A P2X3 and P2X2/3 receptor antagonist (Kis = 22-92 nM in a calcium influx assay); selective over other purinergic and neurotransmitter receptors, ion channels, and enzymes (IC50s = >10 μM); reduces thermal hyperalgesia induced by complete Freund's adjuvant in rats (ED50 = 30 μmol/kg, s.c.) and nociceptive responses to chemically-induced pain; chronic administration reduces early, but not late, phase pain in a mouse model of bone cancer; does not readily cross the blood-brain barrier and reduces pain responses when applied topically,