Doxycycline Prophylaxis to Reduce Incident Syphilis among HIV-Infected Men Who Have Sex With Men Who Continue to Engage in High-Risk Sex: A Randomized, Controlled Pilot Study

Background: Incident syphilis infections continue to be especially prevalent among a core group of HIV-infected men who have sex with men (MSM). Because of synergy between syphilis and HIV infections, innovative means for controlling incident syphilis infections are needed. Methods: Thirty MSM who had syphilis twice or more since their HIV diagnosis were randomized to receive either daily doxycycline prophylaxis or contingency management (CM) with incentive payments for remaining free of sexually transmitted diseases (STDs). Participants were tested for the bacterial STDs gonorrhea (Neisseria gonorrhoeae), chlamydia (Chlamydia trachomatis) and syphilis at weeks 12, 24, 36, and 48 and completed a behavioral risk questionnaire during each visit to assess number of partners, condom use, and drug use since the last visit. Generalized linear mixed models were used to analyze differences between arms in STD incidence and risk behaviors at follow-up. Results: Doxycycline arm participants were significantly less likely to test positive for any selected bacterial STD during 48 weeks of follow-up (odds ratio, 0.27; confidence interval, 0.09-0.83) compared with CM arm participants (P = 0.02). There were no significant self-reported risk behavior differences between the doxycycline and CM arms at follow-up. Conclusions: Daily doxycycline taken prophylactically was associated with a decreased incidence of N. gonorrhoeae, C. trachomatis, or syphilis incident infections among a core group of HIV-infected MSM at high risk for these infections. Safe and effective biomedical tools should be included in the efforts to control transmission of syphilis, especially in this population. A randomized clinical trial should be conducted to confirm and extend these findings.