Coronaviruses cause diseases such as severe acute respiratory syndrome and Middle East respiratory syndrome in humans and feline infectious peritonitis (FIP) in cats. Coronaviruses have high rates of mutation and recombination, which can result in substantial changes in virulence. Once clinical signs develop, FIP is 100% fatal. The pathogenesis of FIP involves depletion of T cells.
This study examined the pharmacokinetics, safety, and efficacy of a 3C-like protease (3CLpro) inhibitor, GC376 (an antiviral drug), in cats with FIP. Pharmacokinetic and safety studies in healthy cats indicated that GC376 administered SC twice a day had good bioavailability and was well-tolerated over 4 weeks. Cats (n = 8) were infected with FIP virus via intraperitoneal injection. All cats developed jaundice, ascites, absolute lymphopenia, and high fevers before treatment began. Four cats were started on GC376 when only inapparent- to-mild ascites was present; 4 were treated once profound ascites developed. In the latter group, 2 were euthanized after 4 and 7 days of treatment because of severe illness.
The remaining 6 cats were treated for 14 to 20 days and demonstrated improvement in clinical signs and lymphopenia within a week, with no signs of disease during a follow-up period of up to 8 months. Viral titers from macrophages from the ascites in the euthanized cats showed decreasing viral RNA for duration of treatment. The authors concluded these results could lead to the development of an effective therapeutic agent for FIP.