Abstract Body


After early demonstration of 65% efficacy in reducing bacterial STIs in the DoxyPEP Study, participants (ppts) in the standard of care (SOC) arm were offered doxy-PEP. We subsequently examined uptake, adherence, sexual activity, and incident bacterial STIs, as awareness of STI prevention efficacy may impact patterns of doxy-PEP use and sexual behavior.


DoxyPEP is an open-label trial conducted in Seattle and San Francisco among men who have sex with men (MSM) and transwomen (TW) living with HIV (PWH) or on PrEP who had a bacterial STI in the past year, randomized 2:1 to doxy-PEP or SOC. After the efficacy threshold was reached in a planned interim analysis, SOC ppts were offered doxy-PEP and both arms were followed in an open label extension (OLE) for up to 12 months total. OLE quarters were defined as those with doxy-PEP for a full quarter after 5/2022 results were disclosed. Self-reported sexual behavior and quarters with ≥1 STI endpoint are compared descriptively during OLE doxy-PEP use vs. SOC as-randomized (SOC-AR) without doxy-PEP.


Of the 637 ppts enrolled, 279 contributed to OLE follow-up: 193 from the doxy-PEP arm (D-OLE) and 86 of 87 ppts from the SOC arm (SOC-OLE). Of those in the OLE: 96% MSM, 4% TW, 78% were on PrEP, 22% PWH, 62% White, 4% Black, 13% Asian, 22% other; 27% Hispanic. ≥1 STI endpoints were observed in 13.4% of D-OLE and 18.2% of SOC-OLE quarters, compared to 12.1% during doxy-PEP as-randomized (D-AR) and 31.2% during SOC-AR (Table). Reductions in each STI (gonorrhea, chlamydia and syphilis) were observed in both D-OLE and SOC-OLE groups compared to the SOC-AR. Doxy-PEP use after condomless sex was 78% in D-OLE and 79% in SOC-OLE ppts, compared to 83% of D-AR ppts. Median self-reported doxy doses taken per quarter were 19 (IQR 7-32) in D-OLE and 16 (5-30) in SOC-OLE, compared to 14 (IQR 4-30) during D-AR. During OLE, SOC-OLE ppts reported higher median sex partners per quarter: 15 (IQR 5-30) compared to 8 (IQR 4-15) during SOC-AR and D-OLE ppts reported a median of 12 (IQR 5-25) partners per quarter vs.10 (IQR 4-25) during D-AR.


In the OLE period after doxy-PEP efficacy was known, almost all SOC ppts accepted doxy-PEP and both OLE groups reported high doxy-PEP coverage (>78%) of condomless sex in the context of a higher number of sexual partners during OLE. Doxy-PEP was associated with sustained decreased rates of incident STI’s in both groups during the OLE compared to no doxy-PEP use among ppts initially randomized to the SOC arm.