THE RELATIONSHIP OF DOSAGE SCHEDULE TO THE BLOOD LEVEL OF QUINIDINE, USING ALL AVAILABLE QUINIDINE PREPARATIONS.

Blood quinidine levels obtained by single and multiple dosage schedules of all available quinidine preparations were ascertained. A maintenance blood level of 4 to 7 mg./l. of quinidine was considered a desirable range to prevent recurrence of auricular fibrillation in patients previously converted to sinus rhythm. Quinidine sulfate, quinidine gluconate, dihydroquinidine gluconate and quinidine polygalacturonate were given in dosage schedules of one tablet (equivalent to 200 mg. quinidine) every eight hours for four days, then two tablets every eight hours for three days. Blood quinidine levels were determined the same time each day. Schedules of two tablets of quinidine sulfate or quinidine gluconate every eight hours resulted in blood levels between 4 and 7 mg./l. Similar dosage schedules of the other preparations did not produce levels of this order, nor did quinidine polygalacturonate administered in a 12-hourly schedule. Serious respiratory arrest occurred in one case following quinidine sulfate. No other toxic reactions were noted in this study.