Short‐ and Long‐Term Therapeutic Efficacy of Quinidine Sulfate for the Treatment of Chronic Ventricular Arrhythmias

To determine the efficacy and tolerance of oral quinidine sulfate in the treatment of chronic ventricular arrhythmias using contemporary definitions of drug efficacy, 20 ambulatory patients underwent a short-term, placebo-controlled, double-blind trial consisting of four days of quinidine therapy at 400 mg every 6 hours. A long-term trial was conducted in 12 additional patients where ventricular ectopic frequency during two weeks of placebo therapy was compared with that during eight weeks on quinidine sulfate at 300 mg every 6 hours. Quinidine efficacy was determined by 48 hours of Holter monitoring. Blood levels were within the therapeutic range in both trials. Side effects consisted of diarrhea, which occurred in 15 per cent of patients on the short-term and 25 per cent of patients on the long-term trial. Drug effect defined as a statistically significant (P less than 0.025) reduction in chronic premature ventricular complexes occurred in 70 per cent of patients on the short-term trial and in 67 per cent of patients on the long-term trial. In both trials, all patients with ventricular tachycardia had statistically significant suppression. Statistically significant reduction in ventricular couplets occurred in all patients on the short-term trial but in only 73 per cent of the patients on the long-term trial. These data can be used as reference standards for quinidine sulfate in new antiarrhythmic drug comparison trials.