Isosorbide dinitrate (ISDN) is a potent organic nitrate vasodilator used primarily for the prophylaxis and treatment of angina pectoris. It is a prodrug that undergoes denitration to form active metabolites, primarily isosorbide-5-mononitrate (IS-5-MN) and isosorbide-2-mononitrate (IS-2-MN). It reduces myocardial oxygen demand by causing venous and arterial dilation, leading to decreased preload and afterload. In the Indian context, it is a widely available, cost-effective antianginal agent, though its use has been partially supplanted by the longer-acting IS-5-MN.
Adult: For angina prophylaxis: 10-40 mg orally 2-3 times daily. A typical regimen is 10-20 mg every 6-8 hours, allowing for a 10-14 hour nitrate-free interval (e.g., last dose at 6 PM, first dose at 8 AM). For acute angina: 5-10 mg sublingually, repeated every 5-10 minutes for up to 3 doses. If pain persists, seek emergency care.
Note: Oral tablets: Swallow whole with a glass of water, with or without food. Do not crush or chew sustained-release formulations. For sublingual: Place tablet under the tongue and allow to dissolve completely. Do not swallow immediately. Do not eat, drink, or smoke until tablet is dissolved. Patient must be sitting or lying down when taking the first dose to avoid syncope.
Isosorbide dinitrate is a prodrug that is converted to nitric oxide (NO) intracellularly, primarily in vascular smooth muscle cells. NO activates soluble guanylyl cyclase, leading to increased intracellular cyclic guanosine monophosphate (cGMP). Elevated cGMP causes dephosphorylation of myosin light chains, resulting in smooth muscle relaxation and vasodilation.
Pregnancy: Category C (US FDA). Animal studies have shown adverse effects. There are no adequate and well-controlled studies in pregnant women. Use only if the potential benefit justifies the potential risk to the fetus, particularly during the first trimester.
Driving: May cause dizziness, lightheadedness, or syncope, especially after the first dose. Patients should not drive or operate machinery until they know how the drug affects them.
| Phosphodiesterase-5 Inhibitors (Sildenafil, Tadalafil, Vardenafil) | Profound, life-threatening hypotension | Contraindicated |
| Other Vasodilators (ACE inhibitors, ARBs, Alpha-blockers, Calcium channel blockers) | Additive hypotensive effect | Major |
| Alcohol | Enhanced vasodilation and hypotension | Major |
| Heparin | ISDN may antagonize anticoagulant effect of heparin (mechanism unclear) | Moderate |
| Dihydroergotamine | ISDN may increase the bioavailability and vasoconstrictive effects of dihydroergotamine | Moderate |
| Antihypertensives | Potentiated hypotensive effect | Moderate |
| Tricyclic Antidepressants (TCAs) | May potentiate hypotensive effects | Moderate |
| Aspirin | Increased nitrate bioavailability | Minor |
Same composition (Isosorbide Dinitrate (10mg)), different brands: