Daily Antibiotic Protects Against Chlamydia, Gonorrhea and Syphilis
A small pilot study conducted with HIV-positive men who have sex with men found evidence that a daily dose of the antibiotic doxycycline provides a protective effect against three sexually transmitted infections (STIs). The results of the study — published in the journal Sexually Transmitted Diseases — show promise that doxycycline could be used as medication-based chemoprophylaxis for chlamydia, gonorrhea and syphilis.
“It wasn’t uncommon in the sixties or seventies for people to take tetracycline or doxycycline on their own before they went out — clubbing, to high-risk venues or to sex parties. So there’s been some use in the community, but — apart from HIV — there hasn’t been any data from a clinical trial context showing how well medications can work to prevent sexually transmitted infections when administered routinely to high risk individuals,” says Jeffrey Klausner, MD, MPH, the study’s senior author.
The primary goal of the study was to determine how well doxycycline, when taken daily, works to prevent syphilis among a high risk group — men who have sex with men with a history of past (and successfully treated) syphilis infection. “Syphilis right now is out of control in men who have sex with men in the U.S., Europe and Australia. So our first interest was to prevent syphilis,” explains Klausner.
Although the study emphasized syphilis prevention, doxycycline is also an effective treatment option for chlamydia and most cases of gonorrhea. Klausner explains that it made sense for his team to also determine if cases of chlamydia and gonorrhea could be averted with daily antibiotic use — especially since rectal infections of both can increase vulnerability to HIV infection during anal sex.
The study was small: There were a total of 30 men living with HIV randomized to one of the study conditions. Fifteen men were assigned to take the antibiotic for a total of 36 weeks. An additional 15 men received “contingency management” incentives: monetary compensation if they remained STI-free. At each study visit (at baseline, 12-, 24-, 36- and 48-weeks post-baseline) participants received rectal and urine gonorrhea and chlamydia tests, a pharyngeal (throat) gonorrhea test, and a syphilis blood test. The levels of the antibiotic in blood samples were measured at every visit for men in the doxycycline group.
The daily 100 mg dose of doxycycline provided a strong protective effect against all three STIs.
Seven cases of syphilis occurred in the contingency management group during the study period compared to two cases in the doxycycline group — a 73% reduction in risk granted by the antibiotic treatment.
There were a total of eight cases of gonorrhea or chlamydia only in the contingency management group compared to four in the doxycycline group (58% risk reduction); and 15 cases of any STI (gonorrhea, chlamydia, syphilis) in the contingency management group compared to six cases in the doxycycline group (70% risk reduction).
The researchers didn’t find any significant differences between the two groups in behaviors that might place men at a greater or lesser risk of acquiring any of the STIs (such as the number of regular or casual sex partners, self-reported condom use, meth use, condomless sex, sex with anonymous partners, or having a main or primary partner) — providing further evidence that the antibiotic treatment was responsible for the reduced number of infections.
Klausner points to one additional salient finding from their study: Men were interested in participating and in taking a medication every day and were able to do so successfully. “One of the big challenges that we’re seeing right now with other types of chemoprophylaxis — whether it be contraceptive pills or PrEP for HIV prevention — is that for some people, it can be challenging to take the medications. In this study, one of the key things is that we were able to enroll and retain high risk individuals, and people who were assigned to the medication actually took the medication.”
According to Klausner, doxycycline is a safe and well-tolerated medication, and one that can be taken for long periods of time. He believes it could be an important option for people who are at high risk of getting syphilis or other STIs to consider, but that “it’s not one-size-fits-all. It’s reasonable for individuals, under medical supervision, to consider using doxycycline as an STI prevention strategy. I think the evidence certainly suggests that — on an individual basis — there is value.”
One concern raised by the study — and addressed by its authors — is the possibility that widespread antibiotic use would lead to increased antibiotic resistance. While Klausner believes using doxycycline to prevent STIs could be useful on an individual basis, he acknowledges that, “the real questions or controversy come when considering this as a public health strategy.”
Bolan, R.K. and others. Doxycycline Prophylaxis to Reduce Incident Syphilis among HIV-Infected Men Who Have Sex With Men Who Continue to Engage in High-Risk Sex: A Randomized, Controlled Pilot Study. Sexually Transmitted Diseases. February 2015.