Al-Ghazawi, Ahmad Khalaf Al Deeb; (1994) The preparation and evaluation of extrudates as oral controlled release dosage systems. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

A unit solid dosage form has been prepared in the form of a hollow cylinder by an extrusion process to provide a controlled release drug delivery system. The steady- state extrusion force, measured by the ram extruder, was used to assess the amenability of each formulation to produce smooth good quality extrudate. The formulation system was based on Avicel PH 101, as a binding and extrusion aid, plus PVP as a binder to ensure a rigid structure on drying. A film coat was applied, using a fluidised bed coater, to provide release of theophylline, a model drug, in a controlled manner. The tube extrudates could be coated in various ways, to produce different drug release profiles, for example:- (i) the external surface coated with impermeable film and no internal coat, (ii) the external surface coated with a permeable film and no internal coat, (iii) the external and internal surface coated with a permeable film. A non-aqueous coating system and an aqueous coating system were successfully applied to the surfaces of tube and rod extrudates to provide a controlled release film. When assessed by the in-vitro dissolution studies, pH-dependent and pH-independent controlled release systems were effectively produced. The factors which influenced the formation of a suitable controlled film coating include type and amount of coating additive, coat thickness and curing time and temperature which have been evaluated. Further variables which influence the formation and in-vitro drug release from tube and rod systems are associated with their dimensions, shape and drug loading. Extruded matrix systems were also produced, which provided a controlled drug delivery system without the need to apply film coat. These systems were based on the hydrophilic polymer, Avicel PH101, and a hydrophobic wax material, glycerylmonostearate, which prevented the disintegration of the system and slowed drug release. The dissolution data were analyzed by different mathematical models to evaluate the rate controlling mechanism. The release of theophylline from the various matrix systems and the externally film coated systems studied was found to be controlled by the mixed processes of diffusion and erosion/swelling and from wholly coated tube and rod extrudates only by a diffusion process.

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