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Research shows 47% reduction in STIs among gay men who took doxycycline after sex

, by Emily Newman

BETA is reporting from the 2017 Conference on Retroviruses and Opportunistic Infections (CROI) this week in Seattle—bringing you the latest news, updates, and research on HIV treatment and prevention.

The antibiotic doxycycline, when taken within 72 hours of condomless sex, can reduce the risk of bacterial sexually transmitted infections (STIs) by 47%, new research presented at CROI this week showed. The antibiotic significantly reduced the number of chlamydia and syphilis infections, but did not reduce gonorrhea infections.

Jean-Michel Molina, the lead investigator of the IPERGAY on-demand PrEP study, presented results of the study conducted with a group of men who have sex with men (MSM) enrolled in the open-label portion of the IPERGAY study.

Jean-Michel Molina

Jean-Michel Molina

“We’ve seen in the last couple of years an increase in the number of STIs across Europe, North America and other countries including Australia, especially among MSM. It would be fair to acknowledge the increase actually pre-dates PrEP. Nevertheless, high rates of STIs have been reported among MSM on PrEP, and in the two European PrEP studies PROUD and IPERGAY, the proportion of men reporting an STI ranged from 41% [in IPERGAY] and 57% [in PROUD]. PrEP programs give a unique opportunity to foster research in testing, treatment and prevention of STIs,” he said.

The idea of giving antibiotics prophylactically to prevent STIs is not a new idea, but one that has been implemented since the 1940s with only “limited success,” said Molina. Most recently, a study published in 2015 showed that daily doxycycline prevented bacterial STIs in a very small group of men who have sex with men.

Read a summary on BETA of Jean-Michel Molina’s symposium presentation about using antibiotics to prevent STIs, delivered at CROI 2017.

In the current study, 232 HIV-negative MSM, who were also taking on-demand PrEP for HIV prevention, were randomized to receive the antibiotic doxycycline or to a no-treatment group. Participants provided with doxycycline were instructed to take two pills (100 mg) of the antibiotic within 72 hours of condomless sex. All participants received condoms, were counseled about sexual risk reduction and were tested every eight weeks for HIV and STIs (syphilis, gonorrhea and chlamydia). Participants were followed for a median of 8.7 months.

There were a total of 73 STIs detected during the study period: 28 in the doxycycline treatment group and 45 in the no-treatment group. Overall, 71% of all STIs were asymptomatic. There were 7 chlamydia infections in the doxycycline group and 21 in the no-treatment group, 3 syphilis infections in the doxycycline group and 10 in the no-treatment group, and 25 gonorrhea infections in the doxycycline group and 22 in the no-treatment group.

Overall, doxycyline was not effective at preventing gonorrhea infections, with the effect of the antibiotic on gonorrhea seeming to vary by anatomic location. In the doxycyline group, there were fewer anal and urethral gonorrhea infections than in people in the no-treatment group. However, there were more pharyngeal (throat) gonorrhea infections (a total of 15) among people in the doxycyline group than people in the comparison group (a total of 12).

Adherence to the antibiotic treatment was high. 83% of participants in the treatment group used doxycycline after sex, and the median time to take doxycycline after sex was less than one day. The median number of pills taken per month was 6.8 in the doxycycline group. Participants who skipped dosing with doxycycline after sex cited the following reasons for not doing so: Not at risk (23%), forgot (10%), fear of adverse events (17%), dosing regimen is too complex (4%), and “other” (46%).

Molina said that the safety profile of doxycycline used for STI prevention was “pretty good.”The same number of adverse events were reported in the doxycycline group and the no-treatment group overall, although more participants in the doxycycline group reported gastrointestinal pain (14 people) and nausea/vomiting (13 people) than in the no-treatment group (8 and 3 people, respectively).

There did not appear to be any evidence of risk compensation among people randomized to the doxycycline group. In other words, this group did not appear to increase their number of sex partners or condomless anal sex during the study as compared to people in the no-treatment group.

“The long-term benefit of this strategy is as yet unknown,” said Molina, as he cautioned against use of this strategy before more is known about drug resistance and efficacy. More research, he said, is needed before public health agencies and other organizations could confidently recommend and move forward with antibiotic prophylaxis for STIs.

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