Potent and selective antagonist for the human adenosine A3 receptor, with low affinity for the rat A3 receptor (Ki values are 2.3 and > 10000 nM respectively). Displays > 1000-fold selectivity over human A1 and A2A receptors (Ki values are 4.1 and 3.3 μM respectively) and > 180-fold selectivity over rat A1, rat A2A and mouse A2B receptors. Acts as an inverse agonist in the [35S]GTPγS binding assay in hA3-CHO cells (IC50 = 36 nM).