An antibiotic taken after having sex without a condom can drastically reduce the rate of three bacterial STDs in high-risk groups, data from a clinical trial showed Wednesday.
The research was presented at the 24th International AIDS Conference in Montreal, where it was hailed as a significant development.
“This has the ability to change the guidelines” for clinical practice, Steven Deeks, an HIV researcher at the University of California, San Francisco (UCSF) who was not involved with the study, told AFP.
Doxycycline reduced the rate of gonorrhea and chlamydia in men who have sex with men (MSM) by more than 60 percent and also appeared to be highly effective against syphilis, but there weren’t enough cases to reach statistical significance.
The study was stopped early because the researchers determined that the drug undeniably worked and it would have been unethical to continue testing.
The study comes amid rising rates of these diseases, particularly among MSM, whose use of condoms has declined since the advent of effective HIV pre-exposure prophylactic (PrEP) pills.
A previous study by French researchers using doxycycline as post-exposure prophylaxis (PEP) showed that it was effective in MSM against syphilis and chlamydia, but not in gonorrhea.
For the new study, researchers at sites in San Francisco and Seattle recruited around 500 people, mostly MSM but also some transgender women and gender-matched individuals.
Some took HIV PrEP while others were living with HIV.
In both groups, about two-thirds received doxycycline and one-third did not. They were observed to monitor their results every three months.
The pill, dosed at 200 milligrams, was administered within three days of exposure. Participants could continue to take it as needed, based on how much sexual contact they had.
The intervention reduced the incidence of STDs by 62 percent in the living with HIV group and by 66 percent in the HIV-PrEP group.
Side effects were few and adherence to therapy remained high.
“We now have two studies supporting the use of doxycycline as a PEP in men who have sex with men,” UCSF study leader Annie Luetkemeyer told reporters at the AIDS conference.
“I really think we’re at a point where we need to think very hard about adoption and how to incorporate that into policies.”
But she stressed that the data currently supports treatment as a targeted intervention in high-risk groups with a high prevalence of STDs — not all.
More studies are also needed to better understand the potential impact on antibiotic resistance, the authors said.
Researchers want to know if it could increase resistance to sexually transmitted diseases – which is more likely for gonorrhea than chlamydia and syphilis – from so-called “bystander” bacteria that live on the body and in the throat.
They also want to study the potentially disruptive effects on the gut microbiome.
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