Combined administration of quinidine with the beta-adrenolytic agent inderal and the local anaesthetic of the beta-aminoketone group, hexacaine, in various experimental models of arrhythmias.

If the antiarrhythmic agents mentioned above are administered in combinations of their respective isoeffective doses, following the "principle of isoeffectivity", a potentiation of their effects takes place. The authors describe methods for the preparation of combined solutions and for the toxicity testing of combined antiarrhythmic agents. When combinations are administered, the toxicity does not increase but on the contrary tends to decrease. If antiarrhythmic agents are combined without regard to the principle of isoeffectivity, the antiarrhythmic effect of the combination deteriorates, and adverse effects may be produced. The basic prerequisite of the potentiation of antiarrhythmic effects in combinations is, in the authors' opinion, the use of drugs differing in both chemical structures and mechanisms of antiarrhythmic actions.