Abstract
Interactions between phenothiazines and pectin in aqueous solution were studied by the equilibrium dialysis method, in order to investigate the relation between binding parameters and drug properties. Scatchard plots were not linear for water-soluble drugs such as promazine hydrochloride, triflupromazine hydrochloride, and so on, and thus the number of binding sites of pectin was considered to be more than two. On the other hand, it was impossible to obtain the γ value (mol of drugs bound per mol of pectin) on Scatchard plots for such slightly soluble drugs as levomepromazine maleate, perazine dimaleate and prochlorperazine dimaleate at higher concentrations. Therefore the data were analyzed simply by assuming that they gave a linear plot. The maximum binding number was significantly larger than the values already reported. A good positive correlation was observed between the binding parameters and adsorption parameters related to hydrophobicity. Among drugs having the same side chain at the 10-position but different substituents at the 2-position, the maximum binding number increased with the bulkiness of the substituents. The micelle formation of phenothiazines was shown to be related to the interaction and also to the formation of coprecipitate.
