The country's largest HIV and sexual health charity, Terrence Higgins Trust, which was forged out of the gay community in the eighties reports on promising trials on treatments for syphilis. Doxycycline post-exposure prophylaxis in Seattle is linked to a halving of syphilis diagnoses overall and a reduction of cases by a third in transgender people. Despite very low uptake, women also experienced a significant drop in syphilis cases, likely partly explained by reduced syphilis transmission within the communities where doxyPEP is being used.
In the study published in the journal of Clinical Infectious Diseases, Dr Timothy Menza and colleagues from Public Health – Seattle and King County and the University of Washington add more population-level evidence suggesting that the use of doxyPEP can significantly lower syphilis diagnoses. They estimate that doxyPEP use was associated with 52% fewer syphilis cases overall, with reductions of 53% in men, 47% in women and 33% in transgender and non-binary people.
DoxyPEP contains a single antibiotic called doxycycline dosed at 200mg once within 72 hours after condomless sex. The antibiotic helps prevent some of the major sexually transmitted bacterial infections – syphilis, chlamydia and to a lesser extent (due to increasing prevalence of resistance) gonorrhoea. It is mainly offered to sexually active gay and bisexual men and transgender people at a higher risk of infection. However, while it has been effective at reducing the burden of syphilis in areas where it was implemented, it is not fail-proof and it’s possible that not taking it in time may be one of the reasons for failure.
The Centres for Disease Control and Prevention (CDC) defines ‘in time’ as within 72 hours after risky exposure; however, the bacterium may already be spreading in the body within the first 24 hours. Even though doxycycline may still reach levels high enough to fight the bacterium, a single dose, especially if taken a little late, may not be able to completely rid the body of all syphilis bacteria.
In a previous small study, genital and rectal concentrations of doxycycline remained above effective levels for up to three days after dosing. However, blood concentrations were substantially lower, suggesting that if the bacterium had already spread beyond local tissues before doxyPEP was taken, suppression might be less effective. In fact, in cases where doxyPEP fails, it may slow the bacterium, mask the infection’s typical early symptoms and delay positive test results, allowing it to progress into the latent (dormant) stage unnoticed. However, it is not yet clear how often this happens in real-world practice. It is also unclear whether this risk is clinically important compared to the overall benefits of doxyPEP.
While doxycycline post-exposure prophylaxis is now increasingly used for prevention, due to the risk of late-dosing, doxyPrEP (doxycycline pre-exposure prophylaxis) has been considered as a potential alternative. This might involve taking half the dose (100mg) on a more regular (perhaps daily) basis. While the idea sounds plausible there are potential downsides to it. Since syphilis can usually be treated with antibiotics, using them more frequently for prevention raises questions about the balance of benefits and risks. Like all medications, doxycycline can cause side effects, and there are concerns about the impact of repeated use on the gut microbiome and other aspects of health. Additionally, increased use of antibiotics may contribute to the development of resistance, which could limit treatment options in the future.
More information at the useful and daily updated sexual health news site AIDSMAP: https://www.aidsmap.com/
