Two cases of life-threatening arrhythmia induced by risperidone: evaluation of risperidone and 9-hydroxy-risperidone concentrations.

Arrhythmia related to risperidone has proven rare but sometimes fatal. Serum concentrations of risperidone and the metabolite 9-hydroxy-risperidone (9OH-RIS) during these events are seldom documented. As 9OH-RIS shows pharmacological activity equivalent to risperidone, it may induce life-threatening arrhythmia (regardless of the intake dosage). It is critical to evaluate the serum concentration of 9OH-RIS in suspected risperidone toxicity.