<prompt> Most common Cytochrome P450 involved in drug metabolism isCYP 3A4CYP 1AICYP 2E1CYP 2D6  <response>: Cytochrome P-450 CYP isoenzymes are grouped into families designated by numerals 1, 2, 3...; each having several sub-families designated by capita: letters A, B, C. ... , while individual isoenzymes are again allocated numerals 1, 2, 3 ... . In human beings, only a few, members of three isoenzyme families CYP 1, 2 and 3 carry out the metabolism of most of the drugs, The CYP isoenzyme: CYP3A45 Carryout biotransformation of largest number: nearly 50 of drugs. 20-30 of metabolism is done by the next common cyp2d6 In addition to liver, these isoforms are expressed in the intestine responsible for the first-pass metabolism at this site and kidney as well. Ref: KD Tripathi pharmacology 7th edition page.no: 24 