A simple method of monitoring antiarrhythmic drugs during short- and long-term therapy

Abstract Since the classic studies by Sokolow and Edgar 1 with quinidine, and Koch-Weser and Klein 2 with procainamide, “therapeutic ranges” have been proposed for most of the available antiarrhythmic drugs. 1–5 One problem with therapeutic ranges of these agents is their determination by a variety of methods in heterogenous samples of patients. Recently, we evaluated the utility of antiarrhythmic concentrations determined during electrophysiologic serial drug testing. 6 An extremely wide range of effective concentrations was found for the type IA agents, e.g., procainamide 2.9 to 22.2 μg/ml and quinidine 1.0 to 9.1 μg/ml. It was suggested that in a given patient with a symptomatic tachycardia, a specific threshold or “target” concentration exists at which efficacy occurs, but this value is quite variable and unpredictable. If the target concentration could be determined during an objective assessment of efficacy, such as electrophysiologic drug testing or continuous electrocardiographic monitoring, then it could be used to develop an effective long-term regimen. In this manner, true drug failure during long-term therapy might be distinguished from a recurrence of the tachycardia due to concentrations below the threshold for efficacy. The purpose of this study is to evaluate this concept.