Poor aqueous solubility is a major limiting factor during the development of BCS Class II drug candidates in a solid oral dosage form. Conventional amorphous solid dispersion (ASD) systems focus on maximizing the rate and extent of release by employing water-soluble polymeric crystallization inhibitors; however, they often encounter rapid supersaturation and solution-mediated phase transformation (SMPT). Therefore, in this work, a controlled release membrane was introduced onto ASD beads to mitigate the SMPT problem. A membrane-reservoir controlled release amorphous solid dispersion (CRASD) bead system was designed, and the effects of the coating thickness and pore former content on drug release profiles were investigated. CRASD beads were manufactured by spray-coating polyvinyl acetate with polyvinylpyrollidone (PVP) as a pore former onto sugar bead substrates layered with the ASD reservoir of celecoxib and PVP. Raising the pore former content and/or lowering the coating level imparted higher release rates and supersaturation levels. The extent of release, measured by the area under the curve, was greatest when an optimal balance between the release rate and peak concentration could be established, corresponding to a high pore former/high coating level combination. Attributed to a thicker membrane structure with a higher pore former, rapid initial release could be achieved, yet controlled gradually for several hours, avoiding the critical threshold where the onset of SMPT predominates. The greater membrane capacity to transiently immobilize drug molecules (i.e., preserve amorphicity) and gradually release drug over a prolonged duration may be key to balancing supersaturation on both sides of the membrane; hence coating variables should be tactfully selected to exploit this benefit.
Keywords: controlled release amorphous solid dispersion; dissolution; fluid-bed coating; membrane-reservoir beads; poor aqueous solubility; solution-mediated phase transformation.