PXR

Nuclear receptor (NR1I2) activated by xenobiotics that regulates expression of metabolic enzymes (CYP3A4, CYP2C9) and transporters (P-gp, MRP2). It is the cellular "sensor" of drugs and the master inducer of CYP3A4.

Drugs that activate PXR (e.g. rifampicin, carbamazepine, phenytoin) increase transcription of CYP3A4 and other targets, lowering concentrations of multiple substrates — the mechanism behind rifampicin's multiple drug interactions.

Rifampicin is the most potent PXR inducer and can reduce efficacy of immunosuppressants, anticoagulants, antiretrovirals and many others — requires dose adjustment or alternative.