This substance, also known as Lagevrio, is an analogue of the ribonucleoside cytidine, but with a
hydroxy group substituting one of the hydrogens on the exposed amino group of
cytosine, and a
methylpropanoate group attached to the
ribose at position 5'.
It is a 'pro-drug' which inside the body cells is converted into (the ribonucleotide) N4-hydroxycytidine triphosphate by the substitution of the methylpropanoate group with (three) phosphate groups, prior to being incorporated into viral RNA. It can take on different molecular forms (tautomers), one being an
oxime replacing the hydroxylamine -
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When this RNA is copied, the viral enzyme RNA dependent RNA polymerase sometimes reads the modified base as if it was uracil, and so effectively creates a mutation, resulting in RNA containing U rather than C, and each replication will add to the mistranscription as long as the drug is present.
The altered RNA potentially codes for ineffective viral proteins, and this breaks the cycle of viral infection.
It was developed by the US drug companies Merck, Sharp and Dohme (MSD) and Ridgeback Biotherapeutics.
Initial tests suggested it can halve hospitalisations and deaths due to COVID-19, but later this factor was reduced to 30%.
In the UK it has been authorised for use in people who have mild to moderate COVID-19 and at least one risk factor for developing severe illness (obesity, age over 60 years, diabetes mellitus, or heart disease), but based on less optimistic test data France has decided not to proceed with this product.
It is the first antiviral medication for Covid which can be taken orally as a pill or capsule rather than being injected.
For maximum effectiveness it needs to be given within five days of the development of COVID symptoms.
Molnupiravir was approved in the UK in November 2021 as a treatment for COVID-19, and initially 480,000 courses of treatment have been purchased.
U.S. Food and Drug Administration issued an emergency use authorization (EUA) for it in December 2021,