Does Nitrofurantoin Lose Effectiveness in Patients with Moderate Renal Impairment?

According to FDA prescribing information, nitrofurantoin use is contraindicated in patients with creatinine clearances <60 mL/minute because of concern about toxicity due to impaired drug excretion. Another theoretical concern in patients with renal dysfunction is that insufficient urinary drug levels might result in treatment failure for cystitis. Nevertheless, nitrofurantoin is prescribed often in patients with mild-to-moderate renal impairment. To determine whether nitrofurantoin loses effectiveness in such patients, researchers used administrative databases in Ontario, Canada, to conduct a population-based study of older women (age, >65) who had received nitrofurantoin, any quinolone (i.e., ciprofloxacin or norfloxacin), or trimethoprim…