Quantitative determination of pamoic acid in dog and rat serum by automated ion-pair solid-phase extraction and reversed-phase high-performance liquid chromatography.

Pamoic acid is used as a counter ion to obtain long-acting pharmaceutical formulations of certain basic drugs. In order to investigate the pharmacokinetics of pamoic acid, a simple, sensitive and reliable method has been established for the quantitative determination of pamoic acid in serum from dog and rat. The method uses ion-pair solid-phase extraction followed by ion-pair reversed-phase high-performance liquid chromatograpy. The influence on recovery of the addition of different agents (tetrabutylammonium acetate, methanol, sodium hydroxide) to the serum samples prior to solid-phase extraction was studied and the analytical method was validated. The method was found to be valid for accurate, precise and selective determination of pamoic acid in the tested concentration range of 5-200 ng/ml serum. The overall performance of the HPLC method was found to be satisfactory for the purpose of determining concentrations of pamoic acid in serum samples from pharmacokinetic studies with pamoic acid in dogs and rats.