Determination of chenodiol bioequivalence using an immobilized multi-enzyme bioluminescence technique

Measurement of the bioequivalence of formulations of chenodiol, a bile acid which is used for gallstone dissolution, is difficult because its high first-pass clearance results in low plasma levels after ingestion of usual dosages. To solve this problem, a new method was developed to determine the bioequivalence of several chenodiol formulations. The method included the following steps: isolation of all bile acids from serum by absorption to a hydrophobic resin, elution of bile acids from the resin by methanol, separation of the unconjugated bile acid fraction by an ion-exchange procedure, and bioluminescence measurement of the unconjugated 7 alpha-hydroxy bile acids using Sepharose beads containing co-immobilized 7 alpha-hydroxysteroid dehydrogenase, diaphorase, and luciferase. The isolation method gave complete recovery, and the bioluminescence procedure was simple, rapid, and sensitive. The peak level of systemic chenodiol occurred 1 to 2 h following oral ingestion and ranged from 4 to 8 microM. This method appears superior to previously reported methods for determining the bioequivalence of chenodiol preparations. In principle, the method is suitable for measurement of the bioequivalence of other bile acids provided the appropriate hydroxysteroid dehydrogenase is available.