According to a substudy of the ANRS IPERGAY trial, Post-exposure prophylaxis (PEP) with doxycycline can sharply reduce the risk of chlamydia and syphilis in high-risk men who have sex with men (MSM). The impact on the selection of antibiotic resistance in chlamydia and syphilis,

The new study, an open-label extension of that trial, included 232 men on PrEP randomly assigned to take one dose of 200 mg doxycycline within 24 hours after having sex (PEP), or to receive no PEP (control). Study participants were tested for STIs every two months. During a median follow-up of 8.7 months, a new STI was diagnosed in 73 participants: 29 PEP patients and 45 controls.

Participants in the PEP group took a median of 680 mg of doxycycline, or fewer than seven pills, per month. The risk of serious adverse events was similar with or without PEP, although the likelihood of gastrointestinal adverse events was higher with PEP. Although PEP was associated with significantly lower risks of first chlamydia or first syphilis infection, it did not reduce gonorrhea risk.

This finding was expected, Dr. Molina noted, as gonorrhea is already resistant to doxycycline – and not amenable to PEP because it can quickly develop resistance to antibiotics. Of the study participants diagnosed with STIs, 71% had no symptoms. Regularly testing at-risk people for STIs and treating them – and their partners – early can help reduce the spread of these diseases, just as this approach helped address the HIV epidemic

Dr. Molina said. “We have to change the way we deal with STIs, because it would not be acceptable to test for HIV only people with AIDS,” he added. At present the Centers for Disease Control and Prevention recommends STI testing every three months, Dr. Molina noted, but only for MSM. “Doctors should be taught that everyone should be tested for STIs, like we ask people to be tested for HIV,” he said. “Anyone who has different sex partners should be tested, and not waiting for symptoms to develop.”

Dr. Christopher K. Fairley of Alfred Health and Dr. Eric P.F. Chow told, Given the absence of data on population-wide benefits and antibiotic resistance, we agree with Molina and colleagues that any recommendation in favour of doxycycline prophylaxis is premature.

The absence of a recommendation, however, will not prevent clinicians from prescribing doxycycline in individual circumstances, but we should use this use of doxycycline as an opportunity to accurately define the risks and benefits of doxycycline prophylaxis in this setting.