1. Clinical Overview
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 therapy for chronic stable angina, valued for its predictable pharmacokinetics and reduced potential for tolerance compared to dinitrate formulations.
| Onset | Duration | Bioavailability |
|---|---|---|
| 30 to 60 minutes | Approximately 12 hours (for immediate-release formulations) | Approximately 93-100% |
2. Mechanism of Action
Isosorbide mononitrate is a prodrug that is denitrated to release nitric oxide (NO). NO activates intracellular soluble guanylate cyclase, leading to increased 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 vasculature.
3. Indications & Uses
- Prophylaxis of chronic stable angina pectoris (effort-associated angina)
- Prevention of angina attacks in patients with coronary artery disease
4. Dosage & Administration
Adult Dosage: For prophylaxis of angina: Initially 10mg to 20mg once or twice daily. Common maintenance dose: 20mg to 40mg once daily (immediate-release) or 30mg to 120mg once daily (sustained-release). The 10mg strength is often used for initiation or in divided doses (e.g., 10mg twice daily with a 14-hour gap).
Administration: Take orally with a full glass of water. Can be taken with or without food. For immediate-release tablets taken twice daily, the doses should be spaced 7 hours apart (e.g., 8 AM and 3 PM) to ensure a daily nitrate-free interval of 10-14 hours to prevent tolerance. Do not crush or chew sustained-release formulations. Avoid sudden discontinuation.
5. Side Effects
Common side effects may include:
- Headache (often dose-related and may subside with continued use)
- Dizziness, lightheadedness
- Flushing
- Postural hypotension
- Nausea
- Weakness
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Phosphodiesterase-5 Inhibitors (Sildenafil, Tadalafil, Vardenafil) | Profound, life-threatening hypotension | Contraindicated |
| Other Vasodilators (e.g., Calcium Channel Blockers, ACE Inhibitors, ARBs, Alpha-blockers) | Additive hypotensive effect | Major |
| Alcohol | Enhanced vasodilation and hypotension | Major |
| Heparin | Possible reduced anticoagulant effect of heparin | Moderate |
| Dihydroergotamine | May reduce the anti-anginal effect of nitrates; may increase ergotamine-induced vasoconstriction | Moderate |
| Antihypertensives | Potentiated hypotension | Moderate |
| Tricyclic Antidepressants (TCAs) | Hypotensive effects may be potentiated | Moderate |
| Riociguat (Soluble Guanylate Cyclase Stimulator) | Hypotensive effects may be potentiated | Major |
7. Patient Counselling
- DO take the medication exactly as prescribed, maintaining the dose schedule to ensure a nitrate-free interval.
- DO sit or lie down at the first sign of dizziness or lightheadedness.
- DO inform all healthcare providers (including dentists) that you are on this medication.
- DONT take Phosphodiesterase-5 inhibitors (e.g., Viagra, Cialis) while on this drug.
- DONT consume alcohol.
- DONT stop taking the medication abruptly without consulting your doctor, as it may worsen angina.
- DONT use it to treat an acute anginal attack. Use sublingual nitroglycerin for that purpose.
8. Toxicology & Storage
Overdose: Severe hypotension with persistent throbbing headache, vertigo, palpitations, visual disturbances, flushing, sweating, nausea, vomiting, syncope, air hunger, dyspnea, bradycardia or tachycardia, methemoglobinemia (cyanosis, dyspnea, fatigue), coma, seizures, and death.
Storage: Store below 30°C, in a cool, dry place, protected from light and moisture. Keep out of reach of children. Do not store in bathroom cabinets. Do not use if the seal is broken or tablets appear discolored.