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The Assessment of QT/QTc Interval Prolongation in Clinical Trials: A Regulatory Perspective*

Excessive prolongation of the QT/QTc interval creates an electrophysiological environment that predisposes the myocardium to torsade de pointes, a polymorphic ventricular tachyarrhythmia that can progress to ventricular fibrillation and sudden cardiac death. Identification of QT/QTc prolongation liability is therefore an important objective of contemporary drug development programs. Nonclinical safety pharmacology studies are useful in early identification of this cardiac safety problem and in preliminary risk assessment. Specialized clinical pharmacology studies play a critical role in characterizing the magnitude, time course, dose dependency, and concentration relationship of drug-induced QT/QTc prolongation, as well as guiding the intensity of electrocardiogram (ECG) safety evaluations in subsequent trials. The reading, analysis, and interpretation of the ECG data acquired through these studies are complex issues that present many challenges to the pharmaceutical industry and regulatory authorities alike.