PREPARATIONS: Capsules: 25, 50, 75, and 100 mg. Oral suspension: 25 mg/5 ml.
DRUG INTERACTIONS: High doses of probenecid (Benemid) or sulfinpyrazone (Anturane) can partially block the kidneys' elimination of nitrofurantoin. This can increase the blood concentrations of nitrofurantoin and the risk of toxicity from nitrofurantoin.
Concomitant administration of a magnesium trisilicate antacid may decrease the absorption of nitrofurantoin, reducing the effectiveness of nitrofurantoin.
NItrofurantoin may reduce the activity of live tuberculosis vaccine (BCG vaccine) and live typhoid vaccine. In laboratory tests, nitrofurantoin reduced the effect of quinolone antibiotics, for example, norfloxacin (Noroxin). Therefore, nitrofurantoin should not be combined with quinolone antibiotics.
PREGNANCY AND BREASTFEEDING SAFETY: Although there are no adequate studies of nitrofurantoin in pregnant women, many women have safely used it during pregnancy. However, nitrofurantoin should not be used near the time of delivery (38-42 weeks gestation) since it interferes with the immature enzyme systems in the red blood cells of newborns, damaging the cells and resulting in anemia.
Nitrofurantoin is distributed into breast milk and should be used with caution in women who are breastfeeding.
STORAGE: All formulations should be kept at room temperature, 15 C TO 30 C (59 F to 86 F).
DOSING: The recommended adult dose for treating urinary tract infections is 50-100 mg 4 times daily (Macrodantin, Furadantin) or 100 mg every 12 hours (Macrobid) for 7 days or for 3 days after obtaining sterile urine.
Nitrofurantoin can be taken with or without meals. Taking it with meals increases its absorption into the body. The suspension can be mixed with water, milk, juice, or infant formula.
It also is used once a day (or in some children, twice daily) to prevent urinary tract infections.
It should not be used in persons with poor kidney function.
DRUG CLASS AND MECHANISM: Nitrofurantoin is an antibiotic that is used for treating urinary tract infections caused by several types of bacteria. It is effective against E. Coli, Enterobacter cystitis, Enterococcus, Klebsiella, and Staphylococcus aureus. Nitrofurantoin interferes with the production of bacterial proteins, DNA, and cell walls. Bacteria cannot survive without a cell wall or multiply without DNA.
Three forms of nitrofurnatoin are available:
- Furadantin, a microcrystalline form,
- Macrodantin, a macrocrystalline, and
- Macrobid, a sustained release form of macrocrystalline used twice daily.
The macrocrystalline form is more slowly absorbed than the microcrystalline form and is useful for patients who cannot tolerate the microcrystalline form. The FDA approved nitrofurantoin in 1953.
Medically reviewed by Eni Williams, PharmD
Reference: FDA Prescribing Information
Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.
Need help identifying pills and medications?
Use the pill identifier tool on RxList.