In vitro activity of minocycline against Chlamydia trachomatis clinical isolates and clinical efficacy of minocycline to C. trachomatis associated nongonococcal urethritis

The in vitro activity of minocycline (MINO) against Chlamydia trachomatis and its efficacy in the treatment of C. trachomatis-associated nongonococcal urethritis were investigated. Six isolates of C. trachomatis were inhibited at 0.06 micrograms/ml of MINO and 5 isolates at 0.03 micrograms/ml. All cases received oral MINO twice daily for 7 or more days in doses of 100 mg. In 5 of 31 cases, 2 g of spectinomycin was intramuscularly administrated together with MINO only once. C. trachomatis was eliminated in all cases tested. Excellent results were obtained in 26 cases (84%); urethral discharge and polymorphonuclear cells (PMN) disappeared or decreased to normal levels (3 cells/hpf or less) in these cases. Ureaplasma urealyticum was isolated from 8 cases, 7 of which became free of ureaplasmal infection. MINO seemed to be less effective on the decrease of PMN in the urethral smear in cases infected coincidentally with C. trachomatis and U. urealyticum than in cases infected with C. trachomatis alone. No subjective side effects were observed in any of the 31 cases studied. In conclusion, MINO was a useful antimicrobial agent for the treatment of C. trachomatis- and U. urealyticum-associated nongonococcal urethritis.