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Urinary Antiseptic Antibiotic Pregnancy: Avoid at term — haemolytic anaemia in neonate; compatible in first and second trimester

Nitrofurantoin (Paediatric — UTI Prophylaxis)

Brand names: Macrobid, Furadantin

Adult dose

Dose: Treatment: 100 mg (MR) BD for 5 days or 50–100 mg QDS for 7 days. Prophylaxis: 50–100 mg OD at night
Route: Oral
Frequency: BD or QDS treatment; OD prophylaxis
Max: 400 mg/day treatment; 100 mg/day prophylaxis
Adult — do not use if eGFR <45 (reduced efficacy and drug accumulation risk)

Paediatric dose

Dose: 750 mcg/kg
Route: Oral
Frequency: QDS (treatment, 3–7 days); OD at night (prophylaxis)
Max: 100 mg per dose
Concentration: 25000 mcg/5 mL (25 mg/5 mL suspension) mcg/ml
BNF for Children: treatment 750 mcg/kg (= 0.75 mg/kg) QDS × 3–7 days (≥3 months), max 100 mg per dose. Prophylaxis (recurrent UTI/VUR): 1–2 mg/kg OD at night, max 100 mg. Do NOT use <3 months (haemolytic anaemia risk). Avoid in G6PD deficiency. Source: BNF for Children 2024; NICE NG224; RIVUR Trial (Hoberman, NEJM 2014)

Dose adjustments

Renal

Avoid if eGFR <45 — risk of drug accumulation and toxicity, and reduced urinary concentration (less effective)

Hepatic

Caution in hepatic impairment

Paediatric weight-based calculator

BNF for Children: treatment 750 mcg/kg (= 0.75 mg/kg) QDS × 3–7 days (≥3 months), max 100 mg per dose. Prophylaxis (recurrent UTI/VUR): 1–2 mg/kg OD at night, max 100 mg. Do NOT use <3 months (haemolytic anaemia risk). Avoid in G6PD deficiency. Source: BNF for Children 2024; NICE NG224; RIVUR Trial (Hoberman, NEJM 2014)

Clinical pearls

  • Brown urine: reassure parents this is harmless and expected
  • Pulmonary hypersensitivity: rare but serious — acute presentation (fever, dyspnoea, eosinophilia) within first month; chronic form (fibrosis) with prolonged use
  • Prophylaxis: 1–2 mg/kg OD at night widely used for VUR-associated recurrent UTI — RIVUR trial supported prophylaxis reducing febrile UTI by 50%
  • Avoid in G6PD deficiency — haemolytic anaemia risk

Contraindications

  • Age <3 months
  • G6PD deficiency
  • Renal impairment (eGFR <45)
  • Pulmonary function compromise (relative)

Side effects

  • Nausea/vomiting (take with food)
  • GI upset
  • Pulmonary reactions (acute, subacute, or chronic — rare)
  • Peripheral neuropathy (rare, prolonged use)
  • Haemolytic anaemia (G6PD deficiency)
  • Benign brown urine discolouration

Interactions

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

Monitoring

  • Urine culture if breakthrough UTI
  • LFTs and pulmonary function if prolonged use
  • Symptoms of peripheral neuropathy

Reference: BNF for Children; NICE NG224 UTI in Children; RIVUR Trial (Hoberman et al, NEJM 2014). Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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