In Vitro Dissolution Studies of Immediate - Release and Extended - Release Formulations Using Flow - Through Cell Apparatus 4

The aims of this study were to evaluate the dissolution performance of solid dosage forms using the open and closed modes of the FTC Apparatus 4 under different flow rates and provide examples to demonstrate the advantages of the FTC method, in particular the possibility of changing the pH during experiments, in studying the release mechanisms of extended-release products. Immediate-release (IR) paracetamol and extended-release (ER) theophylline formulations were used in this study. Results from commercially available IR paracetamol tablets using FTC Apparatus 4 have shown similar dissolution behavior in the closed and open systems, reflecting well-maintained apparent sink conditions and controlled hydrodynamics in the test cells. The flow rate of FTC Apparatus 4 significantly affected the disintegration process of IR tablets. This information can be used as a discriminating tool to support formulation development and to set quality control standards and specifications. To mimic the continuous absorption of theophylline during the passage at different pH values through the whole gastrointestinal tract, dissolution tests were conducted using FTC Apparatus 4 with pH-dependent media for three different commercially available theophylline formulations. Two formulations of Uniphyllin 200-mg tablets and Nuelin SA 175-mg tablets provided a constant release rate during the course of medium pH changes, and their release behavior was predicted with accuracy by appropriate mathematical models. However, wide intervariability and biphasic release in the dissolution profiles were found for Slo-Phyllin 125-mg capsules.