Solubilizing Effect of Caffeine on Precipitate of Risperidone Oral Solution and Tea Beverage.

The rates of risperidone in precipitates from 5 risperidone oral solutions and tea beverages (green, black, and oolong teas) against risperidone used were measured by quantitative (q)NMR, indicating that as the amount of caffeine in the beverages increased, the rate decreased significantly. A solution of caffeine (0, 5, 10, and 30 μmol) in tartaric acid buffer (pH 3.0) was added to a solution of risperidone and (-)-epigallocatechin-3-O-gallate (EGCg) (each 3.0 μmol) in tartaric acid buffer (pH 3.0). Judging from the amounts of risperidone and EGCg in the precipitates, it was considered that risperidone formed a 1 : 1 complex with EGCg. As the amount of caffeine increased, the amounts of risperidone and EGCg in precipitates decreased significantly, suggesting that caffeine has a solubilizing effect on precipitates of the 1 : 1 complex of risperidone and EGCg. Furthermore, the amount of risperidone in precipitates formed when compounds with a xanthine derivative, such as diprophylline, theobromine, and theophylline, were added was less than when they were not added, indicating that such compounds with a xanthine derivative have the same solubilizing effect as caffeine on precipitate of the 1 : 1 complex of risperidone and EGCg.