Formulary
Nitrofurantoin: Uses, Dosing, Side Effects and Indian Brand Names
Nitrofurantoin is a urinary-specific antibiotic with uniquely low resistance rates, first-line for uncomplicated cystitis, ineffective outside the urinary tract, and contraindicated in renal impairment.
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Nitrofurantoin: Uses, Dosing, Side Effects and Indian Brand Names
Nitrofurantoin is a urinary-specific antibiotic with uniquely low resistance rates, first-line for uncomplicated cystitis, ineffective outside the urinary tract, and contraindicated in renal impairment.
NEET PG High-Yield: Multi-target mechanism (DNA + protein + enzyme damage) -- explains slow resistance development. Only works in the URINE (not systemic). Contraindicated in renal impairment (CrCl <30) -- both ineffective AND toxic. Proteus is intrinsically resistant (alkaline urine). Pulmonary toxicity: acute (hypersensitivity) and chronic (fibrosis). G6PD haemolysis. Contraindicated at term (neonatal haemolysis). First-line for uncomplicated cystitis (ICMR stewardship). Take with food. Low resistance rates despite 60 years of use.
Clinical overview
Nitrofurantoin is a nitrofuran antibiotic that occupies a unique niche in antimicrobial therapy: it is effective exclusively for lower urinary tract infections (cystitis) because it achieves therapeutic concentrations only in the urine, not in blood or tissues. This limitation is also its strength -- it does not disturb systemic flora and resistance development is remarkably slow despite 60 years of clinical use, because the drug's multi-target mechanism requires simultaneous mutations in multiple enzyme systems. Nitrofurantoin covers the major uropathogens: E. coli (>95% susceptibility in most Indian centres), Enterococcus faecalis, Staphylococcus saprophyticus, Klebsiella (variable), and Citrobacter. It does NOT cover Proteus (intrinsically resistant due to alkaline urine that reduces drug activity), Pseudomonas, or Serratia. In the era of escalating fluoroquinolone and cephalosporin resistance, nitrofurantoin has experienced a renaissance as a first-line agent for uncomplicated cystitis, endorsed by ICMR antimicrobial stewardship guidelines. Two formulations exist: microcrystalline (rapid absorption, more GI side effects, four-times-daily dosing) and macrocrystalline/monohydrate (slower absorption, better tolerated, twice-daily dosing). The most serious adverse effect is pulmonary toxicity -- acute (hypersensitivity pneumonitis) or chronic (pulmonary fibrosis with long-term use >6 months). It must be avoided in renal impairment (CrCl <30 mL/min) because inadequate urinary concentration renders it ineffective AND increases systemic accumulation and toxicity.
Pharmacological class
Nitrofurantoin belongs to the Nitrofuran Antibiotics (Urinary Antiseptic) class. Reduced by bacterial nitroreductases to reactive intermediates that damage multiple cellular targets: DNA (strand breakage), ribosomal proteins (inhibiting protein synthesis), and various metabolic enzymes. This multi-target mechanism makes resistance development slow and uncommon. Nitrofurantoin achieves therapeutic concentrations ONLY in the urine (not in serum or tissues), making it a true urinary-specific antibiotic.
Indian brand names and formulations
Available as: Furadantin (Sun Pharma), Niftran (Lupin), Urifast (Cipla), MacroBid (Procter & Gamble, not widely available in India).
Capsules: 50 mg (microcrystalline), 100 mg (macrocrystalline/monohydrate). Suspension: 25 mg/5 mL (paediatric, limited availability in India).
Regulatory status
Nitrofurantoin is classified under Schedule H in India under the Drugs and Cosmetics Act, 1940. Prescription-only. Listed on NLEM. Endorsed by ICMR antimicrobial stewardship guidelines as first-line for uncomplicated cystitis.
Indications
- Uncomplicated lower urinary tract infection (acute cystitis) -- first-line
- UTI prophylaxis (recurrent cystitis -- low-dose long-term; not recommended beyond 6 months due to pulmonary toxicity risk)
- NOT effective for pyelonephritis, prostatitis, or any systemic infection (drug does not achieve therapeutic serum or tissue levels)
Dosing
Acute cystitis: Macrocrystalline/monohydrate 100 mg twice daily for 5 days (IDSA-recommended duration). Microcrystalline: 50-100 mg four times daily for 7 days. UTI prophylaxis: 50-100 mg at bedtime. Take with food to improve absorption and reduce GI side effects. Contraindicated if CrCl <30 mL/min.
