ACTG A5418: A Randomized, Placebo-Controlled, Double-Blinded Trial of the Safety and Efficacy of Tecovirimat for the Treatment of Human Monkeypox Virus Disease, Study of Tecovirimat for Human Monkeypox Virus (STOMP)


Treatment Category: Monkeypox

Study Description
A5418 (STOMP) is a study of tecovirimat (also known as TPOXX) for the treatment of human monkeypox virus (HMPXV) disease.

Study Status: Open

Why is this study being done?

  • To see if tecovirimat is safe, and whether it helps treat monkeypox infection.

Who can join?

People with:

  • Laboratory-confirmed or presumptive monkeypox infection
  • Monkeypox illness of less than 14 days’ duration
  • At least one active (not yet scabbed) skin lesion, mouth lesion, or proctitis (inflammation of the lining of the rectum) with or without visible ulcers

What do I need to do in the study?

Participants will be randomly assigned (like flipping a coin) in a 2:1 ratio to receive tecovirimat OR placebo for tecovirimat for 14 days.

People who are at higher risk for severe disease because of their age or their medical history will be assigned to receive open-label tecovirimat for 14 days.

All participants will be followed through a combination of in-person visits, specimen collection, virtual assessments, and self-reports and photographs of symptoms for about 2 months.

What treatments or drugs are involved with this study?

Tecovirimat is a drug that may help to treat infections caused by pox viruses. Tecovirimat is approved by the Food and Drug Administration (FDA) to treat smallpox in adults and children, but its use in this study is considered investigational.

Duration of Study

57 days



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