Characterisation and Application of Grewia Gum in Tabletting.

Abstract

Grewia gum obtained from the inner stem bark of the shrub Grewia mollis, Linn,, (Fam. Tiliaceae) has been studied as an excipient in tabletking, The gum which was purified by precipitating with ethanol, consists mostly of polysaccharides (of glucose, rhamnose and galacturonic acid residues) with traces of metals (6,1%), proteins (1.24%) and lipids (0,021%), It has an estimated viscosity-average molecular weight of 316,000. The gum forms viscous mucilages which are acidic, For instance, a 0.5% w/v dispersion in water had a viscosity of 2.685 mPa.s and pH of 5.4 at 2s0c. Films derived from the gum exhibit ultimate tensile strength, modulus of elasticity and elongation at break of 6.5 x lo6 NM -2 , 5.0 x lo8 Nmg2 and These are comparable to those of methylcellulose, gelatin or polyvfnylpyrrolidone (PVP) when evaluated on equal weight basis. The permeability coefficient of the -1 films to water vapour is 0.573 g dayw1 cm pa-' at 36O~. his is lower tllan values obtained for methylcellulose, gelatin or PVP films. Optimum mechanical and water vapour permeability properties of grewia gum film were achieved when the film is plasticised with 10% w/w glycerol. The gum was as effective as gelatin and more effective than maize starch or acacia when used as a binder at concentrations of 2 to 6% w/w. It however, prolonged the disintegration time of the tablets even at 1% w/w concentra- tion, suggesting a poor disintegrant property. The gum code named DGZ was found to be an effective sustained release matrix as it provided slow release from theophylline hydrate and chlorphenirarnine maleate tablets at concentrations greater than or equal to 10% w/w. Drug release was delayed as the concentration of the gum in the two tablet formulations increased. The release mechanism of the gum conformed predominantly to Fickian diffusion and was consistent with the square root of time profile or Higuchi-type release kinetics. On the basis of these, grewia gum may find application in tablet formulation especially as a sustained release matrix.