PHARMACOKINETICS AND HEMODYNAMIC-EFFECTS OF ISDN FOLLOWING DIFFERENT DOSAGE FORMS AND ROUTES OF ADMINISTRATION

The pharmacokinetics and haemodynamic effects of isosorbide dinitrate (ISDN) have been investigated following administration of single doses as a sublingual (SL) spray (2.5 mg), sublingual tablet (5 mg) and per oral tablet (10 mg) in a randomised, placebo-controlled double-blind c ross-over trial in 16 healthy volunteers. After the sublingual spray C -max was higher (39.0 ng.ml(-1)) and t(max) was shorter (3.9 min) than after the sublingual (22.8 ng.ml(-1) and 13.8 min) and peroral (16.9 ng.ml(-1) and 25.6 min) tablets. The AUC of ISDN did not differ follow ing any of the three formulations (1031; 879; 997 ng.ml(-1) min, for t he spray, SL tablet and PO-tablet, respectively). Mononitrate metaboli tes of ISDN (IS-2-MN and IS-5-MN) and total nitrates in plasma increas ed in proportion to the administered dose. This indicates that the fra ction of the dose absorbed was the same for all the formulations but t hat the extent of first-pass metabolism increased in the order subling ual spray < sublingual tablet < peroral tablet. Thus, compared to the spray, the relative bioavailability of ISDN was 48 % and 28 % from the sublingual and peroral tablets, respectively. The haemodynamic effect s were quantified using the a/b ratio of the finger pulse wave and the systolic blood pressure and heart rate under orthostatic conditions. For the a/b ratio of the finger pulse, the maximal effect was higher ( e(max) = 130 %) and the time to e(max) (t(emax)) shorter (16.6 min) af ter the spray than the sublingual tablet (84.4% and 25.5 min) or peror al tablet (90.2 and 31.3 min). The onset of effect was within 3, 5 and 7.5 min after the spray, sublingual and peroral tablets, respectively . A larger change in the orthostatically-induced decrease in systolic blood pressure and increase in heart rate was obtained following peror al than sublingual administration despite the similar plasma concentra tions of ISDN. This probably reflects the larger amount of pharmacodyn amically active mononitrate metabolites formed after oral dosing. The integrated effect following administration of 2.5 mg ISDN as spray was similar to that of a sublingual tablet of 5 mg.