Appearances of Premature Atrial and Ventricular Contractions After Switching From Brand Name to Generic Cibenzoline

In antiarrhythmic drugs, the therapeutic window is narrower than in other drugs. Brand name and generic drugs do not use the same inactive ingredients and binder substances. We report a 78-year-old male patient who had been treated for asymptomatic atrial fibrillation and atrial/ventricular premature contractions. Brand name cibenzoline had completely suppressed all arrhythmias. When the medication was changed to the generic drug, the patient showed frequent palpitations and arrhythmias. After restarting the brand-name drug, the arrhythmias were completely suppressed again. These results showed clear differences between brand name and generic cibenzoline in a specific patient. This report is the first case to describe the diminished effectiveness of generic oral cibenzoline.