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Specificity:
Specificity:
The capacity of a drug to manifest only one kind of action. A drug of perfect specificity of action might increase, or decrease, a specific function of a given cell type, but it would not do both. Nicotine is not specific in its actions in autonomic ganglia; it both stimulates and depresses ganglionic function by a number of means. Atropine is quite specific in only blocking the actions of acetylcholine at certain receptors; in general atropine does not stimulate cellular activity when it combines with receptors, nor does it block interaction with receptors of agonists other than acetylcholine. In affecting exocrine glands, acetylcholine itself is very specific, in that it causes only stimulation or secretion; acetylcholine, at the same time, is non-selective in its action, in that stimulation of all exocrine glands is produced by about the same dose of acetylcholine.
Selectivity is concerned with site of action; specificity, with the kinds of action at a site.
Cf. Selectivity
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