An orally bioavailable antiviral agent; has activity against poxviruses expressing wild-type p37; inhibits the cytopathic effects induced by various strains of variola and monkeypox viruses in C. aethiops BSC40 kidney epithelial cells (EC50s = 0.019-0.067 and 0.023-0.039 μM, respectively) and decreases viral plaque size in a plaque formation assay at 0.05 μM; inhibits plaque formation by cowpox or vaccinia viruses in a plaque formation assay using human foreskin fibroblasts (EC50s = 0.48 and 0.05 μM, respectively); increases survival in cowpox and vaccinia virus-infected mice at 100 mg/kg per day for 14 days; increases survival of variola and monkeypox-challenged cynomolgus monkeys at 300 mg/kg per day for 14 days