Evaluation of free or liposome-encapsulated ribavirin for antiviral therapy of experimentally induced feline infectious peritonitis

Ribavirin, either free in aqueous solution or incorporated into liposomes, was evaluated in 50 specific-pathogen-free kittens after experimental challenge exposure with feline infectious peritonitis virus (FIPV). Ribavirin was administered daily for 10 to 14 days at 16.5 mg kg-1 bodyweight given per os, intramuscularly or intravenously beginning 18 hours after kittens were challenge-exposed with FIPV. All kittens, including ribavirin-treated and untreated kittens, succumbed to FIP. Clinical signs of disease were more severe in the ribavirin-treated kittens and their mean survival times were shortened. The clinical efficacy of free ribavirin given intravenously at a reduced dosage (5.5 mg kg-1 bodyweight) was compared to that of ribavirin incorporated into lecithin-containing liposomes (5 mg kg-1) intravenously. Drugs were given once daily for three consecutive days of each week for three weeks, beginning 18 hours after virus challenge exposure. There was no significant difference either in survival rate or severity of disease between kittens given free ribavirin, liposomal ribavirin or saline only. Because of its intrinsic toxicity and low therapeutic index against FIPV and its marginal antiviral activities in vivo at maximal doses, ribavirin cannot presently be recommended as primary antiviral chemotherapy against FIP.