Glyceryl trinitrate (GTN), also known as nitroglycerin, is a medication that causes rapid relaxation and widening (dilation) of blood vessels, including the coronary arteries. It is one of the most important drugs for the immediate treatment of angina (cardiac chest pain).
GTN is most commonly used as a sublingual (under the tongue) spray or tablet that is absorbed quickly through the mouth lining, producing an effect within 1 to 3 minutes. This rapid action makes it ideal for relieving angina attacks. GTN can also be given as a skin patch or ointment for longer-acting effects, or as an intravenous infusion in hospital for acute heart failure or unstable angina.
GTN works by releasing nitric oxide, which relaxes smooth muscle in blood vessel walls. This causes the coronary arteries to dilate (improving blood supply to the heart muscle) and the peripheral veins to widen (reducing the preload returning to the heart, which lowers its workload). The result is reduced oxygen demand and improved oxygen supply to the ischaemic heart muscle, relieving chest pain.
Side effects include headache (a common and expected effect of arterial dilation), flushing, and dizziness from a drop in blood pressure. Patients taking GTN for angina are advised to sit or lie down when using the spray. GTN must not be used within 24 to 48 hours of phosphodiesterase-5 inhibitors (such as sildenafil, used for erectile dysfunction), as the combination can cause a dangerous drop in blood pressure. For cardiac arrest survivors with coronary artery disease, a GTN spray is often prescribed to carry at all times for use if chest pain occurs, alongside guidance on when to call 999 if symptoms do not resolve.
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