Eprociclovir potassium is a new acyclovir analogue and a potent inhibitor of EHV1 replication and may have potential for the treatment and/or prophylaxis of infections with this virus. Eprociclovir possess potent anti-herpetic activity against most human herpesviruses. A-5021 proved to be about 15-fold more potent than acyclovir in inhibiting viral replication. Eprociclovir inhibits murine herpetic keratitis. A-5021 eyedrops, which are easily applied onto the affected cornea, ameliorated clinical scores and suppressed virus growth. Eprociclovir is a promising alternative treatment of herpetic keratitis.