The invention provides a pharmaceutical composition for treating impetigo of a human that is induced by Herpes simplex virus (HSV) or varicella zoster virus (VZV), said pharmaceutical composition comprising an effective amount of 2-[(2-amino-6-oxo-6,9-dihydro-3H-purin-9-yl)methoxy]ethyl-2-amino-3-methylbutanoate and an effective amount of an Anti-allergic agent.