Penicillinase-Resistant Penicillin — Staphylococcal Infections Pregnancy: Animal studies show no teratogenic effects; limited human data. Use in pregnancy only when potential benefits outweigh the risks. Trace quantities detected in breast milk - consider possibility of hypersensitivity reactions in breastfed infants.

Flucloxacillin

Brand names: Floxapen

Flucloxacillin is a penicillinase-stable (isoxazolyl) penicillin used for infections caused by beta-lactamase-producing staphylococci, including skin and soft tissue infection, osteomyelitis and staphylococcal endocarditis.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 250 mg to 1 g every six hours

Route: Slow intravenous injection (over 3-4 minutes) or by infusion

Frequency: Every 6 hours

Max: 12 g per day (no single bolus injection or infusion should exceed 2 g)

Usual adult dose (including elderly) by slow IV injection or infusion: 250 mg to 1 g every six hours; these doses may be doubled in severe infections. Osteomyelitis: up to 8 g daily in 3-4 divided doses has been suggested. Endocarditis: 8 g daily in 4 divided doses (patients up to 85 kg), or 12 g daily in 6 divided doses (heavier patients). Surgical prophylaxis: 1-2 g IV at induction of anaesthesia then 500 mg six-hourly IV or IM for up to 48 hours. By IM injection: 250 mg four times daily. By intrapleural injection: 250 mg once daily. By nebuliser: 125-250 mg four times daily. By intra-articular injection: 250-500 mg once daily. Dosage depends on age, weight, renal function and severity/nature of infection. Hepatic impairment: dose reduction not necessary.

Paediatric dose

Dose: 25 mg/kg

Route: IM or IV injection

Frequency: Per 24 hours, administered in three to four equally divided doses

Max: Up to 100 mg/kg/24 hours in three to four divided doses in severe infections; no single bolus injection or infusion should exceed 33 mg/kg

Children under 14 years: 25 to 50 mg/kg/24 hours in three to four equally divided doses by IM or IV injection. Children aged 10-14 years usually receive 1.5 g to 2 g daily and children aged 6-10 years 0.75 g to 1.5 g daily, divided into three to four equal doses. Severe infections: up to 100 mg/kg/24 hours in three to four divided doses. Clinician to verify all paediatric doses against a children's formulary.

Dose adjustments

Renal

Usually no dose reduction required. In severe renal failure (creatinine clearance <10 ml/min) consider dose reduction or extended dose interval; maximum recommended dose 1 g every 8 to 12 hours. Not significantly removed by dialysis - no supplementary dosing needed. Care with very high doses in poor renal function (risk of nephrotoxicity).

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Paediatric weight-based calculator

Patient weight (kg)

Verify in a children's formulary

Contraindications

History of hypersensitivity to beta-lactam antibiotics (e.g. penicillins, cephalosporins)
Previous history of flucloxacillin-associated jaundice/hepatic dysfunction
Ocular or subconjunctival administration

Side effects

Minor gastrointestinal disturbances (common)
Rash, urticaria and purpura (uncommon)
Hepatitis and cholestatic jaundice; changes in liver function tests (very rare, may be delayed up to two months post-treatment)
Anaphylactic shock, angioneurotic oedema (very rare)
Neutropenia, thrombocytopenia, eosinophilia, haemolytic anaemia (very rare)

Interactions

Paracetamol - increased risk of high anion gap metabolic acidosis (HAGMA), especially in severe renal impairment, sepsis or malnutrition; close monitoring recommended after co-administration

Clinical monograph

How it works

It binds penicillin-binding proteins to inhibit bacterial cell wall peptidoglycan cross-linking and resists staphylococcal penicillinase, giving it activity against methicillin-susceptible Staphylococcus aureus.

Prescribing in practice

Flucloxacillin carries an MHRA-highlighted risk of cholestatic hepatitis and jaundice, which can occur up to two months after stopping and is more likely with prolonged courses and in older patients.
It is contraindicated in patients with a history of flucloxacillin-associated jaundice or hepatic dysfunction and in those with penicillin hypersensitivity.
Oral absorption is reduced by food, so doses are best taken on an empty stomach before meals.

Monitoring

Monitor liver function, particularly during prolonged or high-dose intravenous therapy and in older patients, and watch for signs of jaundice.

Counselling the patient

Take it before food, spaced through the day, and complete the full course.
Seek medical advice if you notice yellowing of the skin or eyes, dark urine or pale stools.
Tell the team about any previous penicillin allergy or past reaction to this medicine.

Evidence & guidelines

MHRA Drug Safety advice highlights the risk of cholestatic jaundice and hepatitis with flucloxacillin, especially with courses exceeding two weeks and in the elderly.

Reference: MHRA Drug Safety Update 2016 (Flucloxacillin Hepatotoxicity); NICE CG121 (Cellulitis); Public Health England Antibiotic Guidelines; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

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