The genetic control of bufuralol metabolism in man

Bufuralol (Ro 3 - 4787, Angium) is a non selective beta-adrenoceptor blocking drug with some degree of sympathomimetic action and a longer duration of action than propranolol. Plasma concentrations of bufuralol and 1'-hydroxybufuralol, its main blood derivative which shows similar beta-adrenoceptor blocking properties, were determined in healthy volunteers after a 60 mg oral and a 20 mg intravenous dose. Peak plasma concentrations were higher for the parent drug but due to a longer elimination half-life, the metabolite concentrations became higher after a few hours (bufuralol t 1/2 = 2.7 +/- 0.9 h, metabolite t 1/2 = 6.1 +/- 1.5h). The bioavailability of the tablet tested was 46 +/- 15%. The occurrence of side-effects in a subject with abnormal pharmacokinetics of the drug in this study and in a previous study with this drug suggested the possibility of a pharmacogenetic anomaly. Determination of the plasma metabolic ratio in the family of this subject and in a larger population confirmed that aliphatic hydroxylation of bufuralol is under polymorphic control. Phenotyping of our volunteers with debrisoquine showed the present pharmacogenetic anomaly to be the same as the one reported for debrisoquine alicyclic hydroxylation. The occurrence of side-effects in poor metabolizers as seen with bufuralol illustrates the clinical relevance of the hydroxylation polymorphism. In Switzerland the frequency of poor metabolizers is about 9% as previously reported for caucasian British subjects.