Charles Roncier, Vih.org
The results of the DOXYPEP study confirm the benefit of taking doxycycline after sexual intercourse (PEP for post-exposure) in reducing the risk of bacterial sexually transmitted infections (STIs).
Annie Luetkemeyer, from Zuckerberg San Francisco General Hospital, UCSF, presented these encouraging results at the 2022 Montreal International HIV/AIDS Conference. The DOXYPEP trial studied the benefit of taking antibiotics post-exposure against sexually transmitted infections. The results of quarterly examinations of DOXYPEP show a reduction of about two thirds in the risk of contracting a bacterial STI. Most of the STIs detected were asymptomatic.
The DOXYPEP trial evaluated the benefit of taking 200 mg of the antibiotic doxycycline within 72 hours of having sex without a condom (no more than once every 24 hours). The study was open to men who have sex with men and trans women. These people are particularly exposed to STIs and had to have experienced an episode of sexually transmitted infection in the past year to join the cohorts.
These very positive results prompted the researchers to interrupt the trial a year before the scheduled end: faced with the significant difference in effectiveness between the two arms, the monitoring committee recommended in May 2022 to stop recruiting new people. Everyone in the study had access to doxycycline.
In the randomization arm of HIV-negative people, the efficacy was 66%, with 65 infections in the control arm and 47 in the doxycycline arm, which had twice as many people, giving a quarterly incidence of 29.5% in the control arm and 9.6% in the doxycycline arm. Among HIV-positive participants, efficacy was somewhat lower, with 62% efficacy.
Thirty STIs were counted in the control arm, and 31 in the doxycycline arm, i.e. quarterly incidence rates of 27.8% in the control arm and 11.7% respectively. Efficacy was highest against chlamydia, with 79% in HIV-negative people and 70% in people living with HIV. Against gonorrhea, it was 59% in people without HIV and 57% in people with HIV.
In this trial, post-exposure doxycycline was safe and tolerable (only 1.5% of participants discontinued due to adverse effects), and compliance was high (87% of procedures were covered by taking doxycycline)
Annie Luetkemeyer however underlined the major need for additional bacteriological data, which is lacking in this type of study, regarding the risks of resistance (including S. aureus, commensale Neisseria, and more generally on the intestinal microbiome). The assessment of the impact on sexual behavior is also in progress, and the DoxyVac sub-study of the ANRS Prevenir study should also provide additional data, particularly on gonorrhea.