<p>Molnupiravir inhibits viral reproduction by promoting widespread mutations in the replication of viral RNA by RNA-directed RNA polymerase. It is metabolized into a ribonucleoside analog that resembles cytidine, &beta;-D-N 4-Hydroxycytidine 5&prime;-triphosphate (also called EIDD-1931 5&prime;-triphosphate or NHC-TP). During replication, the virus&#39;s enzyme incorporates NHC-TP into newly-made RNA instead of using real cytidine.<br />
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Molnupiravir can swap between two forms (tautomers), one of which mimics cytidine (C) and the other of which mimics uridine (U). NHC-TP is not recognized as an error by the virus&#39; proofreading exonuclease enzymes, which can replace mutated nucleotides with corrected versions. When the viral RNA polymerase attempts to copy RNA containing molnupiravir, it sometimes interprets it as C and sometimes as U. This causes more mutations in all downstream copies than the virus can survive, an effect called viral error catastrophe or lethal mutagenesis.</p>