Serum concentrations of isosorbide dinitrate produced by a sustained-release capsule

The bioavailability of isosorbide dinitrate (ISDN) and the time course of its serum concentration produced by a standard 20-mg tablet and a sustained-release capsule were compared in six normal volunteers. Following administration of the tablet, serum ISDN concentrations reached a peak of 29 ng/ml at 0.5 h, declined monoexponentially with a t1/2 of 25.5 min, and disappeared after 2 to 3 h. Following the administration of the sustained-release capsule, serum ISDN concentrations reached a plateau of 4 ng/ml between 2 and 5 h, and declined slowly and nonlinearly up to and including the 10-h point. The total amount of ISDN absorbed was 1.32 times greater with the standard tablet; following the absorption of the capsule, there was truncation of the serum concentration curve due to ongoing absorption at and beyond 10 h.