Bacterial sexually transmitted infections (STIs) are repsonsible for significant and disproportionate morbidity and mortality in cisgender women, among whom STI incidence has been rising globally. Doxycycline taken as postexposure prophylaxis (PEP) was efficacious at preventing STIs among cisgender men who have sex with men and transgender women, but no trials among cisgender women have been done.
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 women aged 18-30 years in Kisumu, Kenya. Participants were required to already be taking daily oral HIV preexposure prophylaxis (PrEP). Contraception was not required, and doxycycline was stopped during pregnancy. Weekly SMS surveys were done to assess concomitant doxycycline PEP use with sex. The primary endpoint was any incident Chlamydia trachomatis, Neisseria gonorrhoeae, or Treponema pallidum infection, measured quarterly for one year; the trial had 80% power to detect 50% reduction in incident STIs, anticipating 66 incident STIs.
We enrolled 449 cisgender women; women completed 97% of expected follow-up visits. Median age was 24 years (IQR 21-27), 36.7% reported transactional sex at enrollment, and baseline STI prevalence was 17.9% (14.1% C. trachomatis, 3.8% N. gonorrhoeae, 0.4% T. pallidum). Incident STI events were detected at 109 follow up visits (85 C. trachomatis, 31 N. gonorrhoeae, including 8 with both; 1 T. pallidum): 50 among those assigned to doxycycline PEP and 59 among those assigned STI screening and treatment alone (RR 0.88, 95% CI 0.60-1.29, p=0.51). Analysis with follow-up time censored once participants became pregnant (n=80), analysis of each STI separately, and subgroup analyses (including by age, contraceptive use, transactional sex, and STI detected at baseline) found similar results. There were no serious adverse events determined to be related to use of doxycycline. No incident HIV infections were detected. Weekly SMS surveys had an overall 81% response rate, and women assigned to PEP reported taking doxycycline PEP at least as many days they had sex in 78% of surveys.
Among young cisgender women with high prevalence and incidence of STIs, the use of doxycycline PEP following sex did not reduce incident STIs.