Gemfibrozil is frequently used for lipid-lowering in familial combined hyperlipidaemia (FCHL) and in other forms of combined hyperlipidaemia. This therapy increases biliary cholesterol saturation, enhancing the risk for gallstone formation. Furthermore, in hypertriglyceridaemia, LDL cholesterol levels often tend to rise. We have explored the possibility that addition of a low dose of cholestyramine to gemfibrozil therapy obliterates these phenomena. Eighteen gallstone-free patients with definite (n = 5) or probable (n = 10) FCHL, or combined hyperlipoproteinaemia (n = 3) were randomized to a 6 week treatment with gemfibrozil, 600 mg b.i.d., or gemfibrozil 600 mg b.i.d. plus 4 g cholestyramine o.d. After 6 weeks the patients were crossed over to the alternative treatment. Plasma lipoproteins and biliary lipids were determined at baseline and at the end of each period. Institution of gemfibrozil treatment resulted in a decrease in plasma cholesterol by 15% (P less than 0.05) and in plasma triglycerides by 47% (P less than 0.05); HDL cholesterol increased by 18% (P less than 0.05). Addition of cholestyramine further decreased plasma and LDL total cholesterol by 9% (P less than 0.05). Total triglycerides and HDL cholesterol did not change. Gemfibrozil treatment was associated with a rise in the relative biliary concentration of cholesterol from 5.6 +/- 0.4 to 6.9 +/- 0.5 molar percent (P less than 0.01), and a parallel decrease in the relative concentration of bile acids, resulting in an increased cholesterol saturation of the bile, from 77 +/- 5 to 90 +/- 6% (P less than 0.05). This change was not observed during the combined therapy (mean cholesterol saturation, 82 +/- 4%).(ABSTRACT TRUNCATED AT 250 WORDS)

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