Evaluating doxycycline for preventing bacterial STIs

Randomized Directly Observed Therapy Study to Interpret Clinical Trials of Doxy-PEP

Early Phase 1 Interventional University of California, San Francisco · NCT06414408

This study is testing if taking doxycycline after potential exposure can help prevent bacterial STIs in men who have sex with men and transgender women.

Quick facts

PhaseEarly Phase 1
Study typeInterventional
Enrollment48 (estimated)
Ages18 Years and up
SexAll
SponsorUniversity of California, San Francisco Academic / other
Locations1 site (San Francisco, California)
Trial IDNCT06414408 on ClinicalTrials.gov

What this trial studies

This study investigates the effectiveness of doxycycline post-exposure prophylaxis (PEP) for preventing bacterial sexually transmitted infections (STIs) among specific populations, including men who have sex with men and transgender women. It aims to address previous findings that showed doxycycline PEP was ineffective in cisgender women, potentially due to low medication adherence. By developing and utilizing adherence measurement methods through hair, blood, and urine samples, the study seeks to interpret results from earlier trials and establish reliable adherence metrics for future studies. Participants will be monitored for adherence while using doxycycline as a preventive measure against STIs.

Who should consider this trial

Good fit: Ideal candidates include men who have sex with men, transgender women on estrogen therapy, and transgender men on testosterone therapy who are at risk for STIs.

Not a fit: Patients who are currently at risk of STIs or not willing to use condoms for prevention may not benefit from this study.

Why it matters

Potential benefit: If successful, this study could enhance STI prevention strategies, particularly for populations at higher risk.

How similar studies have performed: Previous studies have shown varying results with doxycycline PEP, indicating a need for further investigation into adherence and effectiveness, making this approach both relevant and necessary.

Eligibility criteria

Show full inclusion / exclusion criteria
Inclusion Criteria:

* not currently at risk of a sexually transmitted infection and willing to use other methods, such as condoms, for STI prevention;
* if diagnosed with an STI in the past two years and/or a partner was diagnosed with an STI in the past year, is willing to use condoms for STI prevention;
* willing to provide hair, blood, and urine samples;
* not currently enrolled in other STI prevention studies;
* able to speak English
* transgender women participants should be currently using estrogen gender affirming hormone therapy with blood estrogen levels demonstrating consistent use
* transgender men participants should be currently using testosterone gender affirming hormone therapy with blood testosterone levels demonstrating consistent use
* able to provide a hair sample of \~50-100 strands of hair that are non-gray, not bleached, and at least 1cm in length
* willing to NOT shave hair or have a very short haircut or apply bleach for the duration of the study
* has suitable venous access for consecutive blood draws

Exclusion Criteria:

* any health condition that may interfere with participation or the ability to provide informed consent, including any debilitating or life-threatening conditions;
* pregnancy or plans to become pregnant;
* liver cirrhosis or fulminant liver disease;
* known hypersensitivity reaction to doxycycline.
* detectable doxycycline in hair at enrollment.
* unable to provide a hair sample of \~50-100 strands of hair that are non-gray, not bleached, and at least 1cm in length
* does not have suitable venous access for consecutive blood draws

Where this trial is running

San Francisco, California

Study contacts

How to participate

  1. Review the eligibility criteria above with your treating physician.
  2. Visit the official trial page on ClinicalTrials.gov for the most current contact information and recruitment status.
  3. Contact the listed study coordinator or principal investigator to request pre-screening. Pre-screening is free and never obligates you to enroll.
Conditions Sexually Transmitted Diseases, Bacterial
Last reviewed 2026-06-09 by the Find a Trial editorial team. Information on this page is for educational purposes and is not medical advice. Always consult qualified healthcare professionals about clinical trial participation.