A single large dose of trimethoprim-sulfamethoxazole fails to cure gonococcal urethritis in men.

In a single-blind study, 50 men who had acute gonococcal urethritis were treated with a single oral dose of either 720 mg trimethoprim (TMP) plus 3,600 mg sulfamethoxazole (SMZ) or 3.5 g ampicillin plus 1 g probenecid. Isolates of Neisseria gonorrhoeae were tested for in-vitro susceptibility to the chemotherapeutic agents administered by agar-dilution and disk-diffusion methods, and results were correlated with cure or failure to cure as determined bacteriologically. Among patients returning for follow up, the cure rate after TMP/SMZ was 69%. Cure was predictable when the isolates of N. gonorrhoeae were inhibited by < or = 0.63/11.87 micrograms/ml of TMP/SMZ (fixed ratio, 1:19) or when the zones of inhibition were > or = 23 mm; failure was predictable when > or = 1.25/23.75 micrograms/ml of TMP/SMZ was necessary for inhibition and when zones of inhibition were < or = 21 mm (P < 0.02). The cure rate after therapy with ampicillin was 100%, a rate significantly higher than that found after TMP/SMZ (P < 0.02); all isolates were inhibited by < or = 0.16 microgram/ml of ampicillin. Adverse reactions were not seen after either TMP/SMZ or ampicillin.