Glyceryl trinitrate
A short-acting nitrate taken under the tongue to relieve or head off angina, also given as patches, by infusion and as an ointment.
Also called nitroglycerin (US name) or GTN (abbreviation).
Drug card
- Class
- Nitrate
- How it works
- Releasing nitric oxide, so veins and arteries relax and preload falls
- Used for
- Relief of an angina attack
- Preventing angina before exertion
- Heart failure with acute myocardial infarction (infusion)
- High blood pressure during surgery (infusion)
- Known for
- Headache, which can be severe
- Severe low blood pressure and fainting
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does glyceryl trinitrate work?
Converted to nitric oxide in smooth muscle, raising cyclic GMP and relaxing vessels, veins most of all. Venous pooling lowers preload, and widening of arterioles and coronary arteries adds to the effect. Under the tongue it starts working in 1 to 3 minutes, peaks by 5 and lasts at least 25 minutes.
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 glyceryl trinitrate used for?
- Relief of an angina attack
- Preventing angina before exertion
- Heart failure with acute myocardial infarction (infusion)
- High blood pressure during surgery (infusion)
- Pain of chronic anal fissure (ointment)
Side effects
Side effects of glyceryl trinitrate
- Headache, which can be severeKnown for
- Severe low blood pressure and faintingKnown forSerious
- Dizziness and light-headedness on standing
- Flushing
- Reflex fast heart rate
- Paradoxical slow heart rate with worse anginaSerious
- Nausea, vomiting and sweating when pressure drops
- Tolerance with frequent or continuous use
- Rebound angina or hypertensionSerious
- Methemoglobinemia (rare)Serious
- Rash or contact dermatitis from patches and ointment
- Dizziness
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- PDE-5 inhibitors and riociguat are contraindicated: together they can cause severe hypotension, fainting or ischemia.
- Contraindicated in severe anemia, raised intracranial pressure, and circulatory failure or shock.
- Volume depletion, aortic or mitral stenosis and constrictive pericarditis raise the risk of severe hypotension.
- It raises the bioavailability of ergotamine, which can itself bring on angina.
Good to know: Unlike isosorbide mononitrate, it acts within minutes under the tongue, so it can stop an attack as well as prevent one.
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:
- Nitroglycerin sublingual tablets: label (DailyMed)
- Nitroglycerin in 5% dextrose injection: label (DailyMed)
- Nitroglycerin ointment 0.4%: label (DailyMed)
- Nitroglycerin (NCI Thesaurus)
- About glyceryl trinitrate (GTN) (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
Glyceryl trinitrate 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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