Isosorbide mononitrate
A long-acting oral nitrate, the active metabolite of isosorbide dinitrate, taken to prevent angina; it is too slow to stop an attack.
Also called ISMN (abbreviation).
Drug card
- Class
- Nitrate
- How it works
- Releasing nitric oxide, so veins and arteries relax and preload falls
- Used for
- Preventing angina in coronary artery disease
- Known for
- Throbbing headache, fading over the first weeks
- Low blood pressure, sometimes with fainting
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does isosorbide mononitrate work?
The main active metabolite of isosorbide dinitrate. Like other nitrates it releases nitric oxide and relaxes vascular smooth muscle, veins more than arteries, lowering preload and afterload. Unlike the dinitrate it escapes first-pass metabolism, so nearly all of an oral dose reaches the blood.
Like other nitrates: They release nitric oxide in vascular smooth muscle, which activates guanylyl cyclase and raises cyclic GMP; myosin light chains lose their phosphate and the muscle relaxes. Veins widen most, so blood pools and preload falls; arterioles and the large coronary arteries widen too. The heart needs less oxygen, which relieves angina.
Uses
What is isosorbide mononitrate used for?
- Preventing angina in coronary artery disease
Side effects
Side effects of isosorbide mononitrate
- Throbbing headache, fading over the first weeksKnown for
- Low blood pressure, sometimes with faintingKnown forSerious
- Dizziness and light-headedness on standing
- Flushing
- Reflex fast heart rate
- Paradoxical slow heart rate
- Nausea and vomiting
- Weakness and drowsiness
- Rash, rarely exfoliative dermatitis
- Tolerance without a daily low-nitrate period
- Methemoglobinemia (rare)Serious
- Angina if stopped suddenlySerious
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- PDE-5 inhibitors such as sildenafil or tadalafil, and riociguat, are contraindicated: severe hypotension.
- Too slow to stop an attack; sublingual glyceryl trinitrate is used for that.
- Dosed so that nitrate levels dip each day; otherwise tolerance develops.
- Contraindicated in hypertrophic obstructive cardiomyopathy, aortic or mitral stenosis, marked anemia or raised intracranial pressure.
Good to know: Most of the effect of isosorbide dinitrate comes from its conversion to this drug in the body.
Remember it
A way to remember it
Headache today, tolerance tomorrow, and never with sildenafil.
Headache is the commonest side effect; steady use brings tolerance, so a low-nitrate gap is kept each day; PDE-5 inhibitors boost the same cyclic GMP pathway and can drop blood pressure dangerously.
Written for biofideX
Its class
Nitrates
Other nitrates with a card:
Easily mixed up with dihydropyridine calcium channel blockers and PDE5 inhibitors.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- Isosorbide mononitrate extended-release tablets: label (DailyMed)
- Isosorbide mononitrate tablets 20 mg: SmPC (emc)
- Isosorbide mononitrate (NCI Thesaurus)
- Common questions about isosorbide mononitrate and isosorbide dinitrate (NHS)
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Heart failure, rhythm and angina
Isosorbide mononitrate is one of 10 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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