What is "pyrithyldione"

n. A psychoactive drug formerly used as a sedative.

Pyrithyldione (Presidon, Persedon) is a psychoactive drug invented in 1949. An improved method of manufacture was patented by Roche in 1959. It was used as a hypnotic or sedative and presumed to be less toxic than barbiturates. Today, this substance is no longer used. Agranulocytosis was sometimes reported as adverse effect.