Dose-finding Study of ASP2151 in Subjects With Herpes Zoster

Inclusion Criteria: * Subjects aged from 20 years to under 80 years on the day informed consent is obtained * Subjects to whom the study drugs can be orally administered within 72 hours after the onset of rash due to herpes zoster * Subjects in whom protocol-specified observations and assessments are considered possible Exclusion Criteria: * Subjects with extremely compromised immune function due to underlying diseases, treatment with Immunosuppressive agents etc., or radiotherapy * Subjects with a serious underlying disease that corresponds to Grade 3 in the Classification Criteria for teh Seriousness of Adverse Drug Reactions * Subjects with concurrent malignant tumors, or those with a history of malignant tumors within the past 5 years