Isosorbide mononitrate 💊
Related Subjects:
|Nitrates
|Glyceryl Trinitrate (GTN)
|Isosorbide Dinitrate
|Heart Failure
💊 Isosorbide mononitrate (ISMN) is a long-acting oral nitrate used for angina prophylaxis. To prevent nitrate tolerance, each day must include a nitrate-low period - asymmetric twice-daily dosing (e.g. 8am and 2pm) or once-daily modified-release in the morning.
📖 About
- The active metabolite of isosorbide dinitrate; well absorbed with no first-pass metabolism (predictable levels).
- NICE CG126 (stable angina): a long-acting nitrate is an option when beta-blockers and/or CCBs are not tolerated or not controlling symptoms.
- Always check the BNF for up-to-date information.
⚙️ Mode of Action
- Nitric oxide donor → activates guanylate cyclase → ↑ cGMP → vascular smooth muscle relaxation.
- Predominantly venodilation → ↓ preload and LV wall stress → ↓ myocardial oxygen demand.
- Also dilates large coronary arteries and relieves coronary spasm.
🎯 Indications
- Prophylaxis of stable angina.
- Adjunct in chronic heart failure (with hydralazine, where an ACEi/ARB is not tolerated - specialist; this evidence is mainly for isosorbide dinitrate).
💊 Dose (adult)
| Preparation | Dose | Nitrate-free strategy |
|---|
| Immediate-release tablets | Initially 20 mg 2–3 times daily (10 mg in nitrate-naïve patients); usual 20–40 mg 2–3 times daily; max 120 mg daily | Give asymmetrically (e.g. 8am and 2pm), not every 12 hours |
| Modified-release (e.g. 60 mg) | 25–60 mg once daily in the morning, increased to 120 mg once daily if needed | Once-daily MR gives a natural overnight trough |
- Start low (e.g. half dose for 2–4 days) to reduce headache.
🔄 Interactions
- PDE-5 inhibitors (sildenafil, tadalafil, vardenafil) and riociguat: profound, potentially fatal hypotension - contraindicated.
- Additive hypotension with antihypertensives, alcohol, TCAs and antipsychotics.
⚠️ Cautions
- Hypotension, hypovolaemia, aortic or mitral stenosis, HOCM, constrictive pericarditis, tamponade (preload-dependent states).
- Recent MI, head trauma or cerebral haemorrhage (raised ICP), hypothyroidism, malnutrition, hypothermia.
- Severe hepatic or renal impairment.
- Older people: postural hypotension and falls.
🚫 Contraindications
- Concurrent PDE-5 inhibitor or riociguat.
- Marked hypotension, circulatory collapse, cardiogenic shock.
- Hypertrophic cardiomyopathy with outflow obstruction, severe aortic or mitral stenosis, constrictive pericarditis, cardiac tamponade.
- Severe anaemia; closed-angle glaucoma.
💥 Side Effects
- Headache (very common, usually settles within 1–2 weeks), flushing, dizziness.
- Postural hypotension, reflex tachycardia, syncope.
- Nausea; tolerance with continuous exposure.
- Rare: methaemoglobinaemia (high doses).
📚 References
