By Marie Rosenthal, MS
Doxycycline pre-exposure prophylaxis (doxyPrEP) appears to be a promising strategy for preventing bacterial sexually transmitted infections (STIs) among men who have sex with men (MSN) as well as women, according to two small studies presented at AIDS 2024, held in Munich.
“In recent years, studies have shown that taking doxycycline after condomless sex can significantly reduce the risk for a number of bacterial STIs in some populations, and this intervention is called doxyPEP, or doxycycline post-exposure prophylaxis,” said Sharon Lewin, MD, PhD, the president of the International AIDS Society, and the international co-chair of AIDS 2024, who moderated a press briefing at the conference.
“But there has been less attention to another approach, something called doxyPrEP, or doxycycline pre-exposure prophylaxis, which involves taking doxycycline before sex to prevent STIs,” added Dr. Lewin, who is also the director of the Peter Doherty Institute for Infection and Immunity at the University of Melbourne, in Australia. Although the two studies presented at AIDS 2024 were small, she called them “intriguing.”
A randomized controlled pilot study enrolled 52 MSM in Toronto and Vancouver, British Columbia. All men were living with HIV and had a history of syphilis. They were randomly selected to receive 100 mg of doxycycline daily or placebo and followed for 48 weeks, according to Troy Grennan, MD, of the British Columbia Centre for Disease Control (abstract 11987).
“Because it was a smaller study, we were primarily focused on feasibility as our primary outcome,” Dr. Grennan said during a press briefing. “And our secondary outcomes were STI incidence, antimicrobial resistance and changes in sexual behavior.
Forty-one participants completed the study. “[The study] looked really good on feasibility; 79% of our participants completed the protocol, which is a measure of acceptability,” he explained.
They used several measures for adherence, including counting pills, and found more than 85% of the participants were adherent.
They intervention was also successful, he reported, with a 79% reduction in syphilis, 92% reduction in chlamydia and 68% reduction in gonorrhea in the doxyPrEP arm compared with the placebo group. These results were similar to another study that looked at doxyPrEP for MSM who did not have HIV.
“And so overall, doxyPrEP led to an 80% reduction in any of the three STIs we were looking at,” he said.
There were no differences between arms related to drug adherence or sexual behaviors.
Because people are on a low dose of antibiotics, there is concern about resistance developing. They saw the development of new doxycycline resistance in three Staphylococcus aureus isolates from baseline to week 48 in the doxycycline arm and two isolates in the placebo group.
“So the bottom line from the study is that it really does support, I think, the ongoing investigation of doxyPrEP as an intervention for STI prevention,” he said.
Dr. Grennan and his colleagues are looking to recruit more than 550 participants into a larger trial comparing the effectiveness of doxyPrEP and doxyPEP, called Doxycycline as an Intervention for bacterial STI ChemOprophylaxis, dubbed the DISCO project.
Dr. Grennan said he also wants to see STI prevention research move forward equitably, dedicating more effort toward key populations that haven’t received as much attention, such as cisgender women and young people.
The second doxyPrEP study enrolled 40 female sex workers in Tokyo; most of the women were in their 20s and were Japanese. The women were each provided with 100 mg of doxycycline daily and followed over time (abstract 7947).
After initiating doxyPrEP, the overall STI incidence rate declined from 232.3 to 79.2 per 100 person-years. Syphilis incidence was reduced to zero, there was a marginally significant reduction in chlamydia, but there was no significant change in gonorrhea, according to Seitaro Abe, MD, of the National Center for Global Health and Medicine, in Japan. Incidence of bacterial vaginosis and vulvovaginal candidiasis did not significantly increase.
They also performed follow-up interviews with the women and found adherence to the regimen and satisfaction with doxyPrEP were high among the participants. In fact, 72.7% of respondents indicated using doxyPrEP reduced their fear of STI transmission. In addition, the women said they visited a health clinic more often after starting the study.
No serious adverse events were reported, but 22.7% of the respondents reported nausea and vomiting after taking doxycycline.
The findings support the introduction of doxyPrEP to highly vulnerable populations, he said.
