Studies on the Film Coating Potential of Anacardium Occidentale (Cashew Tree) Gum

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This research work involved the study of Anacardium occidentale (cashew) gum as a material for pharmaceutical film coating. Both the crude and purified forms of the gum were evaluated for some physicochemical properties. The percentage yield for the purification was appreciable. The gum was found to be acidic and its viscosity significantly increased with increasing concentration and storage time. Both crude and purified gums had acceptable insoluble matter and moisture content. Polymeric films were prepared from homogenous solutions of the purified cashew gum only and mixtures of the cashew gum with either hydroxypropyl methylcellulose (HPMC) or carboxymethyl cellulose (CMC) using the solvent casting method in plastic petri dishes, using different plasticisers. The physical (weight and thickness) and mechanical (folding endurance, tensile strength, percentage elongation, Young’s modulus) properties of these films were determined. Paracetamol tablets were prepared and used as the model drug for the research work. The tablets were film coated with solutions of the cashew gum using different coating times. Quality tests including uniformity of weight, thickness, hardness, friability, disintegration time, assay and dissolution on both the uncoated and film coated tablets were conducted. The results obtained established that propylene glycol is not a suitable plasticiser for cashew gum and that blending cashew gum with hydroxypropyl methylcellulose or carboxymethyl cellulose produced non – uniform and films of poor clarity respectively. Cashew gum on its own produced transparent and smooth, but brittle films. Addition of plasticisers to the gum imparted flexibility to the films. Increasing cashew gum and plasticiser concentrations in the films increased the folding endurance and elongation of the films. Tensile strength was enhanced when gum amount was increased but a decrease in tensile property was observed when plasticiser amount was increased. Young’s modulus decreased when both cashew gum and plasticiser amounts were increased. Both uncoated and coated tablets passed all the quality tests. Application of the gum as a film coat to paracetamol tablets enhanced the mechanical strength of the tablets, in terms of friability and hardness. The rate of drug release was higher for the uncoated paracetamol tablets than for the film coated ones. The percentage drug release in phosphate buffer (pH-6.8) was higher than in 0.1M HCl dissolution medium. Film coating of core paracetamol tablets did not significantly impact on the immediate-release nature of the tablets. The mechanism of drug release from the tablets was found to be by diffusion. Cashew gum can therefore be used successfully as a film coating agent for immediate-release tablets.
A thesis submitted to the School of Graduate Studies in partial Fulfilment of the requirement for the Master of Philosophy (MPhil) Pharmaceutics Degree, 2012