Table 1.

Categories of drugs that may cause TdP³

Category	Definition
Known risk	Substantial evidence supports the conclusion that these drugs prolong the QT interval AND are clearly associated with a risk of TdP, even when taken as directed in official labeling.
Possible risk	Substantial evidence supports the conclusion that these drugs can cause QT interval prolongation BUT there is insufficient evidence at this time that these drugs, when used as directed in official labeling, are associated with a risk of causing TdP.
Conditional risk	Substantial evidence supports the conclusion that these drugs are associated with a risk of TdP BUT only under certain conditions (e.g., excessive dose, hypokalemia, congenital LQTS or by causing a drug-drug interaction that results in excessive QT interval prolongation).
Drugs to avoid in congenital LQTS	Substantial evidence supports the conclusion that these drugs pose a risk of TdP for patients with congenital LQTS. Drugs on this list include those in the above 3 risk categories and other drugs that do not prolong the QT interval per se but have a theoretical risk of causing arrhythmia that is based on their known stimulant actions on the heart.

LQTS, long QT syndrome; TdP, torsades de pointes.