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Urinary Antiseptic Pregnancy: eMC §4.6: animal studies have shown no teratogenic effects and nitrofurantoin has been in extensive clinical use since 1952 with its suitability in human pregnancy well documented; however maternal side effects may adversely affect the course of pregnancy, so the drug should be used at the lowest dose appropriate for the specific indication and only after careful assessment. Nitrofurantoin is CONTRAINDICATED in pregnant women during labour and delivery (and in infants under three months of age) because of the possible risk of haemolysis of the infant's immature red cells. 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 Treatment)

Brand names: Macrobid, Furadantin

Used in: Urinary Tract Infection

An oral nitrofuran antibacterial used as first-line treatment for uncomplicated lower urinary tract infection, where it is concentrated in the urine to act locally on the bladder.

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 use - this medicine should always be taken with food or milk; taking nitrofurantoin with a meal improves absorption and is important for optimal efficacy
Frequency: Four times daily
eMC §4.2 (Nitrofurantoin 100 mg Capsules). OTHER ADULT REGIMENS from the same section: severe chronic recurrent urinary tract infection - 100 mg four times daily for seven days; long-term suppression - 50 to 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; note the precautions and risks to elderly patients associated with long-term therapy, in particular chronic pulmonary reactions, which occur rarely in patients treated continuously for six months or longer and are more common in the elderly. Nitrofurantoin is NOT effective for the treatment of parenchymal infections or of a unilaterally non-functioning kidney, and a surgical cause for infection should be excluded in recurrent or severe cases. US label cross-check (nitrofurantoin oral suspension 25 mg/5 mL, NorthStar Rx): recommended adult dosage 50 mg to 100 mg four times a day, with the lower dose recommended for uncomplicated urinary tract infections, and 50 mg to 100 mg at bedtime for long-term suppressive therapy; continue therapy for one week or for at least 3 days after sterility of the urine is obtained.

Paediatric dose

Dose: 3 mg/kg
Route: Oral - always with food or milk
Frequency: 3 mg/kg per day given in four divided doses, for seven days (acute urinary tract infection, children and infants over three months of age)
Max: Not stated in the eMC source
eMC §4.2 paediatric population. 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 rather than the capsule. Nitrofurantoin is CONTRAINDICATED in infants under three months of age because of the theoretical possibility of haemolytic anaemia due to immature erythrocyte enzyme systems (eMC §4.3). The US label differs and should not be blended with the above: it gives 5 mg/kg to 7 mg/kg of body weight per 24 hours in four divided doses for patients 1 month of age and older, with long-term suppressive doses as low as 1 mg/kg per 24 hours in a single dose or two divided doses, and contraindicates use under 1 month of age. Verify any paediatric dose against a children's formulary before prescribing.

Dose adjustments

Renal

eMC §4.2/§4.3: nitrofurantoin is CONTRAINDICATED in patients with renal dysfunction and in patients with an eGFR of less than 45 mL/minute. §4.4 adds that it 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 and 44 mL/min, to treat resistant pathogens, when the benefits are expected to outweigh the risks. (The US label uses a different threshold, contraindicating use where creatinine clearance is under 60 mL/min or the serum creatinine is clinically significantly elevated.)

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

eMC §4.2 paediatric population. 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 rather than the capsule. Nitrofurantoin is CONTRAINDICATED in infants under three months of age because of the theoretical possibility of haemolytic anaemia due to immature erythrocyte enzyme systems (eMC §4.3). The US label differs and should not be blended with the above: it gives 5 mg/kg to 7 mg/kg of body weight per 24 hours in four divided doses for patients 1 month of age and older, with long-term suppressive doses as low as 1 mg/kg per 24 hours in a single dose or two divided doses, and contraindicates use under 1 month of age. Verify any paediatric dose against a children's formulary before prescribing.

