PGP and breast carcinoma: Cyclosporin A is an inhibitor of P-gp, multidrug resistance-associated protein 2, and the organic anion transporter protein-C; elacridar inhibits the P-gp and breast cancer-resistant protein transporters, and verapamil inhibits several organic cation transporters in addition to the P-gp transporter (US Department of Health and Human Services, 2006).