Antibiotic Prophylaxis Cuts STI Rates
"On-demand" antibiotic treatment reduced the risk of two important sexually transmitted infections (STIs) in a population of men at high risk for both HIV and bacterial STIs, a researcher said here.
In a randomized trial in France, taking 200 milligrams of doxycycline within 72 hours of unprotected sex sharply reduced the number of syphilis and chlamydia infections, according to Jean-Michel Molina, MD, of the Saint-Louis Hospital in Paris.
There was, as expected, no effect on the incidence of gonorrhea because most strains of Neisseria gonorrhoeae in France are already resistant to doxycycline, Molina told reporters at a media briefing at the annual Conference on Retroviruses and Opportunistic Infections (CROI).
The findings are "encouraging," given that the burden of STIs is very high worldwide and is especially worrisome in men who have sex with men, where the rates have been increasing, he said.
But he cautioned that doxycycline prophylaxis is not ready for regular use outside of a trial because the study so far has only a short follow-up and a limited number of participants.
Molina told MedPage Today that one issue that remains is whether the on-demand use of the drug will lead to resistance. Different pathogens vary in their ability to become resistant, and "chlamydia and syphilis particularly have difficulty in developing resistance.
"But we have to be careful, and that's why I said this is not ready for implementation," he said.
The findings are "very exciting," commented the moderator of the briefing, Wafaa El-Sadr, MD, director of the International Center for AIDS Care and Treatment Programs at Columbia University and director of the Global Health Initiative at Columbia's Mailman School of Public Health, who was not part of the study.
"This is a well-conducted study that shows a remarkable impact on two very important sexually transmitted infections," El-Sadr told MedPage Today.
If the findings are borne out with longer follow-up and in a larger number of patients, she added, they could have a "huge public health impact."
Molina is the principal investigator of the so-called IPERGAY trial, which assessed whether "on-demand" pre-exposure prophylaxis (PrEP) would be effective in preventing HIV infection in a cohort of men who have sex with men who were at high risk of acquiring the virus.
Participants in the trial were meant to take anti-HIV medications between 2 and 24 hours before having sex, another 24 hours afterwards, and then 24 hours after that. Volunteers were randomly assigned to received tenofovir/emtricitabine or a matching placebo.
The blinded trial was stopped early because of a positive outcome, and many participants are now being followed in an open-label fashion post-trial, he said. Those still in the trial were re-randomized to test the hypothesis that doxycycline taken within 3 days of condom-less sex would prevent bacterial STI infection -- i.e., post-exposure prophylaxis or PEP.
The participants received risk-reduction counseling and condoms, and were tested every 8 weeks for HIV and syphilis with blood tests and for chlamydia and gonorrhea with polymerase chain reaction assays.
Patients randomized to the doxycycline arm were given medication and told to take two pills (100 mg each) within 72 hours of unprotected sex, but no more than six a week.
All told, 232 patients were included in the study, with 116 in each arm, Molina reported, and have been followed for a median of 8.7 months.
During that time, he said, 73 participants acquired a bacterial STI, including 28 in the PEP arm (24%) and 45 in the no-PEP arm (38.8%). The respective rates of acquisition were 37.7 and 69.7 events per 100 patient-years.
Overall, the hazard ratio, favoring PEP, was 0.53 -- which was highly significant, Molina said.
The hazard ratios for syphilis and chlamydia were both significant, at 0.30 and 0.27, respectively, but there was no effect for gonorrhea, with a non-significant hazard ratio of 0.83.
Some 71% of all STIs were asymptomatic, Molina reported. Patients in the PEP arm used a median of seven pills a month, and safety was good, with only eight patients stopping because of gastrointestinal adverse events. Such events were reported by 61 patients taking PEP and 47 in the no-PEP arm, but the difference did not reach statistical significance.