Daily doxycycline shows promise against STIs in small studies
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Key takeaways:
- Doxycycline post-exposure prophylaxis is a CDC-recommended intervention to prevent STIs in high-risk patients.
- Researchers are also studying dox-PrEP — taking the antibiotic daily — as an STI preventive tool.
In June, the CDC began recommending doxycycline post-exposure prophylaxis — or doxy-PEP, as it is commonly known — as a prevention strategy for STIs in certain high-risk populations.
Doxy-PEP, which involves taking a single dose of doxycycline within 72 hours of having condomless sex, has demonstrated in numerous trials that it can reduce a person’s risk for acquiring a bacterial STI.
“There has been a lot of discussion and excitement about doxy-PEP,” International AIDS Conference co-chair Christoph Spinner, MD, a consultant physician in infectious diseases and head executive of the department of medicine and strategy at Rechts der Isar Hospital in Munich, told reporters before the conference. “There has been less attention to doxy-PrEP, which involves taking doxycycline before sex to prevent STIs.”
Attention may increase following the presentation of two small studies at the conference.
Two studies
Troy Grennan, MD, MSc, physician lead for the HIV/STI program at the British Columbia Centre for Disease Control, and colleagues conducted a pilot, randomized controlled trial of doxy-PrEP in Toronto and Vancouver that enrolled 52 HIV-positive men who have sex with men with a history of syphilis and assigned them in a 1:1 ratio to receive either 100 mg of doxycycline or a placebo every day for 48 weeks.
Based on results from 41 participants, Grennan and colleagues calculated that doxy-PrEP reduced chlamydia by 92%, syphilis by 79% and gonorrhea by 68% compared with placebo, which they said supports “our further evaluation of doxy-PrEP compared to doxy-PEP in an ongoing larger trial.”
In a second, uncontrolled trial, Seitaro Abe, MD, an infectious disease specialist at Japan’s National Center for Global Health and Medicine in Tokyo, and colleagues assessed the impact of 100 mg of daily doxycycline on STI rates among 40 female sex workers in Tokyo.
The intervention was associated with a reduction in the incidence of STIs from around 232 per 100 person years to around 79 per 100 person years, according to Abe and colleagues. In the trial, syphilis cases were reduced to zero, but like some doxy-PEP studies, there was no significant impact on the rate of gonorrhea, according to the researchers, who said the findings support exploring doxy-PrEP for use in high-risk populations.
‘Intriguing’ findings
Spinner said neither studies could answer questions about the potential for doxy-PrEP to increase rates of doxycycline resistance, which he noted are different from region to region. Resistance has been particularly challenging in gonorrhea treatment.
“These are both small studies,” Spinner said. “But the findings are intriguing” and warrant follow-up studies, he told reporters.
References:
- Abe S, et al. Abstract 7497. Presented at: International AIDS Conference; July 22-26, 2024. Munich.
- Doxycycline pre-exposure prophylaxis (DoxyPrEP) significantly reduces STIs in two studies. https://www.iasociety.org/news-release/worlds-seventh-hiv-cure-case-following-stem-cell-transplant-among-scientific. Published July 18, 2024. Accessed July 23, 2024.
- Grennan T, et al. Abstract 11987. Presented at: International AIDS Conference; July 22-26, 2024. Munich.
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