Comparison of in vitro Bile Acid Binding Capacity and in vivo Hypocholesteremic Activity of Cholestyramine

Summary

Methods for in vitro assay of cholate binding capacity and for in vivo assay of hypocholesteremic activity of preparations of cholestyramine, an anion exchange resin, were developed and compared. In the in vitro assay, 20 ml of 0.3 M phosphate buffer at pH 6.0, 20 or 40 mg of the resin and 40 mg of sodium cholate were mixed and shaken for 30 minutes; the filtrates were assayed for cholate spectrophotometrically, and the cholate bound by the resin determined by difference.

In the in vivo method, a hypercholesteremic diet was fed to day-old chicks for 2 weeks; graded levels of the anion exchange resin were added to the diet during the second week. Plasma cholesterol levels were then determined as an indicator of the activity of the resin.

The relative activities of the various preparations of cholestyramine and other anion exchange resins compared very well when tested by the two methods of assay. Addition of excipients in preparations of cholestyramine for clinical use had no effect on cholate binding or hypocholesteremic activity.