Metabolite cumulation during chronic propafenone dosing in arrhythmia

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Abstract
The cumulation of propafenone and 2 of its metabolites, 5-hydroxypropafenone (5-OHP) and N-depropylpropafenone (NDPP), was examined in patients with frequent ventricular ectopy. After 2 wk of propafenone therapy (30 mg twice a day), propafenone was discontinued and blood samples were drawn for 24 h. The mean (.+-. SD) steady-state concentrations of propafenone, 5-OHP, and NDPP were 1010 .+-. 411, 174 .+-. 113, and 179 .+-. 93 ng/ml. The concentration ratios of 5-OHP/propafenone and NDPP/propafenone were 0.177 .+-. 0.049 and 0.227 .+-. 0.203. Plasma concentrations of 5-OHP and NDPP did not decay in a log-linear manner during the sampling period and thus estimates of their disappearance t1/2 were not possible. At 24 h after propafenone dosing, concentrations of 5-OHP and NDPP were 63% .+-. 37% and 50% .+-. 21% of their mean steady-state levels. These propafenone metabolites cumulate in the plasma during chronic oral propafenone therapy, and their clinical role needs to be elucidated.

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