A review of antiviral drugs and other compounds with activity against feline herpesvirus type 1

Abstract

Feline herpesvirus type 1 (FHV-1) is a common and important cause of ocular surface disease, dermatitis, respiratory disease, and potentially intraocular disease in cats. Many antiviral drugs developed for the treatment of humans infected with herpesviruses have been used to treat cats infected with FHV-1. Translational use of drugs in this manner ideally requires methodical investigation of their in vitro efficacy against FHV-1 followed by pharmacokinetic and safety trials in normal cats. Subsequently, placebo-controlled efficacy studies in experimentally inoculated animals should be performed followed, finally, by carefully designed and monitored clinical trials in client-owned animals. This review is intended to provide a concise overview of the available literature regarding the efficacy of antiviral drugs and other compounds with proven or putative activity against FHV-1, as well as a discussion of their safety in cats.

Keywords: antiviral therapy; feline herpesvirus; interferon; lysine; nucleoside analogues; virology.

Figure 1

Absorption, metabolism, and excretion pathways of famciclovir in humans. Following oral administration, famciclovir is absorbed across the intestine and undergoes di-deacetylation. The exact site at which this step occurs is unclear but may be in the enterocytes, bloodstream, or liver. The inactive metabolite BRL42359 is then oxidized by a hepatic aldehyde oxidase to the active antiviral compound, penciclovir, which is ultimately excreted in feces and urine. Based upon famciclovir, BRL42359 and penciclovir concentrations in feline plasma following oral administration of famciclovir, similar steps likely occur in cats.[50, 52, 53] Anatomic images courtesy of www.MedicalGraphics.de (license # CC BY-ND 3.0 DE).

Figure 2

Relative activity of hepatic aldehyde oxidase in various species. All data are shown in percentage activity normalized against humans (100%). Original data from Dick et al.[49]

Figure 3

A 6-week-old, sexually intact male domestic short haired cat with blepharoconjunctivitis in both eyes and dendritic ulcerative keratitis in the right eye prior to (A) and following (B) 8 days of orally administered famciclovir given at 110 mg/kg thrice daily. Note the marked improvement in both eyes following treatment with famciclovir. Left eye of a 14-year-old, female spayed domestic medium haired cat with blepharokeratoconjunctivitis in both eyes prior to (C) and following (D) 15 days of orally administered famciclovir given at 85 mg/kg thrice daily. Note the improvement in the left eye following treatment with famciclovir.