Isosorbide mononitrate is a long-acting organic nitrate used primarily for the prophylaxis and treatment of angina pectoris. It is a major active metabolite of isosorbide dinitrate. In the Indian context, it is a cornerstone of chronic stable angina management due to its predictable pharmacokinetics, reduced tolerance development compared to other nitrates, and cost-effectiveness.
Adult: For prophylaxis of angina: Immediate-release: 20mg twice daily, with the two doses taken 7 hours apart (e.g., 8 AM and 3 PM) to provide a nitrate-free interval. Sustained-release: 20mg to 60mg once daily in the morning. Dose must be individualized; starting dose often 20mg.
Note: Tablets should be swallowed whole with a glass of water, with or without food. Do not crush or chew sustained-release tablets. The dosing schedule must maintain a daily nitrate-low interval of 8-12 hours (usually overnight) to prevent tolerance. The last dose of the day should not be taken at bedtime.
Isosorbide mononitrate is a prodrug that is denitrated to release nitric oxide (NO). NO activates cytosolic guanylyl cyclase, leading to increased intracellular cyclic guanosine monophosphate (cGMP). Elevated cGMP causes dephosphorylation of myosin light chains, resulting in smooth muscle relaxation, particularly in venous capacitance vessels, arteries, and coronary arteries.
Pregnancy: Category C (US FDA). Animal studies show adverse effects. Use only if potential benefit justifies potential risk to the fetus. Not recommended during pregnancy unless absolutely necessary for maternal cardiac condition.
Driving: May cause dizziness, lightheadedness, or syncope, especially at initiation of therapy. Patients should not drive or operate machinery until they know how the medication affects them.
| Phosphodiesterase-5 Inhibitors (Sildenafil, Tadalafil, Vardenafil) | Profound, life-threatening hypotension | Contraindicated |
| Other Vasodilators (ACE inhibitors, ARBs, Calcium channel blockers, Alpha-blockers) | Additive hypotensive effect | Major |
| Alcohol | Enhanced vasodilation and hypotension | Major |
| Heparin | Possible reduced anticoagulant effect of heparin | Moderate |
| Dihydroergotamine | May antagonize the anti-anginal effect of nitrates | Moderate |
| Antihypertensives | Enhanced blood pressure lowering | Moderate |
| Tricyclic Antidepressants (TCAs) | Hypotensive effects may be potentiated | Moderate |
Same composition (Isosorbide Mononitrate (20mg)), different brands: