Pharmacokinetic Interaction Study of Ranitidine and Daijokito in Healthy Volunteers.

Background Ranitidine is a histamine 2 receptor antagonist, and daijokito is a Kampo (Chinese herbal medicine as practiced in Japan) formula, which is traditionally used for treating constipation and digestive trouble. Previous study demonstrated that daijokito significantly affected the pharmacokinetics of ranitidine in rats; however, the doses of ranitidine and daijokito in that study were higher than in clinical practice. Therefore, we examined the pharmacokinetic interaction between ranitidine and daijokito in clinical practice doses in healthy volunteers. Methods This was a randomized, open label, two-period crossover study in healthy volunteers (n = 7). Volunteers received administrations of either a single dose of ranitidine 300 mg, or ranitidine 300 mg in combination with daijokito extract granules 2.5 g. Plasma concentrations of ranitidine were measured over 12 h by LC/MS/MS method. Results Plasma concentrations of ranitidine were lower with co-administration of daijokito compared with ranitidine alone. Co-administration of daijokito significantly decreased ranitidine area under the plasma concentration-time curve from 0 to 12 h (AUC(0-12)) and maximum plasma concentration (C-max) with geometric mean (GM) ratio [90% confidence interval (CI)] for AUC(0-12) of 0.609 (0.449, 0.826) and C-max of 0.515 (0.345, 0.771). Conclusion Co-administration of ranitidine with daijokito resulted in a significant decrease in plasma level of ranitidine in healthy volunteers.