The Cytochrome P450 (P450) superfamily of enzymes is one of three enzyme systems which metabolize the fatty acid arachadonic acid (AA) to regulators of vascular tone. P450 enzymes are monooxygenase enzymes which require several cofactors such as nicotinamide adenine dinucleotide phosphate (NADPH) and P450 reductase. There are over 200 known genes which encode P450s. Epoxygenases are those P450s which metabolize AA to epoxyeicosatrienoic acid (EETs) and omega hydroxylases are those P450s which produce 19- and 20-hydroxyeicosatetraenoic acids (19- and 20-HETE). As well as fatty acid metabolism, P450s also metabolize many drugs and toxins. Cytochrome P450 3A4 is abundantly expressed in liver and small intestine and is inducible by barbiturates, glucocorticoids and rifampicin.