Clinical and Circulatory Effects of Isosorbide Dinitrate

In order to resolve current controversies on isosorbide dinitrate (ISDN), we employed a particularly sensitive testing protocol to evaluate effects of sublingual ISDN and nitroglycerin on the exercise capacity of patients with angina. Ten minutes after ISDN 21 of 23 patients exercised longer (average 2.7 minutes, P < 0.001) than after placebo. Benefit was evident in only a minority of patients tested one hour and in none tested two hours after either ISDN or nitroglycerin. A given amount of exercise resulted in lower mean blood pressure (average 13 mm Hg, P < 0.001), higher heart rate (average 10 beats/min, P < 0.001), and shorter ejection time (average 0.04 second, P < 0.001) after ISDN. Similar changes were seen after nitroglycerin. The product of blood pressure, heart rate, and ejection time, an index of myocardial O 2 consumption, was unchanged at angina after ISDN or nitroglycerin despite the increased exercise capacity, suggesting that clinical improvement after these drugs may be due to circulatory changes causing decreased myocardial O 2 demand. We conclude that sublingual ISDN closely resembles nitroglycerin in its alteration of circulatory responses to exercise and in the duration of the resultant improvement in exercise capacity.