A Phase 4 interventional study of DoxyODPrEP and DoxyPEP in Sexually Transmitted Diseases, Bacterial, Syphilis and Gonorrhea, sponsored by Chinese University of Hong Kong. Active, not recruiting at 1 site in Hong Kong. Open to male participants aged 18 Years and older, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-06-05.
Sponsored by Chinese University of Hong Kong · Phase 4, Interventional, and Prevention
The goal of this clinical trial is to compare the effectiveness of doxycycline taken for on-demand pre-exposure prophylaxis (DoxyODPrEP) and its post-exposure use (DoxyPEP) in preventing bacterial sexually transmitted infections (STI), including chlamydia, gonorrhoea, and syphilis among men who have sex with men (MSM). The main questions it aims to answer are:
Participants will be asked to take doxycycline according to the study arm they are randomly assigned to, and attend regular clinical follow-ups during the 2-year observation period. Researchers will compare the bacterial STI incidences between the two groups to see if DoxyODPrEP is superior to DoxyPEP.
Participants would be randomly assigned to either DoxyODPrEP or DoxyPEP arm, and be instructed to take doxycycline with the respective dosing schedule. They would be followed up for 24 months for nucleic acid amplification test (NAAT) and antibody tests against bacterial STI, namely chlamydia, gonorrhoea, and syphilis. The subjects and investigators would not be blinded due to its open-label nature, as the two arms' dosing schedules are different. Participants in the DoxyODPrEP arm would be instructed to take two doxycycline hyclate 100mg capsules orally 2-24 hours before sex, and one 100mg capsule each 24 and 48 hours after loading dose. If they have sex within 48 hours after the loading dose, they would be asked to continue a daily 100mg until two days after the last sex. Participants in the DoxyPEP arm would be instructed to take two doxycycline hyclate 100mg capsules orally within 24 hours and up to 72 hours after each sex. At each clinic visit, urine, and pharyngeal and rectal swabs would be self-collected on-site by the participants following instructions. Pill count would be performed for each follow-up visit.
126 studies on the registry are indexed under Syphilis; 34 are open to participants now.
This study's planned enrollment of 300 is below the median of 354 across 85 interventional studies indexed under Syphilis.
Browse Syphilis studies →Chinese University of Hong Kong is the lead sponsor of 1,454 studies on the registry; 474 are open to participants now.
Of its 6 completed or terminated interventional studies of FDA-regulated products, 0 (0%) have results posted.
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Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
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The human immunodeficiency virus, which weakens the immune system.
Many studies now accept people whose HIV is controlled on treatment, judged by the viral load and the CD4 count. Check the limits this study sets.
A reason a treatment, test or procedure should not be given to a particular person, such as an allergy, another illness or a medicine they take.
Informed consent
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
HIV
The human immunodeficiency virus, which weakens the immune system.
Many studies now accept people whose HIV is controlled on treatment, judged by the viral load and the CD4 count. Check the limits this study sets.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Contraindication
A reason a treatment, test or procedure should not be given to a particular person, such as an allergy, another illness or a medicine they take.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Participants in the DoxyODPrEP arm would be instructed to take two doxycycline hyclate 100mg capsules orally 2-24 hours before sex, and one 100mg capsule each 24 and 48 hours after loading dose. If they have sex within 48 hours after the loading dose, they would be asked to continue a daily 100mg until two days after the last sex.
Drug: DoxyODPrEP
Participants in the DoxyPEP arm would be instructed to take two doxycycline hyclate 100mg capsules orally within 24 hours and up to 72 hours after each sex.
Drug: DoxyPEP
Participants in the DoxyODPrEP arm would be instructed to take two doxycycline hyclate 100mg capsules orally 2-24 hours before sex, and one 100mg capsule each 24 and 48 hours after loading dose. If they have sex within 48 hours after the loading dose, they would be asked to continue a daily 100mg until two days after the last sex
Also known as: doxycycline on demand PrEP
Participants in the DoxyPEP arm would be instructed to take two doxycycline hyclate 100mg capsules orally within 24 hours and up to 72 hours after each sex.
Also known as: doxycycline PEP
Time to the first episode of gonorrhoea after the enrolment visit
Time to the first episode of gonorrhoea after the enrolment visit
Time frame: Months 1 to 24
Time to the first episode of chlamydia after the enrolment visit
Time to the first episode of chlamydia after the enrolment visit
Time frame: Months 1 to 24
Time to the first episode of syphilis after the enrolment visit
Time to the first episode of syphilis after the enrolment visit
Time frame: Months 1 to 24
Safety profile
Percentage of participants experiencing adverse events and the associated grades
Time frame: Months 1 to 24
Acceptability of regimens
Percentage of participants accepted the regimen
Time frame: Months 1 to 24
Retention
Percentage of participants remained during the follow-up period
Time frame: Months 1 to 24
Time to the first episode of HIV after the enrolment visit
Time to the first episode of HIV after the enrolment visit
Time frame: Months 1 to 24
This study is active, not recruiting, as verified in Jun 2026. You cannot join it, but the record below documents what was studied.
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Chinese University of Hong Kong →