An adenosine A2B receptor antagonist (Ki = 53.4 nM); selective for A2B over A1 and A2A receptors, which have Ki values of 2,200 and 24,000 nM, respectively; selective for A2B over the A3 receptor, which is inhibited only 14% at a concentration of 10 μM; pre-treatment of rat trachea reduces relaxation induced by repeated dosing of the non-selective adenosine agonist NECA