What is the DISCO study all about?
DISCO stands for Doxycycline as an Intervention for bacterial STI ChemOprophylaxis. It’s a Canadian study, aiming to enroll 447 gay, bisexual and other men who have sex with men (gbMSM), including both cisgender and transgender gbMSM, and transgender women. Participants will be enrolled randomly into one of the two study arms: (1) the doxycycline pre-exposure prophylaxis (PrEP) arm, where they will take a doxycycline pill daily; (2) the doxycycline post-exposure prophylaxis (PEP) arm, where they will take two doxycycline pills within 72 hours of a sexual encounter, to a maximum of six pills per week.
What exactly is PrEP?
PrEP stands for pre-exposure prophylaxis, and is a term that first gained widespread use in HIV prevention. Generally speaking, it means taking a medication daily to prevent an infection before exposure, though may be taken intermittently (instead of daily) in some situations for HIV prevention. In the DISCO study, STI PrEP means taking a doxycycline pill daily with the goal of preventing STIs.
What is PEP?
PEP stands for post-exposure prophylaxis, and generally refers to the use of a drug to prevent an infection after exposure. It is used in a number of infections, including HIV. For HIV PEP, someone with an exposure to HIV (e.g. through a sexual encounter or a needlestick injury) can take 28-days of HIV medications to prevent infection. In the DISCO study, STI PEP means taking two doxycycline pills within the three days after sexual activity.
What do we know about using an antibiotic for STI prevention?
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!
What exactly is doxycycline?
Doxycycline is an antibiotic in the tetracycline family of antibiotics, and has been in use since the 1960s. It is used for the treatment and prevention of a number of different infections. Of note, it is one of the few antibiotics for which there is a lot of experience in long-term use. For example, individuals are often prescribed doxycycline (or another tetracycline drug) for the treatment of acne, and they will often remain on this drug daily for months or even years. Additionally, doxycycline has long been used as a prevention drug for malaria, which involves taking it daily for the entire time one is at risk, which – for some people – involves many months.
Why use an antibiotic to prevent STIs?
A lot has changed in the areas of sexual health and STIs in the last several years that has led to some very positive shifts in how people have sex. For one, the use of HIV PrEP dramatically reduces someone’s risk of HIV. Also, effective HIV treatments mean that people with undetectable viral loads (the amount of HIV in the blood) cannot pass HIV on to others. This is more commonly known as Undetectable = Untransmittable, or U equals U. These two innovations have led to really significant improvements in HIV prevention, and have helped many have better sex lives. We have not, however, seen as much innovation in preventing other STIs such as chlamydia and syphilis. In fact, we have seen significant increases in both these STIs in many parts of the world over the last several years. This means that what we’re currently doing is just not enough to prevent these infections, and we need to “think outside the box” and come up with new tools to use against STIs. Using what we know about HIV PrEP, doxycycline’s other uses, and the results of the small studies on STI PrEP and PEP that have been done so far, we designed the DISCO study to test out this innovative idea on a large-scale.
I’m worried about the side effects of taking an antibiotic regularly? Is it safe?
This is a very important consideration. First off, all participants in the DISCO study will be under the direct care of a physician, who will monitor their progress, review all laboratory investigations, help manage side effects, and refer to other health care providers if necessary. No medication is entirely, 100% risk-free, and even very safe medications like doxycycline need to be considered using a ‘pros and cons’ approach. Doxycycline has been used for decades, with many people using it long-term, so as a medical community we have a lot of experience using it. There have also been many studies on doxycycline published over the years. This collective knowledge accumulated over decades means that we have lots of reliable and specific information on how people tolerate it, and how safe it is. Like most antibiotics, doxycycline may cause some gastrointestinal (GI) upset, like reflux (heartburn or indigestion), nausea, vomiting, or diarrhea. Though these are rare (all occur in less than 5% of people taking doxycycline), they do occur, and usually will resolve on their own. Taking this medication with food and water can also help prevent these side effects. Doxycycline can also rarely result in a skin rash, and makes some people more sensitive to the sun, so wearing sunscreen and using other sun-protection measures is important.
Should I be worried about antibiotic resistance if I’m taking doxycycline frequently?
Anytime someone is taking an antibiotic for any reason, resistance is always something that should be considered. Resistance can happen for a number of different reasons, but generally results from bacteria developing the ability to survive in the presence of antibiotics that would normally kill them, or stop their growth. From the many studies that have been published on doxycycline in the last few decades, there hasn’t been very much information on resistance developing. Our team recently completed a systematic review of the research literature, and we did note that some studies indicate that resistance may develop in some commensal bacteria (i.e. bacteria that may normally be found on or in the body) on the skin, in the mouth, and in the stomach/bowels, but it’s unclear how long this lasts or how severe it is.
Our research team is committed to comprehensively monitoring for the development of antibiotic resistance in all DISCO study participants. We have several measures incorporated into our study activities which will be regularly assessing for possible development of resistance in both commensal bacteria, and STI bacteria.