1. Clinical Overview
Isosorbide mononitrate is a long-acting organic nitrate used primarily for the prophylaxis and treatment of angina pectoris. It is the active metabolite of isosorbide dinitrate. The 60mg strength is typically formulated as an extended-release (ER/SR) tablet designed for once-daily administration, providing sustained anti-anginal effect and reducing the risk of nitrate tolerance.
| Onset | Duration | Bioavailability |
|---|---|---|
| Approximately 30 to 60 minutes for extended-release formulations. | Up to 12-14 hours for extended-release formulations. | Approximately 93-100% (due to minimal first-pass metabolism). |
2. Mechanism of Action
Isosorbide mononitrate is a prodrug that releases 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 myocardial oxygen demand.
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: Extended-release 60mg tablet once daily, typically in the morning. Dose may be initiated at 30mg once daily and titrated to 60mg based on response and tolerability. Maximum recommended dose is 120mg once daily.
Administration: Swallow the extended-release tablet whole with a glass of water, do not crush, chew, or split. Take on an empty stomach, at least 1 hour before or 2 hours after food to minimize variability in absorption. To avoid tolerance, ensure a daily nitrate-low interval of 10-14 hours. The once-daily dose is usually taken in the morning upon waking.
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, life-threatening hypotension | Contraindicated |
| Other Vasodilators (e.g., 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 and increase ergot toxicity | Moderate |
| Antihypertensives | Potentiated hypotension | Moderate |
| Tricyclic Antidepressants (TCAs) | Hypotensive effects may be potentiated | Moderate |
7. Patient Counselling
- DO take the tablet exactly as prescribed, usually once daily in the morning.
- DO swallow the tablet whole; do not crush, chew, or break it.
- DO take it on an empty stomach, 1 hour before or 2 hours after food.
- DO sit or lie down if you feel dizzy or lightheaded.
- DONT take double doses to make up for a missed dose. Skip it and take the next dose at the regular time.
- DONT suddenly stop taking this medicine without consulting your doctor, as it may worsen angina.
- DONT consume alcohol while on this medication.
- DONT take any erectile dysfunction drugs (like Viagra, Cialis) while on this medicine.
8. Toxicology & Storage
Overdose: Severe hypotension with persistent throbbing headache, vertigo, palpitations, visual disturbances, flushing, sweating, nausea, vomiting, syncope, methemoglobinemia (cyanosis, dyspnea, anxiety), air hunger, coma, and death due to circulatory collapse.
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.