Acute oral testing for determining antiarrhythmic drug efficacy. I. Quinidine.

Acute oral drug testing with quinidine was used in 18 patients with high grade ventricular arrhythmia. This method involves administering a single large dose of the antiarrhythmic agent, monitoring heart rhythm by means of programmed trendscription and determining blood drug levels at selected intervals. After quinidine was given in a dose of 0.6 g, 10 patients had a positive response, defined as a 50% or greater reduction in ventricular premature beats and abolition of repetitive ectopic beats. Drug action began a mean of 88 minutes after administration, and the mean peak blood quinidine level was 3.2+/-0.5 (standard error) mug/ml. Four patients had a paradoxic increase in arrhythmia. In nine patients the response to acute drug testing was compared with the response to maintenance quinidine therapy with doses of 1.2 and 1.8 g/day. The presence of arrhythmia was assessed with 24 hour ambulatory monitoring and exercise stress testing. With both techniques, seven of nine patients showed results concordant with those of acute testing. Disparity in results of the two methods of drug administration was explained by the serum concentration of quinidine. Acute oral drug testing provides a new approach for determining expeditiously whether quinidine is effective or hazardous in an individual patient.