[Torsades de pointes ventricular tachycardia induced by disopyramide at therapeutic serum concentration]

We describe a patient who developed torsades de pointes ventricular tachycardia after several years of treatment with disopyramide. The case demonstrates that measuring disopyramide serum concentration provides limited information about correct dosages. Life-threatening arrhythmias may arise even at recommended doses and therapeutic serum concentration. Clinical trials have shown that class Ic antiarrhythmic drugs, and perhaps all class I antiarrhythmics, may increase the risk of serious arrhythmias and sudden death in certain groups of patients. Aspects of the pharmacology of disopyramide are discussed, with particular emphasis on the variable plasma protein binding and the narrow therapeutic specter. This complexity seems to be the most important reason for the limited reliability of serum concentration measurements for predicting the best dosage for the individual patient.