Quantification of Risperidone Contained in Precipitates Produced by Tea Catechins Using Nuclear Magnetic Resonance

A mixture of risperidone and eight major tea catechins: (-)-epicatechin-3-O-gallate (ECg), (-)-epigallocatechin-3-O-gallate (EGCg), (-)-catechin-3-O-gallate (Cg), (-)-gallocatechin-3-O-gallate (GCg), (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (+)-catechin (CA), or (+)-gallocatechin (GC), in tartaric acid buffer (pH 3.0) afforded a precipitate. Amounts of risperidone and these catechins in the precipitate were measured by quantitative ¹H-NMR (qNMR). About half or more of risperidone used was precipitated by gallated catechins ECg, EGCg, Cg, and GCg; on the other hand, it was precipitated little by non-gallated catechins EC, EGC, CA, and GC. Furthermore, risperidone was precipitated more by 2,3-trans gallated catechins Cg and GCg than 2,3-cis gallated catechins ECg and EGCg. Regarding the amount of tea catechins in the precipitate obtained by a mixture of risperidone and Catechin Mixture, the amounts of 2,3-cis gallated catechins EGCg and ECg were much larger than those of the other green tea catechins GCg, EC, EGC, CA, and GC. It was considered that risperidone was mainly precipitated by EGCg and ECg in Catechin Mixture. Therefore, it can be concluded that when patients take risperidone with catechin-rich beverages, the efficacy of risperidone reduces, mainly because the 2,3-cis gallated catechins EGCg and ECg form complexes with risperidone and precipitate.