ATP-binding cassette sub-family B member 1 (P-glycoprotein) and Cytochrome P450 family 3 subfamily A member 4 (CYP3A4) (P-gp and CYP3A4)

P-glycoprotein (P-gp) and Cytochrome P450 3A4 (CYP3A4) represent a fundamental biochemical barrier to drug absorption and a major determinant of systemic drug exposure. P-gp, encoded by the ABCB1 gene, is an ATP-binding cassette transporter that actively pumps a wide range of hydrophobic compounds out of cells, while CYP3A4 is the most prevalent hepatic and intestinal enzyme involved in the oxidative metabolism of xenobiotics. These two proteins are frequently co-expressed in the apical membranes of enterocytes and the canalicular membranes of hepatocytes, where they share overlapping substrate specificities and regulatory pathways, such as the pregnane X receptor (PXR). This "efflux-metabolism alliance" is particularly effective in the small intestine, where P-gp-mediated recycling of drugs back into the lumen allows for multiple passes through the CYP3A4 metabolic machinery, significantly reducing oral bioavailability. Beyond their role in normal physiology and pharmacokinetics, the over-expression of P-gp is a hallmark of multidrug resistance (MDR) in various cancers, enabling malignant cells to survive exposure to diverse chemotherapeutic agents. Consequently, this dual system is a primary focus for predicting and managing drug-drug interactions, as the inhibition or induction of either component can lead to profound changes in the safety and efficacy of co-administered medications.

Other names

ABCB1MDR1Multidrug resistance protein 1CYP3A4Cytochrome P450 3A4P-gpATP-binding cassette sub-family B member 1

Drugs interact with this dual system through competitive or non-competitive inhibition and induction of expression, often mediated by the pregnane X receptor (PXR). P-glycoprotein functions as an ATP-dependent efflux pump that extrudes substrates from the cytoplasm or cell membrane back into the extracellular space or intestinal lumen. Cytochrome P450 3A4 performs oxidative metabolism (Phase I), typically via monooxygenation. In the intestine, P-gp-mediated efflux increases the residence time of drugs in the enterocyte, facilitating repeated exposure to CYP3A4 and thereby enhancing first-pass metabolism.