Stereoselective study of fluoxetine and norfluoxetine across the blood–brain barrier mediated by organic cation transporter 1/3 in rats using an enantioselective UPLC‐MS/MS method

Abstract Fluoxetine (FLT) is a widely used antidepressant in clinical practice, which can be metabolized into active norfluoxetine (NFLT) in vivo. The stereoselectivity of FLT and NFLT enantiomers across the blood–brain barrier (BBB) is still to be clarified. In this study, accurate and reliable UPLC‐MS/MS enantioselective analysis was established in rat plasma and brain. The characteristics of FLT and NFLT enantiomers across the BBB were studied by chemical knockout of rat transporters. We found that the dominant enantiomers of FLT and NFLT were S‐FLT and R‐NFLT, respectively, both in plasma and in brain. The FLT and NFLT enantiomers showed significant stereoselectivity across the BBB, and S‐FLT and S‐NFLT were the dominant configurations across the BBB. Chemical knockout of organic cation transporter 1 (OCT1) and OCT3 can affect the ratio of plasma FLT and NFLT enantiomers into the brain, suggesting that OCT1/3 is stereoselective for FLT and NFLT transport across the BBB.