Antibiotic Dosing in CKD Pregnancy: Animal studies have shown no teratogenic effects, although a study in rats showed reproductive toxicity. Nitrofurantoin has been in extensive clinical use since 1952 and its suitability in human pregnancy has been well documented; however, maternal side effects may adversely affect the course of pregnancy, and the drug should be used at the lowest dose appropriate for the specific indication and only after careful assessment. Nitrofurantoin is CONTRAINDICATED in infants under three months of age and 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. Fertility: no data available.

Nitrofurantoin (CKD Contraindication)

Brand names: Macrobid, Macrodantin

Nitrofurantoin is an oral urinary antiseptic for lower urinary tract infection; this entry highlights its restriction in chronic kidney disease, where reduced renal function limits its use.

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 nitrofurantoin with a meal improves absorption and is important for optimal efficacy

Frequency: Four times daily for seven days

Source: UK SPC (eMC) for Nitrofurantoin 100 mg Capsules, section 4.2 (https://www.medicines.org.uk/emc/product/12565/smpc). KEY POINT FOR THIS PAGE: nitrofurantoin is CONTRAINDICATED in patients with renal dysfunction and in patients with an eGFR of less than 45 mL/minute (sections 4.2, 4.3 and 4.4) — see renalAdjustment below. OTHER ADULT REGIMENS IN THE SAME SPC: 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; note the SPC's precaution about risks to elderly patients associated with long-term therapy (section 4.8). NO MAXIMUM DOSE is stated in section 4.2. PAEDIATRIC FORMULATION NOTE: 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. Verify all paediatric dosing against a children's formulary. SOURCE LIMITATION: eMC section 4.5 was NOT captured in this bundle — the interactions listed below are taken from section 7 of the US label (openFDA/DailyMed) and must be checked against the UK SPC. Sections 4.4 and 4.8 were truncated at the fetch limit.

Paediatric dose

Dose: 3 mg/kg/day/kg

Route: Oral (always with food or milk); for children under 6 years or under 25 kg body weight, consideration should be given to the use of nitrofurantoin oral suspension

Frequency: The 3 mg/kg is a TOTAL DAILY dose given in four divided doses, for seven days

Max: No maximum dose is stated for the paediatric population in section 4.2

Children and infants OVER THREE MONTHS of age, acute urinary tract infection, verbatim from section 4.2: '3mg/kg day in four divided doses for seven days.' READ AS 3 mg/kg PER DAY DIVIDED INTO FOUR DOSES — it is NOT 3 mg/kg per dose. Suppressive therapy: 1 mg/kg, once a day. CONTRAINDICATED in infants under three months of age because of the theoretical possibility of haemolytic anaemia in the newborn due to immature erythrocyte enzyme systems. The renal contraindication (eGFR below 45 mL/minute) applies to paediatric patients too. Verify against a children's formulary.

Dose adjustments

Renal

NITROFURANTOIN IS CONTRAINDICATED IN PATIENTS WITH RENAL DYSFUNCTION AND IN PATIENTS WITH AN eGFR OF LESS THAN 45 mL/MINUTE (section 4.2, cross-referring to sections 4.3 and 4.4; section 4.3 lists 'Patients suffering from renal dysfunction with an eGFR below 45 ml/minute'). No reduced-dose regimen is offered for renal impairment — the SPC gives a contraindication, not a dose adjustment. In the elderly, the normal adult dosage applies only provided there is no significant renal impairment.

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, other nitrofurans or to any of the excipients
Patients suffering from renal dysfunction with an eGFR below 45 mL/minute
G6PD deficiency
Acute porphyria
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 infant due to immature erythrocyte enzyme systems

Side effects

Respiratory (frequency not known): acute, subacute and chronic pulmonary reactions, cough, dyspnoea, pulmonary fibrosis, with a possible association with a lupus-erythematosus-like syndrome. Acute reactions commonly present with fever, chills, cough, chest pain, dyspnoea, pulmonary infiltration with consolidation or pleural effusion on chest X-ray, and eosinophilia; chronic pulmonary reactions occur rarely in patients on continuous therapy for six months or longer and are more common in elderly patients
Hepatobiliary (frequency not known): chronic active hepatitis (fatalities have been reported), hepatic necrosis, autoimmune hepatitis, cholestatic jaundice
Nervous system (frequency not known): peripheral neuropathy including optic neuritis (sensory and motor involvement), nystagmus, vertigo, dizziness, headache, drowsiness, benign intracranial hypertension
Blood and lymphatic: aplastic anaemia (rare); agranulocytosis, leucopenia, granulocytopenia, haemolytic anaemia, thrombocytopenia, G6PD deficiency anaemia, megaloblastic anaemia and eosinophilia (frequency not known)
Skin and immune: allergic skin reactions, angioneurotic oedema and anaphylaxis; exfoliative dermatitis and erythema multiforme including Stevens-Johnson syndrome; DRESS syndrome; cutaneous vasculitis; transient alopecia
Also reported: yellow or brown discolouration of urine, interstitial nephritis; nausea, anorexia, emesis, abdominal pain, diarrhoea, pancreatitis, sialadenitis; superinfection by fungi or resistant organisms such as Pseudomonas limited to the genitourinary tract. NOTE: the section 4.8 table was truncated at the source-fetch limit

Interactions

US label section 7.1 — antacids containing magnesium trisilicate: reduce both the rate and extent of nitrofurantoin absorption (probably by adsorption onto the magnesium trisilicate surface); if co-administration cannot be avoided, monitor for lack of efficacy
US label section 7.2 — uricosuric drugs such as probenecid and sulfinpyrazone: inhibit renal tubular secretion of nitrofurantoin; the resulting increase in serum levels may increase toxicity while decreased urinary levels could lessen efficacy as a urinary tract antibacterial — monitor for adverse reactions
US label section 7.3 — laboratory interference: nitrofurantoin can cause a false-positive reaction for urinary glucose with Benedict's or Fehling's copper reduction tests; use enzymatic glucose oxidase-based tests instead (the UK section 4.8 also lists false positive urinary glucose)
eMC section 4.5 was not captured in the source bundle and must be checked on the SPC

Clinical monograph

How it works

It is concentrated in the urine, where it is reduced by bacterial enzymes to reactive intermediates that damage ribosomal proteins, DNA and other macromolecules, giving activity confined largely to the urinary tract.

Prescribing in practice

Nitrofurantoin should be avoided when renal function is significantly impaired because inadequate urinary concentrations make it ineffective while systemic accumulation raises the risk of peripheral neuropathy and pulmonary toxicity; check eGFR before prescribing.
It is contraindicated in infants in the first months of life and in G6PD deficiency owing to the risk of haemolysis.
Long-term use carries risks of chronic pulmonary fibrosis and hepatotoxicity, so prolonged courses need review.

Monitoring

Check renal function before prescribing and, with extended use, monitor for pulmonary, hepatic and neurological adverse effects.

Counselling the patient

Take with food to reduce stomach upset, and expect your urine may turn dark yellow or brown.
Report new tingling or numbness, breathlessness or persistent cough.

Evidence & guidelines

Long clinical experience and current prescribing references define its efficacy in uncomplicated cystitis and the renal threshold below which it is no longer recommended, with the threshold periodically revised.

Reference: MHRA DSU 2014 (Nitrofurantoin in Renal Impairment); NICE NG109 (UTI — Adults); SPC Macrobid; 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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