Effect of Da-Cheng-Qi decoction on the pharmacokinetics of ranitidine in rats.

Da Cheng Qi decoction (DCQD) is composed of Dahuang, Houpu, Zhishi and Mangxiao. It is a formula created under the theory of Chinese medicine to purge the 'evil heat' in the gastrointestitinal tract, which arises from the ileus and acute pancreatitis. The present study was conducted to evaluate the herb-drug interaction between DCQD and ranitidine, which are often co-administered in clinical practice. Ranitidine was administered orally alone or together with DCQD to rats, and plasma ranitidine concentrations were measured by HPLC. Following oral administration, ranitidine plasma levels revealed curves characterized by peaks at 1.8 and 4.2 h corresponding to ranitidine alone and ranitidine with DCQD at mean concentrations of 16.315 and 1.455 microg/mL, respectively. After ranitidine was orally dosed alone or with DCQD, the half-lives were 1.787 and 3.758 h, while the area under the concentration-time curve (0-12 h) was 28.083 and 9.826 microg/L h, respectively, suggesting that DCQD might significantly affect the pharmacokinetics of ranitidine in rats. When physicians or pharmacists administer DCQD and ranitidine, they must make a careful effort to adjust the dosage of the drug and Chinese decoction, or avoid the herb-drug co-administration.