Doxycycline Prophylaxis an Effective Option for Bacterial STIs


In the doxycycline as PrEP arm, there was a 73% reduction (p = .02) in syphilis, Neisseria gonorrhoeae, and Chlamydia trachomatis infections.

As uptake of pre-exposure prophylaxis (PrEP) to prevent HIV infection increases, so too does the rate of some sexually transmitted infections (STIs), especially among gay, bisexual, and other men who have sex with men (MSM), recent studies show. Because of this alarming trend, investigators are exploring prophylactic options for bacterial STIs, including syphilis and chlamydia.

A group of international academic and government investigators conducted a review, published in Clinical Infectious Diseases, to examine the current research, knowledge gaps, and challenges surrounding doxycycline prophylaxis to prevent bacterial STIs.

“The US is experiencing its worst [sexually transmitted infection] epidemic in more than a generation. Syphilis is at its highest level in more than 25 years. Cases of congenital syphilis and deaths in newborns due to syphilis are rising,” Jeffrey Klausner, MD, professor of medicine in the Division of Infectious Diseases and the Program in Global Health at UCLA’s Fielding School of Public Health, and an author on the study, told Contagion®. “We urgently need new strategies to control sexually transmitted diseases like syphilis.”

The research team identified 2 small, short-term, randomized, controlled trials demonstrating high efficacy of doxycycline prophylaxis, and noted 5 additional clinical studies that are underway.

In 1 of the small open-label pilot studies examined by the team, 30 MSM who were HIV-positive and had prior syphilis infections were randomized 1:1 to receive daily doxycycline 100 mg as pre-exposure prophylaxis for 48 weeks vs a control group that received a financial incentive-based behavioral intervention. In the doxycycline as PrEP arm, there was a 73% reduction (p = .02) in syphilis, Neisseria gonorrhoeae, and Chlamydia trachomatis infections.

“Doxycycline has been used to prevent many infectious diseases including Lyme disease, leptospirosis, and malaria,” Klausner said. “Doxycycline is also a recommended alternative treatment for syphilis. Doxycycline is a first-line treatment for chlamydia. We were surprised by how well it worked, [with] a 73% reduction in syphilis either taken as a daily dose or taken as a double dose once after sex.”

Doxycycline, a tetracycline that has been around since the 1950s, is generally well-tolerated, safe, and inexpensive. Infectious disease clinicians who see patients at high risk for STIs should discuss the option of doxycycline either daily or after sex as a strategy to reduce the risk for syphilis, Klausner advises.

“Clinicians managing programs or patients on HIV PrEP should be monitoring the frequency of syphilis in their patients and considering if there are patients who might benefit from the use of doxycycline prophylaxis as well,” he concluded.

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