Doxycycline Cuts STI Risk in Men and Trans Women Having Sex With Men

Kate Johnson

July 29, 2022

MONTREAL — One 200 mg dose of doxycycline taken as post-exposure prophylaxis (PEP) reduced the incidence of three sexually transmitted infections (STIs) by 65% among men who have sex with men (MSM) and transgender women (TGW) living with HIV or taking preexposure prophylaxis (PrEP). The results of the open-label DoxyPEP trial were reported at a press conference here at the 24th International AIDS Conference.

"It is time to take action on the data that we have and really think about incorporating it into guidelines and rolling this out in a safe and thoughtful way," said co-principal investigator Annie Luetkemeyer, MD, from Zuckerberg San Francisco General Hospital, and professor of medicine at the University of California San Francisco (UCSF).

The, open-label trial, conducted in Seattle and San Francisco, randomized MSM/TGW living with HIV or on PrEP, and with a history of N gonorrhoeae (GC), C trachomatis (CT), or early syphilis in the past year, to either doxycycline or none within 72 hours of having condomless sex. It was stopped early in May when a planned interim analysis showed those randomized to take doxycycline had substantially fewer STIs than participants assigned to the control group.

The intent-to-treat analysis included 501 patients with at least one quarter of follow-up: 327 taking PrEP and 174 living with HIV. Among those taking PrEP, new STIs (GC, CT or syphilis) occurred in 31.9% of control participants vs 10.7% of those taking doxycycline — a reduction of 66% per quarter (P < .001). Among participants living with HIV, new STIs occurred in 30.5% of controls vs 11.8% taking doxycycline, for a 62% reduction in STIs per quarter (P < .0001).

"Participants reported taking doxycycline 87% of the time after having condomless sex, about half of participants took fewer than 10 doses per month, 30% took 10-20 doses per month, and 16% took more than 20 doses of doxycycline per month," said Luetkemeyer, adding that there were no serious — grade 2 or greater — adverse events, and "the majority of participants reported that taking doxy was acceptable or very acceptable."

Asked by Medscape Medical News how broadly doxycycline prophylaxis could be used in other populations, Luetkemeyer was cautious. "Our study participants had a very high rate of new STIs — a 30% incidence per quarter  and using doxyPEP was well tolerated and very effective to reduce new STIs. However, this is a fairly limited population," she said. "Whether doxyPEP should be considered for other groups, such women on PrEP or with an elevated risk for STIs, will need more data which will be forthcoming from ongoing studies."  

Luetkemeyer said her group is looking at three possible risks of antibiotic resistance with the doxyPEP regimen: the risk to bystander bacteria such as Staphylococcus aureus or commensal neisseria; the impact on the gut; and the risk of resistance to antibiotic treatments for STI.

For the latter, "we don't really think this is going to be an issue in chlamydia and syphilis, and we're looking carefully at gonorrhea," she said, adding that it will be challenging to get definitive data from this particular study because of its short follow-up.

"Available culture data from those who had gonorrhea infections during the study demonstrated a relatively low rate of tetracycline resistance, which is a proxy for doxycycline resistance, at 20%…However larger studies and population-based surveillance of those taking doxycycline as PEP are needed to understand if doxycycline use could drive the element of tetracycline resistance in gonorrhea," she said, emphasizing that doxycycline is not used to treat active gonorrhea infections.

Calling the doxyPEP regimen a  "game-changing strategy," Sharon Lewin, AO, PhD, president-elect of the International AIDS Society, said many physicians are already prescribing it off-label based on the IPERGAY study (N Engl J Med 2015; 373:2237-2246) "but there's a clear need for more evidence to guide the use of this intervention."

"This study has huge implications for clinical care," commented Monica Gandhi, MD, MPH, an infectious diseases doctor, professor of medicine, and associate chief in the Division of HIV, Infectious Diseases, and Global Medicine at UCSF. "Although the data on drug resistance is very important to evaluate, we should certainly consider at this point using doxycycline PEP within 72 hours of condomless sex for our patients for STI prevention," she told Medscape.

"In our practice, we are very excited about the possibility of a simple one-pill post-exposure prophylactic agent (doxycycline 200 mg) to reduce the risk of a number of STIs. We have used PEP for HIV infection for a number of years and are very familiar with the concept of preventing infections after an exposure," said Gandhi, who is also director of the UCSF Center for AIDS Research and medical director of the HIV Clinic ("Ward 86") at San Francisco General Hospital. "We are planning to institute doxycycline as PEP at my clinic after the release of these findings and will follow the remainder of the study findings closely."

The trial was funded by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, through grant R01AI143439. It was conducted at the HIV clinic at Zuckerberg San Francisco General Hospital and the San Francisco City Clinic, both part of the San Francisco Department of Public Health, and the Madison Clinic and the Sexual Health Clinic at Harborview Medical Center, both at the University of Washington. Medications were provided by Mayne Pharmaceuticals, and lab support by Hologic & Cepheid.

Lewin has the following disclosures: investigator-initiated, industry-funded research for Gilead, Viiv, Merck; scientific advisory board (honoraria paid to her personally) for Gilead, Merck, Viiv, Esfam, Immunocore, Vaxxinity; collaborative research (non-funded) for AbbVie, Genentech, BMS. Luetkemeyer and Gandhi reported no relevant financial relationships.

24th International AIDS Conference (AIDS 2022): Abstract 13231: Presented July 27, 2022 (media event)

Kate Johnson is a Montreal-based freelance medical journalist who has been writing for more than 30 years about all areas of medicine.

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