Doxycycline after sex to prevent gonorrhea, chlamydia, and syphilis in MSM in Bangkok

Is this trial a fit for you?

A plain-English reading of the study's rules. Only the study team can confirm whether you qualify.

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.

Why it matters

Who can join: the full rules

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 it's running

• 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

Similar studies

Other studies for the same condition or treatment. Recruiting studies are listed first.

• At-home STI self-swab testing offered with telemedicine medication abortion

  This project will try offering at-home self-collected vaginal swab tests for chlamydia, gonorrhea, and trichomonas to people getting medication abortion by telemedicine in Hawai'i to see if patients use and accept it.

  Recruiting Queen's Medical Center · Honolulu, Hawaii · NCT06951438

• Doxycycline Prophylaxis to Prevent STIs in Adolescent and Young Women

  This trial tests whether taking doxycycline after sex or every week can reduce gonorrhea, chlamydia, and early syphilis in girls and young women, compared with usual care.

  Recruiting at 12 sites Phase 4 Westat · Los Angeles, California and 12 other locations · NCT06738407

• Free testing and treatment program for chlamydia, gonorrhea, syphilis, and HIV

  This program offers free testing for four STIs and provides counseling and no-cost expedited treatment options for Black people aged 15–26 who live or spend most of their time in Orleans Parish.

  Recruiting Tulane University · New Orleans, Louisiana · NCT06428643

• Improving relationship education to reduce HIV rates among sexual and gender minorities

  This study is testing a new relationship education program to see if it can help reduce HIV rates among gay, bisexual, queer, and transgender individuals who are in relationships with cisgender men.

  Recruiting Northwestern University · Chicago, Illinois · NCT05678556

• Observing HIV infection risks among high-risk individuals in Vienna

  This study looks at the risk factors for new HIV infections among HIV-negative men who have sex with men and transgender individuals in Vienna to better understand how the virus spreads in these groups.

  Recruiting Medical University of Vienna · Vienna · NCT05326061

• TruPlex HIV/HepB/Syphilis Rapid Test performance and usability in real-world settings

  This study tests how well the TruPlex rapid test detects HIV, hepatitis B, and syphilis using fingerstick and other blood samples, and whether trained operators find the test easy to use at point-of-care sites.

  Recruiting bioLytical Laboratories · Melbourne, Victoria · NCT07569913

How to take part

1. Review the eligibility criteria above with your treating physician.
2. Check the official listing on ClinicalTrials.gov for the latest contact details and recruitment status.
3. Contact the study coordinator or principal investigator to ask for pre-screening. Pre-screening is free and never obligates you to enroll.