Flucloxacillin is a penicillin-type antibiotic specifically designed to resist breakdown by an enzyme (penicillinase) produced by certain Staphylococcus bacteria, making it particularly effective against staphylococcal infections that would otherwise be resistant to standard penicillin. It belongs to a class of medicines called penicillinase-resistant penicillins. It is a prescription-only medicine.

• Therapeutic Class: Antibacterial (antibiotic).

• Pharmacological Class: Penicillinase-resistant penicillin (isoxazolyl penicillin).

• Drug Family: Beta-lactam antibiotics.

• ATC Classification: J01CF05 (Flucloxacillin).

Approved: Infections caused by penicillinase-producing staphylococci and other susceptible bacteria, including skin and soft tissue infections, cellulitis, wound infections, bone and joint infections (osteomyelitis), respiratory tract infections, and endocarditis.

Commonly used for: Skin, soft tissue, and bone/joint infections where Staphylococcus aureus is a likely or confirmed cause, particularly methicillin-sensitive strains.

Off-label use (only under medical guidance): Sometimes used for other susceptible bacterial infections based on culture and sensitivity results.

• Oral capsules: commonly 250 mg and 500 mg.

• Oral suspension: for patients unable to swallow capsules, particularly children.

• Injection (intravenous/intramuscular): commonly 250 mg, 500 mg, and 1 g vials, for more severe infections.

Flucloxacillin kills bacteria by binding to proteins involved in building the bacterial cell wall, preventing the wall from forming properly, which causes the bacteria to die. Its chemical structure specifically resists breakdown by penicillinase (also called beta-lactamase), an enzyme that many Staphylococcus bacteria produce to destroy standard penicillin, making flucloxacillin effective against these otherwise resistant strains.

• Standard dose (oral, adults): 250-500 mg taken orally four times daily, on an empty stomach (at least 30 minutes before or 2 hours after food) for optimal absorption.

• Condition-wise dose (severe infections, IV): Higher doses (e.g., 1-2 g given intravenously every 4-6 hours) are used for serious infections such as endocarditis or osteomyelitis, under hospital supervision.

• Route: Oral (capsules/suspension) or intravenous/intramuscular injection, depending on infection severity.

• Missed dose: Take as soon as remembered unless close to the next dose; don't double up; complete the full prescribed course even if symptoms improve.

• Overdose: May cause gastrointestinal upset or, at very high doses, neurological effects (rare); requires medical attention if significantly exceeded.

• Common: Nausea, diarrhoea, stomach upset, and mild skin rash.

• Serious: Cholestatic liver injury (a form of liver inflammation affecting bile flow), which can occur even weeks after stopping the medicine and is more common with longer courses or in older patients; severe allergic reactions; and Clostridioides difficile-associated diarrhoea.

• Emergency symptoms: Yellowing of the skin/eyes, dark urine, pale stools, signs of a severe allergic reaction (swelling of the face/throat, difficulty breathing, widespread rash), or severe/bloody diarrhoea.

• Recovery advice: Completing the full prescribed course, even if symptoms improve early, is important; any new jaundice or unusual fatigue occurring during or after treatment should be reported promptly, given the recognised risk of delayed liver injury.

• Pregnancy: Used when clearly needed, under medical guidance; considered relatively low risk among antibiotics.

• Breastfeeding: Generally considered compatible with medical guidance.

• Liver disease: Used with caution, given the specific recognised risk of flucloxacillin-associated cholestatic liver injury; risk increases with age, longer treatment duration, and repeated courses.

• Kidney disease: Dose adjustment may be needed in significant impairment.

• Elderly: Used with particular caution regarding liver injury risk, which is more common in this age group, especially with longer treatment courses.

• Children: Used with weight-based dosing under medical guidance.

• Methotrexate: flucloxacillin can reduce methotrexate clearance, increasing the risk of methotrexate toxicity; combined use requires caution and monitoring.

• Warfarin and other anticoagulants: antibiotics including flucloxacillin can occasionally affect blood clotting levels, warranting closer monitoring.

• Probenecid: can increase flucloxacillin blood levels by reducing its elimination.

• Oral contraceptives: antibiotics, including flucloxacillin, may theoretically reduce the effectiveness of hormonal contraceptives in some cases, though evidence for this specific interaction is limited; discussing backup contraception is a reasonable precaution during antibiotic courses.

• Liver function tests, particularly with longer treatment courses (more than 2 weeks) or in older patients.

• Clinical response monitoring (fever, infection markers, wound healing) to assess treatment effectiveness.

• Signs of allergic reaction, particularly with the first few doses.

Cloxacillin, Dicloxacillin (other penicillinase-resistant penicillins), Cefalexin (a cephalosporin alternative), Clindamycin (for penicillin-allergic patients) — chosen based on infection type and patient allergy history.

Sometimes combined with other antibiotics (such as rifampicin) for certain bone/joint or biofilm-associated infections, under infectious disease specialist guidance.

• Staphylococcal Infection Treatments

• Penicillin Antibiotics

• Skin & Soft Tissue Infection Medicines

1. Why Not All Viral Infections Need Antibiotics

2. AWaRe Classification Of Antibiotics

3. Buy Natural Antibiotics - Ancient Secrets For Healthy Living

4. Top 4 Treatment Of Fungal Infections Of The Skin

•  https://academic.oup.com/jac/article-abstract/5/4/359/803834

• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3679880/

The information on this page is for educational purposes only and is not a substitute for medical advice. Please consult your doctor to know if this treatment is appropriate for your condition.