Concurrent use of quinidine and disopyramide: evaluation of serum concentrations and electrocardiographic effects.

The effects of concurrent disopyramide phosphate and quinidine sulfate therapy were studied in 16 normal healthy adults. No adverse effects serious enough to warrant discontinuation of therapy were observed. There was a small but significant increase in disopyramide serum concentration when concurrent quinidine therapy was given and a small decrease in quinidine serum concentration when disopyramide was added. No significant change in elimination half-life was seen for either drug. Both drugs produced prolongation of the corrected QT interval. This QT prolongation was greater for quinidine than for disopyramide.