Nitrofurantoin

Nitrofurantoin is an antibiotic used specifically to treat urinary tract infections (UTIs) caused by susceptible bacteria. It is approved across capsule and oral suspension forms, with some differences in which bacteria and patient ages each product covers.

• Macrodantin (capsule) treats UTIs due to susceptible E. coli, enterococci, S. aureus, and certain Klebsiella and Enterobacter species in adults and children
• Nitrofurantoin macrocrystals capsules treat the same range of susceptible organisms as Macrodantin
• Nitrofurantoin capsules (monohydrate/macrocrystals) are indicated only for acute uncomplicated UTIs (acute cystitis) caused by E. coli or S. saprophyticus
• Furadantin and nitrofurantoin oral suspension treat UTIs caused by susceptible E. coli, Enterococcus species, S. aureus, Klebsiella species, and Enterobacter species in adults and children 1 month of age and older
• No form of nitrofurantoin is approved for kidney infections (pyelonephritis) or infections in the tissue around the kidneys (perinephric abscesses)

Nitrofurantoin works differently from most antibiotics. Bacteria convert it into reactive compounds that simultaneously attack multiple vital processes inside the bacterial cell — protein synthesis, DNA replication, RNA production, energy metabolism, and cell wall construction. Hitting so many targets at once is what keeps resistance low: a bacterium would need to mutate all of those systems at the same time to survive, which is essentially lethal to the organism. At the concentrations reached in urine during treatment, nitrofurantoin is bactericidal — meaning it kills bacteria outright.

Because nitrofurantoin concentrates in the urine rather than spreading through body tissues broadly, it is effective against UTIs but not appropriate for deeper infections like kidney infections. Resistance has not been a significant clinical problem since the drug's introduction in 1953, and cross-resistance with other antibiotics or sulfonamides has not been observed.

Nitrofurantoin is taken by mouth, and both the capsule and oral suspension forms are given with food to improve absorption and ease stomach upset. For active UTIs, it is generally taken four times a day; for long-term suppressive therapy to prevent recurring infections, a once-nightly dose may be used in adults. Pediatric dosing for the oral suspension is based on body weight and given in four divided doses daily for children 1 month of age and older.

• Always take with food
• Finish the full prescribed course even if symptoms improve early
• Do not use in infants under 1 month of age
• Follow your prescriber's specific instructions — do not adjust the dose on your own

The most commonly reported side effects are digestive — nausea, vomiting, and loss of appetite top the list, and these can often be reduced by taking the medication with food.

• Lung reactions: Acute, subacute, or chronic pulmonary (lung) reactions have occurred, including cases that contributed to death. Chronic lung scarring (pulmonary fibrosis) can develop slowly in patients on therapy for 6 months or longer. Symptoms include cough, shortness of breath, fever, and malaise — seek care immediately if these appear.
• Liver damage (hepatotoxicity): Hepatitis, cholestatic jaundice, chronic active hepatitis, and liver tissue death have been reported, including fatalities. Onset can be gradual. Watch for yellowing of the skin or eyes, dark urine, or unusual fatigue.
• Nerve damage (peripheral neuropathy): Can become severe or permanent. Risk is higher in people with kidney impairment, diabetes, anemia, electrolyte imbalance, or vitamin B deficiency. Optic neuritis (nerve inflammation affecting vision) has also been reported.
• Hemolytic anemia: Red blood cell destruction can occur, especially in people with G6PD deficiency (more common in people of African, Mediterranean, or Near-Eastern descent). Nitrofurantoin must be stopped immediately if this occurs.
• C. difficile-associated diarrhea: Can range from mild diarrhea to life-threatening colitis. Can occur up to two months after finishing the antibiotic.
• Pregnancy at term: Contraindicated at 38–42 weeks of gestation and during labor and delivery due to risk of hemolytic anemia in the newborn.

Nitrofurantoin has a few important drug and test interactions to know about before you start taking it.

• Magnesium trisilicate antacids: Reduce both the rate and extent of nitrofurantoin absorption, potentially making it less effective — avoid combining if possible
• Uricosuric drugs (probenecid, sulfinpyrazone): Can increase nitrofurantoin in the blood (raising toxicity risk) while lowering it in the urine (reducing its UTI-fighting effect)
• Quinolone antibiotics (e.g., ciprofloxacin): Lab studies show these drugs may work against each other — discuss with your prescriber if both are prescribed
• Urine glucose tests: Nitrofurantoin can cause a false-positive result on older copper-reduction urine glucose tests (Benedict's or Fehling's solution); enzymatic glucose oxidase tests should be used instead
• Propantheline (anticholinergic agent): Can increase nitrofurantoin absorption; clinical significance is unknown but worth mentioning to your doctor

Not a complete list. The label covers the interactions the manufacturer studied or reported, and our own interaction database does not cover every medicine either. Bring your full medication list, including vitamins and herbal products, to your pharmacist.

• Tell your doctor if you have kidney problems or reduced kidney function — nitrofurantoin is contraindicated if creatinine clearance is below 60 mL/min, as the drug can build up and become toxic
• Tell your doctor if you have ever had liver problems or jaundice caused by nitrofurantoin — this is a contraindication
• Let your doctor know if you have G6PD deficiency (a genetic red blood cell enzyme deficiency) — you are at higher risk of hemolytic anemia
• Tell your doctor if you are pregnant — especially if you are close to your due date (38–42 weeks), in labor, or when labor is imminent, as nitrofurantoin is contraindicated in these situations
• If you are breastfeeding, discuss with your doctor — nitrofurantoin passes into breast milk and is not recommended if your baby is under 1 month old or has G6PD deficiency; monitor breastfed infants over 1 month for vomiting, diarrhea, or rash
• Not for use in infants under 1 month of age
• Inform your doctor if you have diabetes, anemia, nerve problems, or low vitamin B levels — these increase the risk of peripheral neuropathy
• Men trying to father a child should speak to their doctor — nitrofurantoin may temporarily lower sperm count at higher doses
• People with debilitating disease or electrolyte imbalances may also be at higher risk for nerve side effects

Acute overdoses of nitrofurantoin (Macrodantin) reported in the literature have not caused symptoms beyond vomiting. There is no specific antidote. Drinking plenty of fluids is recommended to help flush the drug out through the urine, and the drug can be removed by dialysis if needed.

The pharmacodynamic effects of nitrofurantoin oral suspension are listed as unknown in the FDA labeling.

Nitrofurantoin is readily absorbed when taken by mouth, and taking it with food increases how much the body absorbs. Blood levels remain low at therapeutic doses — the drug concentrates in the urine rather than in body tissues, which is why it works for bladder infections but not deeper infections. A significant portion of the dose is excreted unchanged in the urine, and it can give urine a brown color. Nitrofurantoin is dialyzable, meaning it can be removed by dialysis. In patients with reduced kidney function, less drug is excreted into the urine, which both reduces effectiveness and raises the risk of toxicity — this is why it is not recommended when creatinine clearance falls below 60 mL/min.

Avoid exposure to strong light which may darken the drug. stored between 20° to 25°C (68° to 77°F); excursions permitted between 15° to 30°C (59° to 86°F) . Protect from freezing.