A drug that is the salt of an acid will dissociate when placed in solution. The pH max for the solution is the pH at which the salt solution will be fully soluble. Below this pH a solution may form a precipitate.
Parameters:
(1) dissociation constant for the drug
(2) saturation solubility of the free acid
(3) molecular weight of the salt
(4) molar concentration of the salt in solution
molar concentration of hydrogen ion required for pH max =
= (saturation solubility of acid form) * (dissociation constant for the drug) / ((molar concentration of salt in solution) – (saturation solubility of the acid form))
pH max =
= (-1) * LOG10(molar concentration of hydrogen ion required)
If a buffered solution at that pH or higher is prepared, then all of the salt will be in solution.
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