Instead of treating sexually transmitted infections with antibiotics alone, a new public health movement is looking to use such a drug to prevent STIs. Promising research into variations of this method has raised hopes, but also concerns that it could also contribute to another public health crisis: drug-resistant infections.
One thing is clear: the country desperately needs change measures to combat the STI epidemic, as gonorrhea, chlamydia and syphilis have increased dramatically over the past decade.
Syphilis, which public health experts thought could be eradicated by the 1990s, is experiencing a particularly alarming increase among pregnant women in particular. Congenital syphilis (when a mother passes the infection to her baby) can be fatal or cause serious birth defects.
Enter doxycycline: a common, well-tolerated antibiotic that has long been used for a variety of purposes, including treating acne.
Last month, the Centers for Disease Control and Prevention (CDC) released recommendations for the use of doxycycline after sex—as post-exposure prophylaxis (doxyPEP)—to reduce the risk of bacterial STIs in gay and bisexual men and transgender women. The recommendation was limited to this population because a recent clinical trial of doxyPEP in cisgender women showed no benefit. Men who have sex with men also have disproportionately high rates of STIs.
The CDC approval follows three randomized controlled trials that showed that giving doxycycline to gay and bisexual men and transgender women, asking them to take a 200-milligram dose within 72 hours of sex, reduced their risk of chlamydia and syphilis by more than 70 percent and gonorrhea by about 50 percent. Other research on doxyPEP use by the gay community in San Francisco has shown similar promise.
“It’s too early to know whether doxyPEP will reverse the upward trend in STIs that has been going on for years,” said Dr. Jonathan Mermin, director of STI prevention at the CDC. “However, there is considerable enthusiasm in the community and among many health care providers.”
Now, two new studies have helped broaden the debate over doxycycline, asking whether taking just 100 mg of the antibiotic daily – as pre-exposure prophylaxis, or doxycyclinePreparation — might provide a more optimal balance of risks and benefits for some people.
The results of these studies, conducted among HIV-positive gay and bisexual men in Toronto and Vancouver, British Columbia, and among sex workers in Tokyo, will be presented at the 25th International HIV Conference in Munich, Germany, to be held July 22-26.
“Some of my patients prefer the daily dose, adding the pill to their daily medication routine and not worrying about when or how to take it after sex,” Jeffrey Klausner, MD, professor of infectious diseases at the University of Southern California, said of the doxyPrEP regimen. “Other patients prefer the single dose after sex, it’s simple and easy.”
Klausner wasn’t involved in the new studies, but he was the lead author of the first-ever study of doxyprEP, conducted in a small group of gay and bisexual men in Los Angeles. Published in 2015, it found that people in the doxyprEP group were less likely to be diagnosed with STIs than those who received financial incentives to stay STI-free.
The main concern about prescribing doxycycline for prevention is that it may promote the emergence of drug-resistant infections, such as staph. Gonorrhea is the only one of the three STIs for which such resistance has been documented. But although doxycycline is effective in prevent gonorrhea, it is not generally used for to treat this infection.
On the other hand, by reducing STI rates, doxycycline may decrease the need for other antibiotics to treat these infections, thereby reducing the risk that these drugs may lead to drug resistance.
The new double-blind Canadian doxyPrEP study recruited 52 gay and bisexual men and randomly assigned them equally to receive doxycycline or placebo. After one year, the doxyPrEP group had a 68% to 92% lower rate of diagnosis of each of the three STIs — a result comparable to that of the recent doxyPEP study.
There was virtually no difference in drug resistance among staphylococcal infections between the two groups, although from a very small number of samples.
In the Japanese study, 40 women working in the sex trade saw their STI infection rate drop by two-thirds, from about 225 diagnoses per 100 cumulative years of follow-up before receiving doxyPrEP to about 80 diagnoses afterward. Once the women were prescribed daily doxycycline, their syphilis disappeared. Chlamydia declined by about two-thirds, but this change was only marginally statistically significant. There was no significant change for gonorrhea.
The study authors found no change in signs of drug resistance in two infections: bacterial vaginosis and candida vaginitis.
Nearly three-quarters of women said they were less afraid of contracting STIs.
“It is important to emphasize that both studies are small,” Dr. Christoph Spinner, local co-chair of the upcoming HIV conference and chief medical information officer at the University Hospital Rechts der Isar in Munich, said at a recent press conference. “Also, the Canadian study is a pilot study, and the Japanese study has no control group.”
Klausner, more enthusiastic, commented on the results of the study on gay men and said they “are compelling and support the idea that people should have choices” when it comes to STI prevention tools. “The current guidelines may need to be updated.”
Dr. Troy Grennan, a physician lead for the provincial HIV and STI program at the British Columbia Centre for Disease Control in Vancouver and lead author of the study of gay men, said his findings support a national trial his research team launched a year ago in Canada comparing doxyPEP to doxyPrEP. The study enrolled about 150 of a planned 560 participants.
“We cannot assume that this is the conclusion that one would expect by making a blanket statement that doxyPEP is better because it contains less drug,” he said.
On the one hand, some people have frequent enough sexual partners that it makes more sense to take doxycycline daily as PrEP – partly because at the doxyPEP dose, doxyPrEP actually amounts to less overall consumption for them. On the other hand, regular rather than intermittent exposure to antibiotics may reduce the risk of drug resistance emerging in pathogens.
And for some people, especially those who already take daily medications, such as pills to treat or prevent HIV, it’s easier to remember to take a daily pill than to plan doses based on when they recently had sex.
As for the fear of increasing drug resistance, “the trend hasn’t really been convincing one way or the other,” Grennan said. Research to answer that question is ongoing.
Like Klausner, Grennan touted the benefits of choosing STI prevention tools among those at risk.
“There is no one-size-fits-all solution,” he said.
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