AR-A 2 is a selective 5-HT1B receptor antagonist, with a high affinity to guinea pig cortex 5HT1B1D and recombinant guinea pig 5-HT1B receptors (Ki: 0.24 and 0.47 nM) and with 10-fold lower affinity to guinea pig 5-HT1D receptor (Ki: 5 nM).
Alniditan is a receptors agonist of 5-HT1B1D in HEK 293 cells (IC50: 1.7 and 1.3 nM). For 5-HT1B1D receptors, the pKi values are 8.96 and 9.40, respectively.