The multiple modes of action of propafenone

Previous studies of widely different concentrations of propafenone in various species have reported that in addition to having class 1 antiarrhythmic action, the drug was a beta adrenoceptor blocker and a calcium antagonist. High concentration shortened action potential duration in animal experiments, but Q-T interval was reported as being lengthened in man. It was thought desirable to study the effects of propafenone over a range of concentrations equivalent to those used clinically in various cardiac tissues of a single species, the rabbit. It was concluded that although the primary action of propafenone was on fast inward current, the drug being categorised as of group 1c, its potency as a beta blocker was sufficient for the effect to be of clinical significance. Its potency as a calcium antagonist was relatively weak. Action potential duration and effective refractory period were lengthened in both atrium and ventricle, the effects being long-lasting and persisting on wash-out of the drug when other measurements had returned to control values.