COVID-19 antivirals: nirmatrelvir/ritonavir, molnupiravir and favipiravir

These are antiviral medicines used once someone already has COVID-19, to lower the chance of severe illness. They do not prevent infection.

The US Paxlovid and Lagevrio documents both say the medicine is not approved or authorized for pre-exposure or post-exposure prevention.

This is general information from official documents, not personal medical advice.

The US label (revised 02/2026) covers mild-to-moderate COVID-19 in adults at high risk of progressing to severe disease, including hospitalization or death.

The label dose is nirmatrelvir 300 mg with ritonavir 100 mg twice daily for 5 days, with reduced doses for reduced kidney function.

The most common reactions listed are altered taste (5%) and diarrhea (3%).

The shop lists ComboVir, described as a nirmatrelvir plus ritonavir pair. This article uses the Paxlovid label only as a reference. For pack and label details of any brand, follow the leaflet inside the box.

Ritonavir inhibits the CYP3A enzyme and can raise the blood levels of other medicines. The label says some interactions are serious or fatal. Medicines it contraindicates include lovastatin, simvastatin, triazolam, oral midazolam, ergot derivatives and some heart-rhythm drugs (amiodarone, flecainide, propafenone, quinidine).

So a doctor or pharmacist should review everything you take, including herbal products and supplements, first.

The label also warns that people with untreated or undiagnosed HIV-1 can develop resistance to HIV protease inhibitors.

The FDA emergency use fact sheet (revised 06/2024) authorizes it for adults with mild-to-moderate COVID-19 at high risk of severe disease, when other authorized treatments are not accessible or clinically appropriate.

The dose in the document is 800 mg (four 200 mg capsules) every 12 hours for 5 days, started within 5 days of symptoms. It is not authorized under 18, because it may affect bone and cartilage.

Common reactions are diarrhea, nausea and dizziness.

The shop lists Moluzaq-200. The Lagevrio document is a reference only. Brand details come from the leaflet inside the box.

The reference document is the Avigan 200 mg package insert published by Japan's PMDA. It lists two uses: novel or re-emerging influenza when other antivirals are ineffective, and SFTS.

Its main caution: do not use in pregnancy or possible pregnancy. Animal studies showed early embryo loss and birth defects. Women who could become pregnant need a pregnancy test first and effective contraception during treatment and for 10 days after.

Reported effects include raised uric acid, diarrhea and raised liver enzymes. Interacting medicines include pyrazinamide, repaglinide and theophylline.

The shop lists Feravir-400, which its maker lists at 400 mg. This article does not confirm that brand's uses or dose. Follow its own leaflet.

• Molnupiravir: not recommended in pregnancy. People who could become pregnant should use contraception during treatment and for 4 days after the last dose. Sexually active men with partners who could become pregnant should use contraception during treatment and for at least 3 months after. Breastfeeding is not recommended during treatment or for 4 days after.
• Favipiravir: contraindicated in pregnancy per the Japanese leaflet.
• Nirmatrelvir/ritonavir: the label says pregnancy data are insufficient. Ask a doctor.

The Paxlovid label says to start as soon as possible after diagnosis and within 5 days of symptom onset. The Lagevrio document also says within 5 days. Past that window, ask a doctor.

• Before taking any of them, to check whether you are in a high-risk group and whether your current medicines clash.
• If you are pregnant, planning a pregnancy or breastfeeding.
• If you have liver or kidney disease, or past drug allergies.
• Trouble breathing, chest pain, confusion or worsening illness: go to a hospital straight away.