Why was phenobarbital used as one of the drugs for encephalitis?

Sedation and seizure. Phenobarb was used as a way to comtrol seizure and sedate . Peaple with encephalitis many time are very agitated and may risk seizures there is not much use today but it was used in the past successfully. Our area dosen't see this use anymorelike we used to.
Uncertain. Phenobarbital has been used for seizures, for sedation, and to reduce brain swelling. In severe encephalitis a state of barbiturate coma may be necessary. It is rarely used now for prophylaxis against a risk for epilepsy.