FURADANTIN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for FURADANTIN (FURADANTIN).
Nitrofurantoin is reduced by bacterial flavoproteins to reactive intermediates that inhibit bacterial enzymes involved in cell wall synthesis, DNA replication, and RNA transcription. It is bactericidal against susceptible organisms.
| Metabolism | Nitrofurantoin is primarily metabolized in the liver and various tissues; approximately 20% of the drug is converted to inactive metabolites, possibly via glutathione conjugation. Renal excretion is the major elimination pathway, with about 30-50% excreted unchanged in urine. |
| Excretion | Renal: 36% (glomerular filtration and tubular secretion); fecal: 40-50% (biliary excretion and unabsorbed drug); hepatic metabolism: minor (acetylation and reduction) accounting for <10%. |
| Half-life | Terminal elimination half-life is 0.3-1 hour in adults with normal renal function; prolonged to 1-4 hours in renal impairment (creatinine clearance <60 mL/min) and may exceed 20 hours in anuria. |
| Protein binding | 60-90% bound to plasma proteins (mainly albumin); binding is reversible and non-saturable at therapeutic concentrations. |
| Volume of Distribution | 0.3-0.7 L/kg (low Vd, consistent with limited tissue penetration except in kidneys, where tubular cell concentrations are high); not confined to plasma volume. |
| Bioavailability | Oral: 80-95% (rapidly absorbed from proximal small intestine; food may enhance absorption); intravenous: 100%. |
| Onset of Action | Oral: within 30 minutes (therapeutic concentration in urine achieved); intravenous: immediate. |
| Duration of Action | Oral: approximately 6-8 hours (bacteriostatic concentrations maintained in urine for up to 12 hours with standard dosing); intravenous: similar duration but dose-dependent. |
| Action Class | Urinary Antiseptic-Nitrofurantoin |
| Brand Substitutes | Nitfur 100mg Tablet, Urinif 100mg Tablet, Martifur Tablet, Neft 100mg Tablet, Urivron Tablet, Utinift 50mg Tablet, Niftas 50 Tablet, Nifutin 50mg Tablet |
100 mg orally twice daily for 5-7 days; acute uncomplicated cystitis: 50 mg four times daily or 100 mg twice daily for 5 days.
| Dosage form | SUSPENSION |
| Renal impairment | CrCl ≥60 mL/min: no adjustment; CrCl 30-59 mL/min: avoid use; CrCl <30 mL/min: contraindicated. |
| Liver impairment | No specific recommendations; use with caution in severe hepatic impairment (Child-Pugh C) due to potential hepatotoxicity. |
| Pediatric use | Children >1 month: 5-7 mg/kg/day divided every 6 hours (max 400 mg/day) for acute UTI; monohydrate/macrocrystals: extended-release not recommended for <12 years. |
| Geriatric use | Avoid in elderly with CrCl <60 mL/min; increased risk of pulmonary and hepatic toxicity; monitor renal function; use lowest effective dose for shortest duration. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for FURADANTIN (FURADANTIN).
| Breastfeeding | Excreted in breast milk in small amounts (M/P ratio ~0.1). Considered compatible with breastfeeding; monitor infant for diarrhea or rash. Caution in G6PD-deficient infants. |
| Teratogenic Risk | FDA Pregnancy Category B. No evidence of teratogenicity in animal studies; limited human data. Theoretical risk of hemolytic anemia in G6PD-deficient fetuses if used near term. Avoid during first trimester unless essential. |
| Fetal Monitoring |
■ FDA Black Box Warning
Nitrofurantoin is contraindicated in patients with impaired renal function (CrCl < 60 mL/min or serum creatinine > 1.5 mg/dL) because of the risk of accumulation and toxicity. It is also contraindicated in pregnant patients at term (38-42 weeks gestation), during labor and delivery, or when the fetus is at risk of hemolytic anemia.
| Serious Effects |
["Renal impairment: creatinine clearance < 60 mL/min or serum creatinine > 1.5 mg/dL.","Pregnancy at term (38-42 weeks), during labor and delivery, or when the fetus is at risk of hemolytic anemia.","Breastfeeding in infants with suspected or confirmed G6PD deficiency.","Anuria, oliguria, or significant renal impairment.","Known hypersensitivity to nitrofurantoin.","Prior history of cholestatic jaundice or hepatic dysfunction associated with nitrofurantoin."]
| Precautions | ["Pulmonary reactions: acute, subacute, or chronic hypersensitivity reactions including pulmonary fibrosis.","Hepatic reactions: rare but potentially fatal hepatitis and hepatocellular necrosis.","Peripheral neuropathy: risk is increased in patients with renal impairment, anemia, diabetes, electrolyte imbalance, vitamin B deficiency, or debilitating disease.","Hemolytic anemia: may occur in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency.","Clostridium difficile-associated diarrhea (CDAD).","Optic neuritis and neurotoxicity have been reported.","Superinfection with resistant organisms may occur."] |
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| Monitor for pulmonary reactions (cough, dyspnea), hepatic toxicity, and peripheral neuropathy. In pregnancy, assess fetal growth if prolonged use. Periodic CBC and liver function tests. |
| Fertility Effects | No known adverse effects on fertility in humans. Animal studies show no impairment. |