Cytochrome P450 (P450) is a superfamily of heme-thiolate enzymes that are ubiquitous in almost all biological systems. There are more than 35,000 P450 enzymes that have been isolated from all biological organisms, with exception of some primitive prokaryotes, such as Escherichia coli, which are believed to have emerged before the evolution of P450. Members of the same P450 family share ≥40% sequence homology, whereas members of the same P450 subfamily share ≥55% sequence homology. In humans, there are 18 P450 families comprised of 60 P450 enzymes, of which the majority is microsomal P450 belong to CYP2, CYP3 and CYP4 families. P450-mediated metabolism plays a critical role determining the onset and duration of drug action. Hepatic microsomal P450 enzymes, typically CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C18, CYP2C19, CYP2D6, CYP2E1 and CYP3A4, determine how much will be the half-life in the body for most of drugs.


1.El-Sherbeni AA, El-Kadi AO. Drug Metab Rev. 2017;49(1):1–17.