Unsuccessful treatment of non-gonococcal urethritis with rosoxacin provides information on the aetiology of the disease.

In a controlled trial of rosoxacin in patients with non-gonococcal urethritis (NGU), 150 mg of the antibiotic given twice daily for 10 days was compared with 300 mg triple tetracycline (Deteclo) given twice daily for the same period. Only six (19%) of 31 patients treated with rosoxacin were free of urethritis after 10 days; Chlamydia trachomatis was reisolated from 12 (92%) of 13 patients who were chlamydia positive originally, and Ureaplasma urealyticum was reisolated from 12 (80%) of 15 patients who were ureaplasma positive originally. In contrast, 18 (58%) of 31 patients treated with triple tetracycline were cured clinically after 10 days; C trachomatis was not reisolated from any of 10 patients who were chlamydia positive originally, and U urealyticum was reisolated from only three (17%) of 18 patients who were ureaplasma positive originally. These results were consistent with the antimicrobial inactivity of rosoxacin in vitro and they cannot be reconciled with previous reports of successful use of this antibiotic in NGU. Ureaplasmas were isolated more frequently and in larger numbers from chlamydia negative than from chlamydia positive patients, but it is probable that ureaplasmas resistant to tetracycline were not responsible for persistent urethritis.