About The Study

CTN 338 is a clinical trial to evaluate the effectiveness and safety of tecovirimat (TPOXX) for the treatment of Mpox infection compared to placebo. TPOXX is an antiviral medication developed to treat smallpox, but it may also be effective for Mpox as the viruses are closely related. The study is also collecting information about the feasibility and acceptability of conducting this type of trial for non-hospitalized patients with Mpox in Canada.


Mpox is a DNA virus that is in the same family as smallpox. In the past, it has occurred primarily in Central and West Africa. However, since the middle of May 2022, more Mpox cases have been reported across the world, including in Canada. Men who have sex with men have been particularly affected during the recent outbreak where the virus is being transmitted sexually. In general, symptoms start about one to three weeks after exposure and include fever and swollen lymph nodes and painful skin lesions that usually last two to four weeks. Lesions often occur in the rectum, genitals, and mouth. These symptoms can cause considerable pain and discomfort and may require people to isolate until their lesions heal.

Even though Mpox was identified several decades ago, we do not have any effective treatments for it. Oral TPOXX is approved by Health Canada for the treatment of smallpox. Laboratory studies suggest that it may be active against Mpox. However, in Canada, TPOXX is only available for use in severe and hospitalized Mpox cases. We don’t know if TPOXX can speed the time to recovery or reduce symptoms for people with more mild disease. While there is a vaccine available to prevent Mpox, we do not know how effective it is or how long protection lasts. It is therefore important that we conduct studies and learn more about Mpox infection to reduce the impact of this virus for people in Canada and beyond.

Study Approach

PLATINUM-CAN (CTN 338) is the sister study of PLATINUM-UK, led by Oxford University. The two parallel trials follow the same design and will pool their data to answer the primary study questions.

In Canada, 120 participants with laboratory-confirmed or presumptive Mpox who do not require hospitalization will be recruited from Montreal, Toronto, and Vancouver. These locations were chosen because they have had the largest Mpox outbreaks in Canada. Participants will be randomly assigned to receive either TPOXX or an identical placebo; both will be taken twice a day for two weeks. After the first two visits, which will include a clinical exam, lesion swab(s), and blood testing, participants will visit a study clinic for assessment once a week for four weeks. Participants will also be asked to complete a daily questionnaire about their symptoms and pain. Participants may also choose to upload photographs of their lesions to a secure study website. All participants will receive standard of care as needed, which includes the clinical management of lesions and medication for pain.

PLATINUM-UK and -CAN investigators will compare participants receiving TPOXX and placebo to understand whether TPOXX can decrease the time it takes for lesions to resolve. The study will also assess safety of TPOXX and whether it can decrease the duration of the infectious period and improve the severity of symptoms. Platinum-CAN/CTN 338 specifically aims to find out if this type of trial is feasible in Canada by assessing how many people can be enrolled and complete the whole study and adhere to the study procedures. Finally, the CTN 338 team will investigate whether TPOXX can decrease the time it takes for pain to resolve and if treatment improves self-reported quality of life.

Eligibility Requirements


  • 18 years and older
  • Weight ≥ 40 kg
  • Have been diagnosed with or have a high probability of having Mpox
  • Your doctor feels that your infection can be taken care of at home

Not Allowed

  • Current or past use of tecovirimat (TPOXX)
  • Participated recently or plan to participate in another study involving new drugs or vaccines

Additional Information

If you would like to take part in this study or want more information, please contact the site located closest to you (see contact information below), or visit clinicaltrials.gov.

Principal Investigators

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.

Toronto General Hospital

200 Elizabeth Street, Toronto, M5G 2C4

Dr. Sharon Walmsley
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BC Centre for Excellence in HIV/AIDS

608-1081 Burrard St, Vancouver, V6Z 1Y6

Dr. Mark Hull
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