Effects of cholestyramine and colestipol on the plasma concentrations of propranolol

The effect of equivalent hypolipidaemic doses of cholestyramine (8 g) or colestipol (10 g) on the plasma concentrations of propranolol and 4′‐ hydroxypropranolol was studied in 12 normal volunteers following the oral administration of 120 mg of normal release propranolol tablets. When two doses of either cholestyramine or colestipol were administered prior to the propranolol, the peak plasma concentrations and area under the curve for both propranolol and the metabolite 4′‐hydroxypropranolol were reduced significantly (P less than 0.05). We conclude that the drug interaction between cholestyramine or colestipol and propranolol leads to significant reductions in plasma concentrations of propranolol and 4′‐hydroxypropranolol which may cause a clinically diminished effect for a given dosage. Therefore, patients should be observed when either of these resins are added to or deleted from a therapeutic regimen.