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Organic Nitrate Pregnancy: Safety and efficacy during pregnancy or lactation has not been established (§4.6).

Isosorbide Mononitrate

Brand names: Ismo, Imdur, Chemydur 60XL

Isosorbide mononitrate is an oral long-acting nitrate used for the prophylaxis of angina and as an adjunct in chronic heart failure.

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: 60 mg (one prolonged-release tablet) once daily in the morning; may be increased to 120 mg (two tablets) daily, both taken once daily in the morning
Route: Oral — tablets must not be chewed or crushed; swallow whole with a small amount of water
Frequency: Once daily in the morning
Max: 120 mg daily (highest dose stated in §4.2; the SPC does not state a separate maximum)
Source is the UK SPC for 'Carmil XL 60 mg Tablets' (Monomil XL/Carmil XL, eMC product 7997), so 'one tablet' in §4.2 = 60 mg — confirm the strength against the presentation being prescribed. Titration: the dose can be titrated to minimise the possibility of headache by initiating treatment with 30 mg for the first 2-4 days. The score line on the tablet is not intended to divide the tablet into equal halves. Not indicated for the relief of acute angina attacks (§4.4) — in the event of an acute attack, sublingual or buccal glyceryl trinitrate tablets should be used. Elderly: no evidence of a need for routine dosage adjustment, but special care may be needed in those with increased susceptibility to hypotension or marked hepatic or renal insufficiency. Paediatric: safety and efficacy in children has not been established. The tablet core is insoluble in digestive juices and the matrix may very occasionally be visible in the stool after all active substance has been released. Contains lactose — not for patients with rare hereditary galactose intolerance, total lactase deficiency or glucose-galactose malabsorption. NOTE: the US label fetched as cross-check is a different (immediate-release) presentation with a different regimen — 20 mg twice daily with the doses seven hours apart — do not mix the two regimens.

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.

Contraindications

  • Hypersensitivity to the active substance or to any of the excipients
  • Constrictive cardiomyopathy and pericarditis
  • Aortic stenosis, mitral stenosis, cardiac tamponade
  • Severe anaemia
  • Concomitant phosphodiesterase type 5 inhibitors (e.g. sildenafil) — must not be given
  • Severe cerebrovascular insufficiency or hypotension (relative contraindications)

Side effects

  • Headache (common) — may occur on initiation but usually disappears after 1-2 weeks
  • Dizziness (common); fainting (rare)
  • Hypotension (common)
  • Tachycardia (common)
  • Nausea (common); vomiting and diarrhoea (uncommon); rash and pruritus (rare); myalgia (very rare)

Interactions

  • Phosphodiesterase type 5 inhibitors (e.g. sildenafil) — potentiate the vasodilatory effect with potential for serious effects such as syncope or myocardial infarction; must not be given concomitantly (§4.5)

Clinical monograph

How it works

It is converted to nitric oxide, raising vascular smooth-muscle cyclic GMP to produce predominantly venous dilatation that reduces preload and myocardial oxygen demand.

Prescribing in practice

  • A nitrate-free interval each day is needed to prevent tolerance, so dosing is timed to leave a low-nitrate period rather than spread evenly around the clock.
  • Contraindicated with phosphodiesterase-5 inhibitors such as sildenafil because of the risk of severe hypotension.
  • Use cautiously where preload reduction is harmful, such as hypotension, hypovolaemia or aortic and mitral stenosis, and do not stop abruptly after long-term use.

Monitoring

Monitor for postural hypotension, headache and adequacy of angina control, and ensure the nitrate-free interval is maintained.

Counselling the patient

  • Headache is common at first and usually settles; take as prescribed to keep the daily low-nitrate gap.
  • It prevents rather than relieves angina attacks, so keep a short-acting nitrate spray for acute symptoms.

Evidence & guidelines

A long-established antianginal supported by extensive clinical experience and reflected in NICE stable angina guidance.

Reference: NICE NG185; 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).

Related

Curated clinical cross-links plus same-class fallbacks.

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