[Pharmacogenetic study of the response to flecainide and propafenone in patients with atrial fibrillation].

We analyzed cytochrome P450 2D6 polymorphism by determining phenotype as the metabolic ratio between dextromethorphan and its main metabolite, dextrorphan. We studied 18 men and 22 women in whom mean age was 54.6+/-11.9 years. In 9 patients metabolic ratio was determined before antiarrhythmic treatment and again during treatment, with a mean increase of 0.13+/-0.15 (P=.03). We found 19 poor metabolizers and 21 extensive metabolizers. Adverse effects were more frequent in poor metabolizers (21.1%) than in extensive metabolizers (4.8%; P=.12). Antiarrhythmic treatment was effective in 27 patients (67.5%), with no difference between poor and extensive metabolizers.