Old antibiotic proves able to prevent sexually transmitted infections

Doxycycline, when taken after sex without a condom, has been shown in clinical trials to significantly reduce the risk of infection with three diseases: chlamydia, gonorrhea and syphilis.

A new weapon for preventing STIs

The main US federal health agency, the CDC (Centers for Disease Control and Prevention), is responsible for making a decision on new recommendations. It will have to take into account the need to contain epidemics affecting millions of Americans, but also the risk of increasing resistance to the antibiotic. “Innovation and creativity are important in public health, and we desperately need new tools,” CDC official Jonathan Mermin told AFP.

These recommendations, which should be published this summer, will probably only target the groups most at risk: gay men or transgender women with previous infections. But as word spreads, some doctors are already prescribing the antibiotic for this purpose. The California State Department of Health did not wait for a national decision to recommend the use of this drug for groups at risk, from April 2023.

Malik, a 37-year-old Washington resident who declined to give his last name, has already used doxycycline twice for prevention, on the advice of his doctor, after risky reports — including one with a partner not having informed that he had withdrawn his condom.

STI epidemics on the rise

Cases of these three bacterial infections have been increasing for a decade and reached 2.5 million in 2021 in the United States. Firstly because mechanically, the more infections there are, the more they are transmitted. But also because condoms are used less and less since the arrival of Prep – a drug taken as a preventive measure to avoid contracting AIDS. Additionally, people on Prep should get tested every three months, which helps identify more infections.

Doxycycline has been shown to be effective in three out of four clinical trials conducted. “We found a two-thirds reduction in sexually transmitted infections,” Annie Luetkemeyer, who conducted an American trial, told AFP. The latter was carried out on 500 men having sex with other transgender men and women. Efficacy was found to be higher against chlamydia and syphilis (-80% infections) than for gonorrhea (-55%). Side effects were few.

Antibiotic resistance

But expanding access to doxycycline has also raised concerns that antibiotic resistance could develop, especially for gonorrhea, where the bacteria mutate rapidly. Initial analyzes are however reassuring.

During the American clinical trial, the researchers compared samples of this bacterium from infections that occurred despite treatment with doxycycline, with samples from the untreated group. The rate of resistant bacteria was certainly higher for the treated group, but that could simply mean that the antibiotic is less effective against this resistant strain, not that it caused it, explained Connie Celum, co-leader of this work. .

Moreover, since doxycycline could reduce the number of infections by half, it would mean half as many people to treat with the antibiotic normally prescribed for gonorrhea (ceftriaxone). But doctors want to preserve the effectiveness of this drug. More studies need to be done to understand the effect of doxycycline on other bacteria, for example in the nose or intestines.

“Additional tool” that does not replace the condom

Malik says he’s glad he was able to use doxycycline as a last resort, but wishes more men would agree to use condoms. According to him, since he moved from South Asia to come to the United States, fewer men are interested on dating sites when he says he does not want a relationship without this protection. But according to Stephen Abbott, a doctor in Washington who prescribes and uses doxycycline, it is crucial to take into account changes in behavior.

“Talking with patients, and because I’m part of the community on Prep (…), I think the era of prevention via condoms is on the wane”he told AFP.

According to an official of a cultural organization in London testifying on condition of anonymity, the noise around this new treatment spread quickly, and he himself now buys doxycycline on the black market. The 42-year-old man wants the UK to adopt new recommendations too, he told AFP, so that people are better guided in particular on the required dosages.

For researcher Annie Luetkemeyer, doxycycline will not be the only answer to the epidemic of sexually transmitted diseases. The development of a vaccine against gonorrhea would still be very useful. “But I am optimistic”, she says. “I think it’s an additional tool.”