[Principles and rules of the use of nitrates]

Nitrates, which have been used for more than a century, are the second oldest drug (after digitalis alkaloids) in the cardiological pharmacological arsenal. However, several facets of their mode of use still remain controversial. Their vasodilator and arteriolodilator action (especially in coronary vessels) and their platelet aggregation inhibitory effect make them useful drugs, particularly in all clinical forms of ischaemic heart disease (unstable or stable angina and acute myocardial infarction), for the prevention or treatment of ischaemic episodes (silent or not) and also in heart failure where nitrates are useful not only as symptomatic treatment (alone or associated with diuretics), but also in view of their positive effect on survival (associated with hydralazine: V-Heft I trial). At the present time, nitrates can be administered via the sublingual, oral, intravenous of transdermal routes in the form of nitroglycerin and isosorbide dinitrate or mononitrate (short-acting and sustained-effect forms). Their rare contraindications concern patients suffering from severe hypotension (< 70 mmHg), severe anaemia, glaucoma or intracranial hypertension. The most serious adverse effects are pulsatile headache (which usually disappear after several days), postural hypotension (possibly causing fainting), facial erythema, vertigo, palpitations or nausea and vomiting. Most of these adverse effects can be controlled by dosage adaptation and it is rarely necessary to stop treatment. However, the major problem raised by the use of nitrates concerns the development of a tolerance. The pathophysiology of this multifactorial phenomenon is still unclear. The protagonist role played by loss of SH groups or activation of humoral feedback mechanisms, with an increase of circulating catecholamine levels, activation of the R-A-A system and increased plasma volume, has been postulated. This complication can be avoided by prescribing intermittent treatment, with a drug-free interval of 10-12 hours per day. A single dose of a sustained-release preparation (60 mg of isosorbide dinitrate or 40 to 60 mg of isosorbide mononitrate), or 2 or 3 doses of a short-acting preparation (20-40 mg of isosorbide mononitrate) can be prescribed via the oral route. When the transdermal route is used, the patch should be left in place for 12 hours. Treatment should be started at low doses, which are then gradually increased. The free period is usually at night, which can be covered, when necessary, by other antiischaemic drugs (for example, beta-blockers and/or calcium channel blockers), already usually used in combination with nitrates. This interruption is not accompanied by a rebound phenomenon. It must be remembered that nitrates potentiate the action of other vasodilators and calcium channel blockers and that, in some patients, intravenous nitroglycerin reduces the anticoagulant effect of heparin, while indomethacin can inhibit their vasodilator effect. Nitrates are therefore in very good health despite their advanced age and, when used correctly, they continue to be very useful in the pharmacological treatment of cardiovascular diseases.