High affinity P-glycoprotein (P-gp) inhibitor (Ki values are 58 and 94 nM for mouse Pgp1a and Pgp1b isoforms). Inhibits calcein-AM uptake in MDR1-transfected MDCKII cells (IC50 = 0.5 μM) and prazosin transport in BCRP-transfected MDCKII cells (IC50 = 1.5 μM). Displays weak or no inhibitory activity against MRP1, OATP1B1 and several major human P450 enzymes (IC50 > 50 μM).