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Antibiotic Cuts Risk of HIV, STDs After Exposure, Study Says

May 8, 2023 — The antibiotic doxycycline reduces the onset of HIV and sexually transmitted infections (STIs) by two-thirds after exposure, according to research sponsored by the National Institutes of Health. 

The research aimed to ground previous case studies of doxycycline in a clinical trial of men who have sex with men, said lead researcher Anne Luetkemeyer, MD, an infectious disease specialist with the University of California, San Francisco, and an affiliate with several Bay Area hospitals.

Earlier research from France in 2016 seemed to show that doxycycline – or doxy – worked against sexually transmitted diseases. But Luetkemeyer’s team wanted to confirm those findings and study its effects in a different population, she said. 

This randomized, controlled trial found doxycycline reduced occurrence of sexually transmitted infections such as chlamydia and syphilis. Men assigned male at birth demonstrated the benefits of the two-thirds rate of prevention. A 2022 study involving women in Kenya showed limited to no prevention with doxycycline. 

Doxycycline is an antibiotic in the tetracycline class. Like all antibiotics, it stops or slows bacterial infections but not viral ones. Doxycycline is used to treat anthrax, malaria, acne, and other conditions. A prescription for the antibiotic costs only pennies if you have insurance. 

The research published in April in the New England Journal of Medicine shows the wider application of doxycycline in reducing HIV and STIs in men who have sex men and in trans women. 

“How we have been talking about it [doxycycline] among patients is: Think of it as a morning-after pill, but for STIs,” said Aniruddha Hazra, MD, who specializes in infectious disease at University of Chicago Medicine Infectious Disease and Global Health unit and was not involved with the study. “So while a morning-after pill can be a prophylaxis (or prevention) against pregnancy, doxycycline can be used shortly after sexual contact or potential exposure with an STI to prevent acquisition of an infection.” 

The 2023 federally funded study shows that study participants, who reported having a sexually transmitted infection in the past year, reduced their risk of renewed infection by two-thirds with the protection of the antibiotic. 

The study, led by researchers at the University of California, San Francisco, and the University of Washington, enrolled about 500 adults from four clinic sites in San Francisco and Seattle. All the study participants were assigned male at birth, reported sexual activity, and had a history of STI or HIV diagnosis. 

The trial found that 10.7% of patients who took doxycycline had a STI diagnosis compared to 31.9% of the control group  — a two-thirds reduction in STI cases. The HIV diagnosis for doxycycline patients was 11.8% vs. 30.5% in the control – again a nearly two-thirds reduction. 

Even though there have been no reports of doxycycline-resistance in the chlamydia or syphilis cases, Luetkemeyer said researchers are looking at strains of doxy-PrEP for people who have developed breakthrough infections to look for evidence of resistance. 

“We certainly need to be vigilant about that possibility,” Luetkemeyer said. “But it just has not been described yet. And certainly, a lot of syphilis and a lot of chlamydia have been treated with doxycycline so far.” 

Trevor Hedberg, a physician assistant and head of the Sexual and Reproductive Health Walk-In Clinic at Howard Brown Health in Chicago, said two patients have brought up doxy as a pre-exposure treatment in the past 6 months. He said the clinic usually recommend doxycycline for people assigned male at birth who do sex work or who have had a syphilis diagnoses in the past.  

“So, you know, the way I approach the conversations around doxy PrEP is based on STI history,” Hedberg said. “How the patient perceives their risk of exposure to STI is, and going over the side effects and the safety profile of doxycycline and whether it’s something that they feel comfortable taking.”

People have been more accepting of using doxy for pre-exposure protection over the years, and the main concern is on antibiotic resistance, said Zach Bird, a health educator at Center on Halsted, a community center dedicated to the health of LGBTQ+ people in the Chicago area. 

“I do see why there’s a need for the research on doxy because there’s been more recorded cases of bacterial STIs going around and syphilis,” Bird said. 

At first, “a lot of people were shaming people who were taking [doxy] PrEP to be able to access more sex. I don’t really see that happening, at least in the community that I serve,” Bird said. “But the people that I have heard from have more of the like: You don’t know if there’s going to build a resistance, are we going to have super gonorrhea or something over time.”

The reduction of STI and HIV through doxycycline is mostly applicable to those who are assigned male at birth. 

“I would say that in the interim, until we have more information in cisgender women, that’s not a population for whom doxy PrEP is recommended,” Luetkemeyer said. “I would also say this really isn’t an intervention for the general population yet.”

Hazra said doxycycline is one of the most widely prescribed outpatient antibiotics within the last 5 years after the ANRS research in France. However, he advised against prescription for people who are pregnant because of tetracycline’s potential risk of birth defects including discoloration of teeth and abnormality in the bones. 

CDC has released considerations of doxycycline prescription but not detailed guidance. The San Francisco Department of Public Health, where Luetkemeyer practices, has released recommendations for cisgender men and trans women. 

Men who have sex with men are one group most at risk to be disproportionately impacted by HIV. According to the CDC, the lifetime risk for HIV infection among MSM is 1 in 6 compared to one in 524 for heterosexual men or one in 253 for heterosexual women.  

“I think [doxy PrEP] is a really good tool in the toolbox for people who need additional STI prevention measures, and the way we look at it is to try to offer this to people who are carrying the highest risk,” Luetkemeyer said.

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