Flucloxacillin, Uses, Dosage, Side Effects, Interactions, Pregnancy

Last updated: February 7, 2026Reviewed date: February 7, 2026Reading time: 8 min read
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Flucloxacillin is a narrow-spectrum, semisynthetic isoxazolyl penicillin with antibacterial activity. Floxacillin binds to and inactivates penicillin-binding proteins (PBPs) located on the inner membrane of the bacterial cell wall. Inactivation of PBPs interferes with the cross-linkage of peptidoglycan chains necessary for bacterial cell wall strength and rigidity. This interrupts bacterial cell wall synthesis and...

For severe symptoms, danger signs, pregnancy, child illness, or sudden worsening, seek urgent medical care.

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Article Summary

Flucloxacillin is a narrow-spectrum, semisynthetic isoxazolyl penicillin with antibacterial activity. Floxacillin binds to and inactivates penicillin-binding proteins (PBPs) located on the inner membrane of the bacterial cell wall. Inactivation of PBPs interferes with the cross-linkage of peptidoglycan chains necessary for bacterial cell wall strength and rigidity. This interrupts bacterial cell wall synthesis and results in the weakening of the bacterial cell wall, eventually causing cell lysis. Flucloxacillin is only found in individuals that have...

Key Takeaways

  • This article explains Mechanism of Action of Flucloxacillin in simple medical language.
  • This article explains Indications of Flucloxacillin in simple medical language.
  • This article explains Contra Indications of Flucloxacillin in simple medical language.
  • This article explains Dosage of Flucloxacillin in simple medical language.
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Emergency safety firstUrgent warning signs are highlighted below.

Seek urgent medical care if you notice

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  • Severe symptoms, breathing difficulty, fainting, confusion, or rapidly worsening illness.
  • New weakness, severe pain, high fever, or symptoms after a serious injury.
  • Any symptom that feels urgent, unusual, or unsafe for the patient.
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Flucloxacillin is a narrow-spectrum, semisynthetic isoxazolyl penicillin with antibacterial activity. Floxacillin binds to and inactivates penicillin-binding proteins (PBPs) located on the inner membrane of the bacterial cell wall. Inactivation of PBPs interferes with the cross-linkage of peptidoglycan chains necessary for bacterial cell wall strength and rigidity. This interrupts bacterial cell wall synthesis and results in the weakening of the bacterial cell wall, eventually causing cell lysis.
Flucloxacillin is only found in individuals that have used or taken this drug. It is an bacterial infections. সহজ বাংলা: ব্যাকটেরিয়ার সংক্রমণের ওষুধ।" data-rx-term="antibiotic" data-rx-definition="An antibiotic is a medicine used to treat bacterial infections. সহজ বাংলা: ব্যাকটেরিয়ার সংক্রমণের ওষুধ।">antibiotic analog of cloxacillin. By binding to specific penicillin-binding proteins (PBPs) located inside the bacterial cell wall, flucloxacillin inhibits the third and last stage of bacterial cell wall synthesis. Cell lysis is then mediated by bacterial cell wall autolytic enzymes such as autolysins; it is possible that flucloxacillin interferes with an autolysin inhibitor.
Flucloxacillin (INN) or floxacillin is a narrow-spectrum beta-lactam bacterial infections. সহজ বাংলা: ব্যাকটেরিয়ার সংক্রমণের ওষুধ।" data-rx-term="antibiotic" data-rx-definition="An antibiotic is a medicine used to treat bacterial infections. সহজ বাংলা: ব্যাকটেরিয়ার সংক্রমণের ওষুধ।">antibiotic of the penicillin class. It is used to treat infections caused by susceptible Gram-positive bacteria.Flucloxacillin is a narrow-spectrum, semisynthetic isoxazolyl penicillin with antibacterial activity. Floxacillin binds to and inactivates penicillin-binding proteins (PBPs) located on the inner membrane of the bacterial cell wall. Inactivation of PBPs interferes with the cross-linkage of peptidoglycan chains necessary for bacterial cell wall strength and rigidity. This interrupts bacterial cell wall synthesis and results in the weakening of the bacterial cell wall, eventually causing cell lysis.

