Cardiology Section, University of Oklahoma Health Sciences Center, Oklahoma City 73104.
OBJECTIVE: To determine whether isosorbide-5-mononitrate (IS-5-MN), an active metabolite of isosorbide dinitrate, when given twice daily (in the morning and 7 hours later), prevents development of tolerance and reduction in exercise performance or is associated with a rebound increase in anginal attacks in patients with stable angina pectoris. DESIGN: Multicenter, placebo-controlled, parallel-group, double-blind, randomized study. SETTING: Four university teaching hospitals and five private cardiology outpatient clinics. PATIENTS: 116 patients with stable exertional angina who stopped treadmill exercise because of angina pectoris. INTERVENTION: After stopping all antianginal drugs with the exception of beta-blockers, patients received single-blind placebo for 1 week followed by either 20 mg of IS-5-MN (n = 60 patients) or placebo (n = 62 patients) twice daily at 0800 hours and 1500 hours for 2 weeks. MEASUREMENTS: Serial symptom-limited exercise tests and patients' diaries recording activity and date, time, and severity of anginal attacks. RESULTS: Compared with placebo recipients, patients receiving IS-5-MN walked significantly longer at 2, 5, and 7 hours after the 0800-hour dose (P < 0.01) and at 2 and 5 hours after the 1500-hour dose (P < 0.01). Before the morning (0800-hour) dose, exercise duration increased by 0.53 minutes in placebo recipients and by 0.85 minutes in those receiving IS-5-MN therapy (P = 0.10). Neither nocturnal nor early-morning anginal attacks increased during IS-5-MN therapy compared with placebo. Headaches occurred in 19 (32%) patients in the IS-5-MN group and in 9 (15%) patients in the placebo group but necessitated discontinuation of treatment in only 2 (3%) patients in the IS-5-MN group. CONCLUSION: Isosorbide-5-mononitrate, 20 mg twice daily given 7 hours apart, was well tolerated and improved exercise performance for 7 hours after the morning dose and for 5 hours after the afternoon dose without evidence of development of pharmacologic tolerance. No rebound increase in anginal attacks was found.