Elacridar hydrochloride is primarily used as a potent inhibitor of P-glycoprotein and breast cancer resistance protein (BCRP). Its main application lies in enhancing the efficacy of chemotherapeutic drugs by overcoming multidrug resistance in cancer cells. By blocking these efflux transporters, it increases the intracellular concentration of anticancer agents, making them more effective. It is often used in preclinical and clinical research to study drug resistance mechanisms and to improve the delivery of drugs that are typically expelled by these proteins. Additionally, it has potential applications in improving the bioavailability of certain drugs that are substrates of P-glycoprotein or BCRP, particularly in the treatment of brain tumors and other cancers where drug penetration is a challenge.