Assessment of Bioavailability of Organic Nitrates/Comparative bioavailability study of sustained-release isosorbide dinitrate preparations. Relative bioavailabilities of isosorbide dinitrate (ISDN, CAS 87-33-2) and the metabolite isosorbide-5-mononitrate (IS-5-MN, CAS 16051-77-7) were studied after application of Maycor retard 40 (sustained-release capsules, multiple unit formulation, test preparation) in comparison to sustained-release tablets (single unit formulation, reference preparation) with 16 healthy male volunteers in a two-way crossover design. Test and reference formulations were previously characterised in vitro by dissolution tests. ISDN, IS-5-MN (IS-2-MN) plasma concentrations were determined using a selective and sensitive GLC-method with ECD-detection. As pharmacokinetic parameters AUC, Cmax and half value duration (HVD) were evaluated. Bioequivalence was assessed by calculating 90%-confidence intervals (ANOVA, ANOVAlog, Mann-Whitney-test) for ISDN and IS-5-MN. Bioequivalence was accepted if due to the inclusion rule one of the calculated intervals fulfill the requirements of 80 and 120% (AUC) or 70 and 130% (Cmax, HVD), respectively. Relative bioavailability of the test formulation was calculated as 94% (ISDN) and 96% (IS-5-MN). Maximum plasma concentrations of ISDN (IS-5-MN) were determined for the test preparation as 14.3 +/- 3.1 ng/ml (265 +/- 45 45 ng/ml) and as 22.8 +/- 12.6 ng/ml (287 +/- 59 ng/ml) for the reference product. HVD-values were for the test preparation 4.5 +/- 1.3 h (ISDN) and 8.5 +/- 1.3 h (IS-5-MN) and for the reference formulation 3.1 +/- 1.2 h (ISDN) and 8.1 +/- 1.4 (IS-5-MN).(ABSTRACT TRUNCATED AT 250 WORDS)