Cytochrome P450 family 3 subfamily A (CYP3A) (CYP3A)

The Cytochrome P450 family 3 subfamily A (CYP3A) is a critical group of heme-thiolate monooxygenases responsible for the oxidative metabolism of approximately 50% of marketed drugs (Zanger & Schwab, 2013). These enzymes are predominantly expressed in the liver and the epithelial lining of the small intestine, where they serve as a major barrier to the systemic bioavailability of orally administered xenobiotics (StatPearls, 2023). The subfamily consists of four members—CYP3A4, CYP3A5, CYP3A7, and CYP3A43—with CYP3A4 being the most prevalent in adults (UniProt, 2024). Beyond drug metabolism, CYP3A isoenzymes play vital roles in the biotransformation of endogenous substrates such as testosterone, progesterone, and bile acids (NIH, 2022). Due to their broad substrate promiscuity, they are frequently involved in clinically significant drug-drug interactions, where inhibitors or inducers can drastically alter the pharmacokinetics of co-administered medications (PubChem, 2024). Furthermore, genetic polymorphisms and environmental factors contribute to high inter-individual variability in CYP3A activity, necessitating careful dose adjustment for drugs with narrow therapeutic windows (PubMed, 2021).

Other names

CYP3A4CYP3A5CYP3A7CYP3A43Cytochrome P450 3ACYP3A enzymes

Drugs interact with CYP3A isoenzymes as substrates for oxidative biotransformation, as competitive or mechanism-based inhibitors that reduce catalytic activity, or as inducers that increase enzyme expression via nuclear receptor activation, primarily the Pregnane X Receptor (PXR) and Constitutive Androstane Receptor (CAR) (Guengerich, 2008; PubChem, 2024).