LIGHT-SCATTERING-STUDIES ON THE ASSOCIATION OF PHENOTHIAZINE DRUGS IN AQUEOUS-SOLUTIONS OF LOW IONIC-STRENGTH

Time-averaged light scattering measurements on aqueous solutions of the amphiphilic phenothiazine drugs, chlorpromazine hydrochloride, thioridazine hydrochloride, and promethazine hydrochloride, at 30°C in the presence of added electrolyte (0.01-0.10 mol dm−3 NaCl) have shown discontinuities at two critical concentrations. The first of these (c1) decreased with concentration of added electrolyte in accordance with the mass action theory of micellization; the second (c2) occurred at concentrations from 0.20 to 0.25 mol kg−1 and showed no significant variation with electrolyte concentration. Photon correlation spectroscopy (dynamic light scattering) has shown an increase in micellar radius with increase of concentration of the added electrolyte. Data have been interpreted using the DLVO theory to quantify the interaction between the drug micelles. © 1993 by Academic Press, Inc.