“…Because it isolates efflux processes directly rather than considering efflux as modulator of brain distribution, BEI is an excellent method for determining efflux clearance and studying the mechanisms behind active transport of compounds from the brain. This in vivo method has been extensively used to study the brain efflux clearance of various compounds, including steroid conjugates, valproic acid, nucleoside analogs, buprenorphine, human amyloid-b peptide, and benzylpenicillin and quinidine (Kusuhara et al, 1997;Takasawa et al, 1997;Sugiyama et al, 2001;Kakee et al, 2002;Ohtsuki et al, 2002;Kikuchi et al, 2003;Ito et al, 2006;Suzuki et al, 2007). In our study, we first validated the technique by studying the brain efflux index of valproic acid.…”