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First-generation oral cephalosporin

Cefalexin

Brand names: Keflex

Adult dose

Dose: 250–500mg QDS or 1g BD–TDS
Route: Oral
Frequency: BD–QDS

Clinical pearls

  • NICE CKS / NG109 UTI in pregnancy: cefalexin recommended option
  • UKHSA primary care antibiotic stewardship
  • First-line / alternative for cellulitis when penicillin-allergic (mild)

Contraindications

  • Severe beta-lactam hypersensitivity

Side effects

  • GI upset
  • C. difficile
  • Rash
  • Hypersensitivity
  • Hepatitis (rare)
  • Eosinophilia
  • False-positive Coombs

Interactions

  • Probenecid
  • Warfarin (rare INR change)
  • Aminoglycosides (theoretical)

Monitoring

  • Resolution
  • C. diff

Reference: BNF; NICE CKS; NICE NG109; UKHSA; https://bnf.nice.org.uk/drugs/cefalexin/. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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