Urinary Antibiotic — Obstetric Pregnancy: §4.6: animal studies have shown no teratogenic effects and suitability in human pregnancy is well documented (in clinical use since 1952); however the drug should be used at the lowest dose appropriate for the specific indication, only after careful assessment. Contraindicated in pregnant women during labour and delivery because of the possible risk of haemolysis of the infant's immature red cells. Breast-feeding: breast feeding an infant known or suspected to have an erythrocyte enzyme deficiency (including G6PD deficiency) must be temporarily avoided, since nitrofurantoin is detected in trace amounts in breast milk.

Nitrofurantoin (UTI in Pregnancy)

Brand names: Macrobid, Furadantin

Nitrofurantoin is an oral urinary antiseptic antibacterial used as a first-line treatment for lower urinary tract infection in pregnancy.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Acute uncomplicated urinary tract infection: 50 mg four times daily for seven days

Route: Oral — this medicine should always be taken with food or milk; taking it with a meal improves absorption and is important for optimal efficacy

Frequency: Four times daily for 7 days

Source: UK SPC for Nitrofurantoin 100 mg Capsules §4.2. Other adult regimens stated in the same section: severe chronic recurrence (UTIs) 100 mg four times daily for seven days; long term suppression 50-100 mg once a day; prophylaxis 50 mg four times daily for the duration of the procedure and for three days thereafter. Elderly: provided there is no significant renal impairment (in which nitrofurantoin is contraindicated), the dosage should be that for any normal adult. PREGNANCY-SPECIFIC (this page's indication): §4.3 contraindicates nitrofurantoin in pregnant patients at term (during labour and delivery) because of the theoretical possibility of haemolytic anaemia in the foetus or in the newborn infant due to immature erythrocyte enzyme systems; §4.6 states nitrofurantoin has been in extensive clinical use since 1952 and its suitability in human pregnancy has been well documented, but the drug should be used at the lowest dose as appropriate for a specific indication, only after careful assessment. Treatment should be stopped at the first signs of neural involvement (paraesthesia) because peripheral neuropathy may become severe or irreversible. NOTE ON FORMULATION: the fetched SPC is for immediate-release 100 mg capsules and contains no modified-release (e.g. 100 mg m/r twice daily) regimen — if this page is to carry an m/r regimen, the corresponding modified-release SPC must be sourced separately. The US label states a different adult range (50 mg to 100 mg four times a day, the lower level recommended for uncomplicated UTI; 50-100 mg at bedtime for long-term suppression) — UK SPC figures are used above.

Paediatric dose

Dose: 3 mg/kg

Route: oral (with food or milk)

Frequency: In four divided doses, total 3 mg/kg/day, for seven days — acute urinary tract infection in children and infants over three months of age

Max: Not stated in §4.2

UK SPC §4.2 paediatric population: acute UTI 3 mg/kg/day in four divided doses for seven days; suppressive therapy 1 mg/kg once a day. For children under the age of 6 years or under 25 kg body weight, consideration should be given to the use of nitrofurantoin oral suspension. Contraindicated in infants under three months of age (risk of haemolytic anaemia from immature erythrocyte enzyme systems). The US label states a different paediatric range (5 mg/kg to 7 mg/kg of body weight per 24 hours in four divided doses, from 1 month of age; long-term suppression as low as 1 mg/kg per 24 hours) — the UK SPC figure is used above. Verify all paediatric dosing against a children's formulary before administration.

Dose adjustments

Renal

Contraindicated in patients with renal dysfunction and in patients with an eGFR of less than 45 ml/minute (§4.3). §4.4 adds that nitrofurantoin may be used with caution as short-course therapy only for the treatment of uncomplicated lower urinary tract infection in individual cases with an eGFR between 30-44 ml/min, to treat resistant pathogens, when the benefits are expected to outweigh the risks.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Paediatric weight-based calculator

Patient weight (kg)

Verify in a children's formulary

Contraindications

Hypersensitivity to the active substance, to other nitrofurans, or to any of the excipients
Renal dysfunction with an eGFR below 45 ml/minute
G6PD deficiency
Acute porphyria
Infants under three months of age
Pregnant patients at term (during labour and delivery) — theoretical risk of haemolytic anaemia in the foetus or newborn

Side effects

Pulmonary reactions — acute, subacute and chronic (cough, dyspnoea, pulmonary fibrosis); acute reactions usually occur within the first week, chronic reactions occur rarely after six months or more of continuous therapy and are more common in the elderly
Hepatic reactions — cholestatic jaundice, chronic active hepatitis (fatal events reported), hepatic necrosis, autoimmune hepatitis
Peripheral neuropathy including optic neuritis (sensory and motor involvement), nystagmus, vertigo, dizziness, headache, drowsiness; benign intracranial hypertension
Haematological — aplastic anaemia (rare); agranulocytosis, leucopenia, haemolytic anaemia, G6PD-deficiency anaemia, megaloblastic anaemia, thrombocytopenia, eosinophilia
Gastrointestinal — nausea, anorexia, emesis, abdominal pain, diarrhoea; sialadenitis and pancreatitis
Allergic skin reactions, angioneurotic oedema and anaphylaxis, exfoliative dermatitis and erythema multiforme (including Stevens-Johnson syndrome), DRESS, cutaneous vasculitis; yellow or brown discolouration of the urine

Interactions

§4.5 of the UK SPC was NOT captured in the fetched bundle — the following are from the US label §7 and must be checked against the UK SPC §4.5
Antacids containing magnesium trisilicate — reduce both the rate and extent of nitrofurantoin absorption; if co-administration cannot be avoided, monitor for lack of efficacy
Uricosuric drugs such as probenecid and sulfinpyrazone — inhibit renal tubular secretion of nitrofurantoin, increasing serum levels (toxicity) and lowering urinary levels (reduced efficacy)
Laboratory interference: nitrofurantoin can cause a false-positive urinary glucose result with copper-reduction methods (Benedict's/Fehling's); use enzymatic glucose oxidase tests

Clinical monograph

How it works

It is concentrated in urine and reduced by bacterial enzymes to reactive intermediates that damage bacterial DNA, ribosomal proteins and other macromolecules, giving activity against common urinary pathogens.

Prescribing in practice

Avoid at term (around the time of delivery) because of the risk of neonatal haemolysis, and avoid in known glucose-6-phosphate dehydrogenase deficiency.
It is ineffective in pyelonephritis as it does not achieve adequate tissue concentrations, and works only when renal function is adequate to concentrate it in urine.
Counsel that it may turn the urine dark yellow or brown, and that nausea is common.

Monitoring

Routine monitoring is not required for short courses; reserve longer-term use for specialist settings where pulmonary and hepatic effects are watched for.

Counselling the patient

Take with food to reduce stomach upset and complete the full course.
The medicine may darken your urine, which is harmless.
Tell your midwife or doctor how far along you are, as it is avoided close to delivery.

Evidence & guidelines

Nitrofurantoin is recommended as a first-line option for urinary tract infection in pregnancy in NICE and Public Health antimicrobial guidance, with avoidance near term.

Reference: NICE NG109 (UTI in Adults); MHRA Drug Safety Update 2014 (nitrofurantoin); RCOG UTI in Pregnancy Guidance; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

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