Evaluation of Doxycycline Post-exposure Prophylaxis to Reduce Sexually Transmitted Infections in PrEP Users and HIV-infected Men Who Have Sex With Men

The overarching goal is to assess the effectiveness of doxycycline PEP on incidence of STIs and tetracycline resistance among STIs and commensal bacteria to inform public health policy. Participants will be randomized 2:1, with a greater number receiving doxycycline PEP compared with the standard of care control, to maximize data on safety, tolerability, adherence coverage of sexual acts, and resistance data in participants randomized to doxycycline PEP, without negatively impacting power to measure effectiveness. Participants will be counseled about the preliminary effectiveness data from IPERGAY, and the potential for antimicrobial resistance (AMR) in STIs or other bacteria. Possibility of unreported doxycycline us in the control arm (contamination) will be monitored through retrospective batch testing of doxycycline metabolites in hair, to detect doxycycline use in the prior 3 months. 53 Eligible participants randomized 2:1 to receive PEP will receive open-label doxycycline 200 mg to be taken ideally within 24 hours but no later than 72 hours after condomless sexual contact (oral or anal). 200 mg of doxycycline will be taken at most once per 24 hour period regardless of the number of sexual acts occurring during this time period. Sexual activity will be recorded for both arms of the study (doxycycline PEP and control condition) by the participant using a smartphone application that will be adapted for study use; this will enable comparable assessment of risk in the two arms. PEP pill-taking will also be measured by the app to enable assessment of coverage of sex acts by PEP. Sexual activity and adherence will also be assessed in person at quarterly visits. STI testing will be conducted quarterly from three anatomic sites (pharyngeal, rectal and urinary) and blood for syphilis testing. Participants with a positive STI test will return for STI treatment and for swabs of the affected site for resistance testing; culture based for gonorrhea (GC) and molecular methods for CT and syphilis. Those with a serologic test that indicates a new syphilis infection will have swabs of any current active lesion as well as mucosal swabs from the oropharynx. Nares and oropharyngeal swabs will be obtained at baseline, 6 and 12 months to evaluate tetracycline resistance in S. aureus among carriers and in commensal Neisseria species. Stool samples from 100 participants on the doxycycline PEP arm - 50 MSM living with HIV and 50 HIV uninfected MSM on pre-exposure prophylaxis (PrEP) - will be collected at baseline, 6 and 12 months to evaluate effects of intermittent doxycycline on the gut resistome, using 16s ribosomal RNA amplification to study tetracycline resistance genes. Rectal swabs will be collected and archived in all participants at baseline, 6, and 12 months for future studies of the impact of doxycycline PEP on the enteric microbiome and resistome. Study population: This study will enroll 390 HIV-infected participants and 390 persons taking PrEP, for a total sample size of 780. An approximately equal number of participants in each of these cohorts (and in each study arm) will be enrolled in San Francisco and Seattle. Current or planned initiation of PrEP use is an eligibility criterion for enrollment, because this population of MSM has high rates of STIs and are typically seen quarterly for PrEP visits. However, participants may opt to stop PrEP use at any time during the study without affecting their involvement in the study. Any HIV-uninfected participants who subsequently seroconvert will be managed clinically by the study site according to local practice (appropriate counseling, clinical evaluation and immediate linkage to clinical and psychosocial services). These participants will also be retained in the study unless they choose to discontinue study participation.