Increased dissolution rates of carbamazepine--gluconolactone binary blends processed by hot melt extrusion

Carbamazepine (CBZ) shows a poor dissolution, therefore, it is important to enhance its dissolution in GI tract to improve its bioavailability. In the present study, a new hydrophilic carrier, d-gluconolactone (GNL), was extruded with CBZ at various molar ratios to produce granules by using hot melt extrusion (HME) processing. The granular extrudates were characterised by X-ray powder diffraction, differential scanning calorimetry and hot stage microscopy to determine the solid state of CBZ. It was found that bulk CBZ (Form-III) transformed to the polymorphic Form-I during the HME processing. GNL was proved to be an efficient carrier for CBZ to enhance the dissolution rate. The increase in the dissolution rate was observed for both physical mixtures and the extrudates of CBZ-GNL. However, the extrudates showed faster dissolution rates compared to physical mixtures in an ascending order of 2:1 < 1:1 < 1.5:1 (CBZ:GNL). The increase in the dissolution rates was attributed to the transformation of CBZ III to Form-I and also to the increased drug wettability/solubilisation in the presence of the carrier.