Each capsule contains two forms of nitrofurantoin. Twenty-five percent is macrocrystalline nitrofurantoin, which has slower dissolution and absorption than nitrofurantoin monohydrate. The remaining 75% is nitrofurantoin monohydrate contained in a powder blend which, upon exposure to gastric and intestinal fluids, forms a gel matrix that releases nitrofurantoin over time. This capsule is highly soluble in urine, to which it may impart a brown color. When administered with food, the bioavailability of nitrofurantoin is increased by approximately 40%.

For the treatment of and prophylaxis against acute or recurrent, uncomplicated lower urinary tract infections or pyelitis either spontaneous or following surgical procedures. Nitrofurantoin is specifically indicated for the treatment of infections when due to susceptible strains of Escherichia coli, enterococci, staphylococci, Citrobacter, Klebsiella and Enterobacter.

Adults and Pediatric Patients Over 12 Years: One 100 mg capsule every 12 hours for seven days. Capsules should be taken with food.

The administration of high doses of nitrofurantoin to rats causes temporary spermatogenic arrest; this is reversible on discontinuing the drug. Doses of 10 mg/kg/day or greater in healthy human males may, in certain unpredictable instances, produce a slight to moderate spermatogenic arrest with a decrease in sperm count.

In clinical trials of Macrobid, the most frequent clinical adverse events that were reported as possibly or probably drug related were nausea (8%), headache (6%), and flatulence (1.5%)

Overdose Effects

Occasional incidents of acute overdosage of nitrofurantoin have not resulted in any specific symptoms other than vomiting. Induction of emesis is recommended. There is no specific antidote, but a high fluid intake should be maintained to promote urinary excretion of the drug. Nitrofurantoin is dialyzable.

Pregnancy & Lactation

Pregnancy Category B. Nitrofurantoin has been detected in human breast milk in trace amounts. Because of the potential for serious adverse reactions from nitrofurantoin in nursing infants under one month of age, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother.