Comparison of two long-acting forms of quinidine

The bioequivalence of two forms of long acting quinidine compounds was assessed (Kinidin durules and Longacor) using drug plasma level and QT ECG changes. Six healthy volunteers received each preparation on two occasions in random order. The wash out period between successive experiments was at least 7 days. There was no difference in tmax, Cmax and AUC for plasma level and adjusted QT. However, between patient variability was large. A 20% difference in plasma levels could not be excluded but the difference in QT max and QT AUC between the two preparations did not exceed 20% (P less than 0.05, Westlake's method). This study illustrates the fact that pharmacodynamic equivalence, let alone therapeutic equivalence, does not necessarily imply plasma level equivalence, as assessed by the current method.