Understanding the Influence of Molarity, Buffer Capacity, and pH on Product-specific Guidance Dissolution Method for...

Achieving therapeutic intraluminal Mesalamine (MES) concentration at colonic lesion sites is influenced by variable gastrointestinal (GI) pH, buffer capacity (β), fluid volume, viscosity, and transit time. Conventional dissolution tests often overpredict in vivo performance, limiting their relevance for pharmacokinetic prediction. The present study focuses on understanding the impact of pH, molarities, and β on the dissolution behaviour of the MES products and generics. This study evaluates the effect of dissolution media on Prolonged-release granules (PRGs) and Multi-Matrix (MMX®) tablets, and their generics, using product-specific guidance (PSG) protocols across dissolution media and buffer strengths (25, 50, and 160 mM). PRGs showed slower release in low molarity media. It was observed that there was no β effect on the drug release profile in acetate media, where MES remains a poorly soluble zwitterion at pH 4.3. MMX® tablets were sensitive to buffer molarity; 25 mM phosphate buffer caused slower release, revealing differences that were masked under high-molarity Quality Control (QC) media. In 160 mM phosphate buffer, MMX® generics were similar to the reference, but did not meet the f₂ criteria in 25 mM buffer, demonstrating the discriminatory power of low-β media. Overall, molarity, β and pH critically influence MES release, suggesting that different dissolution methods for MES formulations with respect to their discriminatory power should be a valuable tool to mitigate bioequivalence failures in generic development.