PXR (Pregnane X Receptor) is a member of the nuclear receptor family that regulates the expression of genes involved in drug metabolism and clearance. It is primarily expressed in the liver and intestines, where it activates the transcription of downstream target genes by sensing a wide range of exogenous and endogenous compounds. Activation of PXR affects the expression of various drug metabolism enzymes and transport proteins, playing a role in drug metabolism, toxic responses, and drug-drug interactions. Genetic variations can influence PXR activity, thereby affecting an individual's drug metabolism capacity and the efficacy of drug treatment.