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Penicillinase-Resistant Penicillin (Anti-Staphylococcal)

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.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

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. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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