LAUSR

&NA; The antiherpetic drugs acyclovir (ACV, valaciclovir) and penciclovir (famciclovir) are phosphorylated by viral thymidine kinase and terminate DNA synthesis. ASP2151 (amenamevir) and foscavir (PFA) directly inhibit viral helicase‐primase and DNA polymerase, respectively, and inhibit replication of herpes simplex virus (HSV) and varicella‐zoster virus. ACV, ASP2151, and PFA all inhibit HSV with a different mechanism of action and as a consequence, the kinetics of viral DNA accumulation and progeny virus production differ. This study focused on how viral DNA synthesis and its related events in the replication cycle would influence anti‐HSV action of ACV, ASP2151, and PFA. ASP2151 suppressed HSV replication more efficiently than ACV at 10 × 50% effective concentration of plaque formation (EC50), when treatments were started 0–24 h after infection. ASP2151 and PFA were more potent than ACV in suppressing viral DNA synthesis and infectious virus production when they were added up to 3 h following infection. The virus replicated in the presence of ACV was compared for the ratios of HSV DNA copy number to infectivity with that without ACV and infectivity of ACV‐treated virus was less efficient than that without ACV‐treatment. The EC50 of infected cells in the time course after infection was preserved in PFA, limited in ASP2151, and much increased for ACV, indicating that viral DNA synthesis had little effect on antiviral action of PFA and ASP2151 but reduced the susceptibility of ACV. ASP2151 showed a preferable profile as an anti‐herpetic agent with a better pharmacokinetic profile than ACV. HighlightsASP2151 and PFA were much potent than ACV in suppressing viral DNA.ASP2151 showed a stronger anti‐HSV activity than acyclovir in the early phase of infection.Viral DNA synthesis reduced anti‐HSV activity of ACV.Viral DNA synthesis had little effect on anti‐HSV action of ASP2151.