Feline infectious peritonitis (FIP) is a disease caused by a coronavirus that kills 1 in 300 cats in the US and up to 5% of kittens coming from pedigreed catteries, shelters and cat/kitten rescue facilities. In spite of extensive studies, there is yet no effective preventive or treatment for FIP and once clinical signs appear, mortality is essentially 100%. Vaccines to date have proven to be ineffective in preventing FIP. However, antiviral drugs may be able to treat, if not cure, the disease in a manner similar that currently used to treat people infected with HIV/AIDS. HIV contains a number of proteins that have become effective targets for virus inhibitory drugs and these same types of proteins are found in coronaviruses. One particular target protein is the viral protease, an enzyme that is essential in forming infectious virus. Protease inhibitors are currently under development and appear promising based on cell culture and mouse/swine infection models. The goal of this study is to initiate testing these first-‐generation anti-‐corona viral drugs in cats to determine optimal dosage, routes of administration, duration of action, and acute and chronic toxicity. The ultimate goal is to identify compounds that can be safely and effectively used to treat cats with FIP.