Evaluation of the effect on cardiac repolarization (QTc interval) of oncologic drugs.

ABSTRACT

The 12-lead electrocardiograph (ECG) is the standard safety measurement used in clinical trials to identify drug-induced cardiac adverse effects. Drug-induced prolongation of the QTc interval (the measure of cardiac repolarization change), when excessive and in conjunction with the right risk factors, can degenerate into a polymorphic ventricular tachycardia called torsades de pointes and has become a new focus for new drug development. The assessment of an ECG in clinical practice using machine-defined QTc duration is intrinsically unreliable. Current regulatory concepts have focused on the need for measuring ECG intervals using manual techniques using digital processing in a central ECG laboratory. The QT interval is subject to a large degree of spontaneous variability requiring attention to basic clinical trial design issues such as sample size (use as large a cohort as possible), frequency of measurements taken (at least three to six ECGs at baseline and at many time points on therapy with pharmacokinetic samples if possible), and their accuracy. Since most oncologic products are cytotoxic, a Thorough or Dedicated ECG Trial cannot be conducted and in the usual trail, especially in phase I, all changes seen on the ECG will be attributed to the new oncology drug. For most nononcologic drugs, there is regulatory guidance on how much an effect on QTc duration might be related to the risk of cardiac toxicity. For oncology products, the central tendency magnitude and proportion of outliers needs to be well defined to construct a label if the risk-benefit analysis leads to marketing approval. Clinical cardiac findings such as syncope, ventricular tachyarrhythmias, and other cardiac effects will be important in this analysis.