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Urinary Antibiotic — Obstetric Pregnancy: Avoid from 36 weeks gestation onwards; use with caution in first trimester

Nitrofurantoin (UTI in Pregnancy)

Brand names: Macrobid, Furadantin

Adult dose

Dose: 100 mg modified release twice daily for 7 days (treatment); 50-100 mg at night (prophylaxis)
Route: Oral (with food)
Frequency: Twice daily (treatment); once nightly (prophylaxis)
Max: 300 mg/day
NICE NG109 first-line for uncomplicated UTI. Avoid in pregnancy at term (37 weeks onwards) and during labour — risk of neonatal haemolytic anaemia (immature red cell glutathione instability)

Paediatric dose

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

Dose adjustments

Renal

Avoid if eGFR under 45 — inadequate urinary concentrations and metabolite accumulation

Hepatic

Use with caution

Paediatric weight-based calculator

Maternal medication

Clinical pearls

  • AVOID from 36-37 weeks gestation onwards and during labour — neonatal haemolytic anaemia risk; switch to cefalexin from 36 weeks
  • First trimester: historically avoided due to theoretical folate antagonism — NICE NG112 now considers it acceptable in first trimester when alternatives not appropriate
  • MHRA 2014: Long-term use (above 6 months) associated with pulmonary and hepatic toxicity — reassess prophylaxis need regularly; not for long-term use in pregnancy
  • Modified release formulation (Macrobid 100 mg MR): improved GI tolerability over standard release — preferred for treatment
  • Recurrent UTI prophylaxis in pregnancy: cefalexin 125-250 mg nocte is a safer option than long-term nitrofurantoin in pregnancy

Contraindications

  • Third trimester / term (37 weeks onwards)
  • Labour and delivery
  • Neonates under 3 months
  • eGFR under 45

Side effects

  • Nausea (take with food)
  • Pulmonary reactions (prolonged use — rare)
  • Hepatotoxicity (prolonged use — MHRA warning)
  • Peripheral neuropathy (prolonged use)
  • Neonatal haemolysis (if used at term)

Interactions

  • Magnesium trisilicate (reduces absorption)
  • Quinolones (antagonism — avoid combination)
  • Uricosurics (increase nitrofurantoin toxicity)

Monitoring

  • Urine culture test of cure
  • Symptoms resolution
  • LFTs and pulmonary symptoms (long-term use)

Reference: BNFc; BNF 90; NICE NG109 (UTI in Adults); MHRA Drug Safety Update 2014 (nitrofurantoin); RCOG UTI in Pregnancy Guidance. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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