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Urinary Antiseptic Pregnancy: Compatible in second trimester; avoid at term (haemolytic anaemia in neonate)

Nitrofurantoin (UTI Treatment)

Brand names: Macrobid, Furadantin

Adult dose

Dose: Acute UTI: 100 mg modified-release (Macrobid) BD × 5 days. Prophylaxis: 50–100 mg OD at night. Uncomplicated UTI: 3–7 days.
Route: Oral (with food to reduce GI side effects)
Frequency: BD (treatment); OD (prophylaxis)
Max: 400 mg/day treatment; 100 mg/day prophylaxis
Only effective for lower UTI (does not achieve tissue levels). Do NOT use if eGFR <45 — reduced urinary drug concentration (less effective) and risk of drug accumulation. NICE first-line for uncomplicated lower UTI in women.

Paediatric dose

Dose: 750 mcg/kg
Route: Oral
Frequency: QDS (treatment); OD (prophylaxis)
Max: 100 mg per dose
Concentration: 5000 mcg/ml
BNF for Children: treatment 750 mcg/kg (= 0.75 mg/kg) QDS (≥3 months), max 100 mg per dose. Prophylaxis: 1–2 mg/kg OD at night (max 100 mg). See nitrofurantoin_paed entry for full details. Source: BNF for Children 2024; NICE NG224

Dose adjustments

Renal

Avoid if eGFR <45 (MHRA guidance) — reduced efficacy and drug accumulation

Hepatic

Caution in severe hepatic impairment

Paediatric weight-based calculator

BNF for Children: treatment 750 mcg/kg (= 0.75 mg/kg) QDS (≥3 months), max 100 mg per dose. Prophylaxis: 1–2 mg/kg OD at night (max 100 mg). See nitrofurantoin_paed entry for full details. Source: BNF for Children 2024; NICE NG224

Clinical pearls

  • NICE NG109: nitrofurantoin first-line for uncomplicated lower UTI in women (over trimethoprim due to resistance patterns)
  • Brown urine: reassure patient — harmless metabolite excretion
  • NOT for pyelonephritis or systemic UTI — does not achieve tissue/renal parenchymal levels
  • Pulmonary toxicity: acute presents as fever, cough, dyspnoea within months; chronic as progressive ILD — monitor symptoms and CXR with long-term use

Contraindications

  • eGFR <45
  • Age <3 months (neonates — G6PD)
  • G6PD deficiency
  • Pulmonary fibrosis

Side effects

  • Nausea (take with food)
  • Pulmonary reactions (acute: eosinophilic pneumonitis; chronic: fibrosis)
  • Peripheral neuropathy (prolonged use)
  • Haemolytic anaemia (G6PD deficiency)
  • Hepatotoxicity (rare)
  • Brown urine discolouration

Interactions

  • Quinolones — mutual antagonism; avoid combination
  • Antacids (magnesium trisilicate) — reduce absorption

Monitoring

  • LFTs (prolonged use)
  • Pulmonary symptoms
  • Peripheral neuropathy symptoms
  • eGFR before starting

Reference: BNFc; BNF; NICE NG109 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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