Antiarrhythmic effects of optical isomers of cibenzoline on canine ventricular arrhythmias

Antiarrhythmic effects of (+)-cibenzoline and (-)-cibenzoline were examined using two canine ventricular arrhythmia models. Digitalis arrhythmia, which is suppressed by Na channel blockers, was induced by intermittent intravenous (i.v.) injection of ouabain in pentobarbital-anesthetized dogs. Adrenaline arrhythmia, which is suppressed by Ca channel blockers, was induced by adrenaline infusion in halothane-anesthetized dogs. Ten and 5 mg/kg i.v. (+)-cibenzoline suppressed digitalis- and adrenaline-induced arrhythmias, respectively. The minimum effective plasma concentrations of (+)-cibenzoline for digitalis- and adrenaline-induced arrhythmias were 1.4 +/- 0.4 and 2.0 +/- 0.6 micrograms/ml, respectively (mean +/- SD, n = 6). A lower dose of 1 mg/kg i.v. of (-)-cibenzoline suppressed the digitalis-induced arrhythmia, whereas 5 mg/kg i.v. was needed to suppress adrenaline-induced arrhythmias. The minimum effective plasma concentrations of (-)-cibenzoline for digitalis- and adrenaline-induced arrhythmia were 0.06 +/- 0.04 and 0.7 +/- 0.1 micrograms/ml, respectively (mean +/- SD, n = 6). The stronger antiarrhythmic effect of (-)-cibenzoline indicates that (-)-isomer may have an effect nearly 5-20 times stronger in suppressing Na channels, but effects of both drugs on Ca channels may be almost equipotent.