Prazosin in the treatment of severe chronic congestive cardiac failure

Haemodynamic effects of a single low dose of prazosin in patients with chronic congestive cardiac failure correlations with pharmacokinetics

The haemodynamic effects and pharmacokinetics of a single orally administered dose of 0.5 mg of prazosin have been compared in six patients with stable severe congestive cardiac failure. Administration of prazosin induced significant decreases in mean pulmonary capillary wedge pressure (from 27.5, s.e.m. = 4.5 to 19.4, s.e.m. = 5.1 mmHg; P less than 0.001), mean arterial blood pressure (from 94.5, s.e.m. = 6.0 to 85.4, s.e.m. = 5.0 mmHg; P less than 0.01), and systemic vascular resistance (from 1690, s.e.m. = 360 to 1420, s.e.m. = 200 dyn. s/cm5; P less than 0.05) and a rise in cardiac index from 1.98 (s.e.m. = 0.07) to 2.28 (s.e.m. = 0.16) litres/min per m2 (P less than 0.05). There was a non-significant fall in heart rate. Pharmacokinetic analysis revealed maximum plasma prazosin concentrations of 4.1 (s.e.m. = 1.4) ng/ml, occurring 2.1 (s.e.m. = 0.4) h after drug ingestion. The mean elimination half-life was 5.1 (s.e.m. = 0.8) h, which is longer than that found in our previous studies in normal subjects. There was considerable interindividual variation in peak plasma prazosin concentrations, elimination half-life and area under the concentration-time curve. While mean maximal haemodynamic effects of prazosin occurred at similar times to the peak plasma concentration of the drug, there was no significant correlation between the extent of haemodynamic response and individual pharmacokinetic parameters. It is concluded that significant and potentially beneficial haemodynamic effects occur with the initial administration of 0.5 mg oral dose of prazosin in patients with stable congestive cardiac failure and it is suggested that in many patients little advantage will be achieved with higher initial doses.

Comparative pharmacology and clinical efficacy of newer agents in treatment of heart failure

The animal and human pharmacology of several new drugs (prazosin, trimazosin, pirbuterol, and carbazeran) useful in the treatment of congestive heart failure (CHF) is delineated in relation to the pharmacology of other agents employed for CHF management. Prazosin and trimazosin are selective alpha 1-blockers that cause a balanced increase in cardiac output (CO) and reduction in left ventricular filling pressure (LVFP); the reduction in diastolic blood pressure with these drugs is significantly related to increase in treadmill exercise, fall in LVFP, and increase in CO. Pirbuterol is a relatively selective beta 2-agonist with somewhat greater effects on CO than on LVFP. Early promise in CHF therapy is being shown by a novel series of cyclic adenosine monophosphate (cAMP) phosphodiesterase inhibitors with combined direct inotropic and vasodilator effects. Double-blind long-term studies demonstrate persistent efficacy of prazosin and trimazosin in CHF as measured by improvement in New York Heart Association functional class, treadmill exercise performance, and noninvasive measures of cardiac function; these data are supported by studies in which repeat cardiac catheterization has been performed after several months of therapy. Double-blind studies of other CHF drugs are in progress.