Known brand names include Macrobid.
A urinary antibiotic capsule (Macrobid) for uncomplicated bladder infections caused by E. coli or Staphylococcus saprophyticus. It is not for kidney infections, and it can cause lung, liver, and nerve reactions.
Labeled use. Acute uncomplicated cystitis from susceptible E. coli or S. saprophyticus; not for pyelonephritis or perinephric abscess.
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Nitrofurantoin is a first-line choice for uncomplicated cystitis, alongside trimethoprim-sulfamethoxazole and fosfomycin, with low resistance and little effect on gut flora; guidelines often use a 5-day course rather than the 7-day label course. Avoid it for pyelonephritis or any infection beyond the bladder. Guidelines often allow use down to a creatinine clearance of about 30 mL/min, below the label's cutoff of 60. In pregnancy it is commonly used before term but avoided at term, and older adults on long-term prophylaxis need watching for lung and liver toxicity.
A nitrofuran antibacterial. Bacterial flavoproteins reduce it to reactive intermediates that inactivate or alter ribosomal proteins and other macromolecules, blocking protein, DNA, RNA, and cell wall synthesis and aerobic energy metabolism; it is bactericidal in urine at therapeutic doses. Plasma levels stay low (peak usually under 1 mcg/mL), 20% to 25% of a dose appears unchanged in urine over 24 hours, and food raises bioavailability by about 40%. Macrobid combines 25% macrocrystals with 75% monohydrate in a powder that forms a gel matrix and releases drug over time.
The label does not describe a narrow therapeutic index or direct dosing by measured blood levels of the drug.
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Doses come from the FDA label. Study tool, not for clinical decisions.
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Contraindicated with anuria, oliguria, or creatinine clearance under 60 mL/min (or clinically significant elevated serum creatinine), because impaired excretion raises the risk of toxicity. Renal impairment also makes peripheral neuropathy more likely.
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No specific antidote. Acute overdose has caused only vomiting; induce emesis and keep fluid intake high to promote urinary excretion. Nitrofurantoin is dialyzable.
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Animal studies at up to 6 times the human dose showed no fetal harm, but there are no adequate human studies; use only if clearly needed. Contraindicated at term (38 to 42 weeks), during labor and delivery, or when labor is imminent, because immature red cell enzymes put the newborn at risk of hemolytic anemia.
Trace amounts pass into breast milk. Because of possible serious reactions in infants under 1 month, decide whether to stop nursing or stop the drug.
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Contraindicated under 1 month of age because of hemolytic anemia risk. Safety and effectiveness are not established under age 12; children over 12 take the adult dose.
Older adults have had a higher share of pulmonary reactions and severe hepatic reactions, including deaths, largely because more of them receive long-term therapy. Renal function declines with age and creatinine clearance under 60 mL/min is a contraindication, so monitoring renal function may be useful.
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