Compaction, compression and drug release characteristics of xanthan gum pellets of different compositions

Compaction and compression of xanthan gum (XG) pellets were evaluated and drug release from tablets made of pellets was characterised. Three formulations were prepared by extrusion-spheronisation and included, among other excipients, diclofenac sodium (Dic Na), at 10% (w/w); xanthan gum, at 16% (w/w); and one of three different fillers (lactose monohydrated (LAC), tribasic calcium phosphate (TCP) and beta-cyclodextrin (beta-CD)), at 16% (w/w). Five hundred milligrams of pellets (fraction 1000-1400microm) were compacted in a single punch press at maximum punch pressure of 125MPa using flat-faced punches (diameter of 1.00cm). Physical properties of pellets and tablets were analysed. Dissolution was performed according to the USP paddle method. Pellets showed close compressibility degrees (49.27% LAC; 51.32% TCP; and 50.48% beta-CD) but densified differently (3.57% LAC; 14.84% TCP; 3.26% beta-CD). Permanent deformation and densification were the relevant mechanisms of compression. Fragmentation was regarded as non-existent. The release behaviour of tablets made of pellets comprising LAC or beta-CD was anomalous having diffusional exponent (n) values of 0.706 and 0.625, respectively. Drug diffusion and erosion were competing mechanisms of drug release from those tablets.