Gefapixant (AF-219, MK-7264, R1646, RG-1646, RO 4926219) is an orally active small molecule antagonist of human P2X3 receptor with IC50 of about 30 nM, 100–250 nM for recombinant hP2X3 homotrimers and hP2X2/3 heterotrimeric receptors, respectively. Gefapixant has shown promise for the treatment of refractory and unexplained chronic cough.