Acute schizophrenia: Vabicaserin 200 or 400 mg/day. Vabicaserin demonstrated efficacy on primary and secondary endpoints at 200 mg/day, but not at 400 mg/day which showed a trend for efficacy. The 200 mg/day vabicaserin group achieved proof of concept using central ratings. Both vabicaserin doses were well tolerated with no significant safety signals and no weight gain.

Vabicaserin displaces 125I-(2,5-dimethoxy)phenylisopropylamine binding from human 5-HT2C receptor sites in Chinese hamster ovary cell membranes with a Ki value of 3 nM and is >50-fold selective over a number of serotonergic, noradrenergic, and dopaminergic receptors. Binding affinity determined for the human 5-HT2B receptor subtype using [3H]5HT is 14 nM. Vabicaserin is a potent and full agonist (EC50, 8 nM; Emax, 100%) in stimulating 5-HT2C receptor-coupled calcium mobilization and exhibits 5-HT2A receptor antagonism and 5-HT2B antagonist or partial agonist activity in transfected cells, depending on the level of receptor expression. Vabicaserin exhibits lower affinity at the 5-HT2C antagonist binding site (22 nM) labeled with [3H]mesulergine. Additional binding studies indicate that Vabicaserin possesses affinity for the 5-HT2B and 5-HT1A receptors with Ki values of 14 and 112 nM, respectively.