Abstract: AimTo investigate the possible effect of tetramethylpyrazine (TMP), an active ingredient of a commonly used Chinese herb, on the pharmacokinetics of cyclosporine A (CsA) by intragastric administration in rats. MethodsForty male Sprague-Dawley rats were equally divided into four groups by randomized block design according to weight. On the first day, after each fasting rat was intragastrically administered CsA (10 mg·kg^-1), blood samples (0.2-0.25 mL) were collected from the tail vein at 0, 1, 2, 3, 4, 6, 8, 12, 24, 36 and 48 h. From day 4 to day 8, each group began to undergo different pretreatments with intragastric administration of water, verapamil (Ver), low and high dose TMP, separately. On day 9, each group intragastrically co-administered CsA (10 mg·kg^-1) and different pretreatment compounds mentioned above, then blood samples were collected according to the schedule of the first day. The whole blood concentration of CsA was determined by HPLC. Main pharmacokinetic parameters were calculated and compared by statistic analysis. ResultsIn the group of water pretreated and co-administrated with CsA, no significantly different pharmacokinetic parameters of CsA were found. After Ver pretreatment and co-administration with CsA, AUC_{0-48 h} andC_max were increased significantly (P<0.01 andP<0.05);T_1/2β and CL were markedly prolonged and decreased (P<0.05);T_max and V were not apparently influenced. After low dose TMP pretreatment and co-administration with CsA, there was no significant difference in the pharmacokinetic parameters of CsA, in spite of the increasing trends of AUC_{0-48 h} andC_max. After high dose TMP pretreatment and co-administration with CsA, AUC_{0-48 h} andC_max of CsA were increased significantly (P<0.01), but there was no significant change in other parameters. ConclusionIt was indicated that the high dose of TMP could apparently increase the intragastric absorption extent of CsA, while almost had no effect on its elimination process.