Daily Doxycycline for Early Syphillis

Recruiting now · Phase 2

Conditions studied: Syphilis

In brief

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.

Key facts

Study ID: NCT06683638
Run by: University of Washington
People needed: 15
Starts: 2025-03-03
Expected to finish: 2026-06-26
Last updated by the study team: 2025-06-25

Who can join

Age: 18 and older. Sex: any. Healthy volunteers: not accepted.

You may qualify if…

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:
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
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
A laboratory-confirmed diagnosis of early latent syphilis within one month (i.e. <31 days prior).

You may not qualify if…

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

Where it is running

Public Health Sexual Health Clinic — Seattle, Washington, United States (enrolling)

Full record on ClinicalTrials.gov

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