Rhône-Poulenc discovered the compound RP-67580, which has high affinity for the NK1 receptor in rats and mice, but not in humans. SAR studies that were performed in order to improve the selectivity for the human NK1 receptor resulted in the development of a compound called RPR-100893. This compound showed good activity in vivo and in models of pain and was developed up to phase II for the treatment of migraines but then terminated, as was the case with other NK1 receptor antagonists that were tested for the same indication.