Anti-Staphylococcal Penicillin Pregnancy: §4.6: animal studies 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 are detectable 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 potential risks.

Flucloxacillin (Paediatric)

Brand names: Floxapen

Flucloxacillin is a narrow-spectrum penicillinase-resistant penicillin used in children for staphylococcal infections such as skin and soft tissue infections, bone and joint infection and infective 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 by slow intravenous injection or by infusion; these doses may be doubled in severe infections

Route: Slow intravenous injection over three to four minutes, or intravenous infusion (may also be given by intramuscular, intrapleural, intra-articular injection or by nebuliser — see notes)

Frequency: Every six hours

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

IMPORTANT SOURCE CAVEAT: the fetched SPC is the PARENTERAL product — UK SPC (eMC) for Flucloxacillin 1000 mg powder for solution for injection or infusion, §4.2 (https://www.medicines.org.uk/emc/product/12396/smpc). It does NOT contain oral posology; if the page needs oral flucloxacillin dosing, source the oral capsule/suspension SPC separately. The dosage depends on age, weight and renal function of the patient as well as the severity and nature of the infection. OTHER ADULT REGIMENS PER §4.2: osteomyelitis — doses of up to 8 g daily divided in three to four divided doses have been suggested; 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; by intramuscular injection — 250 mg four times daily; by intrapleural injection — 250 mg once daily; by nebuliser — 125 to 250 mg four times daily; by intra-articular injection — 250 to 500 mg once daily. HEPATIC IMPAIRMENT: dose reduction is not necessary in patients with reduced hepatic function. ADMINISTRATION: give by slow intravenous injection over three to four minutes; may also be added to infusion fluids or injected, suitably diluted, into the drip tube over three to four minutes. Flucloxacillin injection contains approximately 51 mg sodium per g (§4.4). PAEDIATRIC POSOLOGY is captured in the paedDose block.

Paediatric dose

Route: Intramuscular or intravenous injection

Frequency: Total daily dose administered in three to four equally divided doses over 24 hours

Max: In severe infections: up to 100 mg/kg/24 hours in three to four divided doses. No single bolus injection or infusion should exceed 33 mg/kg

SPC §4.2, children under 14 years of age: '25 to 50 mg/kg/24 hours administered in three to four equally divided doses by i.m. or i.v. injection.' A range is stated rather than a single figure, so dosePerKg is left null — use the quoted range. The SPC adds that 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. This is the parenteral SPC only — oral paediatric dosing is not covered here. Verify all paediatric dosing against a children's formulary before prescribing.

Dose adjustments

Renal

In common with other penicillins, use in patients with renal impairment does not usually require dosage reduction. However, in the presence of severe renal failure (creatinine clearance <10 ml/min) a reduction in dose or an extension of 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 doses need be given during or at the end of dialysis. §4.4 adds that care is necessary if very high doses are given, especially if renal function is poor, because of the 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.

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

Common: minor gastrointestinal disturbances
Uncommon: rash, urticaria and purpura
Very rare: hepatitis and cholestatic jaundice (may be delayed up to two months post-treatment; hepatic events may be severe and deaths have very rarely been reported, mostly in patients over 50 and those with serious underlying disease); changes in liver function tests
Very rare: anaphylactic shock and angioneurotic oedema; neutropenia (including agranulocytosis), thrombocytopenia, eosinophilia, haemolytic anaemia
Very rare: pseudomembranous colitis; erythema multiforme, Stevens-Johnson syndrome and toxic epidermal necrolysis; not known — acute generalized exanthematous pustulosis (AGEP). In patients with renal failure, neurological disorders with convulsions are possible with IV injection of high doses
NOTE: the §4.8 list was truncated at the source-fetch limit — this list is incomplete

Interactions

NOTE: §4.5 was not present in the fetched bundle — the entry below is drawn from §4.4; source the full interactions section separately
Paracetamol — 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 if maximum daily doses of paracetamol are used; close monitoring is recommended after co-administration (§4.4/§4.8)

Clinical monograph

How it works

It inhibits bacterial cell wall synthesis by binding penicillin-binding proteins and is stable to staphylococcal beta-lactamase, retaining activity against most Staphylococcus aureus.

Prescribing in practice

It is contraindicated in penicillin allergy, and rare cholestatic hepatitis and jaundice can occur up to weeks after stopping, even after a short course.
Take oral doses on an empty stomach, ideally before food, as food reduces absorption; high parenteral doses require attention to renal function and electrolytes.
Dose by body weight using a children's formulary, with higher doses for deep-seated infections such as osteomyelitis.

Monitoring

On prolonged or high-dose courses monitor liver and renal function and observe for signs of hypersensitivity.

Counselling the patient

Give doses about an hour before food and complete the full course.
Report any jaundice, pale stools, dark urine, rash or itching, which can appear after treatment ends.
Tell the team about any previous reaction to penicillin or other antibiotics.

Evidence & guidelines

Flucloxacillin is the established first-line antistaphylococcal penicillin in UK practice, with MHRA advice highlighting the risk of delayed cholestatic hepatic reactions.

Reference: NICE NG141 Cellulitis; 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