Enterohepatic Cycling Of A771726 In Rats

A771726 is the active metabolic product of leflunomide the later is a type of immunoregulatory agents.leflunomide educes the pharacological action by metabolized in A771726,and it has been extensively exerted on rheumatoid arthritis,systemic lupus erythematosus,anti-rejection orgn transplantation and psoriasis.A771726 is a active compound,which is directly absorbed in vivo,abbreviate the transformation of prodrug. The works of this paper were designed to investigate the existence of enterohepatic circulation of A771726 and the amount of A771726 involved in this process after intravenous(iv) or intragastric(ig) administration in the rats and investigate the metabolic profile of it,so as to support the pharmacokinetics study in human and offer the reference for clinical dosage and dosage form changing.Part one:The establishment of analytical method of A771726 in biological matrix A high-performance liquid chromatographic method has been developed for the separation and analysis of A771726 in rats,using a liquid extraction as sample pretreatment for biological matrix.Separation was obtained on a Kromasil C18 column,using an excitation wavelength of 288nm.The chromatographic method used provided good separation and analysis condition.The recovery rate,accuracy rating,precision,saitivity,specificity and the linear range of quantitation of this method all reach the requisition of pharmaceutical analysis.The method has been successfully used to support the study of enterohepatic cycling of A771726 in rats.Part two: Pharmacokinetics of A771726 in Rats after Intravenous Ad -ministration In this part, A771726 in plasma was determined by HPLC in order to assess the degree of absorption after intravenous(iv) administration in the rats.The pharmacokinetic parameters were estimated with the computer program DAS using non-compartmental analysis.Read the parameters such as AUC(0-t),AUC(0-∞),MRT(0-∞),Tmax and Cmax directly,thus the pharmacokinetic parameters can be objectively estimated based on the original data. The pharmacokinetic parameters were estimated to be AUC(0-t):(632.53±51.17) mg/L·h ;AUC(0-∞):(2397.774±178.92) mg/L·h;MRT:(38.11±10.77)h;t1/2:(22.23±9.94)h, and in the enterhepatic cucling model,the bile-donor group's pharmacokinetic parameters were estimated to be AUC(0-t):(502.41±29.47)mg/L·h;AUC(0-∞):(1352.85±184.51)mg/L·h;MRT:(24.77±6.17)h;t1/2:(11.94±3.04)h.Compared the two groups of rats'pharmacokinetic parameters,the bile-donor's parameters were smaller than the normal group's. This result suggested that enterohepatic cycling of A771726 exist in rats .Part three: Enterohepatic Cycling of A771726 in Rats after Intravenous Ad -ministrationRat enterohepatic cycling model was applied to study the process of biliary reabsorption of A771726. Plasma A771726 levels were determined by a HPLC method. The pharmacokinetic parameters were estimated with the soft ware DAS using non-compartmental analysis.In the enterohepatic cycling model, the bile-donor group's pharmacokinetic parameters were estimated to be AUC(0-t):(502.41±29.47)mg/L·h ,AUC(0-∞):(1352.85±184.51)mg/L·h and the bile-recipient group's pharmacokinetic parameters were estimated to be AUC(0-t) :( 127.28±23.69),AUC(0-∞):(314.94±21.15)mg/L·h. The findings suggested that enterohepatic cycling of A771726 exist in rats after iv administration. Approximately 23.8% of the intravenous administration dosage enters the enterohepatic circulation.Part four: Enterohepatic Cycling of A771726 in Rats after Intragastric AdministrationRat enterohepatic cycling model was applied to study the process of biliary reabsorption of of A771726. Bile and urine A771726 levels were determined by a HPLC method. Bile and urine samples were collected within 12 h after ig administration of A771726,and the cumulative percentage of biliary excretion of A771726 in rats was calculated. The findings suggested that enterohepatic cycling of A771726 exist in rats after ig administration. Approximately 16.88% of the bile-donor rats'biliary excretion of A771726 enters the enterohepatic circulation.