COVID-19 Antiviral — RNA Polymerase Mutagenic Agent 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.

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 independently re-sourced from US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — clinician-reviewed. 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

It is metabolised to a ribonucleoside analogue that is incorporated into viral RNA by the SARS-CoV-2 RNA-dependent RNA polymerase, introducing errors that accumulate and render the virus non-viable.

Prescribing in practice

It is not recommended in pregnancy and effective contraception is advised during and for a short period after treatment, as animal data raise a concern about harm to the developing fetus.
It should be started promptly within a defined early window after symptom onset, since benefit depends on early administration.
It is not authorised for or shown to benefit those requiring hospitalisation for severe COVID-19, nor for pre- or post-exposure prophylaxis.

Monitoring

Routine laboratory monitoring is not generally required for a short course; review pregnancy status and contraception before prescribing.

Counselling the patient

Start the course as soon as possible after diagnosis and complete the full treatment.
Use reliable contraception during and shortly after the course and tell your team if you could be pregnant.
Seek urgent help if your symptoms worsen or you become breathless.

Evidence & guidelines

Use derives from the MOVe-OUT trial in at-risk outpatients and reflects MHRA authorisation and NICE guidance on COVID-19 treatments.

Reference: Jayk-Bernal et al. NEJM 2022 (MOVe-OUT); NICE TA871; MHRA SPC Lagevrio; 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).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways