Prediction of efficacy of antimicrobial agents in treatment of infections due to Chlamydia trachomatis.

Although Chlamydia trachomatis is readily eradicated by systemic therapy in patients with acute urethritis, systemic therapy is less satisfactory in treatment of chronic trachoma. The activities of antimicrobial agents against C. trachomatis in cell cultures when the antimicrobial agents are added 1 hr after the C. trachomatis (minimal inhibitory concentration [MIC]) predicts efficacy of the drugs in the treatment of urethritis but does not necessarily predict efficacy in the treatment of chronic ocular trachoma. Concentrations of antimicrobial agents required to eradicate C. trachomatis when the agents were added 48 hr after inoculation of the cell cultures with C. trachomatis exceeded the MIC by several logarithms, and minocycline, doxycycline, and rifampin were markedly more active than tetracycline, erythromycin, or several other antimicrobial agents. Of the three most active antimicrobial agents, only doxycycline has been used systemically to treat ocular infections due to C. trachomatis, and it has been reported to be the most effective antimicrobial agent that has been utilized. In vitro testing of obligate intracellular pathogens such as C. trachomatis presents unique problems. Utilization of several methods of testing may help to identify antimicrobial agents with improved clinical efficacy, particularly in the treatment of ocular trachoma.