A Phase 2 interventional study of Doxycycline 200mg daily for 14 days in Syphilis, sponsored by University of Washington. Recruiting at 1 site in United States. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2025-06-25.
Sponsored by University of Washington · Phase 2, Interventional, and Treatment
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:
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.
This is an open-label prospective cohort of 15 participants diagnosed with early syphilis treated with doxycycline 200mg daily for 14 days. The outcome of interest is clinical improvement and fourfold decline in RPR by 6 months. This study will include rectal and oropharyngeal sampling with syphilis transcription-mediated amplification (TMA), every other day for the 14-day course, returned by mail. The investigators will obtain 6-month point estimates for cure following single-dose intramuscular benzathine penicillin G or 14 days of doxycycline 100mg twice daily in retrospective cohorts of 60 persons. The investigators will use binomial exact calculation with an alpha of 0.05, two-tailed, to create a point estimates of percent cure. The investigators will report TMA positivity descriptively.
126 studies on the registry are indexed under Syphilis; 34 are open to participants now.
This study's planned enrollment of 15 is below the median of 354 across 85 interventional studies indexed under Syphilis.
Browse Syphilis studies →University of Washington is the lead sponsor of 1,433 studies on the registry; 225 are open to participants now.
Of its 158 completed or terminated interventional studies of FDA-regulated products, 136 (86%) have results posted.
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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:
Exclusion Criteria:
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.
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.
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.
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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 weakened immune system. It can come from an illness, such as HIV or some blood cancers, or from medicines that turn the immune system down, for example after an organ transplant or for an autoimmune disease; steroids at higher doses count.
Read whether the line is about a condition or about medicines, and which medicines and doses it means.
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.
Immunosuppression
A weakened immune system. It can come from an illness, such as HIV or some blood cancers, or from medicines that turn the immune system down, for example after an organ transplant or for an autoimmune disease; steroids at higher doses count.
Read whether the line is about a condition or about medicines, and which medicines and doses it means.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
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.
Drug: 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.
Composite clinical and serological response
Clinical response and serological response will be aggregated to arrive at one reported value, a binary outcome of "yes" (1) or "no" (0). Clinical response equates to resolution of clinical symptoms of syphilis the participants presented with, such as rash or chancre, without the development of new symptoms of syphilis. Resolution will be marked as "yes" or "no". Serological response equates to a fourfold decrease in RPR compared to the presenting RPR titer by 6 months. Resolution will be marked as "yes" or "no". Thus, to generate the composite response outcome, participants with outcomes of "yes" for both clinical response and serological response will qualify as a binary outcome of "yes" (1) . Participants who do not have outcomes of "yes" for both clinical response and serological response will qualify as a binary outcome of "no" (0).
Time frame: 6 months
PDFs hosted by the registry, ClinicalTrials.gov.
Plan to share: No
Started Mar 2025 (actual). Primary completion is estimated for Jun 2026, 15 months after the start.
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Studies of the drug tested here: Doxycycline