In cells infected with varicella-zoster virus, there is evidence to suggest that EPB-348 could offer clinically important advantages in the treatment of acute herpes zoster over currently available therapies due to rapid absorption and conversion to the active moiety as well as a longer intra-cellular half-life in infected cells. Clinically, these characteristics could translate into once-daily dosing versus thrice-daily dosing as seen with current therapy, leading to a higher rate of compliance and quality-of-life, especially among elderly patients. The objective of EPB348-0201 is to determine the pharmacokinetics and dosage of EPB-348 that best balances safety and efficacy among adult immunocompetent patients with an acute episode of herpes zoster. This multi-center study will randomly assign patients to either EPB-348 1000 mg once daily or EPB-348 2000 mg once daily or valacyclovir 1000 mg three times daily.