Quigley, Karen Josephine; (1995) Factors influencing formation and the <italic>in vitro</italic> drug release from pellets containing chitosan. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Chitosan is a cationic polysaccharide material produced by deacetylation of chitin, extracted from the shells of crustaceans. Chitosan is a biodegradable, non-toxic material with a variety of pharmaceutical uses. A series of solid dosage form pellets have been produced by an extrusion - spheronization process and the ability to control the release has been investigated without a coating process. A number of pellet formulations containing the model drug diclofenac sodium have been produced, based on varying concentrations of Avicel PH101, lactose and barium sulphate in which chitosan is incorporated as a dry powder, or dissolved in acetic acid as a gel. Incorporation of chitosan as a dry powder showed a concentration effect but did not show controlled drug release properties. The release as assessed by in - vitro dissolution studies was shown to be pH dependent. The effect of pellet size on the release profile was also investigated; a large pellet showing slower release than a small pellet. The effect of including four different electrolytes; potassium chloride, sodium chloride, magnesium chloride and potassium hydrogen carbonate at two concentrations in a standard formulation, on the formation and release properties of the pellets containing chitosan at two levels has been determined. The inclusion of the electrolyte alters the viscosity profile of the chitosan gel when assessed by a cone and plate viscometer and results in differing release profiles. Chitosan is soluble in a number of acids and a series of seven different acids were investigated as possible solvent systems for inclusion in a pellet dosage form. The formation and release profiles of the pellets were examined. The rheological profiles of the seven gels were examined by means of flow curves and creep testing to enable fundamental parameters of viscosity and elasticity to be estimated. Oscillation rheometry provided further information on the viscoelastic behaviour of plugs of extruded material containing chitosan.

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