Nupiravir

Molnupiravir stops a virus from multiplying by causing widespread mutations as the viral RNA is copied by RNA-directed RNA polymerase. The body metabolizes it into a ribonucleoside analog that resembles cytidine, called β-D-N 4-Hydroxycytidine 5′-triphosphate (also known as EIDD-1931 5′-triphosphate or NHC-TP). When the virus replicates, its enzyme builds NHC-TP into the newly made RNA in place of real cytidine.

Molnupiravir can switch between two forms (tautomers). One form mimics cytidine (C) and the other mimics uridine (U). The virus's proofreading exonuclease enzymes, which can replace mutated nucleotides with corrected ones, don't recognize NHC-TP as an error. So when the viral RNA polymerase copies RNA that contains molnupiravir, it reads it as C at times and as U at other times. This causes more mutations in all the downstream copies than the virus can survive, an effect called viral error catastrophe or lethal mutagenesis.

Animal studies with molnupiravir have shown harmful effects on the unborn animal, and the medicine has not been studied in pregnancy. So nobody knows whether it will harm your baby if you take it while pregnant. For this reason, molnupiravir is not recommended in pregnancy. If you are pregnant, think you may be pregnant, or are planning to have a baby, ask your doctor for advice.

If you can become pregnant, use effective birth control while you are taking molnupiravir and for 4 days after the last dose.

If you are breast-feeding or are planning to breastfeed, tell your doctor before you take this medicine. Breast-feeding is not recommended during treatment and for 4 days after the last dose of molnupiravir. This is because it is not known if molnupiravir gets into breast milk and passes to the baby.

Store Molnupiravir at or below 25°C. Keep it away from light and from damp places. Keep it out of the reach of children.