The effects of Gamiondam-tang (GMODT) co-administration within 5min on the pharmacokinetics (PK) of tamoxifen were observed as a process of the comprehensive and integrative medicine, combination therapy of tamoxifen with GMODT to achieve synergic pharmacodynamics and reduce toxicity on the breast cancer. Methods: After 50mg/kg of tamoxifen treatment, GMODT 100mg/kg was administered within 5min. The plasma were collected at 30 min before administration, 30 min, 1, 2, 3, 4, 6, 8 and 24 hrs after end of GMODT treatment, and plasma concentrations of tamoxifen were analyzed using LC-MS/MS methods. PK parameters of tamoxifen (Tmax, Cmax, AUC, t 1/2 and MRT inf) were analysis as compared with tamoxifen single administered rats using noncompartmental pharmacokinetics data analyzer programs. Results: Co-administration with GMODT induced increased trends of plasma tamoxifen concentrations to 1hr after end of administration, and then showed decreased trends of plasma tamoxifen concentrations, and especially significant (p<0.05) increases of plasma tamoxifen concentrations were demonstrated at 0.5hr after end of co-administration with GMODT and also related significant (p<0.05) decreases of AUC 0-inf and MRT inf as compared with tamoxifen single formula treated rats, at dosage levels of tamoxifen 10 mg/kg and GMODT 100 mg/kg within 5 min, in this experiment. Conclusion: Based on the results of the present study, it is considered that single co-administration GMODT within 5min significantly inhibited the oral bioavailability of tamoxifen through variable influences on the absorption and excretion of tamoxifen, can be influenced on the toxicity or pharmacodynamic of tamoxifen.

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