A case of severe respiratory depression due to cibenzoline overdosage induced by a transient renal dysfunction

A 69-year-old man was transferred to our hospital because of severe general fatigue and progressive systemic muscle weakness. He had taken 300 mg/day of cibenzoline for his sustained ventricular tachycardia (VT) for years. At the end of June 2001 he began to feel general fatigue, which slowly progressed to systemic muscle weakness and walking disturbance. On 2nd July 2001, he finally could not stand up by himself. He also felt dyspnea. He was transferred to our emergency room, where he developed severe respiratory depression. Acute myocardial infarction was ruled out based on his ECG and blood chemistry data. Serum BUN and creatinine were elevated to 32 and 2.2 mg/dl, respectively, which returned to normal range 2 weeks later. What we did in our ICU were basically a replacement of cibenzoline with mexiletine and mechanical support of ventilation. As his renal function gradually improved, his spontaneous respiration and muscle power were slowly restored. He was discharged on foot after 1 month of hospitalization. His blood cibenzoline content taken 2 days after the cessation of cibenzoline was 959.6 mg/ml that was abnormally elevated. Considering metabolism and excretion for the 2 days between the cibenzoline cessation and the blood sample drawing, his cibenzoline level on the day of admission must have been extraordinary high. We should be aware of the possibility of abrupt overdosage of cibenzoline even in patients with normal kidney function in the event of a transient or an acute renal dysfunction.