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Abstract
The kinetics of adsorption of the hydrochlorides of chlorpromazine, propranolol, quinine, and quinidine on to an insoluble sodium polyphosphate, Maddrell's phosphate type II (MPI), have been studied in vitro. The data have been fitted to a three-compartment model, in which one compartment represents the aqueous solution of adsorbate and the other two compartments represent hypothetical adsorption sites. One site is labile, i.e., adsorption (and desorption) occur very rapidly, while the second site is a sink at which the adsorption density slowly increases until it eventually dominates the total adsorption density. The initial adsorption rates of the cations increase with temperature and, with the exception of quinidine, are very rapid. The adsorption densities obtained for the drugs substantially exceed the predicted densities and it is suggested that the drugs may form an adhesive layer of insoluble (drug-polyphosphate) complex at the MPI surface which then acts as a diffusion barrier to further uptake.