Penicillinase-Resistant Penicillin (Anti-Staphylococcal) Pregnancy: Animal studies with flucloxacillin have shown no teratogenic effects and limited information is available on use in human pregnancy - flucloxacillin should only be used in pregnancy when the potential benefits outweigh the potential risks. Trace quantities can be detected in breast milk and the possibility of hypersensitivity reactions in the breastfed infant must be considered, so it should only be given to a breast-feeding mother when the potential benefits outweigh the risks.

Flucloxacillin 1–2g IV

Brand names: Floxapen

Used in: Cellulitis & Skin Infection

Intravenous flucloxacillin is a penicillinase-stable (anti-staphylococcal) beta-lactam antibiotic used for bone and joint infections, including osteomyelitis and septic arthritis caused by meticillin-susceptible Staphylococcus aureus and streptococci.

Adult dose

Dose: 250 mg to 1 g every six hours; these doses may be doubled in severe infections. For osteomyelitis, doses of up to 8 g daily divided in 3 to 4 divided doses have been suggested

Route: Slow intravenous injection over three to four minutes, or by infusion (flucloxacillin may also be added to infusion fluids or injected, suitably diluted, into the drip tube over three to four minutes)

Frequency: Every six hours (usual adult dosage, including the elderly); osteomyelitis regimens are divided into 3 to 4 doses per day

Max: The maximum dose of 12 g per day should not be exceeded; no single bolus injection or infusion should exceed 2 g

The dosage depends on age, weight and renal function of the patient, as well as the severity and nature of the infection. Endocarditis: 8 g daily in four divided doses in patients weighing up to 85 kg, and 12 g daily in six divided doses in those weighing more. Surgical prophylaxis: 1 to 2 g intravenously at induction of anaesthesia followed by 500 mg six-hourly intravenously or intramuscularly for up to 48 hours. Other routes stated in the SPC: intramuscular 250 mg four times daily; intra-articular 250 to 500 mg once daily; intrapleural 250 mg once daily; nebuliser 125 to 250 mg four times daily. Ocular or subconjunctival administration is contraindicated. During prolonged treatments (e.g. osteomyelitis, endocarditis) regular monitoring of hepatic and renal function is recommended. Care is needed with very high doses, especially if renal function is poor, because of the risk of nephrotoxicity. Flucloxacillin injection contains approximately 51 mg sodium per gram, which should be included in the daily allowance of patients on a sodium-restricted diet. Hepatic impairment: dose reduction is not necessary, but use with caution in patients with evidence of hepatic dysfunction, patients aged 50 and over and those with serious underlying disease. Some sections of the product information we used were incomplete — check the full SPC.

Paediatric dose

Route: Intramuscular or intravenous injection

Frequency: Three to four equally divided doses per 24 hours

Max: In cases of severe infections, up to 100 mg/kg per 24 hours in three to four divided doses; no single bolus injection or infusion should exceed 33 mg/kg

Children under 14 years of age: 25 to 50 mg/kg per 24 hours administered in three to four equally divided doses by IM or IV injection. Children aged 10 to 14 years usually receive a daily dose of 1.5 g to 2 g, and children aged 6 to 10 years 0.75 g to 1.5 g, divided into three to four equal doses. Verify against a children's formulary before administration.

Dose adjustments

Renal

Usage in renal impairment does not usually require dosage reduction. However, in severe renal failure (creatinine clearance below 10 mL/min) a reduction in dose or an extension of the dose interval should be considered - the maximum recommended dose is 1 g every 8 to 12 hours. Flucloxacillin is not significantly removed by dialysis, so no supplementary dosages are needed during or at the end of the dialysis period.

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via the eMC — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

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

Side effects

Minor gastrointestinal disturbances (common); pseudomembranous colitis (very rare)
Rash, urticaria and purpura (uncommon); erythema multiforme, Stevens-Johnson syndrome and toxic epidermal necrolysis (very rare); acute generalised exanthematous pustulosis (frequency not known)
Hepatitis and cholestatic jaundice and changes in liver function tests (very rare) - may be delayed for up to two months post-treatment, may be severe and have very rarely been fatal, mostly in patients over 50 years and those with serious underlying disease
Neutropenia (including agranulocytosis), thrombocytopenia, eosinophilia and haemolytic anaemia (very rare)
Anaphylactic shock and angioneurotic oedema (very rare); hypokalaemia (frequency not known); neurological disorders with convulsions after IV injection of high doses in patients with renal failure (very rare)

Interactions

Caution is advised when flucloxacillin is administered concomitantly with paracetamol due to the increased risk of high anion gap metabolic acidosis (HAGMA), particularly in patients with severe renal impairment, sepsis or malnutrition and especially at maximum daily paracetamol doses - close monitoring for acid-base disturbance is recommended after co-administration

Clinical monograph

How it works

It inhibits bacterial cell-wall synthesis by binding penicillin-binding proteins and is resistant to staphylococcal beta-lactamase, making it active against meticillin-susceptible staphylococci.

Prescribing in practice

Contraindicated in penicillin allergy, and there is a recognised risk of cholestatic hepatitis that can occur weeks after stopping, particularly in older patients on prolonged courses.
High-dose intravenous therapy carries a sodium load relevant in heart failure or renal impairment, and requires dose adjustment in severe renal impairment.
Bone-penetration concerns mean prolonged courses are usual; ensure adequate hydration and review the line/route as treatment progresses.

Monitoring

Monitor liver function, renal function and inflammatory markers over a prolonged course, with hepatic review if jaundice or dark urine develops.

Counselling the patient

Report yellowing of the skin or eyes, dark urine or pale stools even after the course finishes.
Complete the full course to clear a bone infection.
Tell the team of any previous reaction to penicillin.

Evidence & guidelines

MHRA has warned of the risk of cholestatic jaundice and hepatitis with flucloxacillin, which may be delayed in onset.

Reference: Public Health England Osteomyelitis Guidelines; BSAC Bone and Joint Infection 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.

Calculators

Pathways