QT INTERVAL - A MEASURE OF DRUG-ACTION

Historically, QT prolongation, occurring with or without drug, therapy , has been considered primarily as a clinical marker for risk of arrhy thmia. However, as understanding of cardiac repolarization improves an d ability to measure accurately small changes in QT interval increases , the QT interval will be used as a marker for drug action as well. In addition, QT prolongation may prove to be a valuable tool for detecti ng and quantifying risk of arrhythmia due to drugs. This has been emph asized recently by the experience with terfenadine. Use of the QT inte rval as a marker for toxicity and efficacy will require sensitive and specific methods that are currently being developed and validated. The current methodologies for detecting small changes in the QT interval and the significance of those changes are discussed.