Application of a novel symmetrical shape factor to gastroretentive matrices as a measure of swelling synchronization and its impact on drug release kinetics under standard and modified dissolution conditions.

OBJECTIVES We have assessed the kinetics of drug release in relation to the full or partial hydration and swelling of matrices under standard and modified United States Pharmacopeia (USP) apparatus II using a novel index, defined as the symmetrical shape factor. The symmetrical shape factor describes the regularity of the hydration rate of the matrix perimeter relative to its central regions. METHODS Monolithic and three-layer matrices based on hypromellose, polyethylene oxide, Kollidon SR, theophylline, diltiazem hydrochloride and alfuzosin hydrochloride were subjected to dissolution testing. KEY FINDINGS Our results indicated that Kollidon SR matrices and the three-layer composite systems with and without effervescing components were not significantly affected by the dissolution conditions. However, in the case of the floating monolithic systems based on hypromellose and polyethylene oxide, both release profiles and swelling dynamics in accordance with the similarity factor (f(2)) and symmetrical shape factor values were significantly influenced. CONCLUSIONS The symmetrical shape factor values were positively impacted. Consequently the drug release kinetics were more predictable and reproducible. The modified USP method resulted in a more synchronized axial and radial swelling with symmetrical shape factor values approaching unity. Data further indicated that the modified USP method provided for complete matrix hydration and swelling as the dosage form remained fully submerged, allowing for more reliable release mimicking the in-vivo conditions.