Imdur contains isosorbide-5-mononitrate (IS-5-MN) in a controlled-release (Durules) formulation. It has a significant anti-anginal effect when taken once daily at a dose of 60 mg. This anti-anginal effect persists during long-term treatment without the development of tolerance; once-daily treatment produces a plasma nitrate profile that is high enough to give anti-anginal protection during the daytime, but low enough during the latter part of the dosage interval to avoid the development of tolerance. Evidence shows that once-daily Imdur is equivalent in efficacy to plain tablets of IS-5-MN and isosorbide dinitrate taken three times daily at the same total daily dosage (60 mg), and to the calcium antagonist diltiazem (60 mg three times daily). In addition, the anti-anginal protection provided by Imdur in combination with beta-blocker treatment is superior to that achieved with beta-blocker treatment alone. In long-term studies Imdur has been shown to be well tolerated.