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

CASES: Case 1: A 20‐year‐old woman suffering a suspected overdose was transported to the hospital. She presented bradycardia with wide QRS waves and QT prolongation, followed by cardiac arrest. Extracorporeal cardiopulmonary resuscitation was implemented, improving circulation. Risperidone and 9OH‐RIS levels were 9.6 ng/mL and 127.6 ng/mL, respectively. Case 2: A 54‐year‐old woman was hospitalized for femoral fracture and underwent surgery. Her electrocardiogram showed bradycardia and complete AV block. Risperidone and 9OH‐RIS levels were 3.2 ng/mL and 61.4 ng/mL, respectively. OUTCOME: In both cases, only serum concentration of 90H‐RIS were elevated. CONCLUSION: 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.