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Nitrate / Stable Angina Pregnancy: Use with caution — nitrates cause uterine relaxation; limited data. Use only if essential.

Isosorbide Mononitrate (Stable Angina)

Brand names: Elantan, Imdur, Monosorb

Adult dose

Dose: Standard-release: 10-20 mg twice daily (asymmetric dosing — 8am and 2pm to allow 8-hour nitrate-free interval overnight). Modified-release: 25-60 mg once daily in the morning.
Route: Oral
Frequency: BD (standard-release, asymmetric) or OD (modified-release, morning)
Max: 120 mg/day
Active metabolite of isosorbide dinitrate. Better bioavailability and longer half-life. Standard release — give at 8am and 2pm (NOT 8am and 8pm — inadequate nitrate-free interval causes tolerance). MR formulation once daily in morning provides natural overnight nitrate-free period.

Paediatric dose

Route: Oral
Seek specialist opinion — not licensed in children

Dose adjustments

Renal

No dose adjustment required

Hepatic

No dose adjustment required

Clinical pearls

  • Nitrate tolerance — key prescribing pitfall: continuous nitrate exposure downregulates guanylyl cyclase within 24-48 hours. An 8-12 hour nitrate-free period is MANDATORY. For standard-release ISMN: give at 8am and 2pm (NOT 8am/8pm). For MR: once daily morning naturally provides overnight nitrate-free period.
  • PDE-5 inhibitor interaction is ABSOLUTE and examination-relevant: sildenafil + nitrate = catastrophic hypotension and death. All patients on nitrates must be explicitly warned. Minimum gaps: 24h after sildenafil, 48h after tadalafil.
  • HOCM contraindication: nitrates reduce preload — in HOCM (dynamic LVOT obstruction worsens with reduced filling), nitrates can precipitate haemodynamic collapse.
  • Mechanism: nitrates → vascular smooth muscle guanylyl cyclase → cGMP → vasodilation. Predominantly venodilation at low doses (reduces preload); arteriodilation at higher doses (reduces afterload).
  • Initiation headache: almost universal in first 1-2 weeks. Paracetamol helps. Advise patients in advance — headache is a sign the drug is working (vasodilation). It almost always resolves.

Contraindications

  • Concomitant PDE-5 inhibitors (sildenafil, tadalafil, vardenafil) — severe hypotension, potentially fatal; ABSOLUTE contraindication
  • Concomitant riociguat — ABSOLUTE contraindication
  • Severe hypotension (systolic <90 mmHg)
  • Hypovolaemia
  • HOCM
  • Severe aortic stenosis (reduces preload, drops stroke volume)

Side effects

  • Headache (vasodilation — common at initiation; usually resolves after 1-2 weeks)
  • Flushing
  • Dizziness/postural hypotension
  • Nitrate tolerance (prevent with dose-free interval)
  • Reflex tachycardia

Interactions

  • PDE-5 inhibitors — ABSOLUTE CONTRAINDICATION (24-hour gap after sildenafil, 48 hours after tadalafil minimum before any nitrate)
  • Riociguat — ABSOLUTE CONTRAINDICATION
  • Antihypertensives — additive hypotension
  • Alcohol — additive vasodilation

Monitoring

  • Blood pressure (lying and standing)
  • Headache severity
  • Angina frequency
  • Heart rate (reflex tachycardia)

Reference: BNFc; BNF 90; ESC Stable Coronary Artery Disease Guidelines 2019; NICE CG126 (Stable Angina); SPC Elantan; SPC Imdur. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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