Metisazone

Methisazone (USAN) or metisazone (INN) is an antiviral drug that works by inhibiting mRNA and protein synthesis, especially in pox viruses. It has been used in the past to treat smallpox.
Methisazone has been described as being used in prophylaxis since at least 1965.
The condensation of N-methylisatin with thiosemicarbazide leads to methisazone.