Influence of the extrusion temperature on the physical properties of solid dispersions based on a new graft copolymer

The aim of this work was to investigate the influence of extrusion temperature on the phase behavior of solid dispersions of carbamazepine and Soluplus. For this purpose, physical mixtures in various drug/polymer ratios (1:9, 3:7, 1:1 w/w) were extruded by means of a twin screw miniextruder at 130°C and at 170°C, i.e. approximately 50 and 10°C below the drug melting temperature, respectively. At both temperatures cylindrical extrudates of good quality (shape and surface) were obtained by adjusting the screw rate. Powdered extrudates were produced by means of an ultracentrifugal mill, calibrated and characterized by PXRD, DSC and dissolution test. Solid dispersions prepared at 170°C consisted in all cases in non-crystalline products, able to effect a considerably enhanced drug dissolution rate compared to the corresponding physical mixtures. On the other hand, only for the 1:9 w/w system extruded at 130°C a true molecular dispersion of the drug in the polymer was achieved; for higher ratios, residual crystalline drug (form III) was found in the product. Consequently, dissolution rate was less improved with respect to the corresponding solid dispersion prepared at 170°C.