Nitrofurantoin 100 mg versus 50 mg prophylaxis for urinary tract infections, a cohort study.

Objectives: Guidelines do not distinguish between 50 mg or 100 mg nitrofurantoin as daily prophylaxis for recurrent urinary tract infection (UTI), although 50 mg might have a better safety profile. Our objective was to compare the effectiveness and safety of both regimens.

Methods: Data were retrospectively collected from 84 Dutch GP practices between 2013 and 2020. Nitrofurantoin prescriptions of 100 mg and 50 mg every 24 hours in women were included. Cox proportional hazard regression analysis was used to calculate hazard ratios on first episode of UTI, pyelonephritis and (adverse) events. Patients were followed for the duration of consecutive repeated prescriptions, assuming non-informative right censoring, up to 1 year.

Results: Nitrofurantoin prophylaxis was prescribed in 1893 patients. Median lengths of follow up were 90 days (interquartile range (IQR) 37-179 days) for 100 mg (n = 551) and 90 days (IQR 30-146 days) for 50 mg (n = 1342) with few differences in baseline characteristics between populations. Under 100 mg and 50 mg, 82/551 (14.9%) and 199/1342 (14.8%) developed UTI and 46/551 (8.3%) and 81/1342 (6.0%) developed pyelonephritis, respectively. Adjusted HRs of 100 mg versus 50 mg were 1.01 (95% CI 0.78-1.30) on first UTI, 1.37 (95% CI 0.95-1.98) on first pyelonephritis episode, 1.82 (95% CI 1.20-2.74) on first consultation for cough, 2.68 for dyspnoea (95% CI 1.11-6.45) and 2.43 for nausea (95% CI 1.03-5.74).

Conclusion: Daily prophylaxis for recurrent UTI with 100 mg instead of 50 mg nitrofurantoin was associated with an equivalent hazard on UTI or pyelonephritis, and a higher hazard on cough, dyspnoea and nausea. We recommend 50 mg nitrofurantoin as daily prophylaxis.