Molnupiravir is a
prodrug of the synthetic
nucleoside derivative N4-hydroxy
cytidine and exerts its antiviral action by introducing copying errors during viral RNA replication.[13][14]
Molnupiravir was originally developed to treat
influenza at
Emory University by the university's drug innovation company, Drug Innovation Ventures at Emory (DRIVE), but was reportedly abandoned for
mutagenicity concerns.[15][16] It was then acquired by Miami-based company
Ridgeback Biotherapeutics, which later partnered with
Merck & Co. to develop the drug further.[17]
Based on positive results in
placebo-controlled double-
blind randomized clinical trials,[18][19] molnupiravir was approved for medical use in the United Kingdom in November 2021.[7][20][21][22] In December 2021, the US
Food and Drug Administration (FDA) granted an
emergency use authorization (EUA) to molnupiravir for use in certain populations where other treatments are not feasible.[10] The emergency use authorization was only narrowly approved (13-10) because of questions about efficacy and concerns that molnupiravir's mutagenic effects could create new variants that evade immunity and prolong the
COVID‑19 pandemic.[23][24][25] In September 2023, molnupiravir's mutagenicity was confirmed in a study of global SARS CoV 2 isolates after 2022: genomic changes were more common, especially where molnupiravir had been used.[26]
Medical uses
In the UK, molnupiravir is
indicated for treatment of mild to moderate COVID‑19 in adults with a positive SARS-COV-2 diagnostic test and who have at least one risk factor for developing severe illness.[7]
In the US molnupiravir is unapproved but is authorized under an EUA for emergency use for the treatment of adults with mild-to-moderate COVID‑19 who are at
high risk for progression to severe COVID‑19, including hospitalization or death, and for whom alternative COVID‑19 treatment options approved or authorized by FDA are not accessible or clinically appropriate.[9][10][12]
Contraindications
Use during pregnancy is not recommended.[4] There are no human data on use during pregnancy to assess the risk of adverse maternal or fetal outcomes.[4] Based on animal data, the drug may cause fetal harm.[4]
Adverse effects
Adverse reactions observed in the phase III MOVe-OUT study included
diarrhea (2%),
nausea (1%) and
dizziness (1%), all of which were mild or moderate.[12]
In rats, bone and cartilage toxicity was observed after repeated dosing.[12]
Overdose
The effects of overdose are unknown, treatment consists of general supportive measures such as monitoring of clinical status.[12]
Drug interactions
Based on limited available data, there are no drug interactions.[12]
Mechanism of action
Molnupiravir inhibits viral reproduction by promoting widespread mutations in the replication of viral RNA by RNA-directed
RNA polymerase.[27] It is metabolized into a
ribonucleoside analog that resembles
cytidine, β-D-N4-hydroxy
cytidine 5′-triphosphate (also called EIDD-1931 5′-triphosphate or NHC-TP).[28][29][30] During replication, the virus's enzyme incorporates NHC-TP into newly made
RNA instead of using real cytidine.[30]
Molnupiravir can swap between two forms (
tautomers), one of which mimics cytidine (C) and the other
uridine (U).[31] NHC-TP is not recognized as an error by the virus's proofreading
exonuclease enzymes, which can replace mutated nucleotides with corrected versions.[27] 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.[31]
The
international nonproprietary name of the drug was inspired by that of
Thor's hammer,
Mjölnir. The idea is that the drug will strike down the virus like a mighty blow from the god of thunder.[30]
In March 2020, the research team pivoted to studying
SARS-CoV-2, and successfully used molnupiravir to treat human cells infected with the novel coronavirus.[33][unreliable medical source?] A study found that it is orally active against SARS-CoV-2 in ferrets.[34]
DRIVE then licensed molnupiravir for human clinical studies to Miami-based company Ridgeback Biotherapeutics, which later partnered with
Merck & Co. to develop the drug further.[33][17]
The primary data supporting the US
Food and Drug Administration (FDA)
emergency use authorization for molnupiravir are from MOVe-OUT, a randomized, double-blind, placebo-controlled clinical trial studying molnupiravir for the treatment of non-hospitalized participants with mild to moderate COVID‑19 at high risk for progression to severe COVID‑19 and/or hospitalization.[10][35] Participants were adults 18 and older with a pre-specified chronic medical condition or at increased risk of SARS-CoV-2 infection for other reasons who had not received a COVID‑19 vaccine.[10] The main outcome measured in the trial was the percentage of people who were hospitalized or died due to any cause during 29 days of follow-up.[10] Of the 709 people who received molnupiravir, 6.8% were hospitalized or died within this period compared to 9.7% of the 699 people who received a placebo.[10]
In November 2022, the British
