We conducted a randomized, double-blind, placebo-controlled study to determine the efficacy of postcoital
antibiotic prophylaxis in healthy young women prone to recurrent
urinary tract infections. Sixteen patients were randomized to receive postcoital administration of a combination product of
trimethoprim and
sulfamethoxazole, while 11 received postcoital placebo. The treatment groups were similar with respect to age, parity, diaphragm use, history of lifetime
urinary tract infections, frequency of intercourse, and number of lifetime sexual partners. In over 6 months of observation, postcoital administration of
trimethoprim-sulfamethoxazole was highly effective in preventing recurrent
urinary tract infections. Nine of 11 patients who took the placebo developed
urinary tract infections (
infection rate, 3.6 per patient-year), compared with only two of 16 patients who received postcoital
trimethoprim-sulfamethoxazole (
infection rate, 0.3 per patient-year). Postcoital administration of
trimethoprim-sulfamethoxazole was effective in patients with both low (two or fewer times per week) and high (three or more times per week) intercourse frequencies. Side effects were few and compliance was excellent. We conclude that postcoital
trimethoprim-sulfamethoxazole is a safe, effective, and inexpensive approach to management of recurrent
urinary tract infections in young women.