Doxycycline Intervention for Bacterial STI ChemoprOphylaxis (DISCO)

A Randomized Trial of Doxycycline Chemoprophylaxis for the Prevention of Sexually Transmitted Infections in Gay, Bisexual and Other Men Who Have Sex With Men (gbMSM)

There is a growing epidemic of the bacterial sexually transmitted infections (STIs) syphilis, chlamydia and gonorrhea worldwide; similarly concerning trends have been noted in Canada, where increases of over 160% have been seen in bacterial STIs over the last decade. In Canada, gay, bisexual, and other men who have sex with men (gbMSM) - including those living with HIV - are disproportionately impacted by bacterial STIs5,6These dramatic increases in bacterial STIs, the potential development of serious complications including AMR, and waning effectiveness of the promotion of conventional STI prevention tools (e.g. condoms), signals the need for novel STI prevention strategies and tools to mitigate STI-related complications. A rigorous randomized controlled trial will be conducted to compare STI PrEP vs. STI PEP and definitively assess the efficacy, safety, antimicrobial resistance profiles and costs associated with doxycycline-based STI prevention.

With the rising rates of STIs among gbMSM populations in Canada, there is an urgent need for novel interventions to prevent significant sequelae (e.g. neurosyphilis) and onward transmission of untreated infections. Despite longstanding public health efforts to encourage conventional strategies of STI prevention, gbMSM continue to bear the burden of syphilis which poses synergistic effects in the transmission of HIV. This study will add to this field through providing the first methodologically rigorous, prospective multicentre, open-label randomized controlled trial (RCT) of doxycycline-based STI PrEP (daily 100mg doxycycline) versus STI PEP (200mg doxycycline after exposure event) for the prevention of bacterial STIs among gbMSM over 15 months (60 weeks) of follow-up with adequate power to address drug efficacy in the prevention of bacterial STIs. Beyond the determination of efficacy, our trial will provide insight to the unique challenges of medication adherence through assessing the acceptability, tolerability and safety of therapy with doxycycline. This study aims to provide health care providers one additional tool to address the burden of STIs in populations with an increased likelihood of infection.

Inclusion Criteria:

1. Males, ≥ 18 years of age;
2. Any sexual activity (i.e. oral sex, insertive or receptive anal sex, with or without a condom) with more than one male partner in the preceding 12 months;
3. Intention to remain sexually active with more than one male partner in the next 12 months;
4. At least one prior episode of a previously diagnosed and adequately treated syphilis, gonorrhea or chlamydia infection within 12 months prior to screening.

Exclusion Criteria:

1. Known allergy to doxycycline or tetracyclines;
2. Existing chronic or intermittent tetracycline or doxycycline use (e.g. for chronic osteomyelitis, acne).
3. Use of medications which could lower doxycycline levels, including barbiturates, phenytoin and carbamazepine.
4. Individuals currently using isotretinoin;
5. Any individual capable of becoming pregnant.