e.g., amlodipine, diltiazem, nifedipine, verapamil)
• captopril
• celecoxib
• chloroquine
• cholecalciferol
• cyclosporine
• dantrolene
• domperidone
• “gliptin” diabetes medications (e.g., linagliptin, saxagliptin, sitagliptin)
• gabapentin
• H2 antagonists (e.g., famotidine, ranitidine)
• mirabegron
• montelukast
• non-steroidal anti-inflammatory medications (NSAIDs; e.g., diclofenac, ibuprofenserotonin antagonists (anti-emetic medications;, naproxen)
• phosphodiesterase 5 inhibitors (e.g., sildenafil, tadalafil, vardenafil)
• quinolone antibiotics (e.g., levofloxacin, norfloxacin, moxifloxacin)
• selective serotonin reuptake inhibitors (SSRIs; e.g., paroxetine, fluoxetine,citalopram)
•  e.g., granisetron,ondansetron)
• “statin” anti-cholesterol medications (e.g., atorvastatin, lovastatin,simvastatin)
• theophylline
• thiazide diuretics (water pills; e.g., hydrochlorothiazide, indapamide, metolazone)
• tramadol
• tricyclic antidepressants (e.g., amitriptyline, clomipramine, desipramine,

Pregnancy & Lactation of Trihexyphenidyl

FDA pregnancy category – N( not categorized)

Pregnancy