The number of prescriptions for monkeypox antiviral Tpoxx should be "judicious" because virus mutations can make it ineffective, the FDA said in an updated monkeypox guidance Sept. 14.
"Tpoxx has a low barrier to viral resistance," the FDA said. "This means small changes to [monkeypox's viral] protein could have a large impact on the antiviral activity of Tpoxx."
The antiviral, also known by its generic name tecovirimat, is approved to treat smallpox but is currently in a late-stage clinical trial to prove efficacy in treating monkeypox. This labels Tpoxx as an "investigational drug," meaning physicians first have to enroll in the trial and fill out forms for each patient to whom they wish to prescribe Tpoxx.
Its "investigational" status means it's difficult to obtain the drug, but that may be a good thing since most people don't need it, according to experts.
"Most patients with intact immune systems really need supportive care and pain control, but often do not need to be stepped up to antiviral treatment," Sapna Bamrah Morris, MD, a researcher at the CDC, said in a Sept. 12 webinar hosted by the Infectious Diseases Society of America.