ClinCalc Pro
Menu
Calculators Drugs Pathways AI Dx Donate Get the App
Anti-Staphylococcal Penicillin Pregnancy: Compatible — used throughout pregnancy for skin and soft tissue infections

Flucloxacillin (Paediatric)

Brand names: Floxapen

Adult dose

Dose: 250–500 mg QDS oral (1g QDS severe); 1–2 g IV every 6h
Route: Oral or IV
Frequency: QDS
Max: 8 g/day IV
For Staphylococcal infections — cellulitis, impetigo, bone/joint infections. Take 30 min before food.

Paediatric dose

Dose: 12.5 mg/kg
Route: Oral or IV
Frequency: QDS
Max: 500 mg per oral dose; 1 g per IV dose
Concentration: 125 mg/5 mL oral suspension mg/ml
BNF for Children: oral 12.5–25 mg/kg QDS (calculator uses conservative 12.5 mg/kg). Severe/systemic infections: IV 50 mg/kg every 6h (max 2 g). Neonates: IV 25 mg/kg every 12h (first 7 days), every 8h (7–21 days), every 6h (>21 days). ALWAYS give oral dose 30–60 min before food. Source: BNF for Children 2024; NICE NG141

Dose adjustments

Renal

No dose adjustment for mild-moderate renal impairment; caution in severe

Hepatic

Avoid or use with caution — hepatotoxicity (cholestatic jaundice) associated, risk increases with age and prolonged use

Paediatric weight-based calculator

BNF for Children: oral 12.5–25 mg/kg QDS (calculator uses conservative 12.5 mg/kg). Severe/systemic infections: IV 50 mg/kg every 6h (max 2 g). Neonates: IV 25 mg/kg every 12h (first 7 days), every 8h (7–21 days), every 6h (>21 days). ALWAYS give oral dose 30–60 min before food. Source: BNF for Children 2024; NICE NG141

Clinical pearls

  • Take on empty stomach — food reduces absorption by 50%
  • For neonatal Staphylococcal infections: IV flucloxacillin first-line
  • For MSSA bacteraemia: high-dose flucloxacillin (2g IV every 4–6h) for 2+ weeks
  • Hepatotoxicity: rare but serious — more common in adults than children; usually cholestatic, occurring weeks after stopping

Contraindications

  • Penicillin allergy
  • Previous flucloxacillin-associated hepatotoxicity

Side effects

  • GI upset (nausea, diarrhoea)
  • Cholestatic hepatitis (delayed — more common with prolonged use)
  • Rash
  • Anaphylaxis (rare)

Interactions

  • Anticoagulants — may increase INR (monitor warfarin if long-term)
  • Methotrexate — increased MTX toxicity

Monitoring

  • LFTs (prolonged courses)
  • Clinical response (temperature, inflammatory markers)
  • Renal function

Reference: BNF for Children; NICE NG141 Cellulitis. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

Calculators
Pathways