The aryloxy-pyrimidinediamine, Gefapixant (AF-219) is an orally active small molecule antagonist at human P2X3-containing receptors. The IC50 of Gefapixant has been reported as ~30 nM versus recombinant hP2X3 homotrimers and 100-250 nM at hP2X2/3 heterotrimeric receptors, potencies very similar to those reported for recombinant rat receptors, and it displays no inhibitory impact on any non-P2X3 subunit containing receptors (IC50 values>>10,000 nM at recombinant homotrimeric hP2X1, hP2X2, hP2X4, rP2X5 and hP2X7 channels).