O6.3 - Self-reported adherence to event-driven doxycycline postexposure prophylaxis for sexually transmitted infection prevention among cisgender women

Background
Doxycycline taken as postexposure prophylaxis (PEP) was efficacious at preventing bacterial sexually transmitted infections (STIs) among cisgender men who have sex with men and transgender women. Some trials of daily oral HIV preexposure prophylaxis (PrEP) among cisgender women demonstrated lack of efficacy due to very low rates of adherence. Understanding adherence to doxycycline PEP will be essential to interpreting efficacy results among cisgender women.

Methods
We conducted an open-label randomized trial of doxycycline PEP (doxycycline hyclate 200mg taken within 72 hours of sex) compared with standard of care (e.g., quarterly screening and treating STIs) among cisgender women aged 18-30 years in Kisumu, Kenya from February 2020 to November 2022. Participants were required to already be taking daily oral HIV PrEP. SMS surveys were completed weekly to assess frequency of sex and for participants assigned to the intervention and concomitant number of doxycycline PEP doses with sex each week. Quarterly timeline follow-back calendars were used to directly assess event-driven adherence in preceding 2-week period.

Results
We enrolled 449 cisgender women. Median age was 24 years (IQR 21-27), 36.7% reported transactional sex at enrollment, baseline STI prevalence was 17.9% (14.1% Chlamydia trachomatis, 3.8% Neisseria gonorrhoeae, 0.4% Treponema pallidum), and no incident HIV infections were detected. Among women assigned to doxycycline PEP (n=225), weekly SMS surveys on sexual exposure and adherence had an overall 82% response rate, and women reported full coverage, i.e., taking doxycycline PEP at least as many days as they had sex, in 78% of weekly surveys. Among those who responded to SMS surveys (n=211), 63 women always reported full coverage of sexual exposures and 134 reported full coverage in at least 80% of the weeks. In timeline follow-back calendar reports, >80% of sexual acts were covered 72.8% of the time.

Conclusions
Among young cisgender women with high prevalence and incidence of STIs, self-reported doxycycline PEP adherence was high. Objective measures of adherence are needed to better understand adherence and efficacy of event-driven STI prophylaxis.