Potent, selective GABAB receptor antagonist (IC50 = 5 nM) that prevents agonist binding (pKi = 8.35) and inhibits GABA and glutamate release (pEC50 values are 8.08 and 7.85 respectively). Inhibits GABAB responses to baclofen (IC50 = 130 nM in an isoproterenol assay) and potentiates the hypoglycemic response to glucose in vitro.