Antibiotic (Penicillinase-Resistant Penicillin) Pregnancy: B — safe

Flucloxacillin

Brand names: Floxapen

Adult dose

Dose: 250–500mg four times daily

Route: Oral or IV

Frequency: Four times daily on empty stomach

Cellulitis: 500mg QDS × 5–7 days oral. Severe/IV: 1–2g QDS. Take 30–60 min before food.

Dose: 12.5 mg/kg

Route: Oral

Frequency: Four times daily

Max: 500mg per dose

Neonates: 25mg/kg BD. Over 1 month: 12.5mg/kg QDS. Severe infection: up to 50mg/kg QDS IV.

Paediatric weight-based calculator

Patient weight (kg)

Neonates: 25mg/kg BD. Over 1 month: 12.5mg/kg QDS. Severe infection: up to 50mg/kg QDS IV.

Antistaph penicillin — first-line for MSSA: cellulitis, wound infections, osteomyelitis, septic arthritis
NOT active against MRSA — if MRSA risk, use vancomycin or linezolid
Must be taken on empty stomach — food reduces absorption by 50%
Hepatotoxicity risk increases with duration >2 weeks and age >55 — monitor LFTs
HLA-B*57:01 associated with hypersensitivity reactions (less well-characterised than with co-amoxiclav)

Hepatitis / cholestatic jaundice (idiosyncratic — can be delayed up to 2 months)
GI upset
Rash
Interstitial nephritis

Reference: BNFc; NICE CKS Cellulitis; PHE Antibiotic Guidelines. Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways