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Antibiotic Dosing in CKD Pregnancy: Avoid at term (weeks 38-42) — neonatal haemolytic anaemia risk. Can be used cautiously in 1st and 2nd trimester. Avoid during breastfeeding.

Nitrofurantoin (CKD Contraindication)

Brand names: Macrobid, Macrodantin

Adult dose

Dose: Macrocrystal: 50-100 mg 4 times daily with food (treatment); 50-100 mg at night (prophylaxis). Modified-release (Macrobid): 100 mg BD with food.
Route: Oral
Frequency: 4 times daily (standard) or BD (modified-release)
Max: 400 mg/day
CONTRAINDICATED if eGFR <30 mL/min. Use with caution if eGFR 30-44 — inadequate urinary drug concentrations AND toxic metabolite accumulation risk. Should not be used for prophylaxis if eGFR <45. Only effective for lower UTI — does NOT achieve tissue concentrations for pyelonephritis.

Paediatric dose

Dose: 3 mg/day/kg
Route: Oral
Frequency: Divided into 4 doses
Max: 400 mg/day
Do NOT use if eGFR <30 (or <45 for prophylaxis). Not recommended under 3 months of age.

Dose adjustments

Renal

CONTRAINDICATED if eGFR <30 — dual mechanism: (1) insufficient urinary concentrations to achieve therapeutic effect; (2) accumulation of toxic metabolites causing peripheral neuropathy and pulmonary toxicity. MHRA: caution if eGFR 30-44; avoid prophylaxis if eGFR <45.

Hepatic

Caution in severe hepatic impairment

Paediatric weight-based calculator

Do NOT use if eGFR <30 (or <45 for prophylaxis). Not recommended under 3 months of age.

Clinical pearls

  • The dual eGFR problem: nitrofurantoin must achieve adequate URINARY concentrations for efficacy (concentration in urine depends on renal excretion — impaired in CKD), while TOXIC metabolites accumulate systemically in CKD causing neuropathy. eGFR <30 fails on BOTH counts.
  • MHRA 2014: restricted nitrofurantoin use in eGFR <45 for prophylaxis. The SPC now says eGFR <30 is contraindication for treatment; caution at 30-44; eGFR <45 — do not use for prophylaxis.
  • Pulmonary toxicity: acute reactions (first dose — fever, cough, dyspnoea, eosinophilia) resolve on stopping. Chronic toxicity (months to years of prophylaxis) causes progressive pulmonary fibrosis — CXR and spirometry in long-term prophylaxis patients.
  • Alternative UTI antibiotics in CKD: trimethoprim (but blocks creatinine secretion — see trimethoprim_renal); cefalexin; co-amoxiclav (dose-reduce if eGFR <30); pivmecillinam (safe in CKD).
  • Macrobid (modified-release) is preferred over standard formulation — better GI tolerability; same contraindications apply.

Contraindications

  • eGFR <30 mL/min (ABSOLUTE)
  • G6PD deficiency (haemolytic anaemia)
  • Pregnancy at term (neonatal haemolytic anaemia)
  • Infants under 3 months

Side effects

  • Pulmonary toxicity (acute: hypersensitivity pneumonitis; chronic: fibrosis — rare with long-term prophylaxis)
  • Peripheral neuropathy (especially in renal impairment)
  • Hepatotoxicity (chronic use)
  • Nausea/vomiting (reduced with food and modified-release formulation)
  • Brown discolouration of urine (harmless — warn patients)

Interactions

  • Antacids (magnesium trisilicate) — reduce absorption; avoid
  • Quinolones — pharmacological antagonism (theoretical)
  • Probenecid — reduces renal excretion and therefore efficacy

Monitoring

  • eGFR before starting and periodically during long-term prophylaxis
  • Pulmonary function (CXR/spirometry) for long-term prophylaxis users
  • Neurological symptoms (peripheral neuropathy — especially in CKD)
  • LFTs (prolonged use)

Reference: BNFc; BNF 90; BNFc; MHRA DSU 2014 (Nitrofurantoin in Renal Impairment); NICE NG109 (UTI — Adults); SPC Macrobid. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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