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SARS-CoV-2 RNA polymerase inhibitor Pregnancy: US label §8.1/§5.1: based on animal data, molnupiravir may cause fetal harm when administered to pregnant individuals and it is NOT recommended during pregnancy. There are no available human data to evaluate the risk of major birth defects, miscarriage or adverse maternal or fetal outcomes. In animal reproduction studies, oral molnupiravir given to pregnant rats during organogenesis produced embryofetal lethality and teratogenicity at 8 times the human NHC exposure at the recommended human dose and reduced fetal growth at 3 times or more that exposure; in rabbits it reduced fetal body weights at 18 times the human NHC exposure. If molnupiravir is considered for a pregnant individual, the prescriber must communicate and document the known and potential benefits and risks. Individuals of childbearing potential should be advised of the potential risk to a fetus and to use effective contraception correctly and consistently. A pregnancy registry monitors outcomes after exposure.

Molnupiravir

Brand names: Lagevrio

Molnupiravir is an oral antiviral prodrug used for the treatment of mild to moderate COVID-19 in adults at increased risk of progression to severe disease.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 800 mg (four 200 mg capsules) every 12 hours for 5 days
Route: Oral - taken with or without food; may also be given via NG, OG or gastrostomy tubes that are 12F or larger, or via gastrojejunostomy tubes that are 14F or larger
Frequency: Every 12 hours
Max: Not authorised for use for longer than 5 consecutive days, because the safety and efficacy of a longer course have not been established
US label §2.1 (LAGEVRIO 200 mg capsules, Merck Sharp & Dohme - authorised for EMERGENCY USE in adults; no UK SPC was captured in this bundle, so the clinician must verify against the UK product information). TIMING: take as soon as possible after a diagnosis of COVID-19 has been made, and within 5 days of symptom onset. Completion of the full 5-day treatment course and continued isolation in accordance with public health recommendations are important to maximise viral clearance and minimise transmission of SARS-CoV-2. MISSED DOSE: if a dose is missed within 10 hours of the time it is usually taken, take it as soon as possible and resume the normal schedule; if missed by more than 10 hours, skip the missed dose and take the next dose at the regularly scheduled time - do not double the dose. If a patient requires hospitalisation after starting treatment, they may complete the full 5-day course at the healthcare provider's discretion. TUBE ADMINISTRATION (§2.3): open four capsules and transfer the contents into a clean container with a lid, add 40 mL of water, put the lid on and shake to mix thoroughly for 3 minutes (contents may not fully dissolve; visible undissolved particulates are acceptable); flush the tube with 5 mL of water before administration, draw up the entire contents and administer immediately (via the gastric port if a GJ tube); rinse any residue with 10 mL of water and administer; flush the tube with 5 mL of water twice (10 mL total) afterwards. Do not keep the mixture for future use. PAEDIATRIC (§8.4): NOT authorised for use in patients less than 18 years of age - bone and cartilage toxicity were observed in a 3-month repeat-dose toxicology study in rats and safety and efficacy have not been established in paediatric patients. Verify any under-18 use against a children's formulary. ELDERLY (§8.5): no dosage adjustment is recommended based on age.

Dose adjustments

Renal

US label §2.2: no dosage adjustment is recommended based on renal or hepatic impairment, or in geriatric patients.

Dose auto-extracted from US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • US label §4: no contraindications have been identified based on the limited available data on the emergency use authorised under this EUA

Side effects

  • The US label §6.1 captured in this bundle describes the MOVe-OUT Phase 3 safety analysis (710 subjects treated with molnupiravir vs 701 placebo) but the tabulated list of individual adverse reactions was truncated in the fetched text - the clinician must review §6.1 in full
  • Discontinuation of study intervention due to an adverse event occurred in 1% of subjects receiving molnupiravir and 3% of subjects receiving placebo (§6.1)
  • Serious adverse events occurred in 7% of subjects receiving molnupiravir and 10% of subjects receiving placebo (§6.1)
  • Embryo-fetal toxicity is the principal labelled risk (§5.1) - see pregnancy
  • The label warns that there are limited clinical data available and that serious and unexpected adverse events may occur that have not previously been reported (§5)

Interactions

  • US label §7: no drug interactions have been identified based on the limited available data on the emergency use authorised under this EUA; no clinical drug-drug interaction trials of molnupiravir with concomitant medications, including other treatments for mild-to-moderate COVID-19, have been conducted

Clinical monograph

How it works

Its active metabolite is incorporated into viral RNA by the SARS-CoV-2 RNA-dependent RNA polymerase, introducing copying errors (lethal mutagenesis) that impair viral replication.

Prescribing in practice

  • It is contraindicated in pregnancy because of potential foetal harm, and effective contraception is required for those of childbearing potential during and for a short period after treatment.
  • It should be started as soon as possible after a positive test and within the recommended early window from symptom onset to be effective.
  • It is not authorised for use in those under 18 because of possible effects on bone and cartilage growth.

Monitoring

No routine laboratory monitoring is required, but pregnancy status and contraception should be confirmed before prescribing.

Counselling the patient

  • Do not take this medicine if you are pregnant, and use reliable contraception as advised.
  • Start the course as early as possible after your positive test and complete the full course.

Evidence & guidelines

Authorisation followed the MOVe-OUT trial, and UK use is guided by MHRA conditional marketing authorisation and NICE recommendations.

Reference: UK COVID-19 therapeutic alerts; SmPC; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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