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Nirmatrelvir and Ritonavir Tablets (Paxlovid)

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The FDA has issued an emergency use authorization (EUA) for the oral combination of nirmatrelvir and ritonavir (NIR/RIT) to treat mild-to-moderate COVID-19. 1 NIR is an oral antiviral SARS-CoV-2 protease inhibitor (Mpro), and RIT slows CYP3A-mediated metabolism of nirmatrelvir. It is distributed as Paxlovid.

INDICATIONS

NIR/RIT can be prescribed to treat mild-to-moderate COVID-19 in patients age 12 years and older weighing at least 40 kg with positive results of direct SARS-CoV-2 testing who are at high risk for progression to severe COVID-19, including hospitalization or death. 1 NIR/RIT is not indicated for pre-exposure or post-exposure prevention of COVID-19. It also is not indicated for COVID-19 patients requiring hospitalization. 2 NIR/RIT is not a substitute for vaccination.

DOSAGE

The dose is 300 mg of NIR (2 × 150 mg) with 100 mg of RIT taken together orally twice daily (morning and evening) for five days. The regimen should be taken as soon as possible after diagnosis of COVID-19 and within five days of symptom onset. 1 It may be taken without regard to meals. NIR/RIT is available as five daily blister cards each containing four NIR tablets and two RIT tablets.

POTENTIAL ADVANTAGES

NIR/RIT is the first oral regimen for the treatment of COVID-19 and can be taken at home. Previous EUAs for this indication were monoclonal antibodies (e.g., casirivimab/imdevimab and bamlanivimab/etesevimab), which require intravenous infusion. In contrast to the monoclonal antibodies that target the spike protein, which has been identified with multiple mutations/variants, NIR targets the Mpro in SARS-CoV-2 that seems to be variant-independent. Cell culture data showed similar activity against alpha, beta, gamma, delta, and lambda variants. 1 Biochemical assay results suggest NIR/RIT also is effective against the omicron variant. 1

POTENTIAL DISADVANTAGES

Coadministration with potent CYP3A inducers is contraindicated. It also is contraindicated with drugs that are highly dependent...