Disposition kinetics of two oral forms of quinidine

There are relatively few studies on the disposition properties of quinidine. We have studied in 10 normal subjects conventional quinidine sulfate and a slow-release quinidine bisulfate. Single and repetitive doses were given; blood and urine concentrations were measured by the method of Cramer and Isaakson.⁵ After a single dose of two tablets of quinidine sulfate (400 mg), the average peak concentration was 2.13 ± 0.22 μg/ml (±SEM); following two tablets of the slow-release form, the average peak concentration was 1.17 ± 0.12 μg/ml T_-max was approximately 2 hr with quinidine sulfate and 4 hr with quinidine bisulfate. One fourth of both forms of the drug was recovered in the urine. Total body clearance was 0.36 Llkg ·hr and renal clearance was 117 ± 22 ml/min for both. With multiple dosing the serum quinidine concentration was higher than these predicted from the results of the single-dose study. Based on the mean estimates of quinidine half-life of 6 hr, a rapid method for achieving steady-state levels of quinidine would be to give an initial dose twice that of the maintenance dose. With the slow-release product if an equivalent dose was given every 12 hr, the mean steady-state quinidine serum concentration would be approximately the same.