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Experimental investigation of the release mechanism of hydrophilic solutes from hydrophobic matrices

1. Introduction The controlled release of drugs from hydrophobic polymer monoliths is facilitated markedly by the presence of water-soluble excipients [1]. However, the release profiles of the water-soluble excipients and the organic molecules are governed by different release mechanisms. In the former case, the osmotic action of the water-soluble excipients causes excessive sorption of water, which in turn may give rise to non-Fickian release kinetics. On the other hand, the release of a drug (regardless of whether its initial concentration in the matrix is above or below its solubility in the polymer), frequently follows t 1/2 (t=time) kinetics. Various models have been proposed to account for the observed kinetic behavior [2-4]. In this work we report a comparative study of the kinetics of release of a water-soluble inorganic salt (NaCl) and a model drug (proxyphylline). The study was supplemented by parallel measurements of (i) the concurrent variation of the water content of the matrices (ii) the permeation properties of the depleted matrices and (iii) the mechanical properties of loaded and depleted matrices.