[en] In 42 patients with heart failure who were on long-term treatment with flecainide (2 X 100 mg daily by mouth) plasma concentration of flecainide was measured before the morning dose and compared with the clinical grade of heart failure or left ventricular ejection fraction (in the levo-angiogram). Mean plasma flecainide concentration was 415 +/- 244 ng/ml (110-1035 ng/ml), mean ejection fraction 55 +/- 17.7% (24-84%) (r = -0.60). In seven patients with plasma concentrations over 700 ng/ml (870 +/- 150 ng/ml) in clinical grade III or IV, ejection fractions were 24, 25, 25, 30, 33, 37 and 44%, respectively. In two patients (ejection fraction of 24 and 25%, respectively) the morning plasma concentration was around 1000 ng/ml. The results point to possible high plasma flecainide concentrations--at times in the toxic range--in patients who are in heart failure. In patients with marked reduction in left ventricular pumping function who are on long-term flecainide treatment, a reduction in dosage or monitoring of plasma flecainide concentration is indicated.
