Recruiting
Phase 2

Doxycycline

Sponsor:

University of Washington

Code:

NCT06683638

Conditions

Syphilis

Eligibility Criteria

Sex: All

Age: 18+

Healthy Volunteers: Not accepted

Interventions

Doxycycline 200mg daily for 14 days

Study Details

Brief summary:

The goal of this clinical trial is to learn if doxycycline taken as 200mg daily for 14 days is effective to treat early stage syphilis. This is different from how doxycycline is typically used for syphilis because the full doxycycline dose will be taken at the same time of day, rather than split up into a twice daily regimen. Lab data support that taking the medication as a single daily dose should be effective as treatment, but it has not been studied clinically. The main question this study aims to answer is:

Is doxycycline taken as a single daily dose of 200mg for 14 days an effective treatment for early syphilis based on a combined outcome of clinical improvement and blood test improvement?

Participants will:

1. Take doxycycline 200mg daily for 14 days
2. Submit oral and rectal swabs that test for syphilis bacteria every other day for 2 weeks, returned by mail
3. Complete 2 brief online surveys over the first 2 weeks
4. Return to the clinic for an interview and blood draw every 3 months for a maximum of 3 study visits, including the first visit

The investigators will compare the percentage of participants in the study who have response to treatment by 6 months to that of persons who have received standard (CDC-recommended) regimens. To do this, the investigators will calculate response percentage estimates following a shot of long-acting penicillin or 14 days of doxycycline 100mg twice daily from 60-person samples from the sexual health program's records.

Conditions

Syphilis

Study ID

NCT06683638

Start date

Mar 3, 2025

Status verified date

Jun, 2025

Completion date

Jun 26, 2026

Anticipated

Primary completion date

Jun 26, 2026

Anticipated

Eligibility Criteria

Eligibility Criteria

Sex: All

Age: 18+

Healthy Volunteers: Not accepted

Inclusion Criteria:

Clinical diagnosis of syphilis (primary or secondary) or laboratory-confirmed early latent syphilis. Specifically: This will include persons meeting any one of the following criteria:

1. Clinical diagnosis of primary syphilis (based on the presence of a chancre) and either a positive qualitative RPR in the absence of a prior positive RPR on their most recent serological test for syphilis or a positive darkfield microscope exam of material taken from a chancre, OR
2. Clinical diagnosis of secondary syphilis with a positive qualitative RPR in the absence of a prior positive RPR on their most recent serological test for syphilis, OR
3. A laboratory-confirmed diagnosis of early latent syphilis within one month (i.e. <31 days prior).

Exclusion Criteria:

1. age under 18
2. persons with evidence of neurosyphilis (including ocular and otic syphilis) or tertiary syphilis
3. persons who are unable to give informed consent
4. persons deemed by the study investigators to be unable to complete study follow-up visits
5. persons with an allergy to doxycycline
6. pregnant persons
7. persons with HIV who report that they are off antiretroviral medication or that they are not virologically suppressed
8. persons with other known forms of immunosuppression (e.g., persons taking systemic immunosuppressant drugs, persons with primary immunodeficiencies)
9. persons taking medications that would interact with doxycycline
10. persons whose initial RPR is lower than 1:4
11. persons currently prescribed doxy PEP
12. breastfeeding persons

Persons whose initial laboratory serological tests do not confirm the diagnosis of syphilis with an RPR of 1:4 or higher will be informed that they do not meet study criteria and advised to discontinue doxycycline 200mg once daily. Their subsequent treatment will be based on the judgement of non-research, clinical staff in the clinic and reflect shared decision making between clinical providers and their patient.

Study Design

Enrollment

15 participants

Anticipated

Intervention Model

Single group

Primary purpose

Treatment

Interventions and Outcome Measures

Arms

experimental: Doxycycline 200mg daily for 14 days

Participants diagnosed with early syphilis (primary, secondary, or early latent) with an RPR of 1:4 or greater will receive doxycycline 200mg daily to treat syphilis. Exclusions include pregnant persons, persons under 18 years of age, and persons on doxy PEP. During the two weeks of treatment, participants will perform oral and rectal swabs for syphilis, returned at the end of the 2 weeks by mail. Participants will submit brief online surveys twice over the two weeks of treatment. Repeat blood tests for syphilis, reactive plasma reagin (RPR), will be done at follow-up visits at 3 and 6 months to monitor serological response. Participants with response at the 3-month visit will not need to come to a 6-month visit.

Interventions

Doxycycline 200mg daily for 14 days

Doxycycline will be taken as a single dose of 200mg daily, rather than the current CDC-recommended 100mg twice daily regimen for early syphilis. The duration will still be 14 days of therapy.

Primary outcome measure

  • Composite clinical and serological response [ Time Frame: 6 months ]

Central Contacts and Locations

Central contacts

Travis Hunt, MD

206-685-4456thunt91@uw.edu

Matthew Golden, MD, MPH

206-744-6829golden@uw.edu

Locations

Public Health Sexual Health Clinic

Recruiting

Seattle, Washington, United States, 98104

Contacts

Jakar Delacruz

206-744-3590fkajonny@uw.edu

Travis Hunt, MD

206.685.4456thunt91@uw.edu

Principal Investigator:

Travis J Hunt, MD

More Information

Sponsor

University of Washington

Last update posted

Jun 25, 2025

Last verified

Jun, 2025

Keywords

  • syphilis
  • doxycycline

Trial information was received from ClinicalTrials.gov and was last updated on 2026-09-10. This information was provided to ClinicalTrials.gov by University of Washington on 2025-06-25.