Nitrofurantoin

What it is and how it works

Mechanism of Action The mechanism of the antimicrobial action of nitrofurantoin is unusual among antibacterials. Nitrofurantoin is reduced by bacterial flavoproteins to reactive intermediates which inactivate or alter bacterial ribosomal proteins and other macromolecules. As a result of such inactivations, the vital biochemical processes of protein synthesis, aerobic energy metabolism, DNA synthesis, RNA synthesis, and cell wall synthesis are inhibited. Nitrofurantoin is bactericidal in urine at therapeutic doses.

Indications

INDICATIONS AND USAGE Nitrofurantoin Capsules USP (Macrocrystals) are specifically indicated for the treatment of urinary tract infections when due to susceptible strains of Escherichia coli , enterococci, Staphylococcus aureus , and certain susceptible strains of Klebsiella and Enterobacter species. Nitrofurantoin is not indicated for the treatment of pyelonephritis or perinephric abscesses. To reduce the development of drug-resistant bacteria and maintain the effectiveness of Nitrofurantoin Capsules USP (Macrocrystals) and other antibacterial drugs, Nitrofurantoin Capsules USP (Macrocrystals) should be used only to treat or prevent infections that are proven or strongly suspected to be caused by susceptible bacteria. When culture and susceptibility information are available, they should be considered in selecting or modifying antibacterial therapy. In the absence of such data, local epidemiology and susceptibility patterns may contribute to the empiric selection of therapy.

Dosage and administration (summary)

DOSAGE AND ADMINISTRATION Nitrofurantoin capsules (macrocrystals) should be given with food to improve drug absorption and, in some patients, tolerance. Adults 50 to 100 mg four times a day - the lower dosage level is recommended for uncomplicated urinary tract infections. Pediatric Patients 5 to 7 mg/kg of body weight per 24 hours, given in four divided doses (contraindicated under one month of age). Therapy should be continued for one week or for at least 3 days after sterility of the urine is obtained. Continued infection indicates the need for reevaluation. For long-term suppressive therapy in adults, a reduction of dosage to 50 to 100 mg at bedtime may be adequate.

Contraindications

CONTRAINDICATIONS Anuria, oliguria, or significant impairment of renal function (creatinine clearance under 60 mL per minute or clinically significant elevated serum creatinine) are contraindications. Treatment of this type of patient carries an increased risk of toxicity because of impaired excretion of the drug.

Warnings and precautions

WARNINGS Pulmonary Reactions ACUTE, SUBACUTE, OR CHRONIC PULMONARY REACTIONS HAVE BEEN OBSERVED IN PATIENTS TREATED WITH NITROFURANTOIN. IF THESE REACTIONS OCCUR, NITROFURANTOIN MACROCRYSTALS SHOULD BE DISCONTINUED AND APPROPRIATE MEASURES TAKEN. REPORTS HAVE CITED PULMONARY REACTIONS AS A CONTRIBUTING CAUSE OF DEATH. CHRONIC PULMONARY REACTIONS (DIFFUSE INTERSTITIAL PNEUMONITIS OR PULMONARY FIBROSIS, OR BOTH) CAN DEVELOP INSIDIOUSLY. THESE REACTIONS OCCUR RARELY AND GENERALLY IN PATIENTS RECEIVING THERAPY FOR SIX MONTHS OR LONGER.

Pregnancy

Pregnancy Teratogenic Effects Pregnancy Category B Several reproduction studies have been performed in rabbits and rats at doses up to six times the human dose and have revealed no evidence of impaired fertility or harm to the fetus due to nitrofurantoin.

Storage and supply

HOW SUPPLIED Nitrofurantoin Capsules USP (Macrocrystals) are available as pink opaque/white opaque capsules, imprinted with z, “Zenith 50 mg” on the cap and “2130”, underlined with a double bar, on the body, in black ink, containing 50 mg nitrofurantoin macrocrystals, packaged in bottles of 100 (NDC 0115-1643-01) and 1000 capsules (NDC 0115-1643-03…

Source: Nitrofurantoin Macrocrystals (Nitrofurantoin Macrocrystals) — US FDA prescribing information, 2025-12-18, DailyMed. Summarised and shortened; the full label governs. Iranian registration, indications and labelling may differ.