A guanine analogue antiviral agent used for the treatment of various herpesvirus (HSV) infections. HSV Infection Approved(In Vitro):Famciclovir metabolizes into BRL 42359 by deacetylation and then oxidizes to penciclovir.(In Vivo):Famciclovir (50-400 mg/kg; p.o. three times per day for total 10 doses) effectively cures necrotic hepatitis mice.