Is Isosorbide a Nitrate?
Yes, isosorbide compounds—both isosorbide dinitrate and isosorbide mononitrate—are organic nitrate medications that work by releasing nitric oxide to cause vasodilation. 1, 2
Chemical Classification and Mechanism
Both isosorbide dinitrate and isosorbide mononitrate belong to the organic nitrate class of medications, functioning as exogenous sources of nitric oxide that replenish or restore the actions of endothelium-derived relaxing factor. 3, 4
These compounds work by relaxing vascular smooth muscle through biodegradation to nitric oxide, which stimulates guanylate cyclase in vascular smooth muscle cells, producing cyclic guanosine monophosphate (cGMP) and ultimately causing vasodilation. 5, 6
The FDA explicitly classifies isosorbide mononitrate as an organic nitrate, stating that "the principal pharmacological action of ISMN and all organic nitrates in general is relaxation of vascular smooth muscle." 1
Key Differences Between the Two Formulations
Isosorbide dinitrate is the parent compound that requires hepatic metabolism to produce active metabolites, with a duration of action of 4-8 hours for standard formulations. 3, 7
Isosorbide mononitrate is the major active metabolite of isosorbide dinitrate, with approximately 100% bioavailability and no first-pass metabolism, providing a longer duration of action of 12-24 hours. 1, 4
The American College of Cardiology specifically recommends isosorbide dinitrate (not mononitrate) for heart failure management, with a target dose of 40 mg three times daily when combined with hydralazine. 3
Clinical Context
All three commonly used nitrate formulations—nitroglycerin, isosorbide dinitrate, and isosorbide mononitrate—share the same fundamental mechanism of providing nitric oxide to induce therapeutic vasodilation. 2, 5
The primary hemodynamic effects include venodilation (reducing preload), arterial dilation (reducing afterload), coronary artery dilation (improving myocardial oxygen supply), and decreased myocardial oxygen requirements. 4, 7, 1