Flucloxacillin for Infection: 5 Key Uses, Dosage & Side Effects
Comprehensive guide to flucloxacillin: uses, dosage, side effects, and key precautions for treating bacterial infections effectively.
Flucloxacillin is a narrow-spectrum penicillin antibiotic primarily used to treat bacterial infections caused by susceptible gram-positive bacteria, especially Staphylococcus aureus. It is commonly prescribed for skin and soft tissue infections (SSTIs), ear infections, bone infections, and certain respiratory infections.
About flucloxacillin
Flucloxacillin belongs to the penicillin class of antibiotics, specifically designed to resist breakdown by penicillinase enzymes produced by some bacteria. This makes it particularly effective against beta-lactamase-producing staphylococci. Unlike broader-spectrum penicillins, it targets infections likely caused by S. aureus, which is prevalent in community settings for SSTIs.
In clinical practice, flucloxacillin is the first-line oral treatment for uncomplicated staphylococcal infections. It works by interfering with bacterial cell wall synthesis, leading to bacterial death. It is available in oral capsules, suspensions, and intravenous forms, though oral use predominates in primary care.
Flucloxacillin is also combined with ampicillin in co-fluampicil for broader coverage against mixed infections.[10]
What is flucloxacillin used for?
Flucloxacillin treats a range of bacterial infections, focusing on those caused by staphylococci:
- Skin and soft tissue infections (SSTIs): Including cellulitis, boils, carbuncles, impetigo, folliculitis, abscesses, and infected wounds. It is the drug of choice for SSTIs in UK primary care.
- Ear infections: Such as otitis externa or media when staphylococcal involvement is suspected.
- Bone and joint infections: Like osteomyelitis, particularly staphylococcal.
- Respiratory infections: Heart and chest infections, including staphylococcal pneumonia.
- Prophylaxis: Before certain surgical procedures to prevent postoperative infections.
In boils and carbuncles, a seven-day course is recommended for fever, cellulitis, facial lesions, carbuncles, severe pain, or comorbidities like diabetes. For cellulitis, flucloxacillin 500 mg four times daily is standard first-line therapy.
Studies show flucloxacillin prescribing is almost exclusively for SSTIs in community settings, with cellulitis/abscess and secondary skin infections being common indications.
Before taking flucloxacillin
Inform your doctor if you have:
- Allergy to penicillins or other beta-lactam antibiotics.
- Liver or kidney problems, as flucloxacillin can affect liver function, especially in prolonged use.
- History of jaundice or hepatic dysfunction with previous flucloxacillin courses.
- Phenylketonuria (for liquid formulations containing aspartame).
- Mononucleosis or lymphatic leukemia, increasing rash risk.
Pregnancy and breastfeeding: Generally safe, but consult your doctor. It passes into breast milk in small amounts.
Interactions: May reduce efficacy of oral typhoid vaccine. Additional contraception needed if vomiting/diarrhea affects the pill.
How to take flucloxacillin
Follow your doctor’s instructions precisely. Key guidelines:
- Dosage for adults: Typically 250-500 mg four times daily. For severe infections like cellulitis, 500 mg QDS (four times daily).
- Children: Dose by weight, e.g., 125 mg QDS for younger children, up to adult dose for older.
- Timing: Take one hour before or two hours after food to improve absorption, as food reduces bioavailability.
- Duration: Complete the full course, usually 7 days for SSTIs. Longer for chronic or deep infections (e.g., 2 weeks initially for furunculosis, up to 6-8 weeks).
| Condition | Adult Dosage | Duration |
|---|---|---|
| Cellulitis/Boils | 500 mg QDS | 7 days |
| Impetigo (oral) | 500 mg QDS or alternative | 7 days |
| Osteomyelitis | 500 mg QDS (may IV initially) | Weeks |
Do not stop early even if symptoms improve, to prevent resistance or relapse. About 1 in 5 patients may need subsequent antibiotics within 4 weeks, indicating potential treatment failure or new infection.
Flucloxacillin side effects
Most side effects are mild and transient:
- Common (>1/100): Nausea, vomiting, diarrhea, skin rash.
- Serious (seek immediate help): Allergic reactions (itchy rash, swelling, breathing difficulty), severe diarrhea (possible C. difficile), jaundice, dark urine (liver issues).
- Rare: Thrush (oral/vaginal candidiasis), blood disorders.
Liver toxicity is more common with prolonged courses (>2 weeks) or high doses, especially in elderly patients.
How to manage flucloxacillin side effects
| Side Effect | Management |
|---|---|
| Feeling sick/vomiting | Stick to simple foods – crackers, toast, rice. Take with water. |
| Diarrhea | Drink plenty of fluids. If severe, bloody, or persistent, contact doctor (may indicate C. difficile). |
| Skin rash | Inform doctor promptly; may need switch to alternative like clarithromycin (penicillin-allergic). |
| Allergic reaction | Stop medicine, seek urgent medical help. |
Getting the most from your treatment
- Space doses evenly (every 6 hours).
- If you miss a dose, take it as soon as remembered unless near next dose.
- Complete the course to avoid resistance.
- For thrush: Consult pharmacist for antifungal treatment.
- Contraception: Use barrier methods if GI upset >24 hours.
- Monitoring: Regular blood tests for long-term use to check liver/kidney function.
- Vaccinations: Inform vaccinator about current antibiotic use.
Frequently Asked Questions (FAQs)
Q: Can I take flucloxacillin on an empty stomach?
A: Yes, ideally 1 hour before or 2 hours after food for best absorption.
Q: What if I forget a dose?
A: Take it as soon as you remember, but skip if almost time for next. Do not double up.
Q: Is flucloxacillin safe in pregnancy?
A: Category B; generally considered safe, but consult your doctor.
Q: How long until flucloxacillin works?
A: Symptoms improve within 48-72 hours; complete full course.
Q: What alternatives for penicillin allergy?
A: Clarithromycin, erythromycin, or doxycycline depending on infection.
If you take too much
Overdose may cause nausea, vomiting, diarrhea. Seek medical advice immediately; treatment is supportive.
Further information and advice
Store at room temperature. Discard unused medicine after course. For persistent symptoms post-treatment, revisit doctor – may indicate resistance or complication.
Antibiotic stewardship is crucial: Flucloxacillin’s targeted spectrum helps combat resistance when used appropriately for confirmed/suspected staphylococcal infections.
References
- Boils and Carbuncles — Patient.info. Accessed 2026. https://patient.info/doctor/dermatology/boils-and-carbuncles
- Flucloxacillin for infection — Patient.info. Accessed 2026. https://patient.info/medicine/flucloxacillin-for-infection
- Blind Treatment of Bacterial Infection — Patient.info. Accessed 2026. https://patient.info/doctor/paediatrics/blind-treatment-of-bacterial-infection
- Understanding flucloxacillin prescribing trends and treatment non-completion — PMC (PubMed Central). 2016-06-21. https://pmc.ncbi.nlm.nih.gov/articles/PMC4896409/
- Cellulitis and Erysipelas: Symptoms and Treatment — Patient.info. Accessed 2026. https://patient.info/doctor/dermatology/cellulitis-and-erysipelas-pro
- Flucloxacillin — Johns Hopkins ABX Guide. 2024-07-13. https://www.hopkinsguides.com/hopkins/view/Johns_Hopkins_ABX_Guide/540661/all/Flucloxacillin
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