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Doxycycline post-exposure prophylaxis for STI prevention among MSM and transgender women on HIV PrEP or living with HIV: high efficacy to reduce incident STI's in a randomized trial

Title
Doxycycline post-exposure prophylaxis for STI prevention among MSM and transgender women on HIV PrEP or living with HIV: high efficacy to reduce incident STI's in a randomized trial
Presenter
Annie Luetkemeyer
Authors
A. Luetkemeyer * (1), J. Dombrowski (2,3), S. Cohen (4,5), D. Donnell (2), C. Grabow (2), C. Brown (2), C. Malinski (2,3), R. Perkins (2), M. Nasser (4), C. Lopez (6), S. Buchbinder (4), H. Scott (4), E. Charlebois (5), D. Havlir (6), O. Soge (2), C. Celum (2)
Institutions
(1) Zuckerberg San Francisco General Hospital, University of California San Francisco, Division of HIV, Infectious Diseases and Global Medicine, San Francisco, United States, (2) University of Washington, Seattle, United States, (3) Public Heath - Seattle & King County, Seattle, United States, (4) San Francisco Department of Public Health, San Francisco, United States, (5) University of California San Francisco, San Francisco, United States, (6) Zuckerberg San Francisco General Hospital, University of California San Francisco, San Francisco, United States

BACKGROUND: With a sexually transmitted infection (STI) epidemic among men who have sex with men(MSM) and transgender women(TGW), interventions to reduce STIs are needed.
METHODS: DoxyPEP is a randomized open-label trial among Seattle and San Francisco MSM/TGW living with HIV or on PrEP who had N. gonorroheae (GC), C. trachomatis (CT), or early syphilis in the past year. Randomization was 2:1 to 200 mg doxycycline hyclate within 72 hours of condomless sex or no doxycycline with STI testing at enrollment, quarterly, and when symptomatic. An independent committee adjudicated STIs. The trial had >80% power to detect a 50% reduction in STI incidence, assuming a 10% quarterly STI incidence. The intent to treat analysis compared relative risk of an STI per quarter. A single interim analysis at ~50% of follow-up time occurred May 2022; the DSMB recommended stopping the control arm based on prespecified efficacy thresholds measured independently in PLWH and PrEP cohorts.
RESULTS: Of 554 enrolled, 360 were on PrEP, 194 PWLH, 65% white, 8% Black, 10% Asian, 30% Latinx. 19 (3%) identified as TGW or nonbinary. Median sex partners in past 3 months was 9. In the past year 67% had GC, 58% CT, 20% syphilis; at enrollment, 18% had GC, 10% CT, 2% syphilis . Among 360 on PrEP, 65 STI endpoints (29.5%) occured in controls and 47 (9.6%) in doxyPEP participants (RR 0.33; 95%CI 0.23-0.47; p<0.0001). Among 194 PLWH, 30 STI endpoints (27.8%) in controls and 31 (11.7%) in doxyPEP participants (RR 0.42; 95% CI 0.25-0.75; p=0.0014). GC, CT, and syphilis were each reduced. No serious or '¥ Grade 2 AEs were attributed to doxycycline.


CONCLUSIONS: Doxycycline 200 mg taken within 72 hours after condomless sex significantly reduced STIs in MSM/TGW. Effects on antimicrobial resistance, gut microbiome, and sexual behavior are being assessed as important considerations for this STI prevention strategy.