CHARACTERISATION AND APPLICATION OF NATIVE AND CROSS-LINKED CASHEW (Anacardium occidentale L.) GUM IN TABLETTING

ABSTRACT

The exudate from cashew tree, referred to as cashew gum (CG) had been investigated for use as binder in conventional tablet formulations. In this study, cross-linked derivatives of the gum were synthesized and investigated for their physicochemical and physicotechnical properties and applicability in modifying drug release in tablet formulations. The crude dried latexes of CG were purified by extraction using acetone. Two cross-linked derivatives of the gum were synthesized by heating (a), a 1:1 weight ratio of CG and citric acid (CTR) at 140 oC for 30 min and (b), a 1:1:1 weight ratio of CG, CTR and glycerol (GLY) at 170 oC for 30 min. In each case, monobasic sodium phosphate was used as catalyst at 2 %w/w concentration. The cross-linking was demonstrated qualitatively by Differential Scanning Calorimetry (DSC), Fourier Transform Infrared (FTIR) and 13C Nuclear Magnetic Resonance (13C NMR) and quantitatively by polymer yield. Determinations of moisture content, moisture loss on drying, swelling ratio, water holding and water sorption capacities were used to characterize the derived polymers. Sub-acute toxicity studies were carried out to ascertain the safety or otherwise of the cross-linked derivative, CrosCCG. Wistar rats were fed with the polymer over a 28-day period and blood samples from the animals were assessed for changes in hematological and biochemical parameters. The purified CG and its derivatives were used to formulate tablets of Venlafaxine hydrochloride (Ven. HCl), a water soluble antidepressant, using the wet granulation method. Increasing concentrations of CG and its admixtures with MCC PH 102 were used as binder/matrix former in formulating the tablets. The synthesized derivative, CrosCCG, was assessed for drug release modification when used either alone or in admixtures with HPMC ER (K100). The drug release vii enhancing property of the derivative was also investigated and compared with some known superdisintegrants, Croscamellose and Crospovidone at 3 %w/w disintegrant concentration. Results obtained revealed that cross-linking of CG with CTR yielded an esterified derivative that was insoluble in all common solvents. The esterification reaction occurred between – OH of the sugar from the gum and –COOH of CTR. While being insoluble, on contact with water, however, the polymer sorped water and swelled. Cross-linking of CG with a combination of CTR and GLY yielded a polymer with improved yield and swelling potentials. Toxicity studies showed the polymer to have no apparent harmful effect on the animals and did not cause changes in the blood parameters tested. When used in tableting, CG was found to form good tablets of Ven. HCl with a crushing strength of 5.9 KN and friability of 0.03 %. Increasing concentration of CG or its admixture with MCC PH 102 offered no added advantage. CrosCCG could not modify the release of drug from the formulated tablets when used alone. Admixtures of CrosCCG at concentrations of 15 and 25 %w/w respectively with HPMC K100 at 7.5 %w/w showed a further delay in release of the drug. Concentrations lower than 10 %w/w of CrosCCG, however, showed a release enhancing ability. At 3 %w/w concentration, CrosCCG surpassed both Croscamellose and Crospovidone in enhancing drug release as observed from a 30 min in vitro dissolution data. It can thus be concluded that, this work has led to the discovery of a safe novel cross-linking process that uses safe and environmentally friendly cross-linking agents in derivatisation processes. Cross-linking CG using this method has led to the production of a powerful drug release enhancing agent.

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