Nitrate therapy in angina and congestive heart failure

Nitrates are vasodilators of venous and arterial smooth muscle commonly prescribed both for angina and congestive heart failure. Primarily venodilators, nitrates also affect the systemic circulation if administered in sufficient dosage. In the coronary circulation, the principal effect is on the large epicardial and collateral vessels. Blood is shunted toward the ischemic subendocardium. In the majority of patients with angina, relief of symptoms by nitrates is primarily due to hemodynamic effects on preload and afterload, unless the patient has coronary spasm. In patients with congestive heart failure, nitrates decrease the resistance to the emptying of blood from the left ventricle as well as the filling pressure. Nitrates are relatively well tolerated, except for an initial throbbing headache which rapidly resolves as tolerance develops. Nitrates are available in a multitude of forms including sublingual, oral, topical, transmucosal, intravenous, and spray preparations. Oral preparations undergo a firstpass effect in the liver, requiring larger doses. Other forms avoid this problem by direct transdermal absorption or the intravenous route. The latter has the advantage of rapid administration and ease of titration. The choice of nitrate depends upon the clinical situation.