Antibiotic — Penicillinase-Resistant Pregnancy: Should only be used in pregnancy when potential benefits outweigh the potential risks; animal studies show no teratogenic effects, limited human data (UK SPC §4.6)

Flucloxacillin

Brand names: Floxapen

Used in: Cellulitis & Skin Infection

Flucloxacillin is a penicillinase-resistant penicillin used for staphylococcal and streptococcal infections, including skin and soft-tissue infections.

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

Route: IV (slow injection or infusion)

Frequency: Every six hours

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

UK SPC (1000 mg powder for solution for injection/infusion); ENT/infection use. Usual adult dose (including elderly), by slow IV injection or infusion: 250 mg to 1 g every six hours; doses may be doubled in severe infections. Osteomyelitis: up to 8 g daily in 3-4 divided doses. Endocarditis: 8 g daily in four divided doses (patients up to 85 kg), 12 g daily in six divided doses (heavier patients). Surgical prophylaxis: 1-2 g IV at induction of anaesthesia then 500 mg six-hourly IV/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. No single bolus/infusion to exceed 2 g; maximum 12 g/day.

Paediatric dose

Dose: 25 mg/kg

Route: IM or IV

Frequency: Per 24 hours, in three to four equally divided doses (25 to 50 mg/kg/24 h)

Max: Up to 100 mg/kg/24 h in severe infections; no single bolus injection or infusion to exceed 33 mg/kg

UK SPC, children under 14 years: 25 to 50 mg/kg/24 hours in three to four equally divided doses by IM or IV injection (dosePerKg shown as the lower bound of the daily range). By age band: children 10-14 years usually 1.5-2 g/day; children 6-10 years 0.75-1.5 g/day, each divided into three to four doses. Severe infections: up to 100 mg/kg/24 h. No single bolus/infusion to exceed 33 mg/kg. Verify against a children's formulary.

Dose adjustments

Renal

Usually no dose reduction required; in severe renal failure (creatinine clearance <10 ml/min) consider reduced dose or extended interval — maximum recommended dose 1 g every 8 to 12 hours

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 (very rare; may be delayed up to two months)
Anaphylactic shock and angioneurotic oedema (very rare)
Neutropenia, thrombocytopenia, eosinophilia, haemolytic anaemia (very rare)

Interactions

Paracetamol (increased risk of high anion gap metabolic acidosis, especially with severe renal impairment, sepsis or malnutrition; monitor)

Clinical monograph

How it works

A beta-lactam, stable to staphylococcal penicillinase, that inhibits bacterial cell-wall synthesis.

Prescribing in practice

Contraindicated in penicillin allergy and in previous flucloxacillin-associated jaundice or hepatic dysfunction.
Cholestatic hepatitis can occur, sometimes up to several weeks after stopping, and is more common in older patients and with prolonged courses.
Take it on an empty stomach for better absorption.

Monitoring

Consider liver function with prolonged courses; review clinical response.

Counselling the patient

Take it before food and complete the course.
Report yellowing of the skin or eyes or dark urine, even after finishing the course.

Evidence & guidelines

First-line for staphylococcal skin and soft-tissue infection (e.g. cellulitis) per NICE/PHE guidance.

Reference: RCOphth Orbital Cellulitis Guidelines; MHRA Drug Safety Update (cholestatic jaundice); 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