Clinical Use of Tecovirimat (Tpoxx) for Treatment of Monkeypox Under an Investigational new Drug Protocol

United States, May-August 2022

Kevin O'Laughlin, MD; Farrell A. Tobolowsky, DO; Riad Elmor, MS; Rahsaan Overton, MPH; Siobhán M. O'Connor, MD; Inger K. Damon, MD, PhD; Brett W. Petersen, MD; Agam K. Rao, MD; Kevin Chatham-Stephens, MD; Patricia Yu, MPH; Yon Yu, PharmD


Morbidity and Mortality Weekly Report. 2022;71(37):1190-1195. 

In This Article

Abstract and Introduction


Currently, no Food and Drug Administration (FDA)–approved treatments for human monkeypox are available. Tecovirimat (Tpoxx), however, is an antiviral drug that has demonstrated efficacy in animal studies and is FDA-approved for treating smallpox. Use of tecovirimat for treatment of monkeypox in the United States is permitted only through an FDA-regulated Expanded Access Investigational New Drug (EA-IND) mechanism. CDC holds a nonresearch EA-IND protocol that facilitates access to and use of tecovirimat for treatment of monkeypox.§ The protocol includes patient treatment and adverse event reporting forms to monitor safety and ensure intended clinical use in accordance with FDA EA-IND requirements. The current multinational monkeypox outbreak, first detected in a country where Monkeypox virus infection is not endemic in May 2022, has predominantly affected gay, bisexual, and other men who have sex with men (MSM).[1,2] To describe characteristics of persons treated with tecovirimat for Monkeypox virus infection, demographic and clinical data abstracted from available tecovirimat EA-IND treatment forms were analyzed. As of August 20, 2022, intake and outcome forms were available for 549 and 369 patients, respectively; 97.7% of patients were men, with a median age of 36.5 years. Among patients with available data, 38.8% were reported to be non-Hispanic White (White) persons, 99.8% were prescribed oral tecovirimat, and 93.1% were not hospitalized. Approximately one half of patients with Monkeypox virus infection who received tecovirimat were living with HIV infection. The median interval from initiation of tecovirimat to subjective improvement was 3 days and did not differ by HIV infection status. Adverse events were reported in 3.5% of patients; all but one adverse event were nonserious. 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.

Tecovirimat is an antiviral drug developed as a medical countermeasure to treat smallpox, a serious and life-threatening infection caused by Variola virus, of genus Orthopoxvirus; Monkeypox virus belongs to the same genus but typically causes less severe disease.** Global eradication of smallpox was declared by the World Health Assembly in 1980.†† Because opportunities to develop clinical trials in countries where Monkeypox virus infection is considered endemic have been limited, the efficacy of tecovirimat to treat monkeypox has not been fully evaluated in humans. Instead, efficacy data that supported FDA approval of tecovirimat for smallpox were based on nonhuman primate and rabbit studies§§;[3] efficacy studies were also conducted in macaque monkeys and prairie dogs.[4,5]

During May 2022, a multinational monkeypox virus outbreak (Clade II) was first reported, principally affecting MSM.[1,2] Interim CDC guidance currently recommends that tecovirimat be considered in patients with severe disease, those at high risk for severe disease, or those with aberrant infections.¶¶ This report describes the available demographic and clinical characteristics, clinical indications for use, clinical outcomes, and adverse events reported among some of the first known recipients of tecovirimat treatment under the EA-IND protocol for Monkeypox virus infection in the United States.

During May 29–July 20, 2022, the EA-IND protocol required patient assessment forms at the start of treatment and once during three follow-up time points (assessment A: day 1–7, assessment B: day 8–14, and assessment C: posttreatment). Initially, the protocol's eligibility criteria included laboratory confirmation of Monkeypox virus or Orthopoxvirus infection, or a presumptive diagnosis based on clinical signs and symptoms. The revised EA-IND protocol (version 6, dated July 20, 2022) was amended as follows: 1) a patient may be eligible for tecovirimat based on clinical signs and symptoms and if there was an epidemiologic link to a case of or exposure to Monkeypox virus, 2) the number of follow-up visits was reduced to one during and one posttreatment, and 3) only reporting of serious adverse events using MedWatch forms was required.*** Data abstracted from patient intake forms included demographic characteristics, orthopoxvirus vaccination status, immune status,††† laboratory test result, clinical signs and symptoms, reason for tecovirimat administration (i.e., lesions in sensitive anatomic areas, at risk for severe disease, and pain), formulation at the start of treatment (i.e., intravenous or oral), and number of days from symptom onset to administration of the first dose. Data from clinical outcome forms included whether the patient was hospitalized, number of days from initiation of treatment to subjective improvement, recovery status (i.e., recovered with or without sequelae or not yet recovered), and adverse events during and after treatment. The EA-IND protocol was reviewed and approved by CDC's Institutional Review Board, reviewed and authorized by FDA, and conducted consistent with applicable federal law and CDC policy.§§§ Analyses were conducted using SAS software (version 9.4; SAS Institute). Difference in time to subjective improvement between HIV-positive and patients without HIV-positive status documented were compared using a 2-sided Wilcoxon rank-sum test; p<0.05 was considered statistically significant.

