Enteric coated quinidine compared to sustained release preparations during repeated administration.

The concentration of quinidine in plasma was measured in 12 healthy subjects during multiple administration of an enteric coated tablet (Systodin) and two sustained release preparations (Kinidin Duretter and Kinilentin). In a second study, involving another 12 subjects, the enteric coated tablet and the most widely used sustained release preparation (Kinidin Duretter) were compared with plain uncoated quinidine sulphate tablets in order to calculate the relative bioavailability of the formulations used for maintenance therapy. The largest area under the plasma concentration-time curve (AUC12h) during a dosage interval (12 hours) was obtained with the plain tablets and with the enteric coated formulation. The variation of the plasma concentrations during the dosage interval was not larger with the enteric coated tablets than with the sustained release preparations. The time of appearance of peak concentration after administration was longer and more variable with the enteric coated tablets. In relation to the plain quinidine tablets, the bioavailability of Systodin and Kinidin Duretter was 96% and 84%, respectively. In 21 out of 24 crossover experiments with Kinidin Duretter and Systodin the AUC12h was larger with the latter formulation. Enteric coating appears to be a simple and reliable means of achieving delayed absorption and stable quinidine plasma levels during maintenance therapy.