terminal half life - 藥物,藥學討論

藥品仿單上看到terminal half life
上google查了一下
似乎有別於一般half time的定義
但是又看不大懂(下面有三個連結)
煩請專業藥學人士指點
謝謝

http://www.netwellness.org/question.cfm/71892.htm
The half life is the time it takes for the plasma concentration or the amount
of drug in the body to be reduced by 50%. In the simplest model of drug
elimination from the body, a drug declines at a constant rate.
However, many drugs are not eliminated from the body at a constant rate.
These drugs leave the body in a more complicated pattern of decline. Factors
such as how widely the drug is distributed throughout the body and how easily
the body is able to remove the drug from the plasma influence the rate of
elimination. The rate may change over time rather than being constant. The
term "terminal half life" is used for the slowest process of concentraton
decrease of a drug from the body.

http://www.ncbi.nlm.nih.gov/pubmed/15601438
Terminal plasma half-life is the time required to divide the plasma
concentration by two after reaching pseudo-equilibrium, and not the time
required to eliminate half the administered dose. When the process of
absorption is not a limiting factor, half-life is a hybrid parameter
controlled by plasma clearance and extent of distribution. In contrast, when
the process of absorption is a limiting factor, the terminal half-life
reflects rate and extent of absorption and not the elimination process
(flip-flop pharmacokinetics). The terminal half-life is especially relevant
to multiple dosing regimens, because it controls the degree of drug
accumulation, concentration fluctuations and the time taken to reach
equilibrium.

http://www.alprolix.com/efficacy/half-life.html
Terminal half-life is the time it takes for a drug's activity to decrease by
half after the drug has been distributed throughout the body. The longer the
terminal half-life, the longer factor is active in your system.



--