Posted by chemist on August 22, 2004, at 12:47:15
In reply to IC_{50}: being deferred, Dr. Bob » dondon, posted by chemist on August 22, 2004, at 12:25:30
dondon, sorry....in my haste, somehow translated your query into one concerning LD_{50}: the IC_{50} is the concentration of an inhibitor needed to result in 50% inhibition of the target. the smaller the amount of an inhibitor required to achieve this, the more strongly it binds to the receptor. thus, a drug with an IC_{50} in the nM range is a weaker inhibitor than a drug in the pM range. this can be misleading, however, because in order to get pM concentrations of the inhibitor to the binding site, a lot of parent drug might have to be administered. thus, look at the fraction of unbound drug in the blood over the IC_{50} (or K_{i}, inhibition constant): if this number is large, then a small dose produces stong inhibition, and the converse is true....all the best, chemist
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