Simple bicarbonate buffer system for dissolution testing: Floating lid method and its application to colonic drug delivery system

Abstract

In this study, we developed a simple and easy method to use bicarbonate buffer solutions for dissolution tests. A floating lid was newly introduced to prevent the evaporation of CO2 from bicarbonate buffer solutions (the floating lid method). This method was used to evaluate the dissolution profiles of 5-aminosalicylic acid (5-ASA) colonic delivery tablets with a pH-sensitive film coating (5-ASA CDT) (Asacol® 400 mg tablet and the generic products A and B). A sodium bicarbonate solution was added to the dissolution test vessel, covered with the floating lid made of foamed styrol, and adjusted to each pH with an HCl solution (total 500 mL, 2–50 mM, pH 6.0 to 7.5). Without the floating lid, the pH value increased by more than one pH unit within 3.5 h. The floating lid suppressed the increase in pH to less than 0.1 pH unit at 3.5 h and 0.7 pH unit at 22 h. According to the drug product information, all 5-ASA CDTs show similar disintegration times (approximately 0.5 h) and release profiles in the diluted McIlvaine buffer (pH 7.5, 50 mM phosphate, 25 mM citrate). However, in the bicarbonate buffer (pH 7.5, 10 mM), the disintegration time was prolonged to 4.3 h for Asacol®, 8.0 h for generic A, and 7.6 h for generic B. The floating lid method would be useful for formulation development.