A daily dose of antibiotic might curb an STI epidemic

In Canada, rates of syphilis, chlamydia, and gonorrhea are increasing. This contrasts with HIV, where preventative drugs have successfully decreased infection rates in many areas. Now, new research is suggesting a promising approach for bacterial STI prevention: pre-exposure prophylaxis (PrEP) using the common antibiotic doxycycline (i.e., doxyPrEP).

Doxycycline taken after sex, called post-exposure prophylaxis (doxyPEP), is an established intervention, while studies on doxyPrEP are still early. But Dr. Troy Grennan’s recent studies are showing the efficacy of taking doxycycline preventatively, before any exposure occurs.

Dr. Grennan’s research, based at the British Columbia Centre for Disease Control (BCCDC), has found a notable decrease in bacterial STIs for people taking daily doxycycline. In his latest pilot study examining the use of doxyPrEP in gay, bisexual, and other men who have sex with men (GBM) with HIV, there was a 92% reduction in chlamydia, a 79% reduction in syphilis, and a 68% reduction in gonorrhea.

“The data for doxyPEP is solid—and even recommended by the U.S. Centers for Disease Control—but doxyPrEP currently only has a bit of pilot data,” explains Dr. Grennan. His next big project, a Canada-wide study called DISCO, is comparing the efficacy of doxyPrEP to doxyPEP on a larger scale. “We want to be able to prove that doxyPrEP is another option for people to use,” says Dr. Grennan.

Dr. Grennan’s recent paper states that participants receiving doxyPrEP were significantly less likely to have any bacterial STI.

Doxycycline is a common and easily available antibiotic. “There are not huge barriers to prescribing doxycycline,” says Dr. Grennan. “It’s not a niche medication that you need special access to, and most providers would be able to prescribe it and counsel patients on its proper use.”

It’s also a safe medication. “Doxycycline has been around since the 1960s, and while there are always possible side effects with any antibiotics, they are not super common with doxycycline,” says Dr. Grennan.

Key populations for doxyPrEP (and doxyPEP) studies are gay, bisexual, and men and transgender women who have sex with other men, who have had an STI within the past year. But Dr. Grennan points out that the potential impact is broader: “There is really no reason to think that they shouldn’t work to prevent STIs in most people at risk.”

One of the key considerations with doxyPEP and doxyPrEP is antimicrobial resistance. Thus far, though there have been no definitive trends showing increased or persisting resistance with doxycycline, Dr. Grennan and his team are vigilant in monitoring for that risk in their clinical trials. As this research unfolds, a little pill could become a game-changing tool for curbing this bacterial STI epidemic.

At a glance

Issue

Rates of syphilis, chlamydia, and gonorrhea are increasing in Canada. There is a need for novel options that reduce the risk of catching a bacterial STI.

Research

Doxycycline is a common antibiotic that has proven useful for treating STIs, with recent evidence showing that its use as post-exposure prophylaxis (doxyPEP) also prevents STIs. Now, Dr. Troy Grennan is examining the efficacy of doxycycline as pre-exposure prophylaxis (doxyPrEP), with the goal of reducing the risk of bacterial STIs before they happen.