Doxycycline has long been used to treat a number of STIs, and remains a recommended treatment for both chlamydia and syphilis. It is not common practice to use doxycycline (or any antibiotic for that matter) for the prevention of STIs like syphilis or chlamydia, but there is a long history of using doxycycline and other medications for the prevention of other types of infections. One of the most well-known uses of a medication to prevent an infection is the use of HIV PrEP, used by many people to prevent HIV.
That said, there is emerging evidence from research studies demonstrating promising results for doxycycline’s ability to prevent some STIs (see the Resources section of the website for more information). Notably, two previously-published small studies from California and France have shown promise for doxycycline’s use as both STI PrEP and PEP. Specifically, the PrEP study showed an overall reduction of STIs in the treatment arm , and the PEP study showed a reduction in both syphilis and chlamydia (but not gonorrhea) in the treatment arm. More recently, our study team at the BC Centre for Disease Control completed a small study in 52 HIV-negative people, where participants took both STI and HIV PrEP, and the results of our study once again showed promise for STI prevention However, most of these studies were quite small, and they need to be repeated in a larger number of participants. This is what the DISCO study is aiming to do!