A multimechanistic drug release approach in a bead dosage form and in vitro predictions

The objective of this study was to prepare a combination of immediate release, enteric coated, and controlled release (CR) beads and to mathematically model in vitro drug release characteristics of the combination based on the release profiles of individual beads. Uncoated beads were manufactured by using extrusion/spheronization technology. Fluid-bed bottom spraying was used for coating: Eudragit-L-30D for enteric coating and Eudragit-NE-30D for CR coating. In vitro drug release profiles for uncoated and coated beads were each fitted to appropriate mathematical equations. The drug release from the bead combination dosage form was predicted from the individual mathematical models and verified experimentally in vitro. The in vitro dissolution was conducted in 0.1 N HCl for 2 hr and then in buffer (pH 6.5 phosphate, 0.05 M) to mimic in vivo conditions using USP dissolution apparatus I. The results showed that uncoated beads gave similar release profiles in water, acid, and buffer with complete release within 2 hr. The release from CR beads was about 50% at 10 hr and was independent of the dissolution medium. As expected, enteric coated beads showed drug release < 5% at 2 hr in water and acid, whereas the release in buffer was comparable to that of uncoated beads. Exposure of enteric coated beads to acid for 2 hr produced a slower release rate in buffer compared with the release from beads added directly in the buffer. The release characteristics of the three beads can be described by square root and zero-order kinetics. The release characteristics from the combination dosage form were 39%, 69%, and 81% at 1, 4, and 8 hr, respectively. The experimental and predicted profiles agreed to within +/- 6% (residuals at individual data points). Our results suggest that release from the combined multimechanism oral dosage form can be predicted from the performance of individual beads.