Background: Current US Food and Administration (FDA) guidance recommends that the primary efficacy endpoint for uncomplicated urinary tract infection (uUTI) clinical trials be a composite of clinical and microbiological responses. We applied these criteria to a previous clinical trial to determine the impact on treatment outcomes.

Methods: We conducted a patient-level reanalysis of a randomized clinical trial of nitrofurantoin versus fosfomycin for treatment of uUTI in nonpregnant adult women. Women were included in the reanalysis if they had 2 or more signs/symptoms of uUTI and a single bacterial species isolated from baseline urine culture at =10⁵ colony-forming units (CFU)/mL. The applied primary efficacy endpoint-therapeutic response-required both clinical resolution of signs/symptoms and reduction of the infecting bacterial pathogen to <10³ CFU/mL at day 14 post-treatment completion.

Results: Two hundred eleven of 513 (41%) patients were eligible for inclusion in the reanalysis. Among these patients, 74% (76/103) and 69% (75/108) in the nitrofurantoin and fosfomycin groups, respectively, achieved clinical resolution by day 14. Similarly, 70% (72/103) and 67% (72/108) in each group achieved microbiological success at day 14. As such, 59% (61/103) and 57% (62/108) of women in each group met the primary efficacy endpoint-therapeutic success-at day 14. In comparison, 75% and 66% of patients in each group achieved clinical resolution at day 14 in the initial clinical trial.

Conclusions: Applying current FDA guidance resulted in lower composite efficacy rates than clinical resolution alone as observed in the initial clinical trial. This may limit the ability to compare antibiotic treatment effects between historical and future clinical trials.