Antimicrobial therapy of chancroid: an evaluation of five treatment regimens correlated with in vitro sensitivity

One hundred fifty-one men with genital ulcer disease were assigned randomly to treatment with one of five oral antimicrobial regimens: (1) sulfadimidine (1 g four times daily for seven days); (2) tetracycline (500 mg four times daily for seven days); (3) trimethoprim-sulfamethoxazole (TMP-SMZ; 160 mg of TMP and 800 mg of SMZ twice daily for seven days); (4) doxycycline (300 mg as a single dose); or (5) TMP-sulfametrole (640 mg of TMP and 3,200 mg of sulfametrole once as a single dose). Haemophilus ducreyi was isolated from 81 (54%) of the men, and 35 strains were available for testing of antimicrobial susceptibility. The TMP-SMZ and TMP-sulfametrole regimens were more effective than sulfadimidine, tetracycline, or single-dose doxycycline in curing ulcers. Only one of 35 strains tested was susceptible to tetracycline (less than or equal to 8 mg/liter), and only ten of 35 strains were susceptible to doxycycline (less than or equal to 4 mg/liter), whereas all were susceptible to trimethoprim (less than or equal to 2 mg/liter). The correlation between in vitro susceptibility and bacteriologic response to the antimicrobial agents requires further investigation. In particular, sulfonamide resistance did not always identify failure to respond to sulfadimidine.