SOLUBILITY EFFECTS ON DRUG TRANSPORT THROUGH PH-SENSITIVE, SWELLING-CONTROLLED RELEASE SYSTEMS - TRANSPORT OF THEOPHYLLINE AND METOCLOPRAMIDE MONOHYDROCHLORIDE

The swelling behavior of and solute transport in swellable, ionic copolymers of 2-hydroxyethyl methacrylate and methacrylic acid was studied for a wide range of copolymer compositions. The swelling behavior was determined by investigating the time-dependent change of the swelling and erosion front positions and the associated gel layer as a function of the percentage of the ionic component (MAA). Release of theophylline and metoclopramide-HCl were studied as a function of time. The swelling and release behavior were interpreted in terms of the significant solubility of the drugs tested and their possible association with the polymer matrices. It was concluded that the water uptake was mainly governed by the degree of ionization, and that the diffusion of non-ionized drugs in the hydrogels was controlled only by the volume swelling ratio of the polymer. For metoclopramide monohydrochloride, the drug diffusivity varied with copolymer composition.