Independence of the product of solubility and distribution coefficient of pH.
OBJECTIVE
The relationship between the pH, solubility, and partition coefficient was investigated to show that the product of intrinsic values of solubility and partition coefficient is equal to the product of total values of solubility and distribution coefficient at different pH.


METHODS
The pH distribution profiles were obtained from the literature and the pH solubility profiles were obtained from the literature or calculated from their intrinsic solubility and pK(a).


RESULTS
The pH solubility and pH distribution coefficient profiles of 25 compounds were investigated to show that the product of intrinsic solubility (S(w)) and intrinsic octanol-water partition coefficient (K(ow)) is equal to the product of total solubility of a partially ionized solute (ST) and its octanol-buffer distribution coefficient (K(D)) at any pH where ion pair formation and salt precipitation are not present.


CONCLUSIONS
The fact that S(w) x K(ow) can be used instead of S(T) x K(D) to model the absorption of partially ionized drugs in the gastrointestinal tract has important biopharmaceutical implications.
Ni
Nina
N
College of Pharmacy, The University of Arizona, Tucson, Arizona 85721, USA. na@pharmacy.arizona.edu
Sanghvi
Tapan
T
Yalkowsky
Samuel H
SH
D006863:Hydrogen-Ion Concentration; D004364:Pharmaceutical Preparations / Q000737:chemistry*; D012995:Solubility
D004364:Pharmaceutical Preparations