US public health officials are deploying a powerful new weapon in the war against rising sexually transmitted infections: a common antibiotic that works as a morning-after pill, but there’s concern in some quarters that while effective, it could also contribute to antibiotic resistance.
The drug is the latest advancement as the sexual health field shifts to preventive medicine – not just condoms, abstinence and tests – as the best hope for annihilating the pathogens that can spread during sex.
The Washington Post reports that for the past decade, people have been able to have unprotected sex with a low risk of contracting HIV, thanks to daily pills known as PrEP (pre-exposure prophylaxis). But they have still been susceptible to bacterial bugs, including the recent spike in syphilis, gonorrhoea and chlamydia – until now.
Recent studies show the antibiotic doxycycline, taken after sexual encounters, works well as a post-exposure prophylaxis to prevent those infections. But experts are also worried about unintended consequences.
The US Centres for Disease Control and Prevention (CDC) is planning to release guidelines for deploying the treatment, known as DoxyPEP, in hopes of addressing fears among medical professionals that preventive use would fuel antibiotic resistance – and the rise of drug-resistant superbugs.
“It’s the first major intervention we’ve had for STIs since the human papillomavirus virus nearly two decades ago,” said Jonathan Mermin, who leads STI prevention for the CDC. “But it is a new intervention, and because of that, there are potential benefits and potential risks.”
Doctors, public health officials and sexual health clinics have embraced preventive pills as a realistic way to curb STIs because they preserve pleasure while protecting partners. Some doctors have started prescribing it to a narrow segment of the gay community considered at elevated risk for STIs.
“Just as PrEP was a game changer, this empowers individuals to make choices about their sexual health,” said Jorge Roman, senior director of clinical services at the San Francisco Aids Foundation, one of the first to widely distribute DoxyPEP. “It doesn’t always have to be about condoms.”
Doxycycline is already used as a front-line antibiotic treatment for chlamydia and occasionally for syphilis and gonorrhoea. But its use for prevention has drawn concerns that it would no longer be effective in patients who use it regularly and that it may facilitate the evolution of antibiotic-resistant strains of the pathogens.
The drug’s proponents say these concerns are overblown because the criteria for eligibility are often narrow: transgender women and men who have sex with men – and only if they have condomless sex and contracted an STI in the preceding year.
Those were the demographics recruited for a study of 500 patients in San Francisco and Seattle that found DoxyPEP effective. The study found a roughly 65% reduction in syphilis, gonorrhoea and chlamydia cases in those who used the antibiotic between 2019 and 2022, mirroring similar results from European studies.
Another study of DoxyPEP use by cisgender women in Kenya between 2020 and 2022 did not find the treatment effective, which surprised and baffled researchers. Anatomical differences could play a role, but health officials say other studies suggest doxycycline becomes concentrated enough in vaginal fluid to confer protection against STIs.
Experts say it’s too early to conclude that DoxyPEP won’t work for women and more research is needed. Another possible explanation is that the women in the Kenyan study may not have consistently used doxycycline after sex.
Researchers note early studies that found PrEP ineffective in protecting African women from HIV were eventually explained by poor adherence to the drug regimen rather than biological differences.
They are now scrutinising DoxyPEP to see whether it could also render antibiotic treatments less effective. The US study found a slight increase in antibacterial resistance, which the study’s authors said merits long-term attention.
But they also said the finding should be tempered by the fact doctors would also be administering fewer antibiotics if people avoid catching and spreading STIs.
David Hyun, director of the Antibiotic Resistance Project at The Pew Charitable Trusts, said he was concerned by patients in the study using DoxyPEP as frequently as 20 times a month. More data are needed to understand the long-term effects, for individuals as well as broader communities, he said.
“If you keep exposing a patient to antibiotics like doxycycline, you are raising their risk of being colonised or infected with a resistant strain sometime in the future,” he said.
Some LGBTQ+ health providers suspect doctors may be using antibiotic resistance concerns to mask discomfort with condomless gay sex. They say syphilis has yet to become resistant to penicillin since the antibiotic became the front-line treatment for the STI in the 1940s. And they say doxycycline is widely used for other reasons, including long-term acne treatment and malaria prevention.
Proponents of DoxyPEP said it offers a long-needed solution to a spike in STIs. The CDC recorded more than 2.5m cases of syphilis, gonorrhoea and chlamydia in 2021, up from 1.8m in 2011.
In 2021, 36% of syphilis and gonorrhoea cases were in men who have sex with men. The CDC said these disparities cannot be explained by differences in sexual behaviour alone. When people have a smaller pool of potential sexual partners with higher rates of STIs, they are more likely to have sex with someone with an infection. Cases in cisgender women and heterosexual men have also been rising.
Experts say everyone would benefit from DoxyPEP being limited to those most at risk because that would break chains of transmission early and reduce the likelihood of infections spreading more broadly.
Some physicians say allowing people to have worry-free sex is a worthy goal on its own.
“My goal as a physician is to make sure my patients can have whatever type of sex they want and however much sex they want, as safely as possible,” said Boghuma Kabisen Titanji, an infectious diseases specialist in Atlanta. “And if DoxyPEP would allow them to do it, then I have no problem offering it.”
Mermin, the CDC official, said equity is a top concern as the agency crafts its guidance for the use of DoxyPEP. It would be essential to ensure the medication is available in clinics serving people at the highest risk for STIs, he said, and to raise awareness outside medical settings, such as on dating apps.
In San Francisco, the first major jurisdiction, public health officials recommend DoxyPEP after higher-risk sexual encounters rather than after every encounter.
“We need to do more analysis to see if that could be making DoxyPEP less effective or if perhaps people are making really good decisions about when to use it,” said Stephanie Cohen, who leads STI prevention for the San Francisco Department of Public Health.
The San Francisco Aids Foundation, which says it has connected more than 1 800 people to DoxyPEP, does not limit the antibiotic to people who have recently contracted a sexually transmitted infection, but counsels patients on the unknown risks of antibiotic resistance.
Anu Hazra, co-medical director of Howard Brown Health, an LGBTQ+ health provider in Chicago, said antimicrobial resistance is “probably the largest public health threat we have” but doxycycline for a small group of people pales in comparison to the rampant use of antibiotics in the meat industry and other sectors.
He and other experts say vaccines to prevent STIs could be another game-changer that does not carry the same baggage as antibiotics. A recent study showing that a vaccine for meningitis can also reduce the likelihood of contracting gonorrhoea offers promise on that front. But DoxyPEP offers an immediate solution to an ongoing problem and could be pared back if antibiotic resistance emerges, Hazra said.
“We have been seeing rising rates of STIs for nearly a decade now. What we are doing now is not working. We need to try something new.”
See more from MedicalBrief archives:
Doxycycline slashes STI risk among MSM, trans women – US study
STD numbers at an all-time high — US Centers for Disease Control
More than 1m new curable STIs reported worldwide every day
South Africa in phase three trial to combat global gonorrhoea threat