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Assume that we are dealing with an acidic drug (such as aspirin), that distributes between urine (pH = 8), plasma (pH = 7.4) and gastric juice (pH = 3.0). At equilibrium, the concentration of the uncharged (protonated) form of the drug=1 (arbitrary units). This concentration tends toward being the same in all the compartments.

 

 

 

 

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