Differences in the production of methemoglobin during high-dose treatment with isosorbide dinitrate or isosorbide 5-mononitrate.

12 patients with coronary heart disease were studied to see whether high doses of isosorbide dinitrate (ISDN, Corovliss) or isosorbide 5-mononitrate (IS-5-MN, Ismo) increase the erythrocyte methemoglobin production in an acute experiment and after 4 days of medication. The patients were divided into two groups. Group 1 (6 patients) was given a single dose of 80 mg ISDN on the morning of day 1 and Group 2 (6 patients) was given 80 mg IS-5-MN as a single oral dose. Under the influence of the IS-5-MN no change was observed from the initial methemoglobin (met-Hb) value (0.81% of the total Hb) at measurements performed 1 and 2 h after the administration of the drug. In Group 1 (ISDN) the initial met-Hb value was 0.58% of the total Hb, a slight increase to 0.70% being observed after 1 h and to 0.77% after 2 h (p less than 0.05). The patients were then treated as follows for a further 4 days: Group 1 480 mg ISDN/d, Group 2 480 mg IS-5-MN/d. On day 5 the initial met-Hb values in both groups were unchanged compared to day 1. The patients were then given first 80 mg ISDN (Group 1) or 80 mg IS-5-MN (Group 2) and 4 h later a single dose of 160 mg of the appropriate substance. In Group 2 (IS-5-MN) the met-Hb content remained unaffected. In Group 1 a slight increase of the met-Hb to 0.79% occurred 1 h after 80 mg ISDN and to 0.9% after 2 h (p less than 0.05). The dose of 160 mg ISDN gave rise to a further slight increase to 1.00% (after 1 h) and 1.13% (after 2 h) (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)