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Sexually Transmitted Diseases, BacterialPhase 4NCT06188442

Superiority of On-demand PrEP Versus PEP on Using Doxycycline for Preventing STI in MSM

A Phase 4 study testing DoxyODPrEP and DoxyPEP in people with Sexually Transmitted Diseases, Bacterial and Syphilis, run by Chinese University of Hong Kong at 1 site in Hong Kong.

Active, not recruiting

Under way, not looking for participants. Everyone needed has enrolled. The study is still running.

Official record
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Trial summary

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… Read more about this study

Who is it for?
Ages 18 years and older, men onlyHealthy volunteers can take part
What is being tested?
DoxyODPrEP and DoxyPEP
Type of treatment
Pill or oral medicine
Could I receive a placebo?
No, everyone receives an active treatment
How many people
300 participants
Where
1 siteHong Kong
Study dates
29 Mar 2025to Dec 2028
Phase
Phase 4
Are there results?
Not yet: the study is under way

Key requirements

Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.

  • Ages 18 years and older
  • Men only
  • Healthy volunteers accepted
  • Adult, Older adult

Who may be able to join

  • has had sex with another male in the past six months
  • normally reside in Hong Kong
  • can communicate in written and spoken Chinese or English
  • willing and able to give written informed consent
  • being willing and able to attend scheduled study clinic visits
  • at risk of STI (had condomless sex with more than one man in the past 12 months, history of STI diagnosis in the past 12 months, inclination to have condomless sex, and other HIV-PrEP-eligible criteria)

Who cannot join

  • Being allergic to tetracycline class medicines
  • Currently taking medications that are contraindicated with doxycycline
  • Using antibiotics for more than 14 days in the month preceding enrolment

Trial locations and contacts

1 site in 1 country.

Hong Kong1 site

  • Stanley Ho Centre for Emerging Infectious Diseases

    Shatin

Other trials in Hong Kong

About this study

Official title: Superiority of On-demand Pre-exposure Prophylaxis Versus Post-exposure Prophylaxis on Using Doxycycline for Preventing Sexually Transmitted Infections in Men Who Have Sex With Men

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:

  1. Is DoxyODPrEP superior to DoxyPEP?
  2. Are both regimens safe?
  3. Does the MSM community accept the use of doxycycline to prevent bacterial STI?

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.

Read the detailed description

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.

Being tested
DoxyODPrEP, DoxyPEP
Keywords
doxycycline, men who have sex with men, sexually transmitted infections
Medical subject headings
Sexually Transmitted Diseases, Bacterial, Syphilis, Gonorrhea, Chlamydia Infections, Homosexuality, Sexually Transmitted Diseases

What participants receive

What participants receive. In a randomised study each person is assigned to one group by chance.

  • DoxyODPrEPDrug

    Also called doxycycline on demand PrEP

    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

  • DoxyPEPDrug

    Also called doxycycline PEP

    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.

Study groups in NCT06188442
Study groupRoleWhat they receive
DoxyODPrEPActive comparatorParticipants 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.
Receives: Drug: DoxyODPrEP
DoxyPEPActive comparatorParticipants 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.
Receives: Drug: DoxyPEP

What is being measured

The primary outcome is the main question the study is designed to answer.

  1. Time to the first episode of gonorrhoea after the enrolment visit

    Time to the first episode of gonorrhoea after the enrolment visit

    Measured: Months 1 to 24

  2. Time to the first episode of chlamydia after the enrolment visit

    Time to the first episode of chlamydia after the enrolment visit

    Measured: Months 1 to 24

  3. Time to the first episode of syphilis after the enrolment visit

    Time to the first episode of syphilis after the enrolment visit

    Measured: Months 1 to 24

Secondary outcomes (4)

  1. Safety profile

    Percentage of participants experiencing adverse events and the associated grades

    Measured: Months 1 to 24

  2. Acceptability of regimens

    Percentage of participants accepted the regimen

    Measured: Months 1 to 24

  3. Retention

    Percentage of participants remained during the follow-up period

    Measured: Months 1 to 24

  4. Time to the first episode of HIV after the enrolment visit

    Time to the first episode of HIV after the enrolment visit

    Measured: Months 1 to 24

Timeline

From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.

  1. First posted3 Jan 2024
  2. Study start29 Mar 2025
  3. Primary completion31 Dec 2027 (estimated)
  4. Study completionDec 2028 (estimated)

Resources

More details

For doctors and researchers: how the study is designed, who runs it, and its registry IDs.

Study design
Study type
Interventional
Phase
Phase 4
Primary purpose
Prevention
Allocation
Randomised
Intervention model
Parallel groups
Model description
With a 3:1 intervention-to-control allocation ratio (198 and 66 participants would receive intervention and control, respectively), a total of 264 participants would be recruited.
Masking
None (open label)
Enrolment
300 participants (estimated)
IDs, dates and publications
ClinicalTrials.gov ID
NCT06188442
Sponsor's protocol ID
23220262
Status last verified
Jun 2026
First submitted
18 Dec 2023
Last updated
5 Jun 2026
Results posted
No
Data monitoring committee
Yes
FDA-regulated drug
No
FDA-regulated device
No

Questions about this trial

What is this clinical trial studying?

A Phase 4 study testing DoxyODPrEP and DoxyPEP in people with Sexually Transmitted Diseases, Bacterial and Syphilis, run by Chinese University of Hong Kong at 1 site in Hong Kong.

The full registered description is in the About this study section and the official record.

Who may be eligible to take part?

The sponsor lists 6 inclusion and 3 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.

Is this clinical trial currently recruiting?

The record says: under way, not looking for participants, as of the sponsor's last update on 5 Jun 2026. Status can change between updates, so confirm with the study contact before making plans.

Where is the study taking place?

The record lists 1 site in Hong Kong. Whether a site is taking part right now should be confirmed with that site. See every site.

What are the possible benefits and risks?

They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.

What does this phase mean?

Phase 4 studies take place after a treatment is approved, to learn more about its long-term benefits and risks in everyday use.

Not every study follows the same path, and some studies (observational studies, device studies) have no phase.

Are results available for this study?

This study is still under way. Results are not available in the source record yet.

How can a doctor refer a patient or contact the research team?

The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.

What does the primary outcome measure?

Time to the first episode of gonorrhoea after the enrolment visit (time frame: Months 1 to 24). The study lists 3 primary outcomes in all. It is what the study was designed to measure, not a finding.

Where can I read the original study information?

On the ClinicalTrials.gov record for NCT06188442.

Does a listing mean the treatment is approved or proven to work?

No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.

How often is this information updated?

AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 5 Jun 2026.

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