nitrofurantoin
Nitrofuran antibiotic· Brands: Macrobid, Macrodantin, FuradantinPO
Mechanism of action
Nitrofurantoin is activated by bacterial nitroreductases to unstable intermediates that bind to ribosomal proteins and DNA, inhibiting protein synthesis and damaging genetic material. This produces bactericidal activity against susceptible urinary pathogens.
Pharmacokinetics
Nitrofurantoin is well absorbed from the gastrointestinal tract, with food enhancing absorption. It is rapidly cleared renally, reaching high concentrations in urine. It undergoes extensive metabolism in the liver and tissues, with renal excretion of metabolites and unchanged drug. The elimination half-life is approximately 20 to 60 minutes in patients with normal renal function.
Indications & dosing
Acute uncomplicated urinary tract infection (cystitis)
Usually continued for 5 days; local guidelines may recommend 3 days for women.
- adult · PO: 100 mg twice daily · Usually continued for 5 days; local guidelines may recommend 3 days for women.
Prophylaxis of recurrent urinary tract infections
Usually taken at bedtime. Dose depends on renal function and local formulary.
- adult · PO: 50–100 mg once daily · Usually taken at bedtime. Dose depends on renal function and local formulary.
Contraindications & precautions
- Renal impairment (CrCl < 60 mL/min or eGFR < 45 mL/min/1.73m²) · Inadequate urine concentration and increased risk of toxicity.
- Pregnancy at term (38-42 weeks) and during labour · Risk of haemolytic anaemia in the neonate.
- Neonates under 3 months of age · Risk of haemolytic anaemia due to immature erythrocyte enzyme systems.
- Hypersensitivity to nitrofurantoin
- Known glucose-6-phosphate dehydrogenase (G6PD) deficiency · Risk of haemolysis.
- Use caution in patients with anaemia, diabetes mellitus, electrolyte imbalance, or vitamin B deficiency; monitor for neurological symptoms.
- Follow recommended dosing and duration; prolonged use increases the risk of pulmonary and hepatic toxicity.
- Take with food or milk to enhance tolerability and reduce gastrointestinal adverse effects.
- Avoid concurrent use of magnesium trisilicate antacids, which reduce absorption.
- Ensure adequate hydration to maintain urine flow and prevent crystalluria.
Adverse effects
- Nausea and vomiting
- Headache
- Urine discoloration (brown or yellow)
- Peripheral neuropathyserious
- Pulmonary hypersensitivity reactions (including fibrosis)serious
- Hepatotoxicity (cholestatic jaundice, hepatitis)serious
- Blood dyscrasias (agranulocytosis, haemolytic anaemia)serious
Renal & hepatic adjustment
- eGFR 0–29: Contraindicated. Use alternative antibacterial agent. (avoid)
- eGFR 30–44: Use with caution for short-term treatment only if no alternative. Check local formulary; some advise avoiding if eGFR <45.
- eGFR 45+: No dose adjustment required.
- Hepatic impairment (mild): No dose adjustment required.
- Hepatic impairment (moderate): No dose adjustment required.
- Hepatic impairment (severe): Avoid as hepatotoxicity may occur; consider alternative. (avoid)
Monitoring, pregnancy & toxicity
- Pulmonary symptoms (cough, dyspnoea, fever, chest pain) · During each review, especially on long-term therapy
- Liver function tests · If symptoms suggestive of hepatitis occur
- Peripheral neuropathy signs (paraesthesia, weakness) · Periodic assessment during prolonged use
- Renal function (eGFR) · Baseline and periodically, particularly in elderly or at-risk patients
- Pregnancy: Nitrofurantoin is generally safe for use in pregnancy for the treatment of uncomplicated lower UTIs. It should be avoided at term (from 38 weeks gestation) due to the risk of haemolytic anaemia in the newborn. It is not associated with major teratogenic effects, but consider alternatives in the first trimester if possible.
- Toxicity: Acute overdose: nausea, vomiting, and abdominal pain. · Supportive care; maintain hydration and monitor electrolytes.
- Toxicity: Pulmonary toxicity (acute pneumonitis or chronic fibrosis). · Stop the drug; arrange chest radiograph and pulmonary function tests; supportive care.
- Toxicity: Peripheral neuropathy (paresthesias, weakness). · Stop the drug; consider neurological assessment; symptoms may be irreversible.
- Toxicity: Hepatotoxicity (cholestatic hepatitis). · Stop the drug; monitor liver function tests; supportive care.
Clinical notes
Nitrofurantoin is used for the treatment and prophylaxis of uncomplicated lower urinary tract infections. It is not effective for systemic infections or pyelonephritis because of poor tissue penetration. Contraindications include significant renal impairment, pregnancy at term, and infants under 3 months. Adverse effects include gastrointestinal upset, pulmonary fibrosis, hepatotoxicity, and peripheral neuropathy.
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BNF; local formulary