Half-life - Half-life in Biology and Pharmacology

Half-life in Biology and Pharmacology

A biological half-life or elimination half-life is the time it takes for a substance (drug, radioactive nuclide, or other) to lose one-half of its pharmacologic, physiologic, or radiological activity. In a medical context, the half-life may also describe the time that it takes for the concentration in blood plasma of a substance to reach one-half of its steady-state value (the "plasma half-life").

The relationship between the biological and plasma half-lives of a substance can be complex, due to factors including accumulation in tissues, active metabolites, and receptor interactions.

While a radioactive isotope decays almost perfectly according to so-called "first order kinetics" where the rate constant is a fixed number, the elimination of a substance from a living organism usually follows more complex chemical kinetics.

For example, the biological half-life of water in a human being is about seven to 14 days, though this can be altered by his/her behavior. The biological half-life of cesium in human beings is between one and four months. This can be shortened by feeding the person prussian blue, which acts as a solid ion exchanger that absorbs the cesium while releasing potassium ions in their place.

Read more about this topic:  Half-life

Famous quotes containing the words half-life and/or biology:

    I could draw Bloom County with my nose and pay my cleaning lady to write it, and I’d bet I wouldn’t lose 10% of my papers over the next twenty years. Such is the nature of comic-strips. Once established, their half-life is usually more than nuclear waste.
    Berkeley Breathed (b. 1957)

    Nothing can be more incorrect than the assumption one sometimes meets with, that physics has one method, chemistry another, and biology a third.
    Thomas Henry Huxley (1825–95)