Pharmacy Author: Omudhome Ogbru, PharmD
Medical and Pharmacy Editor: Jay W. Marks, MD

GENERIC NAME: nitrofurantoin

BRAND NAMES: Macrodantin, Furadantin, Macrobid

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 are available: 1) a microcrystalline form (Furadantin), 2) a macrocrystalline form (Macrodantin), and 3) a sustained release macrocrystalline form used twice daily (Macrobid). 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.

PRESCRIPTION: Yes

GENERIC AVAILABLE: Yes

PREPARATIONS: Capsules: 25, 50, 75, and 100 mg. Oral suspension: 25 mg/5 ml.

STORAGE: All formulations should be kept at room temperature, 15-30 C (59-86 F).

PRESCRIBED FOR: Nitrofurantoin is used to treat or prevent urinary tract infections.

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). 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 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.

In laboratory tests, nitrofurantoin reduced the effect of quinolone antibiotics, for example, norfloxacin (Noroxin). Therefore, nitrofurantoin should not be combined with quinolone antibiotics.

PREGNANCY: 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.

NURSING MOTHERS: Nitrofurantoin is distributed into breast milk and should be used with caution in women who are breast- feeding.

SIDE EFFECTS: Common side effects include headache, rash, itching, nausea, vomiting, loss of appetite, diarrhea, and abdominal pain. The macrocrystalline form (Macrodantin) appears to cause less stomach upset. Stomach upset also can be minimized by using a lower dose or by taking nitrofurantoin with food or milk.

Nitrofurantoin can cause serious lung injury. The reaction can occur within hours of the start of treatment if the patient has previously received nitrofurantoin or within a few days of starting nitrofurantoin for the first time. Symptoms include difficulty breathing, chills, fever, chest pain, and cough. In other persons, lung injury may occur after approximately a month of treatment. Symptoms include difficulty breathing, rapid breathing, and cough. Fortunately, the symptoms usually resolve within a week if the medication is stopped. In still other persons, lung injury may not develop until after several months or years of therapy. Unless it is recognized and treated, this delayed lung injury can result in permanent lung damage that remains even after the drug is stopped.

A condition known as peripheral neuropathy (damage to the sensory nerves of the arms and legs), may occur with nitrofurantoin therapy, most commonly causing tingling in the extremities. The condition can become severe and is more likely to occur in patients with diabetes mellitus, vitamin B deficiency, or general debilitation.

A type of anemia (reduced red blood cell count) called hemolytic anemia can occur during therapy with nitrofurantoin. This reaction occurs most frequently in persons with a deficiency of an enzyme called glucose-6-phosphate dehydrogenase which is very important to the survival of red blood cells.

Nitrofurantoin also can cause liver damage leading to jaundice or a form of hepatitis which can be fatal. Elevated liver enzymes indicate liver damage and are a reason to stop the drug.

Treatment with nitrofurantoin can cause urine to change color to a dark yellow or brown.

Reference: FDA Prescribing Information