AR-A 2 is a selective 5-HT1B receptor antagonist, with a high affinity to guinea pig cortex 5HT1B 1D 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).
SB 243213 dihydrochloride is an orally active, selective and high-affinity antagonist of 5-hydroxytryptamine (5-HT)2C receptor(pKi of 9.37 and a pKb of 9.8 for human 5-HT2C receptor).