Establishment of a Novel In Situ Rat Model for Direct Measuring of Intestinal Drug Absorption: Confirmation of Inhibitory Effects of Daijokito on the Absorption of Ranitidine

【Background】 Daijokito (DJKT), a classical traditional Kampo and Chinese medicine, has been used to treat acute pancreatitis in China. In our previous study, DJKT was found to reduce the area under the plasma concentration-time curve (AUC) of ranitidine in humans. Therefore, we established a novel rat model to examine the direct absorption of ranitidine after daijokito administration. 【Methods】 An in situ intestinal injection with portal vein sampling (IIPS) model was created to determine the rate of intestinal drug absorption. Rats were divided into two groups: the ranitidine group (R, n = 6) or the ranitidine and daijokito group (RD, n = 6). Blood was collected after intestinal injection of drugs. After the experiment, the concentrations of ranitidine were measured by LC/MS/MS analysis. 【Results】 The concentrations of ranitidine increased linearly with time in both groups. Compared with the R group, the concentrations of ranitidine in RD group significantly decreased throughout the experiment. 【Conclusion】 Co-administration of ranitidine with DJKT resulted in significant decreases in intestinal absorption in rats. The reduction of the systemic ranitidine concentration by co-administration of DJKT may be due, at least in part, to the inhibition of intestinal absorption of ranitidine.