Nitrofurantoin is primarily used as an antibiotic to treat urinary tract infections (UTIs) caused by susceptible bacteria. It works by inhibiting bacterial enzymes and DNA synthesis, effectively stopping the growth of bacteria in the urinary system. It is particularly effective against Escherichia coli, Enterococcus, Staphylococcus aureus, and certain strains of Klebsiella and Enterobacter. Due to its specific concentration in the urine, it is not typically used for systemic infections outside the urinary tract. It is often prescribed for acute uncomplicated lower UTIs and is sometimes used for long-term prevention of recurrent infections. However, it is not suitable for patients with severe kidney impairment, as it relies on renal excretion for its effectiveness. Common side effects include nausea, headache, and, in rare cases, pulmonary or hepatic reactions. It is available in both immediate-release and macrocrystalline forms, with the latter causing fewer gastrointestinal side effects.