Tariquidar dimesylate (XR9576 dimesylate) is a P-glycoprotein (P-gp) inhibitor. Tariquidar dimesylate increases the concentration of the drug in the brain by binding to P-glycoprotein , preventing it from transporting the drug from inside to outside the brain. Tariquidar dimesylate can be used in the study of blood-brain barrier penetration and multidrug resistance.