REMINDER: The QTdrugs List includes three distinct risk categories for Torsades de Pointes (TdP) and QT prolongation but not all drugs in the List should be considered “QT prolonging”.
Because of the inherent complexity of drug-induced QT prolongation and the ensuing risk of developing TdP, AZCERT has sub-divided the QTdrugs List into three categories of risk of causing TdP.1 We want to remind those who wish to use the QTdrugs List in clinical decision making of the differences between these categories and caution that the QTdrugs List should not simply be thought of as a list of “QT-prolonging drugs”… it is not.
Drugs that are in the Known Risk of TdP category have clear and compelling evidence that they can cause TdP. By definition, they prolong the QT interval because that action is required for induction of TdP. These drugs should be avoided in patients with known QT prolongation unless there is a compelling reason for their use. This category has been extensively evaluated and found useful in clinical decision support programs and, when used as factors in QT/TdP risk scores, has been proven to be a major contributor to the score’s accuracy for predicting increased mortality2 and excessive QT prolongation.3-5 Because of the extensive supporting data, we recommend that this category be used in clinical decision support systems for QT risk management.
Drugs in the Possible Risk of TdP category have definite evidence of QT prolongation when they are taken as intended BUT they do not, at this time, have convincing evidence for risk of TdP. In patients known to have QT prolongation, these drugs may increase TdP risk and we would not recommend using them unless clinical benefit is expected to be high. When evaluated in clinical decision support programs, these drugs have not been found to contribute to their predictive accuracy6 and we do not recommend they be used to calculate a clinical QT risk score at this time.
Drugs in the Conditional Risk of TdP are a complex group of drugs that have been associated with TdP BUT only under certain conditions such as overdose or when they are used in combination with drugs or conditions known to prolong the QT interval. Since many of these drugs do not per se prolong the QT interval, we do not consider the category to be “QT-prolonging” and do not recommend they be used as risk factors in clinical decision support programs.
Lastly, in addition to the QTdrugs List, the CredibleMeds website offers a separate list of Drugs to Avoid in congenital long QT syndrome (cLQTS). This list includes all drugs in the QTdrugs List plus some additional non-QT-prolonging drugs that could have special risk for some patients with cLQTS. Whereas the list is extremely useful to inform those with cLQTS, we do not recommend that the Drugs to Avoid in cLQTS list be used in clinical decision support programs at this time.
We hope this information is clarifying and we would be glad to answer any questions about how the QTdrugs list has been constructed and the definitions of its risk categories for TdP. Contact us at firstname.lastname@example.org.
Raymond L. Woosley, MD, PhD and C. William Heise, MD, AZCERT