Use of oral prazosin hydrochloride in congestive failure following acute myocardial infarction.

The hemodynamic effects of the new oral vasocilator prazosin were evaluated in 11 patients with congestive failure following myocardial infarction. Prazosin decreased pulmonary trunk, pulmonary capillary, and right atrial pressures, systemic blood pressure, systemic vascular and total pulmonary resistances, and the heart rate X systolic blood pressure product (P less than 0.001). Cardiac and stroke indexes increased (P less than 0.001 and P less than 0.02, respectively). Heart rate, myocardial perfusion gradient, and stroke work index remained unchanged (P less than 0.05). Prazosin effect began in most patients 30 minutes after an oral administration of 2.5 to 7 mg; the maximum effect occurred from one to three hours later. The action is sustained for at least 6 hours in most patients and sometimes is present even 12 hours after a single dose administration. We conclude that prazosin, with a nitroprusside-like effect, improves left ventricular performance and myocardial O2 supply-demand relationship in patients with acute myocardial infarction, but optimal doses vary significantly, and the hazard of severe and sustained hypotension, or decline in cardiac output in patients with normal blood pressure or slightly elevated filling pressure, is present.