The Efficacy of Doxycycline Post Exposure Prophylaxis for Preventing STIs Among MSM in Bangkok, Thailand. (ThaiDoxyPEP)

February 2, 2026 updated by: Rossaphorn Kittiyaowamarn, Bangrak STIs Center

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.

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.

Study Overview

Status

Recruiting

Conditions

Intervention / Treatment

Study Type

Interventional

Enrollment (Estimated)

400

Phase

  • Phase 4

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Contact Backup

Study Locations

  • Thailand
    • Bangkok
      • Sathorn, Bangkok, Thailand, 10120
        • Recruiting
        • Bangrak STIs Center
        • Contact:
        • Contact:
        • Principal Investigator:
          • Rossaphorn Kittiyoawamarn, MD

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Child

Accepts Healthy Volunteers

Yes

Description

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

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Prevention
  • Allocation: Randomized
  • Interventional Model: Parallel Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Experimental: DoxyPEP arm
Participants will receive DoxyPEP for STIs prophylaxis in this arm
Drug: Doxycycline (200mg/day)
Doxycycline 200 mg single dose after unprotected sex within 24-72 hours
No Intervention: Control arm
Participants will receive standard STIs prevention

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
To evaluate the efficacy of doxycycline in preventing sexually transmitted infections (gonorrhea, chlamydia, and syphilis) among men who have sex with men in Thailand.
Time Frame: 12 weeks
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.
12 weeks

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Bangrak STIs Center

Collaborators

Mahidol University

Investigators

  • Principal Investigator: Rossaphorn KITTIYAOWAMARN, MD, Bangrak STIs Center

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Helpful Links

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

October 6, 2025

Primary Completion (Estimated)

October 5, 2026

Study Completion (Estimated)

May 31, 2027

Study Registration Dates

First Submitted

February 2, 2026

First Submitted That Met QC Criteria

February 2, 2026

First Posted (Actual)

February 9, 2026

Study Record Updates

Last Update Posted (Actual)

February 9, 2026

Last Update Submitted That Met QC Criteria

February 2, 2026

Last Verified

October 1, 2025

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • 1/2568

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

IPD Plan Description

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.

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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