A phase 3, randomized, double-blind, placebo-controlled study evaluating a single, patient-initiated dose of amenamevir for recurrent herpes labialis. Amenamevir (ASP2151), a novel, non-nucleoside analog, antiviral drug, inhibits the enzyme activities of helicase and primase, which are essential for replication of herpes viral genomic DNA. In this phase 3, randomized, double-blind, placebo -controlled, multicenter study, the authors investigated the efficacy and safety of a single patient-initiated dose of amenamevir to treat recurrent herpes labialis. Adult immunocompetent patients with recurrent herpes labialis who had the experience and ability to recognize prodromal symptoms were randomly assigned to administer amenamevir 1200 mg or placebo as a patient-initiated therapy within 6 hours