A Phase 4 interventional study of Doxycycline (200mg/day) in Syphilis Infection, Gonorrhea and Chlamydia, sponsored by Bangrak STIs Center. Recruiting at 1 site in Thailand. Open to male participants aged 18 Days to 60 Days, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-02-09.
Sponsored by Bangrak STIs Center · Phase 4, Interventional, and Prevention
The objective of this research is to evaluate the efficacy and safety of doxycycline in MSM for preventing sexually transmitted infections (gonorrhea, chlamydia, and syphilis) in Thailand
Participation in this study will last approximately 12 weeks and will include 2-3 clinic visits, along with 10-11 follow-up phone contacts over a period of 11 weeks.
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
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Exclusion Criteria:
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
Participants will receive DoxyPEP for STIs prophylaxis in this arm
Drug: Doxycycline (200mg/day)
Participants will receive standard STIs prevention
Doxycycline 200 mg single dose after unprotected sex within 24-72 hours
To evaluate the efficacy of doxycycline in preventing sexually transmitted infections (gonorrhea, chlamydia, and syphilis) among men who have sex with men in Thailand.
Measure the proportion of participants who test positive by NAAT for gonorrhea or chlamydia at any anatomical site (genital, pharyngeal, or rectal), or who are diagnosed with syphilis during the study period.
Time frame: 12 weeks
Plan to share: No — Individual participant data (IPD) from this study will not be publicly shared due to ethical and legal considerations. The study involves sensitive sexual health information from key populations, and even de-identified datasets may carry a risk of re-identification. Data sharing is also subject to Thai data protection regulations and the conditions approved by the institutional ethics committee and participant informed consent.
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