MK-4409

MK-4409, also known as molnupiravir, is an orally bioavailable antiviral drug. It was developed initially to treat influenza and later repurposed as a potential treatment for COVID-19. Molnupiravir functions by introducing errors into the viral RNA code, which inhibits replication of the virus.

The drug is a ribonucleoside analog and is metabolized in the body to its active form, NHC (N4-hydroxycytidine). NHC is incorporated into the viral RNA by the viral RNA polymerase, leading to mutations and ultimately, the inhibition of viral replication.

Molnupiravir has been authorized for emergency use or conditional approval in several countries for the treatment of mild-to-moderate COVID-19 in adults who are at high risk of progressing to severe disease. The authorization is often conditional due to concerns regarding its efficacy and safety profile compared to other treatments.

Studies on molnupiravir's efficacy have shown varying results. Some studies indicate a significant reduction in hospitalization and death in high-risk patients when administered early in the course of infection. However, other studies have demonstrated lower efficacy, especially against newer variants of the virus.

Potential safety concerns associated with molnupiravir include potential mutagenic effects, although this has been debated. Regulators have generally limited its use to specific high-risk populations due to these concerns. The long-term effects of molnupiravir are still under investigation.

The drug is generally administered as a course of oral capsules over a period of several days, typically five days. Prescribing guidelines vary depending on the country and the specific regulatory authorization in place.