Paxlovid™ (Nirmatrelvir/ritonavir) Why should Nirmatrelvir be used in combination with Ritonavir?

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Ritonavir is administered with Nirmatrelvir as a pharmacokinetic enhancer resulting in higher systemic concentrations of Nirmatrelvir.

Ritonavir is not active against the SARS-CoV-2 3CL protease. Ritonavir inhibits the CYP3A-mediated metabolism of Nirmatrelvir, thereby providing increased plasma concentrations of Nirmatrelvir.

In healthy participants, the mean half-life of a single dose of 150 mg Nirmatrelvir administered alone was approximately 2 hours compared to 7.5 hours after administration of a single dose of 250 mg/100 mg dose of Nirmatrelvir/ritonavir thereby supporting a twice‑daily administration regimen.