Molnupiravir is the isopropylester prodrug of [N4-hydroxycytidine]. With improved oral bioavailability in non human primates, it is hydrolyzed in vivo, and distributes into tissues where it becomes the active 5’-triphosphate form. The active drug incorporates into the genome of RNA viruses, leading to an accumulation of mutations known as viral error catastrophe. Recent studies have shown EIDD-2801 inhibits replication of human and bat coronaviruses, including SARS-CoV-2, in mice and human airway epithelial cells. A [remdesivir] resistant mutant mouse hepatitis virus has also been shown to have increased sensitivity to N4-hydroxycytidine.