Prolongation of the PQ interval as a measure of therapeutic inequivalence between two formulations of diltiazem

We studied the use of atrioventricular (AV) conduction time to assess the therapeutic equivalence of two diltiazem formulations in 20 volunteers in a double-blind, cross-over trial. ECG recording was carried out before and at several intervals after drug administration, and prolongation of the PQ interval (ΔPQ) was taken as a pharmacodynamic response. In addition, diltiazem plasma concentrations were determined in 8 subjects.