Pritelivir mesylate hydrate is the first in a class of antiviral agents that inhibit HSV replication by targeting the viral helicase–primase enzyme complex. Pritelivir mesylate hydrate has potent and resistance-breaking antiviral efficacy with potential for the treatment of potentially life-threatening HSV type 1 and 2 infections, including herpes simplex encephalitis. Pritelivir mesylate hydrate (0.03-45 mg/kg) significantly increases survival. Pritelivir mesylate hydrate (0.3-30 mg/kg) reduces mortality against HSV-1, E-377. Combination therapies of Pritelivir mesylate hydrate at 0.1 or 0.3 mg/kg/dose with Acyclovir (10 mg/kg/dose) are protective when compared to the vehicle treated group against HSV-2, strain MS [2][3].