​Paxlovid is a combination of two drugs that must be taken together: Nirmatrelvir, which blocks an enzyme needed for the SARS-CoV-2 virus to reproduce, and ritonavir, a commonly used HIV treatment. In the Paxlovid combination, ritonavir slows the breakdown of nirmatrelvir so it works longer. The three pills must be taken twice a day for five consecutive days.