Nitrofurantoin is a commonly used first-line antibiotic for uncomplicated urinary tract infections, particularly those caused by E. coli and other common uropathogens. It works by damaging bacterial DNA and is highly concentrated in the urine, which makes it effective for bladder infections while limiting effects elsewhere in the body. Nitrofurantoin is generally well tolerated, but it should not be used for kidney infections or in patients with significantly reduced kidney function. Possible side effects include gastrointestinal upset, headache, and rarely pulmonary or liver toxicity with long-term use.