Feline infectious peritonitis (FIP) is a common and highly lethal coronavirus 
disease of domestic cats. Recent studies of diseases caused by several RNA 
viruses in people and other species indicate that antiviral therapy may be 
effective against FIP in cats. The small molecule nucleoside analog GS-441524 is 
a molecular precursor to a pharmacologically active nucleoside triphosphate 
molecule. These analogs act as an alternative substrate and RNA-chain terminator 
of viral RNA dependent RNA polymerase. We determined that GS-441524 was 
non-toxic in feline cells at concentrations as high as 100 uM and effectively 
inhibited FIPV replication in cultured CRFK cells and in naturally infected 
feline peritoneal macrophages at concentrations as low as 1 uM. We determined 
the pharmacokinetics of GS-441524 in cats in vivo and established a dosage that 
would sustain effective blood levels for 24 h. In an experimental FIPV infection 
of cats, GS-441524 treatment caused a rapid reversal of disease signs and return 
to normality with as little as two weeks of treatment in 10/10 cats and with no 
apparent toxicity.