A recently awarded grant will allow Connie Celum, a University of Washington professor of Global Health and Medicine, to evaluate whether doxycycline—an antibiotic commonly used to treat acne and Lyme disease—is safe and effective in reducing bacterial sexually transmitted infections. The study focuses on men who have sex with men (MSM) and transgender women (TGW) living with HIV and taking pre-exposure prophylaxis (PrEP), a daily pill used to prevent HIV.

“There is an ongoing STI epidemic among MSM and TGW with increasing rates of early syphilis, gonorrhea, and rectal chlamydia,” Celum said. “One intervention that could reduce the incidence of these STIs is doxycycline used as post-exposure protection.”

The $678,884 grant, titled “DoxyPEP: Evaluation of doxycycline post-exposure prophylaxis to reduce sexually transmitted infections in PrEP users and HIV-infected men who have sex with men and transgender women”, will be researched in conjunction with the University of California, San Francisco.

Sexually-transmitted infections (STI) have been increasing, particularly cases of gonorrhea, chlamydia, and syphilis among MSM. While PrEP against HIV is increasingly being used among MSM and transgender populations, and STI testing is a routine aspect of PrEP distribution, there has still been a rise in disease symptoms and congenital syphilis.  

“Given the increasing rates of sexually transmitted infections among MSM and TGW, it is important to find innovative and effective interventions,” Celum said. “We are testing an innovative approach of doxycycline post-exposure prophylaxis (PEP) after condomless sex to augment the current standards of screening, treatment and messaging about safer sex. Post-exposure prophylaxis has been effective for many infectious exposures, including viruses (e.g. HIV, HBV), spirochetes (e.g. Lyme disease, leptospirosis) and bacterial infections (e.g. meningococcus). Most of these PEP strategies are intended to address a single exposure with a single dose or short course of antibiotics.”

Post-exposure doxycycline has shown early effectiveness. In a randomized open-label trial among 232 HIV-negative MSM, doxycycline PEP resulted in a 47% relative reduction in new STIs. Doxycycline PEP reduced the incidence of chlamydia and syphilis, but not gonorrhea.

Still, PEP usage raises questions when it comes to STIs with repeated exposures, which become difficult to treat with a single treatment. Giving the community responsibility of its own prevention represents an important step in they journey toward reducing HIV.

“PEP remains largely untested for prevention of STIs with repeated exposures. This proactive approach targets every condomless sexual contact, putting additional control of STI prevention into the hands of MSM and TGW populations at highest risk for STI acquisition.”

As of now, doxycycline PEP has not been evaluated in HIV-infected MSM or TGW. One of the concerns surrounding doxycycline PEP comes in selection of antibiotic resistance, both in the bacterial STI pathogens and in flora, where resistance can be archived and contribute to wide-ranging antimicrobial resistance in the community.

“Before making recommendations about doxycycline use for STI prevention, policy-makers need additional data on the safety and efficacy of doxycycline PEP, as well as the impact on antimicrobial resistance about which there was limited data,” Celum said.

“Safe and effective prevention of these sexually transmitted infections is needed in addition to our current approach of frequent screening, treatment and partner services including empiric treatment of partners.”