Efficacy of antiviral agents in feline herpetic keratitis: Results of anin vitrostudy

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Abstract
Purpose. To determine, by a plaque reduction assay, the in vitro efficacy of novel antiviral agents in the treatment of feline herpes virus 1 (FHV-1) keratitis in the domestic cat (Felis felis). Materials and methods. A standard plaque reduction assay was performed using a laboratory strain of FHV-1 and embryo-derived feline kidney cells to determine the in vitro efficacy of the antiviral drugs penciclovir (PCV), bromovinyldeoxyuridine (BVdU), and (S)-9-(3-hydroxy-2-phosphonylmethoxypropyl) adenine (HPMPA) and to compare these with the drugs acyclovir (ACV) and trifluorothymidine (TFT). Efficacy was assessed by determining the dose of drug at which 50% plaque reduction was noted (ED50). Results. HPMPA was found to have greatest antiviral activity (ED50 0.07 µg/ml). ACV was least active (ED50 24 µg/ml), while TFT was active with an ED50 of 5.7 µg/ml. PCV and BVdU had intermediate activity (ED50 1.6 and 1.7 µg/ml, respectively). Conclusions. This study suggests that the efficacy of HPMPA, BVdU, and penciclovir in cats with herpesviral keratitis should be determined in vivo as their efficacy in vitro was substantially greater than that of acyclovir, already shown to have demonstrable but limited clinical antiviral activity.