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Antibiotic (Nitrofuran) Pregnancy: B (first/second trimester) — D (third trimester)

Nitrofurantoin

Brand names: Macrobid, Macrodantin, Furadantin

Adult dose

Dose: 50–100mg four times daily × 3–7 days (MR: 100mg BD)
Route: Oral
Frequency: Four times daily (standard) or twice daily (MR)
Macrobid MR 100mg BD preferred for compliance. UTI prophylaxis: 50–100mg nightly. Always take with food.

Clinical pearls

  • Acts only in urine — NO systemic activity. Only for lower UTI, NOT pyelonephritis
  • Pulmonary toxicity (rare but serious): acute (weeks — eosinophilia, fever) and chronic (months–years — fibrosis)
  • Urine turns yellow-brown — warn patients (not harmful)
  • Good activity against E. coli including trimethoprim-resistant strains
  • Avoid in eGFR <30 — inadequate urinary drug levels AND accumulation of toxic metabolites

Contraindications

  • eGFR <30 (insufficient urinary concentration)
  • Third trimester of pregnancy (haemolytic anaemia risk to neonate)
  • G6PD deficiency
  • Neonates <3 months

Side effects

  • Nausea (reduce by taking with food)
  • Pulmonary toxicity (acute: eosinophilic pneumonia; chronic: fibrosis)
  • Peripheral neuropathy (prolonged use)
  • Hepatotoxicity
  • Haemolytic anaemia (G6PD)

Interactions

  • Magnesium salts — reduced absorption
  • Uricosuric agents — increased levels

Monitoring

  • CXR and LFTs if prolonged treatment (>6 months)
  • eGFR before starting

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

Related

Curated clinical cross-links plus same-class fallbacks.

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