Table 6: Relative risk of QTc interval prolongation with common antipsychotic agents.

Risk levelAgent

ECG required or strongly recommended before prescribing (most commonly associated with QTc interval prolongation and torsade de pointes)Thioridazine
Mesoridazine
Droperidol
Pimozide
Haloperidol in large doses IV (commonly ≥100 mg/d)

Mild to moderate risk of QTc interval prolongation (~20 ms) when prescribed alone or with a metabolic inhibitorQuetiapine
Ziprasidone
Chlorpromazine

Little or no risk of QTc interval prolongation (~20 ms) when prescribed alone or with a metabolic inhibitorHaloperidol (oral)
Olanzapine
Risperidone
Clozapine