A serious drawback of Nirmatrelvir is that it metabolizes too quickly in the liver . The cytochrome P450 class (aka CYP ###: gene family, subfamily, isoform/individual type) of enzymes is common, occurring in different species and contain a heme iron network that makes them function as oxygenases . There are 57 encodings for CYPs in the human body, of which 6 are liver enzymes: CYP 1A2, 2C9, 2C19, 2D6, 2E1, 3A4, some of which are also found in the abdominal gut, and estimated to account for 80% of drug metabolism. These enzymes are the main source of metabolism and excretion of drugs in the human body. These, primarily CYP 3A4, eliminate Nirmatrelvir from the body and reduce the plasma concentration in the bloodstream.