A topical antiviral composition comprising acyclovir, penciclovir and/or omaciclovir in a glucocorticoid-free pharmaceutical carrier comprising 15 to 25 weight % propylene glycol and 10 to 25 weight % isopropyl C.sub.12-C.sub.22 alkanoic ester. The compositions have utility in the treatment or prophylaxis of herpesvirus infections. Clinical results demonstrate that treatment commencing at the prodromal stage can prevent the development of a classic cold sore lesion in a large proportion of patients.