Mechanism of Action of Flucloxacillin

Definition

Flucloxacillin is a penicillin beta-lactam bacterial infections. সহজ বাংলা: ব্যাকটেরিয়ার সংক্রমণের ওষুধ।" data-rx-term="antibiotic" data-rx-definition="An antibiotic is a medicine used to treat bacterial infections. সহজ বাংলা: ব্যাকটেরিয়ার সংক্রমণের ওষুধ।">antibiotic used in the treatment of bacterial infections caused by susceptible, usually gram-positive, organisms. The name “penicillin” can either refer to several variants of penicillin available, or to the group of antibiotics derived from the penicillins. Flucloxacillin has in vitro activity against gram-positive and gram-negative aerobic and anaerobic bacteria. The bactericidal activity of Flucloxacillin results from the inhibition of cell wall synthesis and is mediated through flucloxacillin binding to penicillin binding proteins (PBPs). Flucloxacillin is stable against hydrolysis by a variety of beta-lactamases, including penicillinases, and cephalosporinases and extended spectrum beta-lactamases.By binding to specific penicillin-binding proteins (PBPs) located inside the bacterial cell wall, flucloxacillin inhibits the third and last stage of bacterial cell wall synthesis. Cell lysis is then mediated by bacterial cell wall autolytic enzymes such as autolysins; it is possible that flucloxacillin interferes with an autolysin inhibitor.

Or

By binding to specific penicillin-binding proteins (PBPs) located inside the bacterial cell wall, flucloxacillin inhibits the third and last stage of bacterial cell wall synthesis. Cell lysis is then mediated by bacterial cell wall autolytic enzymes such as autolysins; it is possible that flucloxacillininterferes with an autolysin inhibitor.

Indications of Flucloxacillin

It is most commonly used to treat infections.

  • Chest, ear, nose and throat (e.g. tonsillitis, sinusitis, pneumonia)
  • Skin and soft tissue (e.g. boils, burns, wounds, abscesses, infected eczema, infected acne)
  • Staphylococcal skin infections and cellulitis – including impetigo, otitis externa, folliculitis, boils, carbuncles, and mastitis
  • Pneumonia 
  • Osteomyelitis, septic arthritis
  • Septicaemia
  • Empirical treatment for endocarditis
  • Surgical prophylaxis
  • Other infections including those of the heart (endocarditis), bones and joints (osteomyelitis), membranes of the brain (meningitis), guts (enteritis), blood (septicaemia), and the kidney, bladder or urethra
  • Lung abscess
  • Empyema
  • Respiratory tract infections:
  • Osteomyelitis
  • Enteritis
  • Endocarditis
  • Septicaemia
  • Meningitis
  • Urinary tract infection
  • Used to treat bacterial infection by susceptible microorganisms.
  • Other infections caused by flucloxacillin-sensitive organisms

Contra Indications of Flucloxacillin

  • History of severe hypersensitivity (e.g. anaphylactic reaction) to any other type of betalactam antibacterial agent (penicillins, monobactams and carbapenems).
  • Hemolytic anemia
  • Liver problems
  • Interstitial nephritis
  • Subacute cutaneous lupus erythematosus
  • Systemic lupus erythematosus
  • use should be avoided in pregnant or lactating women, and in children with developing teeth because they may result in permanent staining (dark yellow-gray teeth with a darker horizontal band that goes across the top and bottom rows of teeth), and possibly affect the growth of teeth and bones.

Dosage of Flucloxacillin

Strengths: 125 mg; 200 mg; 250 mg ;400 mg;500 mg,  875 mg   125 mg/5 mL; 50 mg/mL; 250 mg/5 mL; ; 200 mg/5 mL; 400 mg/5 mL; 600 mg;

Bacterial Endocarditis

American Heart Association (AHA) recommendations

  • Immediate-release: 2 g orally as a single dose 30 to 60 minutes prior to procedure

Helicobacter pylori Infection

Immediate-release

  • Dual Therapy: 1 g orally every 8 hours for 14 days in combination with lansoprazole
  • Triple Therapy: 1 g orally every 12 hours for 14 days in combination with clarithromycin and lansoprazole

Pneumonia

Immediate-release

  • Mild, moderate, or severe infection: 500 mg orally every 8 hours or 875 mg every 12 hours

IDSA and American Thoracic Society (ATS) recommendations, Pneumonia

  • Immediate-release: 1 g orally 3 times a day

Bronchitis

Immediate-release

  • Mild, moderate, or severe infection: 500 mg orally every 8 hours or 875 mg every 12 hours

Sinusitis

Immediate-release

  • Mild to moderate infection: 250 mg orally every 8 hours or 500 mg every 12 hours
  • Severe infection: 500 mg orally every 8 hours or 875 mg every 12 hours

Urinary Tract Infection

Immediate-release

  • Mild to moderate infection: 250 mg orally every 8 hours or 500 mg every 12 hours
  • Severe infection: 500 mg orally every 8 hours or 875 mg every 12 hours

Tonsillitis/Pharyngitis

Extended-release

  • 775 mg orally once a day within 1 hour after a meal for 10 days

IDSA recommendations

  • Immediate-release: 1000 mg orally once a day or 500 mg orally twice a day

Skin and Structure Infection

Immediate-release

  • Mild to moderate infection: 250 mg orally every 8 hours or 500 mg every 12 hours
  • Severe infection: 500 mg orally every 8 hours or 875 mg every 12 hours

