<prompt> Which of the following drugs is not an inhibitor of P - glycoprotein?QuinidineErythromycinVerapamilPhenobarbitone  <response>: Ans. is d i.e., Phenobarbitone P-glycoprotein P-glycoprotein P gp is a product of multidrug resistance 1 gene ABCB1. P-glycoprotein plays an important role in pharmacokinetics of drugs. P-glycoprotein is an ATP-binding cassette ABC transporter and is an important factor to limit membrane permeability in several tissues andor elimination pathways into urine renal tubles and bile liver. P-glycoprotein has following effects on drugs which are substate for P-gp-i Decreasing the absorption of drugs and toxins in intenstine by efflux transport from enterocyts, i.e., exsorption of drug.ii Decreasing the distribution of drug in brain by efflux transport at BBBiii Excretion of drug by kidney renal tubular secretion and liver secretion into bileiv Multiple drug resistance of a cancer by export explusion of anticancer drugs from the cells. It is worth noting that in the intestine enterocytes both P-glycoprotein and CYP3A4 A drug metabolizing enzyme also present in liver are found. Both of these have same effect, i.e., decreasing the absorption of drug.i P-glycoprotein - by efflux of drug from enterocytes into the lumen.ii CYP3A4 - by metabolizing the drug into the enterocytes, so that less drug is available for absortion into the circulation. Some drugs are substrate for both CYP3A4 and P-gp. Examples :i CCBs: Verapamil, diltiazamii Anticancer drugs: Etoposide, daunorubicin, doxorubicin, paclitaxel, vincrisitineiii Antimicrobials: HIV protoease inhibitors indinavir, ritonavir, erythromycin, ketoconazoleiv Immunosuppressants: Cyclosporine, tacrolimus, sirolimus.v Other: Digoxin, fexofenadine, loperamideInibitors of P - glycoprotein Verapamil Quinidine ErythromycinInducers of P - glycoprotein Phenobarbitone Rifampicin 