National Institute for Health and Care Excellence decided molnupiravir should not be routinely used to treat COVID‑19, as research showed it made no significant difference to hospitalization or death rates and was not cost effective.[36] The drug was added to its "not recommended" list in draft COVID‑19 treatment guidance for consultation.[37][36]
Society and culture
Economics
In September 2021, Merck signed a voluntary licensing agreement with the
Medicines Patent Pool (MPP) that allows MPP to sublicense molnupiravir and supply the COVID‑19 oral medication to 105 low- and middle-income countries. The cost of the US government's initial purchase was about $712 per course of treatment; treatment with generics in developing countries can cost as little as $20.[38][39]
Sales of molnupiravir were $952 million in the fourth quarter of 2021.[40]
Legal status
In October 2021, Merck submitted an EUA application to the FDA, and in November 2021, the FDA's Antimicrobial Drugs Advisory Committee (AMDAC) at the
Center for Drug Evaluation and Research met to discuss the application.[41][42] The committee narrowly voted, 13 for and 10 opposed, to recommend authorization for adults with mild to moderate illness who are at high risk of developing severe COVID‑19.[43] Concerns were expressed over the drug's low effectiveness in preventing death, which in the final trial was only 30%, as well as the increased mutation rate the drug causes, which could theoretically worsen the pandemic by driving the evolution of more dangerous variants.[43][16] In December 2021, the US
Food and Drug Administration (FDA) issued an
emergency use authorization (EUA) for molnupiravir for the treatment of mild-to-moderate COVID‑19 in adults with positive results of direct SARS-CoV-2 viral testing who are at high risk for progression to severe COVID‑19, including hospitalization or death, and for whom alternative COVID‑19 treatment options authorized by the FDA are not accessible or clinically appropriate.[10]
In November 2021, molnupiravir was approved in the UK by the
Medicines and Healthcare products Regulatory Agency (MHRA) for the treatment of established infections of COVID‑19.[7] The MHRA issued a conditional marketing authorization applicable in the UK, and an emergency use authorization for Northern Ireland.[7][20][47][48]
At a November 2021 AMDAC meeting, multiple advisors raised the concern that molnupiravir could accelerate the emergence of
variants of concern.[57][58] Other scientists raised similar concerns both before and after the meeting.[59][25][60][24] These concerns were confirmed with the September 2023 publication of a study of 15 million global SARS-CoV-2 sequences: after molnupiravir had been introduced in 2022, genomic changes were more common, especially where it had been used.[26]
Research
Alternative patented routes to molnupiravir have been reviewed.[61]
COVID-19 clinical trial
In October 2021, preliminary results from a clinical trial (MOVe-OUT)[62][63][full citation needed] indicated that treatment with molnupiravir may reduce the risk of hospitalization and death from COVID‑19.[64][65] The final analysis reported a 30% reduction in hospitalizations and deaths.[18][66]
Since December 2021, the
PANORAMIC trial has been testing molnupiravir's effectiveness.[67][68] Results showed that for higher risk, vaccinated adults molnupiravir does not reduce the chances of hospitalisation and death. However it results in faster recovery and reduced
viral load.[69][70]
In February 2023, Merck reported that the phase III MOVe-AHEAD trial to evaluate the safety and efficacy of Lagevrio compared to placebo in preventing the spread of SARS-CoV-2 within households did not meet its primary endpoints. With more than 1,500 participants who were free of COVID‑19 and lived with someone who was recently diagnosed with the virus, patients treated with Lagevrio were 23.6% less likely than those on placebo to develop COVID after 14 days.[71][72][73]
^
abUS application 20200276219, Painter GR, Bluemling GR, Natchus MG, Guthrie D, "N4-hydroxycytidine and derivatives and anti-viral uses related thereto", published 2020-09-03, assigned to Emory UniversityArchived 5 October 2021 at the
Wayback Machine
^World Health Organization (2021). "International nonproprietary names for pharmaceutical substances (INN): recommended INN: list 85". WHO Drug Information. 35 (1).
hdl:10665/340684.
^World Health Organization (2022). "International nonproprietary names for pharmaceutical substances (INN): recommended INN: list 87". WHO Drug Information. 36 (1).
hdl:10665/352794.
^Wruhs O (1986). "[Comparative study of stability following the nailing of fractures of the femur shaft. An experimental study with cadaver bones]". Wiener Klinische Wochenschrift. Supplementum (in German). 169: 3–16.
PMID3464133.
^Clinical trial number NCT04575597 for "Efficacy and Safety of Molnupiravir (MK-4482) in Non-Hospitalized Adult Participants With COVID-19 (MK-4482-002)" at
ClinicalTrials.gov