Myasthenia-like syndrome induced by overdosage of cibenzoline

A case of cibenzoline-induced myasthenia-like syndrome is reported. A 67-year-old woman with renal failure and no previous disorder of neuromuscular junction complained of fatigue during climbing up a flight of stairs and experiencing heavy eyelids after administration of 100 mg/day of cibenzoline. Repetitive nerve stimulation tests revealed decrement at 5-10 Hz. After reduction of the dosage, myasthenia-like signs and symptoms disappeared. The peak cibenzoline concentration was still high even after the dose reduction (666.4 ng/ml). In conclusion, cibenzoline, at a high plasma level, may induce myasthenia-like syndrome without any disorder of the neuromuscular junction.