Comparison of haemodynamic effects of oral prazosin, oral hydralazine, and intravenous nitroprusside in same patients with chronic heart failure

Prazosin in chronic congestive heart failure due to ischemic heart disease

Oral prazosin hydrochloride (2-20 mg/day) was administered to 38 patients with chronic congestive heart failure due to ischemic heart disease for 6-18 months. Half (19) of the patients were hypertensive and half (19) nonhypertensive. All were receiving furosemide (80 mg/day, orally) and 19 were receiving digoxin (0.25-0.5 mg/day, orally) in addition to prazosin. Clinical radiological, mechanocardiographic, echocardiographic, and biochemical observations were made initially, at peak response, and at the end of 6 months. Prazosin improved left ventricular function indexes at rest, relieved symptoms and signs of congestion, and remained effective for 6-18 months with little or no increase in dose. There was no reflex tachycardia, tension-time indexes fell in all patients, angina was relieved in 8 patients who complained of it, and dyskinesia of left ventricular wall was corrected in 8 of 13 patients. The New York Heart Association functional class improved in all patients, but to a greater extent in hypertensive patients and in those not receiving concomitant digoxin. Mild, transient side effects occurred in 6 patients.

Prazosin update. A review of its pharmacological properties and therapeutic use in hypertension and congestive heart failure

Prazosin is an orally active post-synaptic selective alpha 1-adrenoreceptor antagonist that has been widely used in treating hypertension and congestive heart failure (CHF). Its role in the treatment of hypertension has previously been reviewed in this journal. Subsequent reports confirm its efficacy in treating mild to severe hypertension as a single agent or, more frequently, in combination with another antihypertensive agent and/or a diuretic. Recent studies of the metabolic effect of prazosin indicate that the drug may have a favourable effect on plasma lipids in hypertensive patients. Its recent use in treatment of congestive heart failure has shown prazosin to be comparable with nitroprusside in producing balanced arterial and venous dilation with generally sustained haemodynamic and clinical effects during long term therapy. Initial studies in Raynaud's phenomenon and in patients with aortic regurgitation or aortic stenosis or with mitral regurgitation are promising, but require confirmation from wider clinical experience. The drug has generally been well tolerated. The primary side effect of orthostatic hypotension can be largely avoided by beginning treatment with a low dose.

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.

Clinical, hemodynamic, and neuroendocrine effects of chronic prazosin therapy for congestive heart failure

We report our hemodynamic, clinical, and neuroendocrine observations during long-term (8 weeks) prazosin (PZN) administration to assess the efficacy of this agent in the long-term therapy of congestive heart failure (CHF) and to emphasize the potential role of neuroendocrine mechanisms in the determination of overall drug effect. During long-term PZN therapy there is improvement in functional status, exercise tolerance, and left and right ventricular ejection fractions. However, we also observed an increase in fluid retention and attenuation of the initial hemodynamic and clinical responses to the drug. Plasma renin activity and plasma norepinephrine concentration are increased during long-term PZN therapy despite clinical and hemodynamic improvement and potentially may be involved in the pathogenesis of the increased fluid retention and hemodynamic attenuation. Three pharmacologic considerations appear relevant to the use of an alpha-adrenergic antagonist such as PZN in CHF therapy: (1) the drug response may be related to the baseline level of sympathetic tone. (2) The dose-response pattern exhibits a plateau phase, beyond which higher doses cause little further effect. (3) The overall drug effect is the sum of its direct actions and the secondary actions of the neuroendocrine response it elicits.

Improved right ventricular function and reduced pulmonary vascular resistance during prazosin therapy of congestive heart failure

Although the effect of systemic vasodilator therapy on left ventricular function in congestive heart failure has been extensively evaluated, little is known about its effect on pulmonary vascular resistance and right ventricular function. Since pulmonary vascular resistance is mediated in part by alpha-adrenergic receptors, we studied the effects of the alpha-adrenergic antagonist prazosin on right ventricular function as determined by a radionuclide ventriculographic technique which assessed right and left ventricular ejection fractions simultaneously. In 11 patients treated for two months with prazosin, right ventricular ejection fraction increased from 0.28 +/- 0.04 to 0.44 +/- 0.07 (p less than 0.01). In 10 patients who received a single dose of prazosin 48 hours after withdrawal of prior prazosin therapy, right ventricular ejection fraction increased from 0.29 to 0.05 to 0.38 +/- 0.06 (p less than 0.02). In nine patients who received a single dose of prazosin during right sided heart catheterization, pulmonary vascular resistance decreased from 358 +/- 70 to 236 +/- 60 dyne-sec-cm -5 (p less than 0.01). These studies suggest that prazosin has beneficial effects on right ventricular function both immediately and long-term in patients with severe congestive heart failure. Although the mechanism of this effect is not known, possibilities include a direct effect of prazosin on the pulmonary vasculature, a secondary reduction in right ventricular afterload due to improved left ventricular performance and a withdrawal of reflex-mediated pulmonary vasoconstriction due to improved left ventricular performance.

Acute and chronic haemodynamic effects of prazosin in left ventricular failure

We evaluated the acute and chronic effects of prazosin treatment in 11 patients with chronic congestive heart failure, NYHA functional class III and IV. Before treatment mean arterial pressure averaged 100 +/- 15 mmHg, left ventricular filling pressure 29 +/- 11 mmHg, and systemic vascular resistance 2372 +/- 1121 dynes s cm-5. Prazosin administration resulted in haemodynamic improvement in all but one patient with significant lowering of the mean arterial pressure, left ventricular filling pressure, and systemic vascular resistance. Nine patients completed a 10-week course of ambulatory treatment. Five patients remained improved while four developed significant fluid retention; two of these had transient exacerbation of congestive heart failure. This was controlled by increasing diuretic and/or prazosin treatment. After 10 weeks all nine patients had advanced to NYHA functional class II. Repeat haemodynamic measurements disclosed complete haemodynamic tolerance in one patient while three other patients showed partial tolerance with a lower cardiac output (CO) response to prazosin. The nine patients, however, still showed significant lowering of the mean arterial pressure, left ventricular filling pressure, as well as the systemic vascular resistance. Though pharmacodynamic tolerance was noted in four out of nine patients, beneficial clinical and haemodynamic effects could be demonstrated after 10 weeks of prazosin treatment in most patients. Further evaluation of the long-term effects of prazosin in chronic congestive heart failure is warranted.