About The Study

This CTN pilot study will gather data to help determine appropriate penicillin dosages for treating syphilis. The study researchers will also examine the extent to which the standard treatment of syphilis is affected by HIV co-infection. HIV-positive and HIV-negative study participants seeking treatment for syphilis will receive the Health Canada recommended dose of benzathine penicillin G (Bicillin®). Study researchers will measure penicillin levels in participants’ blood samples and compare syphilis treatment success rates. The main purpose of the study is to determine if higher concentrations of penicillin during treatment result in better syphilis treatment results.

About The Disease

Syphilis is a sexually transmitted infection caused by bacteria. Over the last 10 years there has been a dramatic increase in the number of reported cases of syphilis in Canada. Forty to 50 percent of individuals diagnosed with syphilis in Canada are co-infected with HIV. Penicillin has long been used to treat syphilis but according to study researchers there are no published clinical trials to guide dosing or duration of treatment. The Canadian guidelines on sexually transmitted infections (2010) recommends treatment of syphilis with Bicillin®, however there is very little information on whether body mass, kidney function, or HIV infection affect treatment. The appropriate penicillin dose to treat HIV-positive individuals with syphilis remains unknown. This study seeks to begin to address these gaps.

Study Approach

This study is a non-interventional study; meaning no experimental treatment will be administered. At the time of enrolment eligible participants will receive one dose of Bicillin®, which is the standard Health Canada recommended treatment for syphilis. Researchers will also draw two tubes of blood. One tube (10 mL or 2/3 Tbsp) will be taken to test for syphilis. The second tube (10 mL or 2/3 Tbsp) will be drawn to assess kidney function.

Participants are asked to return to the clinic for additional blood tests on the third and seventh day after the injection to monitor penicillin levels in the blood and then again one, three, six and 12 months later to see if the syphilis is cured. At these visits, the following assessments will be done:

  • One tube (10 mL or 2/3 Tbsp) of blood will be drawn and sent for syphilis testing
  • Adverse events will be recorded
  • Participants will be asked the following questions about their recent sexual behaviour in order to differentiate between treatment failure and re-infection
    • Number of partners
    • Nature of the sexual encounters (oral/anal/vaginal)
    • Use of safer sex practices

Eligibility Requirements


  • At least 18 years of age
  • Presenting with clinical signs of either primary or secondary syphilis; or with early latent syphilis and documented negative serology within the past 12 months
  • Positive syphilis serology (CMIA and TP-PA reactive) with a defined RPR titer at the time of diagnosis and enrolment
  • Able to provide informed consent
  • Able to communicate in either English or French
  • Able to return for follow-up

Additional Information

For more information about this study, please contact a participating site.

Principal Investigator

Here’s who is leading this study.

Can’t find what you’re looking for? Email ctninfo@hivnet.ubc.ca.

Participating Sites

Here’s where this study is being conducted.