IDSA recommendations

  • Immediate-release: 500 mg orally 3 times a day for 7 to 10 days

Pediatric 

Sinusitis

Immediate-Release Formulations ,Mild, Moderate, or Severe Infection

  • 3 months or younger: Up to 30 mg/kg/day orally in divided doses every 12 hours

Immediate-Release Formulations, Mild to Moderate Infection ,4 months or older

  • Less than 40 kg: 20 mg/kg/day orally in divided doses every 8 hours or 25 mg/kg/day in divided doses every 12 hours
  • At least 40 kg: 250 mg orally every 8 hours or 500 mg every 12 hours

Severe Infection, 4 months or older

  • Less than 40 kg: 40 mg/kg/day orally in divided doses every 8 hours or 45 mg/kg/day in divided doses every 12 hours
  • At least 40 kg: 500 mg orally every 8 hours or 875 mg every 12 hours

Skin or Soft Tissue Infection

Immediate-Release Formulations , Mild, Moderate, or Severe Infection
3 months or younger: Up to 30 mg/kg/day orally in divided doses every 12 hours

Immediate-Release Formulations,Mild to Moderate Infection ,4 months or older

  • Less than 40 kg: 20 mg/kg/day orally in divided doses every 8 hours or 25 mg/kg/day in divided doses every 12 hours
  • At least 40 kg: 250 mg orally every 8 hours or 500 mg every 12 hours

Severe Infection, 4 months or older

  • Less than 40 kg: 40 mg/kg/day orally in divided doses every 8 hours or 45 mg/kg/day in divided doses every 12 hours
  • At least 40 kg: 500 mg orally every 8 hours or 875 mg every 12 hours

Urinary Tract Infection

  • Immediate-Release Formulations, Mild, Moderate, or Severe Infection
  • 3 months or younger: Up to 30 mg/kg/day orally in divided doses every 12 hours

Side Effects of Flucloxacillin

The most common side effects 

More common

Rare

Drug Interactions of  Flucloxacillin

Flucloxacillin may interact with following drugs, supplements, & may change the efficacy of drugs

Pregnancy & Lactation of Flucloxacillin

FDA Pregnancy Category B

Pregnancy

Animal studies with flucloxacillin have shown no teratogenic effects. The product has been in clinical use since 1970 and the limited number of reported cases of use in human pregnancy have shown no evidence of untoward effects. The decision to administer any drug during pregnancy should be taken with the utmost care. Therefore flucloxacillin should only be used in pregnancy when the potential benefits outweigh the potential risks associated with treatment.

Lactation

Trace quantities of flucloxacillin can be detected in breast milk. The possibility of hypersensitivity reactions must be considered in breastfeeding infants. Therefore flucloxacillin should only be administered to a breastfeeding mother when the potential benefits outweigh the potential risks associated with the treatment.

References

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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: Orthopedic / spine specialist, physical medicine doctor, or qualified clinician
Tests to discuss with doctor
  • Neurological examination for leg power, sensation, reflexes, and straight leg raise
  • X-ray only if injury, deformity, long-lasting pain, or doctor suspects bone problem
  • MRI discussion if severe nerve symptoms, weakness, bladder/bowel problem, or persistent symptoms
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?
  • Is physiotherapy, posture correction, or activity modification needed?

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.

Safe pathway to proper treatment

Care roadmap for: Flucloxacillin, Uses, Dosage, Side Effects, Interactions, Pregnancy

Use this simple roadmap to understand the next safe steps. It is educational and does not replace examination by a doctor.

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.
  1. Step 1

    Check danger signs first

    If danger signs are present, seek emergency care and do not wait for online information.

  2. Step 2

    Record the symptom story

    Write when symptoms started, severity, medicines already taken, allergies, pregnancy status, and test results.

  3. Step 3

    Visit a qualified clinician

    A doctor, nurse, or qualified healthcare provider can examine you and decide which tests or treatment are needed.

  4. Step 4

    Do only useful tests

    Do tests after clinical assessment. Avoid unnecessary tests, random antibiotics, or repeated medicines without diagnosis.

  5. 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.

RX Patient Help

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Write your symptom story. A health professional or site editor can review it before any answer is prepared. This box is not for emergency care.

Emergency first: Severe chest pain, breathing trouble, unconsciousness, stroke signs, severe injury, heavy bleeding, or rapidly worsening symptoms need urgent local medical care now.

Frequently Asked Questions

Is this article a replacement for a doctor?

No. It is educational content only. Patients should consult a qualified clinician for diagnosis and treatment.

When should I seek urgent care?

Seek urgent care for severe symptoms, rapidly worsening condition, breathing difficulty, severe pain, neurological changes, or any emergency warning sign.

References

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