Background-Stimulated bile acid synthesis preferentially utilises newly synthesised cholesterol, raising the posssiblity that combination of simvastatin (an inhibitor of cholesterol synthesis) with ursodeoxycholic acid (UDCA; a stimulator of bile acid synthesis) may result in reduced bile acid synthesis and greater enrichment of the pool with UDCA than that achieved with UDCA treatment alone. Aims-To investigate the eVect of simvastatin and UDCA given alone and in combination on serum and biliary lipid and biliary bile acid composition. Methods-Eighteen patients with primary non-familial hypercholesterolaemia were studied during treatment with simvastatin 20 mg/day, UDCA 10 mg/kg/day, and a combination of the two drugs. Each regimen was given in random order for three months following a three month lead in period. Results-Simvastatin significantly reduced serum low density lipoprotein (LDL) cholesterol but biliary cholesterol concentration remained unchanged. Combination of the two drugs had no synergistic eVect on serum cholesterol concentration, but significantly increased the proportion of UDCA in the bile acid pool from 35% during UDCA to 48% during combination treatment (p<0.04). Conclusions-Results showed that: (1) simvastatin reduces serum LDL cholesterol but has no eVect on biliary cholesterol concentration, supporting the concept that newly synthesised cholesterol is not the preferential source for biliary cholesterol; and (2) combination of simvastatin with UDCA has the predicted eVect of enhancing the proportion of UDCA in the pool. This eVect may be of benefit in the treatment of cholestatic liver diseases. (Gut 1999;44:552-556)

By contrast with acute administration in patients with interrupted enterohepatic circulation, chronic administration of tauro-hyodeoxycholic to man with intact enterohepatic circulation has little effect on biliary lipid composition and secretion.