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首次通过效应(First pass effect)又称第一关卡效应,是指口服给药药物在经肠道吸收或随血流首次进入肝脏时,某些药物可被代谢灭活,使进入体循环药量减少。因此有明显首次通过效应的药物不仅口服生物利用度较低,而且给药途径不同血浆药物浓度差异也较大,临床应用时应特别注意。如心得安口服用量要比注射剂量大几倍甚至几十倍。此外,具有首次通
First pass effect (First pass effect), also known as the first level effect, refers to the oral administration of drugs in the intestinal absorption or with the blood for the first time into the liver, some drugs can be metabolically inactivated, so that into the systemic circulation dose reduced . Therefore, there is a clear first-pass effect of the drug not only oral bioavailability is low, and the route of administration of different plasma drug concentrations are also greater, clinical application should pay special attention. Such as propranolol oral dose than injection times several times or even several times. In addition, with the first pass