The Impact of Doxycycline Post-Exposure Prophylaxis on Antibiotic Use at a Boston Sexual Health Clinic.

BACKGROUND: Doxycycline post-exposure prophylaxis (doxy-PEP) reduces the incidence of bacterial sexually transmitted infections (STIs) among men who have sex with men and transgender women (MSMTW), but it may select for antimicrobial resistance (AMR). AMR development will depend in part how doxy-PEP changes rates of antibiotic use. METHODS: We conducted a retrospective electronic medical record review of antibiotic prescriptions received by patients at the Massachusetts General Hospital Sexual Health Clinic from January 1, 2023, to December 27, 2025. Using a Bayesian negative binomial regression, we assessed the direct, indirect, and combined effects of doxy-PEP implementation on antibiotic prescription rates among doxy-PEP-eligible MSMTW who were receiving HIV pre-exposure prophylaxis. RESULTS: Controlling for direct effects, the cohort's total antibiotic prescription rate decreased by 10% (0.90, 95% CI 0.87 - 0.94) for every 100 doxy-PEP starts. Doxy-PEP users were prescribed antibiotics at double the rate predicted in the absence of doxy-PEP implementation, and, controlling for indirect effects, received 3.40 (95% CI 2.95 - 3.91) times the antibiotic prescriptions of patients not using doxy-PEP. Doxy-PEP non-users were prescribed antibiotics at less than half the rate predicted in the absence of doxy-PEP. The full cohort's overall antibiotic prescription rate increased by 1.4 times after doxy-PEP implementation. CONCLUSIONS: Individuals who are taking doxy-PEP have higher antibiotic prescription rates, increasing selection for antibiotic-resistant bacteria in these individuals. However, doxy-PEP-driven decreases in the overall incidence of bacterial STIs have the potential to decrease selective pressure for resistant organisms in those not using doxy-PEP.