Comparison of the therapeutic efficacy of continuous and intermittent injection of isosorbide dinitrate: a randomized study on unstable angina.

Therapeutic efficacy of intermittent and continuous injection of isosorbide dinitrate (ISDN) was compared in 22 patients (mean age 64 +/- 10, 18 males and 4 females) with unstable angina at rest. They were randomized into 2 groups that received either continuous (10 mg/h, group A) or intermittent (10 mg/10 min every 2 hours, group B) injection of ISDN for 3 days (phase 1). Each injection protocol was switched (phase 2) and subsequently switched back to the initial protocol (phase 3) in a cross-over fashion. The serum concentrations of ISDN, 2-isosorbide mononitrate (2-ISMN) and 5-ISMN were measured serially during both intermittent and continuous injection protocols. In addition, the incidence and duration of angina and changes in systolic blood pressure were analyzed. There were 3 treatment-failure cases during the intermittent injection period and 1 during the continuous injection period. Three of these treatment-failure cases developed small acute myocardial infarcts despite emergent coronary arteriography followed by intra-coronary thrombolysis and percutaneous balloon angioplasty. There was no difference in therapeutic efficacy between continuous and intermittent ISDN in terms of the incidence, duration of angina attacks and the number of patients whose angina was suppressed. After bolus injection of ISDN (10 mg/10 min), the serum concentration of ISDN increased rapidly and returned to the control level at 60 minutes after the injection. The serum 5-ISMN and 2-ISMN concentrations also increased immediately after injection and then decreased gradually reaching statistically insignificant level to the control values at 60 minutes after injection. With continuous injection, ISDN and its metabolites increased gradually and reached similar but slightly lower serum concentrations to the peak levels during intermittent injection. We conclude that the therapeutic efficacy of intermittent and continuous injection of ISDN is similar in patients with unstable angina.