CDC abstracted data from patient intake forms for 549 persons with confirmed or suspected monkeypox who were prescribed tecovirimat therapy by August 20, 2022, and outcome forms for 369 patients. Data from both intake and outcome forms were available for 174 of these patients. Among 527 patients with intake forms and available data, 515 (97.7%) were male (Table 1). The median age was 36.5 years (IQR = 31.4–43.9 years). Among 464 patients with race and ethnicity data, 180 (38.8%) were White persons, 161 (34.7%) were Hispanic or Latino persons, and 83 (17.9%) were non-Hispanic Black or African American persons. Among 359 patients with available data, approximately two thirds (232, 64.6%) of tecovirimat recipients had lesions affecting <10% of their body; 17 (4.7%) had lesions affecting 75%–100% of their body. Among 529 patients with available data on number of lesions, 299 (56.5%) reported 10–100 lesions at the start of tecovirimat; 210 (39.7%) had fewer than 10 lesions, and 20 (3.8%) had more than 100 lesions. The presence of lesions in anatomic areas that might result in serious sequelae was reported on 191 (79.6%) of the 240 revised intake forms with available data. The most frequently reported underlying medical condition affecting immune status was HIV infection (254, 46.3%); viral load and CD4 count were not reported. Among 495 persons with available data on route of administration, the oral formulation of tecovirimat was prescribed to 494 (99.8%) at the start of therapy. Median interval from symptom onset to receipt of first tecovirimat dose was 7 days (IQR = 5–10 days) (Figure). Among 260 persons with revised intake forms, 124 (47.7%) had laboratory-confirmed Orthopoxvirus infection when tecovirimat treatment commenced.


Interval from symptom onset to receipt of first tecovirimat (Tpoxx) dose* among symptomatic patients with Monkeypox virus infection treated under the Food and Drug Administration–regulated Expanded Access Investigational New Drug protocol (N = 518) — United States, May–August 2022
*Calculated from nonmissing values (444).
Overall, 31 patients with missing symptom onset date were excluded.

Among 369 patients with outcome forms, data on hospitalization status was available for 331; among these, 23 (6.9%) were hospitalized after symptom onset (Table 2), and the median duration of hospitalization was 4 days (IQR = 1–5 days). Among 255 patients with available data, the median time to subjective improvement after starting treatment was 3 days (IQR = 2–4 days).¶¶¶ Among 317 patients with available outcome information, 230 (72.6%) recovered with or without sequelae**** by or before completion of the posttreatment assessment; 87 (27.4%) patients were reported by clinicians to be not yet recovered, 78 of whom had not yet completed the standard 14-day tecovirimat treatment course. Adverse events were reported for 12 (3.5%) of 340 patients with information on adverse events; these included headache (three), nausea (two), visual disturbance (two), weakness (two), and hospitalization for psychiatric reasons (one).†††† At the time of the posttreatment follow-up visit, three (2.2%) of 137 persons with information available had developed new lesions compared with 25 (13.1%) who had developed new lesions during the first week of treatment. Most (119, 89.5%) patients reported that all lesions were crusted and healing with a new layer of skin under the scab following treatment. Among 174 patients with available data, the interval to subjective improvement did not differ between HIV-positive persons (42; median = 3 days) and persons without documentation of HIV positive status (64; median = 3 days) with available data (p = 0.83).

*These authors contributed equally as first authors.
These authors contributed equally as senior authors.
Initially developed by the U.S. government, and, during later stages, in partnership with SIGA Technologies, Incorporated.
§§Animals were challenged, respectively, with Monkeypox virus and Rabbitpox virus.
¶¶Aberrant infections involve accidental implantation in eyes, mouth, or other sensitive anatomic areas where Monkeypox virus infection might constitute a special hazard (e.g., the genitals or anus). It was previously thought that Monkeypox virus infections rarely affected these regions, so the term "aberrant" was used early in the 2022 multinational outbreak. The revised intake form used the phrase "sensitive anatomic areas" as shorthand for the preceding definition. The preferred phrase is "anatomic areas which might result in serious sequelae".
***Serious adverse event (AE) defined as death, life-threatening event, inpatient hospitalization or prolongation of existing hospitalization, persistent or significant incapacity or substantial disruption of the ability to conduct normal life functions, congenital anomaly/birth defect, or an important medical event that based on appropriate medical judgment might jeopardize the patient and might require medical or surgical intervention to prevent one of the aforementioned outcomes.
†††Includes receipt of immunosuppressive therapies and the following categories collected from the investigational new drug protocol paperwork: leukemia, lymphoma, bone marrow or organ transplant, congenital immune defects, or other cancers.
§§§45 C.F.R. part 46, 21 C.F.R. part 56; 42 U.S.C. Sect. 241(d); 5 U.S.C. Sect. 552a; 44 U.S.C. Sect. 3501 et seq.
¶¶¶Time to first observed (including patient-reported) improvement.
****Per clinical judgment of the treating provider.
††††All adverse events included headache (three), nausea (two), visual disturbance (two), weakness (two), vomiting (one), asymptomatic elevated liver function tests (one), depression with suicidality (one), rash (one), hives (one), numbness (one), fatigue (one), and dizziness (one).