OBJECTIVES: The Centers for Disease Control and Prevention recently released draft guidelines for the use of doxycycline post-exposure prophylaxis (DoxyPEP) to reduce the transmission of sexually transmitted infections (STIs), including syphilis, for men who have sex with men (MSM) or transgender women (TGW) who have had an STI in the past year. This study aims to measure potential syphilis cases averted in Colorado by varying rates of DoxyPEP uptake.

METHODS: A Markov model estimated DoxyPEP’s impact on preventing syphilis among eligible adults in Colorado. The primary outcomes were the number of individuals prescribed DoxyPEP and the number of potential syphilis cases averted. The number of potential DoxyPEP users was estimated based on the Colorado MSM and TGW population, prevalence of STIs, and varied rates of prescribing (15%-50%). The model used a syphilis diagnosis rate for MSM and TGW from previous literature to estimate the number of syphilis diagnoses without DoxyPEP. The number of syphilis cases averted from DoxyPEP was estimated using clinical trial data for DoxyPEP efficacy, reported patient adherence, and varied prescribing rates. The model used a public health perspective, 1-month cycle, and a 1-year time horizon. Sensitivity analyses tested model robustness and uncertainty in model inputs.

RESULTS: An estimated 11,500 (range 3,800-27,600) individuals in Colorado are eligible for DoxyPEP. Prescribing rates of 15%, 30%, and 50% would result in approximately 1,700, 3,400, and 5,700 individuals prescribed DoxyPEP, respectively. Without DoxyPEP, there were 417 new syphilis infections estimated in one year. DoxyPEP prescribing rates of 15%, 30%, 50% would avert an estimated 43 (10%), 85 (20%), and 142 (33%) new syphilis infections among this population annually.

CONCLUSIONS: Uptake of DoxyPEP by 15%-50% of eligible Coloradans would result in 1,700-5,700 new DoxyPEP prescriptions and would prevent approximately 10%-33% of new syphilis infections among MSM and TGW in Colorado each year.