Preparation of starch-based pellets by hot-melt extrusion

Spherical starch pellets were directly and continuously produced using hot-melt extrusion and die-face pelletisation. In contrast to conventional pelletisation procedures, a discontinuous spheronisation step can be dropped. Pellets were produced based on four different starches (corn starch, pea starch, potato starch and waxy corn starch), four different active ingredients (ibuprofen, paracetamol, phenazon and tramadol-HCl) and various additives. The resulting pellets exhibit a large mechanical stability, low porosity and small surface area. Pellets with a very narrow particle size distribution and particle sizes even in the micron scale can be produced. The drug is either dispersed or dissolved in the starch melt. Drug loadings of up to 80% are achievable. The drug release rate is controlled by the particle size, the combination of starch, active ingredient and additives. The release mechanism is determined by the used starch and the additives. Under normal circumstances, the starch matrix remains intact during dissolution with the exception of waxy corn starch pellets. Pellets based on that starch completely erode. Mathematical modelling revealed that the drug release mechanism from corn starch, pea starch and potato starch pellets is complex and based on diffusion as well as relaxation of the matrix.