Tecovirimat Safe in Monkeypox, but Efficacy Is Less Clear

Tecovirimat (Tpoxx) was well tolerated among patients with monkeypox virus infection, though its efficacy in monkeypox is currently unclear, CDC researchers said.

Among over 300 patients taking tecovirimat under the FDA-regulated Expanded Access Investigational New Drug (EA-IND) protocol, 6.9% were hospitalized after symptom onset, with a median duration of hospitalization of 4 days, reported Farrell A. Tobolowsky, DO, of the CDC Monkeypox Emergency Response Team, and colleagues, in Morbidity and Mortality Weekly Report.

Of 255 patients with available data, the median time to subjective improvement after starting treatment was 3 days, with no differences noted between patients with HIV positivity and those with no information on HIV status. Furthermore, among 317 patients with available outcome data, 72.6% recovered with or without sequelae, while 27.4% were reported to be not yet recovered, though 78 had not yet completed the standard 14-day tecovirimat treatment course.

“These data support the continued access to and treatment with tecovirimat for patients with or at risk for severe disease in the ongoing monkeypox outbreak,” Tobolowsky and team wrote.

Tecovirimat, which is approved by the FDA for smallpox, is recommended by the CDC as soon as monkeypox has been clinically or laboratory confirmed. However, “because there is the potential for false-positive test results, tecovirimat should be considered only in those with a high pretest probability of being infected with monkeypox virus to avoid unnecessary treatment or implementation of other public health measures,” the researchers noted.

“Inappropriate uses could potentially lead to resistance,” they added.

During the first week of treatment, 13.1% of patients with available data reported new lesions, while 31.8% reported that all lesions crusted and healed. During the second week, 13.5% of patients reported developing new lesions, and 49.7% indicated that lesions crusted and healed. Following treatment, 2.2% said they had new lesions, and 89.5% had lesions that were crusted over and healing with a new layer of of skin under the scab.

Among 340 patients, 3.5% reported adverse events, including headache, nausea, visual disturbance, weakness, and hospitalization for psychiatric reasons. “Among reported adverse events, most were not serious, and it is not known whether tecovirimat caused the adverse events reported,” the researchers noted.

For this study, Tobolowsky and colleagues included 549 patients, of whom 99.8% were treated with oral tecovirimat. Median age was 36.5, and 97.7% were men. Outcome data were available for 369 patients.

Of the 464 patients who reported race and ethnicity, 38.8% were white, 34.7% were Hispanic or Latino, and 17.9% were Black or African American.

About two-thirds of patients had lesions on less than 10% of their bodies, and 4.7% had lesions affecting 75% to 100% of their bodies. “Lesions in anatomic areas that might result in serious sequelae” were reported in 79.6% of the 240 patients with available data.

Patients were given their first dose of tecovirimat a median 7 days (interquartile range 5-10) following onset of symptoms.

The study was limited by its lack of a control group, Tobolowsky and team noted. In addition, data were made available from EA-IND forms that were submitted to the CDC. Variable data were collected by “free text,” possibly resulting in conditions that went unreported. Furthermore, assessment time points were different across patient profiles, and those with worse baseline symptoms may have been more likely to have follow-up.