Verify in a children's formulary

Contraindications

  • Hypersensitivity to the active substance, to other nitrofurans, or to any of the excipients (eMC §4.3)
  • Patients suffering from renal dysfunction with an eGFR below 45 mL/minute (eMC §4.3)
  • G6PD (glucose-6-phosphate dehydrogenase) deficiency (eMC §4.3)
  • Acute porphyria (eMC §4.3)
  • Infants under three months of age, and pregnant patients at term (during labour and delivery), because of the theoretical possibility of haemolytic anaemia in the foetus or newborn due to immature erythrocyte enzyme systems (eMC §4.3). The US label additionally contraindicates a previous history of cholestatic jaundice or hepatic dysfunction associated with nitrofurantoin, and anuria, oliguria or significant renal impairment (CrCl under 60 mL/min)

Side effects

  • Pulmonary reactions (frequency not known) - acute, subacute and chronic; acute reactions usually occur within the first week and present with fever, chills, cough, chest pain, dyspnoea, pulmonary infiltration and eosinophilia; chronic reactions include pulmonary fibrosis and diffuse interstitial pneumonitis, occur rarely with continuous therapy of six months or longer, and are more common in elderly patients (eMC §4.8/§4.4)
  • Hepatobiliary (not known): cholestatic jaundice, chronic active hepatitis (fatal events reported), hepatic necrosis, autoimmune hepatitis
  • Nervous system (not known): peripheral neuropathy including optic neuritis with sensory and motor involvement - may become severe or irreversible and may be life threatening, so treatment should be stopped at the first sign of neural involvement (paraesthesia); also nystagmus, vertigo, dizziness, headache, drowsiness, benign intracranial hypertension
  • Blood (rare/not known): aplastic anaemia (rare); agranulocytosis, leucopenia, granulocytopenia, haemolytic anaemia, thrombocytopenia, G6PD deficiency anaemia, megaloblastic anaemia and eosinophilia
  • Gastrointestinal and skin (not known): nausea, anorexia, emesis, abdominal pain, diarrhoea, sialadenitis, pancreatitis; allergic skin reactions, angioneurotic oedema and anaphylaxis, cutaneous vasculitis, exfoliative dermatitis, erythema multiforme including Stevens-Johnson syndrome, urticaria, rash, pruritus, DRESS syndrome, transient alopecia; also yellow or brown discolouration of urine and interstitial nephritis

Interactions

  • The eMC §4.5 interactions section was not captured in this bundle - clinician to review it in the SPC. The entries below are from the US labelling
  • Antacids containing magnesium trisilicate reduce both the rate and extent of nitrofurantoin absorption (adsorption onto the magnesium trisilicate surface); if co-administration cannot be avoided, monitor for lack of efficacy (US label §7.1)
  • Uricosuric drugs such as probenecid and sulfinpyrazone inhibit renal tubular secretion of nitrofurantoin - the resulting rise in serum levels may increase toxicity, while lower urinary levels may reduce efficacy as a urinary tract antibacterial; monitor for adverse reactions (US label §7.2)
  • Laboratory interference: nitrofurantoin can cause a false-positive reaction for urinary glucose when Benedict's or Fehling's copper reduction methods are used - use enzymatic glucose oxidase-based tests instead (US label §7.3; eMC §4.4 also notes false positive urinary glucose and that urine may be coloured yellow or brown)

Clinical monograph

How it works

It is reduced by bacterial flavoproteins to reactive intermediates that damage ribosomal proteins, DNA and other macromolecules, producing broad activity against common urinary pathogens; therapeutic urinary concentrations depend on adequate renal function.

Prescribing in practice

  • Avoid in significant renal impairment because inadequate urinary concentrations make it ineffective while increasing systemic toxicity, and avoid at term in pregnancy owing to the risk of neonatal haemolysis.
  • Reserve for lower (bladder) infection only — it does not achieve therapeutic tissue levels and is unsuitable for pyelonephritis or other upper urinary tract or systemic infection.
  • Acute and chronic pulmonary reactions and hepatic and peripheral neuropathy adverse effects are recognised, particularly with prolonged use, so keep courses short.

Monitoring

For short treatment courses no routine monitoring is needed, but be alert to respiratory, hepatic and neurological adverse effects, especially in older patients or with repeated use.

Counselling the patient

  • Take with food to improve absorption and reduce stomach upset, and complete the prescribed course.
  • The medicine may turn your urine a dark yellow or brown colour, which is harmless.
  • Report any new breathlessness, persistent cough, tingling in the hands or feet, or yellowing of the skin.

Evidence & guidelines

NICE guidance on urinary tract infection recommends nitrofurantoin as a first-line option for uncomplicated lower UTI when renal function is adequate.

Reference: NICE NG109 UTI; 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).

Related

Curated clinical cross-links plus same-class fallbacks.

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