Nitrates belong to a class of drugs called vasodilators that relax the walls of the coronary arteries, widen them and increase blood flow to the heart muscle. Improved oxygen supply to the heart removes chest pain (angina) caused by restricted blood flow to the heart due to narrowing or blockages in coronary arteries in coronary artery disease. By enlarging the blood vessels and reducing blood pressure, nitrates also reduce the resistance against which the heart has to pump and can be therefore used in a continuous infusion for acute treatment of hypertensive crisis or heart failure. Nitrates become less effective if used continuously over a period of time.
Nitrates are available in the form of tablets, sprays, skin patches, and injections. An example of a long-acting preparation is Isosorbide Mononitrate (brand name Monomil, Monosorb, Chemydur); a short-acting nitrate is Glyceryl Trinitrate (GTN spray or GTN tablets for sublingual use). Nitrates do not improve prognosis but are very useful for symptom control and GTN spray is one of the most commonly prescribed medicines in cardiology.
Nitrates may produce side effects like headache, dizziness, and burning under the tongue in the case of nitroglycerin. Patients using nitrates must avoid medication to treat erectile dysfunction, such as sildenafil (Viagra), because the combination of these drugs may cause life-threatening hypotension (low blood pressure).