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Antibiotic — Penicillinase-Resistant Pregnancy: Use with caution — limited data; considered appropriate for severe ENT infections in pregnancy

Flucloxacillin

Brand names: Floxapen

Adult dose

Dose: 500 mg–1 g
Route: Oral / IV
Frequency: Every 6 hours (30–60 minutes before food for oral)
Max: 8 g/day (IV in severe infections)
Used in ENT for periorbital/orbital cellulitis (Staphylococcal), post-auricular cellulitis, infected pinna, infected wounds. IV doses for severe or orbital infections. Take oral doses on empty stomach — food reduces absorption by up to 50%.

Paediatric dose

Dose: 12.5–25 mg/kg mg/kg
Route: Oral / IV
Frequency: Every 6 hours
Max: 1 g per dose (IV); 500 mg per dose (oral)
BNFc: neonates 25–50 mg/kg/day divided every 6–12h; 1 month–2 years 62.5 mg QDS; 2–10 years 125–250 mg QDS; 10–18 years 250–500 mg QDS

Dose adjustments

Renal

No dose adjustment required in mild-moderate renal impairment

Hepatic

Avoid if history of flucloxacillin-associated jaundice/hepatic impairment

Paediatric weight-based calculator

BNFc: neonates 25–50 mg/kg/day divided every 6–12h; 1 month–2 years 62.5 mg QDS; 2–10 years 125–250 mg QDS; 10–18 years 250–500 mg QDS

Clinical pearls

  • Only β-lactam effective against MSSA (penicillinase-producing Staphylococcus aureus) — essential for staphylococcal ENT infections
  • Orbital cellulitis: ADMIT, IV flucloxacillin ± metronidazole + urgent ophthalmology + CT orbits; risk of cavernous sinus thrombosis and visual loss
  • MHRA: cholestatic jaundice risk — check LFTs if jaundice develops; more common with prolonged courses (>14 days) and in older patients
  • Must be taken on EMPTY STOMACH — food reduces absorption by up to 50%; counsel patients specifically
  • MRSA: flucloxacillin is ineffective — use vancomycin or teicoplanin IV, or doxycycline/trimethoprim for mild MRSA

Contraindications

  • Penicillin hypersensitivity
  • History of flucloxacillin-associated cholestatic jaundice

Side effects

  • GI disturbance
  • Cholestatic jaundice (rare — more common with prolonged use or age >55)
  • Rash
  • Anaphylaxis
  • Interstitial nephritis

Interactions

  • Methotrexate — reduced excretion
  • Warfarin — may affect INR

Monitoring

  • LFTs (prolonged use or jaundice)
  • Clinical response
  • Signs of orbital extension (proptosis, ophthalmoplegia, reduced visual acuity)

Reference: BNFc; BNF 90; BNFc; RCOphth Orbital Cellulitis Guidelines; MHRA Drug Safety Update (cholestatic jaundice). Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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