For cases where a drug reaches its target locations through passive mechanisms ( i . e ., diffusion through membranes ), the ideal distribution coefficient for the drug is typically intermediate in value ( neither too lipophilic, nor too hydrophilic ); in cases where molecules reach their targets otherwise, no such generalization applies.
12.
Hence, a single experiment can be used to measure the logs of the partition coefficient ( log " P " ) giving the distribution of molecules that are primarily neutral in charge, as well as the distribution coefficient ( log " D " ) of all forms of the molecule over a pH range, e . g ., between 2 and 12.
13.
The "'distribution coefficient "', "'log " D " "', is the ratio of the sum of the concentrations of all forms of the compound ( ionized plus un-ionized ) in each of the two phases, one essentially always aqueous; as such, it depends on the pH of the aqueous phase, and log " D " = log " P " for non-ionizable compounds at any pH . For measurements of distribution coefficients, the pH of the aqueous phase is buffered to a specific value such that the pH is not significantly perturbed by the introduction of the compound.
14.
The "'distribution coefficient "', "'log " D " "', is the ratio of the sum of the concentrations of all forms of the compound ( ionized plus un-ionized ) in each of the two phases, one essentially always aqueous; as such, it depends on the pH of the aqueous phase, and log " D " = log " P " for non-ionizable compounds at any pH . For measurements of distribution coefficients, the pH of the aqueous phase is buffered to a specific value such that the pH is not significantly perturbed by the introduction of the compound.
