ABSTRACT
I. ACID DISSOCIATION CONSTANT (pKa) A. Introduction Ionization of drugs is important because it affects not only the physicochemical properties of the drugs, such as lipophilicity (1,2) and solubility (3-6), but also several parameters related to cell-drug interactions, such as membrane permeability, plasma protein binding, metabolism, tissue penetration, and target protein binding (7 -9). The acid dissociation constant (pKa ) is an index of the extent of ionization of a drug at different pH values and is therefore an important parameter that reflects optimization of the drug structure (Fig. 1).
