Feline herpesvirus type-1 (FHV-1) causes respiratory and ocular disease in cats. Lifelong neural latency and later viral reactivation occur in many cats after infection. Most human antiherpes drugs have low efficacy in FHV-1, demonstrated systemic toxicity, and low bioavailability; the nucleoside deoxyguanosine analog penciclovir is effective but has poor bioavailability. Its prodrug, famciclovir, is often used instead in humans. Famciclovir efficacy was assessed in FHV-1–infected cats in this study; 16 healthy, nonvaccinated, specific pathogen-free, FHV-1/FeLV/FIV-negative cats were included. Cats either received oral famciclovir (n = 10, 90 mg/kg Q 8 H for 21 days) or lactose (n = 6, 400 mg Q 8 H for 21 days). Cats were inoculated with an FHV-1 strain into the nares and conjunctival fornices on day 0 and then underwent multiple physical and ophthalmic examinations. The severity of ocular and nasal disease was assessed and total clinical disease scores assigned. Blood and conjunctival samples were collected pre- and postinoculation for assessment of tissue inflammation, serology, and FHV-1/feline genomic DNA/RNA quantification and shedding, goblet cell density, complete blood count, serum biochemical profile, urinalysis, and plasma penciclovir concentrations. Disease scores were significantly lower in famciclovir cats than in lactose cats on days 4 to 18, and lactose cats displayed decreases in weight during the first 7 days after inoculation; conversely, famciclovir cats increased in weight throughout the study. In addition, the percentage weight change was greater in famciclovir cats on days 7 and 14. In famciclovir cats, serum globulin concentrations were lower on days 3 through 9, the conjunctivitis histologic score was lower on day 14, herpetic DNA was shed significantly less frequently throughout the study duration, goblet cell density was higher on day 21, and anti-FHV-1 antibody concentrations at study end were lower in famciclovir-treated cats. Peak plasma penciclovir concentrations were therapeutically appropriate in the study.

Commentary: FHV-1–associated respiratory and ocular disease is a continuing and frustrating clinical problem in veterinary medicine. Famciclovir improved outcomes for systemic, ophthalmic, clinicopathologic, virologic, and histologic variables in FHV-1–infected cats in this study, without significant adverse events. It may therefore serve as an important part of the therapeutic arsenal against FHV-1 in veterinary medicine. Future studies should evaluate famciclovir effects in studies with larger sample sizes.—Indu Mani, DVM, DSc

Evaluation of orally administered famciclovir in cats experimentally infected with feline herpesvirus type-1. Thomasy SM, Lim CC, Reilly CM, et al. AM J VET RES 72:85-95, 2011.