CYP3A, the most abundant p450 enzyme in human liver, is responsible for the metabolism of more than 50% of the clinical test & lt; RTI ID = 0.0 & gt; (cYP3A) genes encode monooxygenases-enzymes which catalyze drug metabolism and the synthesis of cholesterol, steroids and other lipids. CYP3A family members localize in organs that associate with drug disposition, including the liver, gastrointestinal tract and kidney. The CYP3A cluster maps to gene locus 7q22.1 and consists of four genes (CYP3A4, CYP3A5, CYP3A7 and CYP3A43) and two pseudogenes ( CYP3A4 is abundant in the endoplasmic reticulum of liver cells and upper intestinal enterocytes. CYP3A4 expression is isducible by glucocorticoids pharmacological agents.