Nitrofurantoin
Brand names: Macrobid, Macrodantin, Nitrofurantoin MR
Nitrofurantoin is an antibiotic used for lower urinary tract infection and, at low dose, for UTI prophylaxis.
ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.
US labelling (FDA)
Reference — US labelling, may differ from UK2 DOSAGE & ADMINISTRATION Adult Patients: 50 mg to 100 mg four times a day -the lower dosage level is recommended for uncomplicated urinary tract infections. (2.2) Pediatric Patients: 5 mg/kg to 7 mg/kg of body weight per 24 hours, given in four divided doses (contraindicated under one month of age). (2.3) 2.1 Recommended Dosage and Administration in Adult Patients The recommended dosage is 50 mg to 100 mg of nitrofurantoin four times a day. For long-term suppressive therapy in adults, a reduction of dosage to 50 mg to 100 mg at bedtime may be adequate . The benefits of long-term suppressive therapy should be balanced against the increased potential for systemic toxicity and for the …
Source: US FDA prescribing information (openFDA / DailyMed), label dated 2024-03-29. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.
Clinical monograph
How it works
It is concentrated in the urine, where its reactive metabolites damage bacterial DNA, ribosomal proteins and other macromolecules; this urinary concentration is why it treats lower UTI but not systemic or upper-tract infection.
Prescribing in practice
- Effectiveness depends on adequate renal function and urinary concentration — avoid when eGFR is low, where it is both less effective and more toxic.
- Avoid at term in pregnancy and in babies under about 3 months because of the risk of neonatal haemolysis.
- Rare but serious pulmonary and hepatic reactions can occur, particularly with long-term prophylactic use.
Monitoring
Short courses need no routine monitoring; with long-term prophylaxis review renal, pulmonary and hepatic status periodically.
Counselling the patient
- Take it with food to improve absorption and reduce nausea.
- It can turn the urine dark yellow or brown, which is harmless.
- Report new breathlessness, persistent cough, or yellowing of the skin or eyes.
Evidence & guidelines
Nitrofurantoin is a first-line option for uncomplicated lower UTI where eGFR is adequate, per NICE/PHE antimicrobial guidance.
Reference: NICE NG112 UTIs; PHE Antimicrobial Guidelines; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).
Related
Curated clinical cross-links plus same-class fallbacks.