Calorimetric evaluation of hydration of cholestyramine.

We have investigated the mechanism of hydration of cholestyramine, a water-insoluble resin used pharmaceutically. Two types of water of hydration (freezing and non-freezing) and the amounts of heat evolved or absorbed during the hydration of cholestyramine were determined. From differential scanning calorimetry, 0.57 g water was observed to be tightly bound per gram of resin (non-freezing water). The hydration of dry cholestyramine was found to be exothermic. The heats of hydration of cholestyramine with chloride or nitrate counter-anions were found to be -6.05 and -3.46 cal g-1, respectively. Some of the partially hydrated cholestyramine samples showed absorption of heat during hydration. The data generated in the study were utilized to better understand the mechanism of hydration and swelling of cholestyramine.