Propafenone, like other cardioactive drugs (metoprolol, propranolol, encainide) is submitted to oxidative metabolism, evaluable by assessment of debrisoquine oxidative capacity. Two phenotypes have been described: extensive and poor oxidizers, with interethnic differences in the prevalence of poor oxidizers. Aims of this study were: 1) to assess the oxidative phenotype in a sample of the Italian population and 2) to evaluate the relationships between oxidative capacity and propafenone pharmacokinetics or pharmacodynamics. The ratio between debrisoquine (D) and 4-hydroxy-debrisoquine (4-OH-D) in the urines after D administration (10 mg) was employed to characterize oxidative phenotype in 90 subjects (42 arrhythmia patients and 48 healthy volunteers). In 10 patients, extensive oxidizers of debrisoquine, we studied propafenone (P) and 5-hydroxy-propafenone (5-OH-P) kinetics after acute oral administration (450 mg) and chronic oral treatment (300 mg tid for 2 weeks), followed by wash out.
Results: 1) the prevalence of poor oxidizers (D/4-OH-D ratio greater than 12.6) in our population resulted to be 6.6%, like in other studies in Caucasians; 2) propafenone kinetics was strictly related to oxidative capacity since D/4-OH-D ratio strictly correlated with the ratio of P and 5-OH-P areas under curve in acute (r = 0.91) and in chronic administration (r = 0.90) and with P half-life in acute (r = 0.82) and in chronic administration (r = 0.82); 3) QRS widening both during chronic treatment and after acute administration correlated with oxidative capacity (r = -0.78 and -0.68 with D/4-OH-D ratio respectively) and with 5-OH-P areas under curve (r = 0.84 and 0.70 respectively); it did not correlate with P areas under curve. In conclusion both kinetics and electrophysiological effects of propafenone strictly correlate with oxidative capacity, even in extensive oxidizers. Thus even a small reduction in oxidative capacity may have relevant consequences during propafenone oral treatment.