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. The 40mg strength is typically formulated as a sustained-release (SR) or extended-release (ER) tablet in the Indian market, designed to provide prolonged anti-anginal effect with once-daily dosing, improving compliance and reducing nitrate tolerance.
| Onset | Duration | Bioavailability |
|---|---|---|
| 30 to 60 minutes (for immediate-release). For sustained-release formulations, onset is delayed but provides prolonged effect. | Approximately 12 to 24 hours for sustained-release formulations (like 40mg SR). Immediate-release acts for 6-8 hours. | Nearly 100% (due to minimal first-pass metabolism, unlike isosorbide dinitrate). |
2. Mechanism of Action
Isosorbide mononitrate is a prodrug that releases nitric oxide (NO) within vascular smooth muscle cells. 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 veins and arteries.
3. Indications & Uses
- Prophylaxis of chronic stable angina pectoris (effort angina)
- Prevention of angina in patients with coronary artery disease
4. Dosage & Administration
Adult Dosage: For prophylaxis of angina: 40mg (sustained-release) once daily. Some brands recommend 20mg once daily initially, increased to 40mg if needed. The dose should be taken in the morning to provide a nitrate-free interval.
Administration: Swallow the sustained-release tablet whole with a glass of water, do not crush, chew, or break. Can be taken with or without food. Best taken in the morning upon waking. Maintain a consistent daily schedule.
5. Side Effects
Common side effects may include:
- Headache (often dose-related and may diminish with continued use)
- Dizziness, lightheadedness
- Flushing
- Postural hypotension
- Nausea
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Phosphodiesterase-5 Inhibitors (Sildenafil, Tadalafil, Vardenafil) | Profound hypotension, cardiovascular collapse | 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 reduce the anti-anginal effect of nitrates | Moderate |
| Antihypertensives | Enhanced blood pressure lowering | Moderate |
| Tricyclic Antidepressants (TCAs) | May exacerbate hypotension | Moderate |
7. Patient Counselling
- DO take the tablet exactly as prescribed, usually once daily in the morning.
- DO swallow the sustained-release tablet whole; do not crush, chew, or break it.
- DO sit or lie down if you feel dizzy or lightheaded.
- DO inform all your doctors and dentists you are taking this medicine.
- DO NOT take this medicine to treat an acute angina attack. Use sublingual nitroglycerin as prescribed for that purpose.
- DO NOT suddenly stop taking this medicine without consulting your doctor, as it may worsen angina.
- DO NOT consume alcohol while on this medication.
8. Toxicology & Storage
Overdose: Symptoms primarily related to vasodilation: 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 use after the expiry date printed on the pack.