NITRATES

Therapeutic uses

Angina

Currently, studies show that nitrates do not have any effect on overall mortality in patients with acute coronary syndromes. Their benefit is symptomatic only (see GISSI-3 trial and ISIS-4 trial).

Glyceryl trinitrate (GTN)

Sublingual GTN spray is used primarily in the pre-hospital setting for the rapid symptomatic relief of ischaemic chest pain in patients with stable angina or acute coronary syndromes (MI/unstable angina).
It can also be given as a sublingual/buccal tablet or intravenous infusion. GTN has low oral bioavailabilty (10-20%) because it undergoes first-pass metabolism in the liver.
The effects of GTN typically only last around 20-30mins.
In patients who have chronic angina, GTN can be given as prophylaxis in the form of a transdermal patch. Some patients may use their sublingual GTN spray as prophylaxis, by taking it just prior to any exertion.
GTN spray also has diagnostic value in the acute setting, in that, it can help differentiate ischaemic chest pain from other causes of chest pain.

Isosorbide mononitrate

Isosorbide mononitrate (ISMN) is given as an oral tablet because it does not undergo first-pass metabolism to the same extent GTN or ISDN.
ISMN is the longest acting of the nitrates (half-life =6 hours) and for this reason it is the often the preferred oral nitrate for angina prophylaxis.

Isosorbide dinitrate

Isosorbide dinitrate (ISDN) can be given as an oral tablet (however like GTN it undergoes first-pass metabolism and therefore only has an oral bioavailability of 10-20%) or via intravenous infusion.
The active metabolite of ISDN is isosorbide mononitrate.
ISDN is short-acting (half-life = 2 hours) but when given orally is given as a slow-release preparation.
It is generally given orally as angina prophylaxis but can also be given intravenously in the management of acute left ventricular failure.

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