Potent and highly selective antagonist for the human adenosine A3 receptor, with low affinity for the rat A3 receptor (Ki values are 0.44 and > 17000 nM respectively). Displays > 3800-fold selectivity over human A1, A2A and A2B receptors (Ki values are 4.1, 3.3 and 30 μM respectively) and > 1800-fold selectivity over rat A1 and A2A receptors. Acts as an inverse agonist in the [35S]GTPγS binding assay in hA3-CHO cells (IC50 = 4 nM). Produces thermal hyperalgesia in mice in vivo.