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First-Generation Cephalosporin — Obstetric Antibiotic Pregnancy: Safe throughout pregnancy

Cefalexin (UTI / GBS Prophylaxis in Pregnancy)

Brand names: Ceporex, Keflex

Adult dose

Dose: 500 mg four times daily for 7 days (UTI treatment); 500 mg four times daily intrapartum (GBS — if penicillin allergic, low risk)
Route: Oral
Frequency: Four times daily
Max: 4 g/day
UTI in pregnancy: 7-day course recommended (longer than non-pregnant). GBS carrier with low-risk penicillin allergy: cefalexin oral for low-risk labours; benzylpenicillin IV preferred intrapartum for GBS prophylaxis

Paediatric dose

Dose: Not applicable in this obstetric context N/A/kg
Route: Oral
Frequency: N/A
Max: N/A
Maternal medication

Dose adjustments

Renal

Reduce frequency in severe renal impairment

Hepatic

No adjustment required

Paediatric weight-based calculator

Maternal medication

Clinical pearls

  • Preferred antibiotic for UTI in pregnancy — safe in all trimesters; nitrofurantoin avoided at term (neonatal haemolysis risk), trimethoprim avoided in first trimester (folate antagonist)
  • GBS (Group B Streptococcus): RCOG advises benzylpenicillin IV intrapartum as first-line; cefalexin oral is NOT adequate intrapartum GBS prophylaxis for high-risk labours — only IV antibiotics achieve sufficient fetal blood levels
  • 7-day course for UTI in pregnancy: longer than non-pregnant (3-5 days) due to physiological changes (ureteric dilatation, increased renal blood flow, glycosuria) increasing risk of ascending infection and pyelonephritis
  • Test of cure: urine culture 7 days after completing treatment mandatory in pregnancy — asymptomatic bacteriuria recurrence is common
  • Penicillin allergy assessment: document exact reaction — if anaphylaxis/urticaria, avoid cephalosporins; if rash only (non-IgE-mediated), cefalexin generally safe

Contraindications

  • Hypersensitivity to cephalosporins
  • Severe penicillin allergy (10% cross-reactivity — use alternative)

Side effects

  • GI upset
  • Candidal superinfection
  • Hypersensitivity reactions

Interactions

  • Warfarin (enhanced anticoagulant effect)

Monitoring

  • Urine culture test of cure (7 days after treatment)
  • Symptoms resolution

Reference: BNFc; BNF 90; RCOG Green-top 36 (Group B Streptococcal Disease 2017); NICE NG112 (UTI in Adults). Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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