Isosorbide dinitrate is an organic nitrate vasodilator used primarily for the prophylaxis and treatment of angina pectoris. It is a prodrug that undergoes denitration to form the active metabolites, isosorbide-2-mononitrate and isosorbide-5-mononitrate. It reduces myocardial oxygen demand by decreasing preload and afterload through venous and arterial dilation. In the Indian context, it is a widely available, cost-effective antianginal agent, though its use has been partially supplanted by newer agents and the mononitrate formulation in chronic management.
Adult: Angina Prophylaxis: Initially 5mg to 10mg orally two to three times daily. Usual maintenance: 10mg to 20mg two to three times daily. Maximum: 120mg/day in divided doses. MUST incorporate a nitrate-free interval of 10-14 hours (e.g., last dose at 6 PM, first dose at 8 AM).
Note: Take on an empty stomach (1 hour before or 2 hours after meals) for more predictable absorption. Tablets should be swallowed whole with a glass of water. Do not crush or chew. For sublingual tablets (not 5mg standard), place under the tongue and allow to dissolve. Adhere strictly to the prescribed dosing schedule to maintain the nitrate-free period and prevent tolerance.
Isosorbide dinitrate is converted to nitric oxide (NO) within vascular smooth muscle cells. NO activates soluble guanylyl cyclase, increasing intracellular cyclic guanosine monophosphate (cGMP). Elevated cGMP leads to dephosphorylation of myosin light chains, resulting in smooth muscle relaxation, vasodilation, and reduced cardiac workload.
Pregnancy: Category C: Animal studies show adverse effects; no adequate human studies. Use only if potential benefit justifies potential risk to the fetus.
Driving: May cause dizziness, lightheadedness, or syncope. Patients should not drive or operate machinery until they know how the drug affects them, especially during initiation and dose titration.
| 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 decreased anticoagulant effect of heparin | Moderate |
| Dihydroergotamine | May antagonize antianginal effects of nitrate; may increase ergot toxicity | Moderate |
| Antihypertensives | Potentiated hypotension | Moderate |
| Tricyclic Antidepressants (TCAs) | Hypotensive effects may be potentiated | Moderate |
Same composition (Isosorbide Dinitrate (5mg)), different brands: