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First-Generation Cephalosporin Antibiotic Pregnancy: Safe in pregnancy; preferred antibiotic for UTI in pregnancy

Cefalexin (Cephalexin)

Brand names: Ceporex, Keflex

Adult dose

Dose: 250-500 mg four times daily (UTI treatment); 125-250 mg at night (prophylaxis)
Route: Oral
Frequency: Four times daily (treatment); once daily at night (prophylaxis)
Max: 4 g/day
Used for UTI in pregnancy (safe alternative), UTI prophylaxis after urological procedures, and catheter-associated UTI. Preferred over nitrofurantoin in late pregnancy and trimethoprim in early pregnancy

Paediatric dose

Dose: 12.5-25 mg/kg twice daily mg/kg
Route: Oral
Frequency: Twice daily
Max: 100 mg/kg/day (severe infection); 1 g/day (standard)
Child under 1 year: 125 mg twice daily. Child 1-4 years: 125 mg three times daily. Child 5-11 years: 250 mg three times daily

Dose adjustments

Renal

Reduce frequency in renal impairment: eGFR 10-40: every 8-12 hours; eGFR under 10: every 12-24 hours

Hepatic

No adjustment required

Paediatric weight-based calculator

Child under 1 year: 125 mg twice daily. Child 1-4 years: 125 mg three times daily. Child 5-11 years: 250 mg three times daily

Clinical pearls

  • Drug of choice for UTI in pregnancy — safe in all trimesters (unlike nitrofurantoin at term and trimethoprim in first trimester which is a folate antagonist)
  • Penicillin cross-hypersensitivity: approximately 1-2% true cross-reactivity; severe penicillin allergy (anaphylaxis) is a relative contraindication — assess risk-benefit
  • UTI prophylaxis: 125-250 mg nocte used after urological procedures (TURP, cystoscopy) or for recurrent UTI in women
  • E. coli resistance rates to cefalexin are increasing locally — check local antibiogram before prescribing empirically
  • Not active against Enterococcus — if enterococcal UTI suspected, use amoxicillin or nitrofurantoin instead

Contraindications

  • Hypersensitivity to cephalosporins
  • Severe hypersensitivity to penicillins (10% cross-reactivity — use with caution)

Side effects

  • GI upset (nausea, diarrhoea)
  • Candidal superinfection
  • Hypersensitivity reactions
  • C. difficile-associated diarrhoea (less commonly than broad-spectrum agents)

Interactions

  • Warfarin (enhanced anticoagulant effect)
  • Probenecid (increases cefalexin levels)

Monitoring

  • Symptom response
  • Urine culture to confirm organism and sensitivity
  • Renal function if prolonged use

Reference: BNFc; BNF 90; NICE NG109 (UTI in adults); NICE NG113 (UTI in under 16s); PHE Antimicrobial Guidelines. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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