NPS-2143 (SB-262470A), an orally active calcilytic agent, is a selective and potent calcium ion-sensing receptor (CaSR) antagonist. NPS-2143 (SB-262470A) blocks increases in cytoplasmic Ca2+ concentrations (IC50=43 nM) elicited by activating the Ca2+ receptor in HEK 293 cells expressing the human Ca2+ receptor[1][2].