[Studies on antiarrhythmic effects and toxicity of quinidine and dihydroquinidine as well as defined mixtures of both in rats (author's transl)].

The antiarrhythmic and acute toxic actions of quinidine (Q) and dihydroquinidine (DHQ) were investigated in experiments in rats. 1. No significant difference was found between Q and DHQ with regard to the doses necessary to suppress electrically induced ventricular fibrillation in the heart (p greater than 0.05). 2. On oral administration, pure DHQ was slightly less toxic than pure Q. This difference is significant (p less than 0.05). It may be explained by a lower absorption rate of DHQ in the rat. Addition of 15 or 30% DHQ to Q did not produce any significant difference in the acute toxic doses (LD50) in comparison with pure Q (p greater than 0.05). 4. The results of a published clinical study showed that the antiarrhythmic actions of pure Q and "commercial" Q are the same with regard to quality, potency and duration. The frequency of side-effects after adminstration of the two alkaloids also did not differ. 5. Limitation or reduction of the DHQ content of pharmaceutical quality quinidine below a technically practicable level does not seem to be justified from a medical point of view from the results of the animal experiments presented and from the clinical study mentioned.