Dynamic responses to continuous use of prazosin and hydralazine in patients with refractory heart failure

The hemodynamic effects of oral doses of prazosin and hydralazine were studied in the same group of patients with chronic congestive heart failure. Prazosin, 3 to 10 mg, and hydralazine, 75 to 100 mg, were given by mouth every 6 hr and the responses to the first and the fifth consecutive dose were compared. The first dose of prazosin was followed by a predominant effect of left ventricular filling pressure and concomitantly by reduction of left ventricular afterload. Hydralazine acted primarily on left ventricular afterload with no significant effect on the filling pressure. A marked difference was noted in respect to the dynamic responses to continuous therapy with these two drugs. While the initial hemodynamic effect of prazosin was markedly attenuated in most of the cases after the fifth consecutive oral dose, the response to hydralazine was augmented by continuous therapy. These findings suggest that the reported hemodynamic tachyphylaxis seen with prazosin does not occur with hydralazine when given to the same patients with chronic congestive heart failure. Our study also indicates the importance of prolonged monitoring for the assessment of the hemodynamic effect of prazosin and hydralazine in patients with severe chronic congestive heart failure.