Contraindications
- Renal impairment (CrCl <30 mL/min or eGFR <45 mL/min -- ineffective due to inadequate urinary concentrations, and increased systemic toxicity)
- G6PD deficiency (risk of haemolytic anaemia)
- Pregnancy at term (38-42 weeks) -- risk of neonatal haemolytic anaemia (immature enzyme systems)
- Neonates and infants <3 months (immature enzyme systems, haemolysis risk)
- Pyelonephritis or systemic infection (not effective outside the urinary tract)
Adverse effects
- GI disturbances (nausea, vomiting, anorexia -- most common; reduced with macrocrystalline formulation and taking with food)
- Pulmonary toxicity: acute hypersensitivity pneumonitis (fever, dyspnoea, eosinophilia -- reversible on discontinuation) or chronic pulmonary fibrosis (insidious onset with long-term use >6 months -- may be irreversible)
- Peripheral neuropathy (with prolonged use or in renal impairment -- may be irreversible)
- Haemolytic anaemia in G6PD deficiency
- Harmless brown-yellow discolouration of urine
- Hepatotoxicity (rare, cholestatic or hepatocellular)
Drug interactions
- Antacids containing magnesium trisilicate: reduce nitrofurantoin absorption
- Probenecid: reduces renal tubular secretion of nitrofurantoin, reducing urinary levels (makes it LESS effective) and increasing serum levels (more toxicity) -- avoid combination
- Quinolones: antagonistic in vitro (nitrofurantoin may reduce quinolone bactericidal activity in urine)
- Urine alkalinising agents (sodium bicarbonate): reduce nitrofurantoin activity (more effective in acidic urine)
Pregnancy and lactation
Category B. Safe in pregnancy for UTI treatment in the first and second trimesters. Contraindicated near term (>36 weeks) due to risk of neonatal haemolytic anaemia (the neonate's immature erythrocyte enzyme systems cannot handle the oxidative stress). Preferred agent for UTI in pregnancy (along with amoxicillin and cephalexin) when not near term.
Exam-style clinical scenario
A 25-year-old woman presents with dysuria, frequency, and urgency for 2 days. Urine dipstick shows nitrites and leukocyte esterase. She has no fever, flank pain, or signs of systemic infection. What is the first-line empiric antibiotic? Nitrofurantoin monohydrate 100 mg twice daily for 5 days -- first-line for uncomplicated cystitis per IDSA, ICMR, and WHO guidelines.
Cost in India
Rs 20-50 for a strip of 10 capsules (100 mg). Very affordable compared to fluoroquinolones and cephalosporins.
Clinical governance
Author: MedNext Editorial Team. Clinical reviewer: Awaiting clinical review. Jurisdiction: India (Drugs and Cosmetics Act, 1940). Sources: CIMS India, Indian Pharmacopoeia. Publication state: Awaiting clinical review. Correction: Report errors at support@mednext.academy.
Frequently Asked Questions
Why is resistance to nitrofurantoin so uncommon?
Nitrofurantoin's reactive intermediates damage multiple unrelated cellular targets simultaneously -- DNA, ribosomes, and metabolic enzymes. For resistance to develop, a bacterium would need simultaneous mutations in multiple nitroreductase enzymes and repair systems, which is statistically improbable. Single-target antibiotics (like fluoroquinolones targeting DNA gyrase) need only one or two mutations for resistance. This multi-target mechanism is analogous to why combination TB therapy prevents resistance.
Why can't nitrofurantoin treat pyelonephritis?
Nitrofurantoin achieves therapeutic concentrations only in the urine (200-300 mcg/mL vs MIC of most uropathogens ~32 mcg/mL). It does NOT achieve significant concentrations in renal parenchyma, blood, or other tissues. Pyelonephritis is an infection of the kidney tissue (not just the urine), requiring antibiotics with tissue penetration -- fluoroquinolones, cephalosporins, or aminoglycosides.
Why is nitrofurantoin contraindicated in renal impairment?
Two reasons: (1) Reduced renal function means less drug is filtered into the urine, so urinary concentrations fall below the MIC -- the drug becomes ineffective. (2) Reduced excretion increases serum levels and systemic exposure, raising the risk of toxicity (peripheral neuropathy, pulmonary fibrosis). It is a double problem: less efficacy AND more toxicity.
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