Results from two small studies suggest that doxycycline pre-exposure prophylaxis (DoxyPrEP) is a promising strategy for preventing STIs.
In recent years, studies have shown that DoxyPEP – taking doxycycline within 72 hours after sex – can prevent bacterial STIs among men who have sex with men and trans women, and evidence suggests that DoxyPEP is now helping to lower STI incidence in some communities. However, there has been less research on DoxyPrEP, which involves taking doxycycline before sex.
AIDS 2024 features two studies of DoxyPrEP. The first is a pilot, randomized controlled trial that enrolls 52 men who have sex with men in Toronto and Vancouver, Canada. All of the men are living with HIV and have a history of syphilis. They are randomized to receive 100mg of doxycycline daily or a placebo and followed for 48 weeks.
Forty-one participants (78.8%) complete the study protocol. There is a 79% reduction in syphilis, a 92% reduction in chlamydia, and a 68% reduction in gonorrhoea in the doxycycline arm compared with the placebo arm. There are no differences between arms related to drug adherence or sexual behaviors. New doxycycline resistance develops in three of 19 and two of 19 (p=0.57) S. aureus isolates from baseline to week 48 in the doxycycline and placebo arms, respectively.
According to presenter Troy Grennan of the British Columbia Centre for Disease Control, these pilot findings support further evaluation of DoxyPrEP compared with DoxyPEP in an ongoing larger trial.
The second DoxyPrEP study enrolls 40 female sex workers in Tokyo, Japan; the women are each provided with 100mg of doxycycline daily and followed over time. After initiating DoxyPrEP, the overall STI incidence rate declines from 232.3 to 79.2 per 100 person-years. Syphilis incidence is reduced to zero, there is a marginally significant reduction in chlamydia, and there is no significant change in gonorrhoea. Incidence of bacterial vaginosis and vulvovaginal candidiasis do not significantly increase.
Follow-up interview summaries reveal that adherence to DoxyPrEP is high. Nausea and vomiting are reported by 22.7% of respondents, but no serious doxycycline-related adverse events are observed. Notably, 72.7% of respondents indicate a reduction in their fear of STI transmission.
According to presenter Seitaro Abe of the National Center for Global Health and Medicine in Japan, these findings support the introduction of DoxyPrEP in populations that are highly vulnerable to STIs.