UC San Diego Joins National Trial to Test Drug for Treating MPOX

The University of California San Diego will be one of multiple sites assessing the safety and efficacy of tecovirimat as a potential treatment for human monkeypox. Marketed as TPOXX, tecovirimat is an antiviral currently approved for treatment of human smallpox in adults and children caused by the variola virus.

The Study of Tecovirimat for Human Monkeypox Virus (STOMP) is a Phase III, randomized, placebo-controlled, double-blind trial, funded by the National Institute of Allergy and Infectious Diseases and led by the AIDS Clinical Trial Group (ACTG), the world’s largest and longest running HIV clinical trials network. The AntiViral Research Center (AVRC) at UC San Diego School of Medicine is part of ACTG.

A colorized electron microscopic image shows mature, oval-shaped monkeypox virus particles (pink). Photo credit: CDC

“There is an urgent need for MPOX treatments and this study will help us determine whether tecovirimat should be one of them,” said Susan Little, MD, professor of medicine at UC San Diego School of Medicine and infectious disease specialist at UC San Diego Health, co-director of AVRC and lead investigator of the UC San Diego site STOMP trial. “People living in the San Diego region who have confirmed or probable Mpox have the opportunity to make a huge contribution by participating in this study.”

The current monkeypox or MPOX outbreak emerged in the spring of 2022 and has since spread throughout the world, with more than 75,000 cases in 109 countries and more than 28,000 cases in the United States. The County of San Diego has documented 440 cases, as of October 22.

MPOX was first identified in 1958 and has caused an increasing number of infections annually in endemic countries, primarily portions of Africa. The current outbreak has been characterized primarily by increased person-to-person transmission. Close contact during sexual activity is believed to play an important role in the current outbreak. While most cases have been reported among men who have sex with men, women, children and men who have sex with women have also been infected. There are currently no therapies approved to treat human MPOX.

TPOXX is approved by the U.S. Food and Drug Administration to treat smallpox, but its safety and effectiveness against MPOX is unknown. The MPOX virus belongs to the same family of viruses as variola virus. MPOX symptoms are similar to smallpox symptoms, but milder, and MPOX is rarely fatal. MPOX is not related to chickenpox.

The new trial, with more than 60 sites, will enroll more than 500 adults with MPOX virus infections. The trial will include people with severe disease and those at high risk of severe disease, including pregnant and breastfeeding persons, children and individuals with underlying immune deficiency and active inflammatory skin conditions who will receive open-label tecovirimat.

Study participants with symptomatic MPOX virus infection who do not meet the criteria for the open-label cohort will be randomly assigned in a ratio of 2:1 to receive either tecovirimat or a placebo orally for 14 days.

Participants who are randomized in the double-blinded cohort who subsequently progress to severe disease will be offered the option to switch to open-label tecovirimat, as will participants who report persistent severe pain from MPOX virus infection.

Susan Little, MD, is a professor of medicine at UC San Diego School of Medicine, infectious disease specialist at UC san Diego Health, co-director of the Antiviral Research Center and lead investigator of the UC San Diego site of the STOMP trial.

All STOMP participants will be followed for at least eight weeks through a combination of virtual and in-person visits, and daily self-reports to determine if those receiving tecovirimat heal more quickly compared to those receiving the placebo. STOMP will also provide critical data on the optimal dosing and safety of tecovirimat in children and people who are pregnant or breastfeeding.

Individuals who have presumptive or confirmed MPOX infections (testing positive within seven days) and who begin experiencing symptoms within 13 days are eligible. Testing will be provided by the study. Participants with presumptive MPOX who have not yet been tested are able to enroll as long as their study-provided test is positive. Participants must also have at least one active skin lesion that has not yet scabbed, a mouth lesion or proctitis (inflammation in the lining of the rectum).

“The ACTG has designed this study to give us the greatest possible insights into whether and how tecovirimat works against monkeypox, including whether the virus develops resistance to the treatment,” said ACTG chair Judith Currier, MD, professor of medicine at UCLA David Geffen School of Medicine.

“An important part of that design is the inclusion of children and pregnant people. The study will also evaluate markers that may tell us that the drug is working so we can identify future promising drugs. Beyond addressing the current outbreak, this study has the potential to profoundly inform the treatment of individuals who acquire monkeypox virus in endemic countries.”