Doxycycline
Treatment for Syphilis
Typical Dosage: 100 mg orally twice daily
Effectiveness
93%
Safety Score
70%
Clinical Trials
14
Participants
50K
Comparative Safety Scale(Higher is safer)
Cyanide☠️
Meth💀
Cigarettes🚬
Chemo☢️
Alcohol🍺
Morphine💊
Antibiotics💉
Tylenol💊
Exercise🏃
Water💧
70
DangerousModerateSafe
Treatment Details
Dosage Range
100 mg orally twice daily
Time to Effect
1-2 weeks for serologic response
Treatment Duration
14-28 days
Evidence Quality
MODERATENumber Needed to Treat (NNT)
2(Treat 2 patients to see 1 additional successful outcome)
Number Needed to Harm (NNH)
15(Treat 15 patients to see 1 additional serious adverse event)
Confidence Score
90%confidence in effectiveness data
Health Economics
Annual Cost of Care
Drug Cost:$20
Monitoring:$200
Side Effect Mgmt:$35
Total Annual:$255
Cost-Effectiveness Analysis
Cost-Effectiveness Rating
EXCELLENTICER
$12,000/QALY
QALYs Gained
2.2
Outcome-Based Costs
Cost per Responder
$283
Cost per Remission
$283
Prescription Access Economics
Annual Societal Loss per Patient
$395
Cost of prescription-only barriers (visits, time, admin, price premium)
Physician Visit Cost
$300/year
Time Cost
$60/year
Travel + wait time
Insurance Admin Cost
$20/year
Prior auth, claims
Rx Price
$30/year
Potential OTC Price
$15/year
Estimated if OTC available
Early Treatment Benefit
+0.10 QALYs
From faster OTC access
Risk Assessment
Misuse Risk
MODERATEMissed Diagnosis Risk
HIGHRequires Monitoring
YesNeeds lab work/checkups
Active Clinical Trials
9 active trials recruiting for Doxycycline in Syphilis
Daily Doxycycline for Early Syphillis
NCT06683638RECRUITINGPHASE2
15 participants
INTERVENTIONAL
Seattle, United States
Started: Mar 3, 2025
The Efficacy of Doxycycline Post Exposure Prophylaxis for Preventing STIs Among MSM in Bangkok, Thailand.
NCT07397403RECRUITINGPHASE4
400 participants
INTERVENTIONAL
Sathorn, Thailand
Started: Oct 6, 2025
Doxi-Rio: Study on the Use of Doxycycline to Prevent Sexually Transmitted Infections in Rio de Janeiro
NCT07500415RECRUITINGNA
200 participants
INTERVENTIONAL
Rio de Janeiro, Brazil
Started: Oct 28, 2025
A Clinical Study to Assess the Efficacy of Weekly Doxycycline Prophylaxis to Reduce Bacterial Sexually Transmitted Infections (STI) in Young African Women
NCT07884240NOT YET RECRUITINGPHASE3
580 participants
INTERVENTIONAL
Gaborone, Botswana +3 more
Started: Nov 30, 2026
Superiority of On-demand PrEP Versus PEP on Using Doxycycline for Preventing STI in MSM
NCT06188442ACTIVE NOT RECRUITINGPHASE4
300 participants
INTERVENTIONAL
Shatin, Hong Kong
Started: Mar 29, 2025
A Randomized Controlled Trial of Doxycycline Post Exposure Prophylaxis to Prevent Incident Bacterial STIs Among Women in the United States
NCT07704957NOT YET RECRUITINGPHASE4
519 participants
INTERVENTIONAL
Started: Jan 1, 2027
Comparisons of Treatment Responses of Early Syphilis to Benzathine Penicillin G With or Without Doxycycline
NCT06069141RECRUITINGNA
688 participants
INTERVENTIONAL
Hsinchu, Taiwan +8 more
Started: Jan 1, 2024
Doxycycline Prophylaxis for Prevention of Sexually Transmitted Infections
NCT06738407RECRUITINGPHASE4
760 participants
INTERVENTIONAL
Los Angeles, United States +12 more
Started: Feb 27, 2026
Periodic Presumptive Treatment vs. doxyPEP for STI Control in Kenyan MSM
NCT06468462ACTIVE NOT RECRUITINGPHASE4
2.9K participants
INTERVENTIONAL
Kisumu, Kenya +2 more
Started: Oct 29, 2025
Completed Clinical Trials
7 completed trials for Doxycycline in Syphilis
Clinical Trial of Doxycycline VS BPG for Early Syphilis (SY-DOXY)
NCT04838717COMPLETEDPHASE3
200 participants
INTERVENTIONAL
Besançon, France +6 more
Started: Dec 6, 2021
Azithromycin/Bicillin Syphilis
NCT00031499COMPLETEDPHASE3
593 participants
INTERVENTIONAL
Birmingham, United States +9 more
Started: Jun 1, 2000
Oral Doxycycline for the Prevention of Syphilis in Men Who Have Sex with Men (DaDHS)
NCT02864550COMPLETEDPHASE4
52 participants
INTERVENTIONAL
Vancouver, Canada
Started: Aug 15, 2019
Evaluation of Doxycycline Post-exposure Prophylaxis to Reduce Sexually Transmitted Infections in PrEP Users and HIV-infected Men Who Have Sex With Men
NCT03980223COMPLETEDPHASE4
641 participants
INTERVENTIONAL
San Francisco, United States +2 more
Started: Nov 26, 2019
Efficacy of Doxycycline Prophylaxis to Reduce Syphilis in High-Risk, HIV-Positive MSM
NCT02257658COMPLETEDNA
30 participants
INTERVENTIONAL
Started: Sep 1, 2011
Tenofovir/Emtricitabine With Doxycycline for Combination HIV and Syphilis Pre-exposure Prophylaxis in HIV-negative MSM
NCT02844634COMPLETEDPHASE4
52 participants
INTERVENTIONAL
Vancouver, Canada
Started: May 15, 2018
Doxycycline PEP for Prevention of Sexually Transmitted Infections Among Kenyan Women Using HIV PrEP
NCT04050540COMPLETEDPHASE4
449 participants
INTERVENTIONAL
Kisumu, Kenya
Started: Feb 5, 2020