Doxycycline after sex to prevent gonorrhea, chlamydia, and syphilis in MSM in Bangkok
The Efficacy of Doxycycline Post Exposure Prophylaxis for Preventing Sexually Transmitted Diseases (Gonorrhea, Chlamydia, Syphilis) Among Men Who Have Sex With Men in Bangkok, Thailand.
This research tests whether taking doxycycline after sex can prevent gonorrhea, chlamydia, and syphilis in men who have sex with men in Bangkok.
Quick facts
| Phase | Phase 4 |
|---|---|
| Study type | Interventional |
| Enrollment | 400 (estimated) |
| Ages | 18 Days to 60 Days |
| Sex | Male |
| Sponsor | Bangrak STIs Center Government |
| Drugs / interventions | chemotherapy, methotrexate |
| Locations | 1 site (Sathorn, Bangkok) |
| Trial ID | NCT07397403 on ClinicalTrials.gov |
What this trial studies
This Phase 4 interventional study gives doxycycline (200 mg/day as used for post‑exposure prophylaxis) to eligible men who have sex with men and follows them for about 12 weeks. Participants will attend 2–3 clinic visits and receive 10–11 follow‑up phone contacts over an 11‑week period while being tested for gonorrhea, chlamydia, and syphilis. Enrollment is limited to biologically male, Thai nationals aged 18–60 with recent sexual risk factors (e.g., condomless sex with multiple partners, recent STI diagnosis, or current PrEP use). Safety monitoring will include assessing adverse reactions to doxycycline and tracking STI outcomes during the follow‑up period.
Who should consider this trial
Good fit: Biological males who are Thai nationals, aged 18–60, who have sex with men and have recent risk factors (condomless sex with multiple partners, recent STI, or current PrEP use) and who can attend clinic visits and follow‑up calls.
Not a fit: People with a tetracycline (doxycycline) allergy, those who are not MSM or are outside the 18–60 age range, those unwilling to attend required visits or follow‑up, or those with antibiotic‑resistant infections are unlikely to benefit.
Why it matters
Potential benefit: If successful, this approach could reduce new cases of gonorrhea, chlamydia, and syphilis among high‑risk MSM by preventing infections after exposure.
How similar studies have performed: Previous DoxyPEP studies in MSM populations have shown reductions in bacterial STIs but have also raised concerns about emerging antibiotic resistance and variable results across settings.
Eligibility criteria
Show full inclusion / exclusion criteria
Inclusion Criteria: Biological male, aged not over 60 years Thai nationality Able to read, communicate, and understand the Thai language Men who have sex with men (MSM), aged 18 years or older and not over 60 years Having at least one of the following risk factors: A history of condomless sex, or condom failure (breakage, leakage, or slippage), via any sexual route with at least two sexual partners within the past 3 months A diagnosis of gonorrhea, chlamydia, or syphilis within the past 6 months Current use of HIV pre-exposure prophylaxis (PrEP) Willing and able to participate in study procedures (e.g., able to return to the clinic for scheduled testing for gonorrhea, chlamydia, and syphilis; able to complete doxycycline use records; and able to receive follow-up phone calls from the research team) Willing and able to provide written informed consent to participate in the study \- Exclusion Criteria: * History of allergy to tetracycline-class antibiotics Diagnosed with syphilis and not yet treated, or currently receiving treatment with benzathine penicillin G or doxycycline Receipt of benzathine penicillin G within the past 12 weeks Prior receipt of a gonorrhea vaccine Current use of medications or products that may interact with doxycycline, including: Vitamin A derivatives (e.g., isotretinoin, acitretin) Antiepileptic drugs (e.g., phenytoin, carbamazepine, phenobarbital) Immunosuppressive agents (e.g., methotrexate) Medications for heart failure or cardiac arrhythmias (e.g., digoxin) Anticoagulants (e.g., warfarin) Use of oral or injectable medications that affect blood cells, such as anticancer drugs, chemotherapy, systemic corticosteroids, or targeted therapies History of renal impairment (eGFR \< 60 mL/min/1.73 m²) or hepatic impairment (AST or ALT \> 3 times the upper limit of normal) Uncontrolled or unstable underlying diseases, such as hematologic disorders, cancer, autoimmune diseases, or neurological disorders Severe medical or psychiatric conditions that, in the investigator's judgment, may increase study-related risk or impair the participant's ability to provide informed consent Alcohol dependence (inability to control alcohol consumption, withdrawal symptoms upon reduction or cessation, or continued use despite harm) or illicit drug dependence (regular, uncontrolled use) within the past 12 months prior to enrollment, which may affect doxycycline use for STI prevention Previous participation in this study with prior randomization
Where this trial is running
Sathorn, Bangkok
- Bangrak STIs Center — Sathorn, Bangkok, Thailand (Recruiting)
Study contacts
- Principal investigator: Rossaphorn KITTIYAOWAMARN, MD — Bangrak STIs Center
- Study coordinator: Rossapnorn Kittiyaowamarn, MD
- Email: rossaphorn@gmail.com
- Phone: +66814501066
How to participate
- Review the eligibility criteria above with your treating physician.
- Visit the official trial page on ClinicalTrials.gov for the most current contact information and recruitment status.
- Contact the listed study coordinator or principal investigator to request pre-screening. Pre-screening is free and never obligates you to enroll.