Distribution Coefficients by Curve Fitting: Application to Ionogenic Nonsteroidal Antiinflammatory Drugs

Abstract

A thorough investigation on the dependence of distribution coefficients of acidic drugs on pH and pK_a values has been carried out. The results give evidence that the Henderson‐Hasselbach equation is an idealization and only an approximation for real systems.It is shown that a multiparametric curve‐fitting technique may constitute a useful alternative to the previously reported methods to describe the hydrophilic/lipophilic pH‐profiles of ionogenic substances. Calculated values at any given pH value are in very good agreement with the experimental partition (log P) and distribution coefficients determined by shake‐flask method and reversed‐phase high performance liquid chromatography.