Nitrate / Stable Angina Pregnancy: Safety in pregnancy has not been established. Nitrates are excreted in breast milk and may cause methaemoglobinaemia in infants; the extent of excretion of isosorbide mononitrate in human breast milk has not been determined. Use in pregnancy and lactation only if, in the opinion of the physician, the possible benefits outweigh the hazards; caution in nursing women. No human fertility data.

Isosorbide Mononitrate (Stable Angina)

Brand names: Elantan, Imdur, Monosorb

Isosorbide mononitrate is a long-acting oral nitrate used for the prophylaxis of angina.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: One 10 mg tablet, taken asymmetrically (to allow a nitrate-low period), two or three times a day; may be increased up to 120 mg per day

Route: Oral

Frequency: Twice daily (second dose 8 hours after the first) or three times daily (one every 6 hours, ensuring a 12-hour treatment-free interval every 24 hours)

Max: 120 mg per day

Posology taken from the UK SPC for Isosorbide Mononitrate 10 mg Tablets — check the SPC for the specific strength/formulation being prescribed (modified-release products dose differently). Dosage regimen should be designed according to the clinical response of the patient and the lowest effective dose used. Tablets should be swallowed whole with water, unchewed, after meals. If tablets are not taken as indicated, tolerance may develop. Treatment must not be stopped suddenly — both dose and frequency should be tapered gradually. Elderly: no evidence that dosage adjustment is necessary. Paediatric population: safety and efficacy in children has not been established. This page covers stable angina prophylaxis: the SPC states the product is NOT suitable for an acute angina attack (onset of action is not sufficiently rapid) — a sublingual treatment such as GTN spray or tablet should be used instead. For cross-reference only, the US label (ANI Pharmaceuticals) recommends 20 mg twice daily with the doses seven hours apart, with a 5 mg starting dose for persons of particularly small stature increased to at least 10 mg by the second or third day — this differs from the UK SPC regimen above.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

US labelling (FDA)

Reference — US labelling, may differ from UK

DOSAGE AND ADMINISTRATION The recommended regimen of isosorbide mononitrate tablets is 20 mg twice daily, with the doses seven hours apart. A starting dose of 5 mg (½ tablet of the 10 mg dosing strength) might be appropriate for persons of particularly small stature but should be increased to at least 10 mg by the second or third day of therapy. Dosage adjustments are not necessary for elderly patients or patients with altered hepatic or renal function. As noted above ( CLINICAL PHARMACOLOGY ), multiple studies of organic nitrates have shown that maintenance of continuous 24-hour plasma levels results in refractory tolerance. The asymmetric (2 doses, 7 hours apart) dosing regimen for …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2026-03-27. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Contraindications

Known sensitivity to isosorbide mononitrate, the listed ingredients or other nitrates
Acute myocardial infarction with low filling pressures; low cardiac filling pressures
Acute circulatory failure (shock, vascular collapse); very low blood pressure (systolic below 90 mmHg); severe hypotension; severe hypovolaemia
Hypertrophic obstructive cardiomyopathy (HOCM), constrictive pericarditis, cardiac tamponade, aortic/mitral valve stenosis
Diseases associated with raised intracranial pressure (e.g. following head trauma, including cerebral haemorrhage)
Severe anaemia; closed angle glaucoma
Co-administration with phosphodiesterase type-5 inhibitors (sildenafil, tadalafil, vardenafil)
Concurrent use of the soluble guanylate cyclase stimulator riociguat

Side effects

Headache (very common)
Dizziness, including postural dizziness, and somnolence (common)
Tachycardia (common); aggravated angina pectoris (uncommon)
Orthostatic hypotension (common); asthenia (common)
Nausea and vomiting (uncommon); circulatory collapse, sometimes with bradyarrhythmia and syncope (uncommon)

Interactions

Phosphodiesterase type-5 inhibitors (sildenafil, tadalafil, vardenafil) — potentiate the hypotensive effects of nitrates; co-administration is contraindicated, and nitrate therapy should not be interrupted in order to take them
Riociguat (soluble guanylate cyclase stimulator) — must not be used during nitrate therapy
Alcohol — should be avoided; may potentiate the hypotensive effect (severe postural hypotension with light-headedness and dizziness is frequently observed after alcohol)

Clinical monograph

How it works

It is converted to nitric oxide, causing venodilatation (reduced preload) and coronary vasodilatation, lowering myocardial oxygen demand.

Prescribing in practice

Tolerance develops with continuous exposure — use an asymmetric schedule or a modified-release form to provide a nitrate-free interval.
Headache, flushing and hypotension are common, especially initially.
It is contraindicated with PDE5 inhibitors (e.g. sildenafil).

Monitoring

Review angina frequency and blood pressure.

Counselling the patient

It prevents angina — it is not for an acute attack (use your GTN spray/tablet for that).
Headaches are common at first and usually settle.
Never take it with erectile-dysfunction tablets such as sildenafil.

Evidence & guidelines

A long-acting nitrate for angina prophylaxis, dosed to allow a nitrate-free interval to limit tolerance (NICE NG185).

Reference: ESC Stable Coronary Artery Disease Guidelines 2019; NICE CG126 (Stable Angina); SPC Elantan; SPC Imdur; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways