Glyceryl trinitrate (GTN) is an alternative name for the chemical nitroglycerin, which has been used to treat angina and heart failure since the experiments of William Murrell were widely reported in 1879. Despite this history, the mechanism of nitric oxide (NO) generation from GTN and the metabolic consequences of this bioactivation are still not entirely understood.
It is useful in decreasing angina attacks, perhaps more so than reversing angina once started, by supplementing blood concentrations of nitric oxide, also called endothelium-derived relaxing factor, before the structure of the nitric oxide as the responsible agent was known. This led to the development of transdermal patches of glyceryl trinitrate, providing 24-hour release. However the effectiveness of glyceryl trinitrate is limited by development of tolerance/tachyphylaxis within 2–3 weeks of sustained use. Continuous administration and absorption (such as provided by daily pills and especially skin patches) accelerate onset of tolerance and limit the usefulness of the agent. Thus glyceryl trinitrate works best when used only short term, pulse dosing. Glyceryl trinitrate is useful for acute myocardial infarction (heart attack) and pulmonary edema,[citation needed] again working best if used quickly, within a few minutes of symptom onset, as a pulse dose.[citation needed] It may also be given as a sublingual or buccal dose in the form of a tablet placed under the tongue or a spray into the mouth for the treatment of an angina attack.
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