Taking an antibiotic after unprotected sex can dramatically reduce the risk of contracting three bacterial sexually transmitted diseases (STDs) in high-risk people, according to a clinical study revealed Wednesday.

These findings were presented at the International AIDS Conference in Montreal, Canada, where they were hailed as a milestone.

“This could lead to changes in clinical guidelines,” Steven Deeks, an AIDS specialist at the University of California-San Francisco (UCSF) who was not involved in the study, told AFP.

Effective against various STIs.

Taking doxycycline reduced rates of gonorrhea and chlamydia infections among men who have sex with men by more than 60%, and it also appeared to be highly effective against syphilis, but it isn’t. There weren’t enough cases for these latest results to be statistically significant .

The drug was so effective that researchers stopped clinical trials earlier than expected.

The publication of this study comes at a time when infection rates for these diseases are on the rise, especially among men who have sex with men, among whom condom use has decreased since the generalization of PrEP (pre-exposure ), an effective preventive treatment against infection by the AIDS virus, HIV.

An earlier clinical trial by French researchers had shown the efficacy of doxycycline as post-exposure prophylaxis (PEP) against syphilis and chlamydia, but not against gonorrhea.

About 500 people participating in the study

This new study was conducted among approximately 500 people, mainly men in same-sex relationships, in San Francisco and Seattle.

Some were taking PrEP treatment for HIV, others were carriers of this virus. Within each of these two groups, about two-thirds of the participants received doxycycline while the others did not. Follow-up was ensured by collecting the results every three months.

Treatment was given within three days of exposure and for as long as needed based on the frequency of intercourse.

mild side effects

Taking the antibiotic reduced the incidence of these STDs by 62% among participants with HIV and 66% among those taking PrEP. Side effects were mild and, in general, the participants followed the treatment diligently.

“We now have two studies that support the use of doxycycline as PEP in men who have sex with men,” lead author Annie Luetkemeyer of UCSF said at a news conference Wednesday.

“I really think we need to think very seriously about implementing (this treatment) and how to incorporate it into guidelines” to recommend its use.

However, he noted that the available data supports the use of this treatment specifically among groups at high risk for STDs, but not for all. Further studies will be needed to look at the potential impact on resistance of these STDs or other bacteria to antibiotics, the authors added, as well as the potentially disruptive consequences on the gut flora.