Quinidine in the Treatment of Auricular Arrhythmias
THE clinical efficacy of a drug is determined by weighing the anticipated benefits from its use against the danger of toxic effects. Lack of appreciation of this fact has led to misunderstanding relative to the value of quinidine. When properly employed, quinidine is a safe and effective drug in the treatment of certain auricular arrhythmias. Increasing interest in the cardiac arrhythmias in recent years warrants a review of the toxic and therapeutic effects of quinidine.
Physiologic Action, Dosage, and Toxic Effects of Quinidine
Quinidine prolongs conduction recovery in the auricular muscle and slows the rate of discharge from cctopic foci. It raises the threshold in experimental production of auricular arrhythmias.1 The importance of decrease in vagal tone secondary to the use of the drug is not known.
It has been demonstrated that the maximum level of concentration in the blood after oral administration of quinidine is attained in about two hours.2 For this reason, when quinidine is used in the treatment of important auricular arrhythmias, it should be given at intervals of two hours, usually in a dosage of 0.4 Gm. of quinidine sulfate for five closes. Quinidine has cumulative action, so that gradually increasing concentrations in the blood arc achieved. Even 12 hours after the last dose, the blood level remains about 40 per cent of the maximum level; for this reason, the same dosage schedule on the second day may be of therapeutic benefit. If the arrhythmia persists, the dosage may be increased to 0.6 Gm. every . . .