Effects of phenobarbital on unconjugated bilirubin clearance, gamma-glutamyltranspeptidase and urinary d-glucaric acid in patients with Gilbert's syndrome.

Plasma unconjugated bilirubin kinetics, gamma-glutamyltranspeptidase (GGT) and urinary excretion of d-glucaric acid were determined in 7 patients with Gilbert's syndrome, before and after phenobarbital treatment. The clearance of unconjugated bilirubin from plasma was significantly improved after treatment (p less than 0.005). Kinetic analysis of plasma disappearance data was associated with an increase in uptake and conjugation, and a decrease in reflux. Phenobarbital treatment resulted in significant increases in serum GGT activity (p less than 0.05) and urinary d-glucaric acid excretion (p less than 0.005). These results suggest that measurement or urinary d-glucaric acid by short-term administration of phenobarbital may be a better clinical index for hepatic microsomal enzyme induction than serum GGT activity.