ETHACRYNIC ACID PARENTERALLY IN THE TREATMENT AND PREVENTION OF PULMONARY OEDEMA

Outpatient management of chronic heart failure

INTRODUCTION

Heart failure (HF) treatment attracts a share of intensive research because of its poor HF prognosis. In the past decades, the prognosis of HF has improved considerably, mainly as a consequence of the progress that has been made in the pharmacological management of HF.

AREAS COVERED

This article reviews the outpatient pharmacological management of chronic HF due to left ventricular systolic dysfunction and offers recommendations on the use of various drugs. In addition, the present article attempts to provide practical therapeutic algorithms based on current clinical strategies.

EXPERT OPINION

Continued research directed toward identifying factors associated with high pharmacotherapy guideline adherence and understanding of variants that influence response to drugs will hopefully halt or reverse the major pathophysiological mechanisms involved in this syndrome.

The management of heart failure: a matter of definition?

The term heart failure has become a label for more than one clinical entity. For many years heart failure has been used to denote patients with various heart diseases who have begun to suffer from fluid retention, pulmonary venous hypertension, or systemic venous hypertension, either alone or in combination. More recently, the term heart failure has been applied to the combination of effort intolerance and reduced left ventricular contractility due to ischemic heart disease or other myocardial disease. Comparison of the results of epidemiological studies and therapeutic trials is complicated by variation in the composition of the patient populations selected for study. Drug treatment of heart failure remains fairly empirical. Distinction should be made between immediate or prognostic benefits related to the etiological diagnosis, and benefits related specifically to prevention and relief of, for example, fluid retention, rhythm disturbances, or ventricular hypertrophy. The response of individual patients to several forms of drug treatment, including digoxin, ACE inhibitors, and beta-blockade, is unpredictable. Prospective identification of patients liable to respond well to these drugs is not yet possible, but would greatly assist the choice of treatment. At present, trial of therapy is required in each patient to establish benefit and to avoid long-term treatment of nonresponders.

Management of hypertensive crises

Malignant hypertension still constitutes a medical emergency, particularly when complicated by renal failure, encephalopathy, or left ventricular failure. A shift to the right of the autoregulatory curve of cerebral blood flow (and probably of renal blood flow) is known to occur in patients with hypertension. Local cerebral edema, complicating the malignant phase, is likely to aggravate this trend. While inadequate or tardy treatment leads to encephalopathy, renal and cardiac failure, over aggressive treatment may also result in damage to brain, heart, and kidney. Recent reports of neurological damage, sometimes fatal, following aggressive hypotensive treatment suggests the need for a reappraisal of current practices. More investigation is needed to determine the effects of the various classes of antihypertensive drugs on organ perfusion, particularly of brain, heart, and kidney, in both normal and hypertensive humans. Other hypertensive crises include raised arterial pressure in association with acute dissection of the aorta and in the presence of stroke or subarachnoid hemorrhage. While there is agreement about the need for urgent hypotensive treatment in patients with aortic dissection, there is no information with which to base rational decisions in the management of high arterial pressure in the acute phase of stroke or subarachnoid hemorrhage.

Diuretics: mechanism of action and clinical application

Despite the bewildering number of diuretics available to the physician, these drugs can be divided into 4 main groups, characterised by their site of action on sodium reabsorption in the kidney. Drugs acting on the ascending limb of the loop of Henle have a powerful but short acting diuretic effect; they include frusemide, ethacrynic acid and bumetanide. The benzothiadiazines and related compounds have a moderate diuretic action spread over a longer period, whilst the potassium-sparing diuretics, triamterene, amiloride and spironolactone, have only a weak diuretic effect but a marked ability to diminish urinary potassium excretion. The fourth group is made up of miscellaneous substances which function as vasodilator or osmotic agents. The pathogenesis of oedema formation in heart failure is outlined and a logical approach to treatment suggested. Duiretics are being increasingly used in the treatment of non-oedematous states, in particular hypertension, diabetes insipidus and hypercalciuria; their exact role in pregnancy and acute renal failure remains controversial. Side-effects can be related to their effect on electrolyte excretion and include hypokalaemia, hyponatraemia, hyperkalaemia and hyperuricaemia. The incidence of disturbed carbohydrate tolerance in previously normal individuals is low. Other less common side-effects are also discussed.

Ethacrynic acid in blood transfusion--its effects on plasma volume and urine flow in severe anaemia in pregnancy

Thirty grossly anaemic pregnant Nigerian women with venous haematocrit levels varying between 6 and 17%, had their plasma volumes estimated by the Evans blue dye dilution technique, both before and immediately after direct transfusion of packed blood cells. Parenteral ethacrynic acid was added to the blood for transfusion in 20 patients, seven of whom were in anaemic heart failure on admission. Ethacrynic acid used in this way was successful in the prevention of acute pulmonary oedema, and it produced acute diuresis as well as a reduction of plasma volume in the majority of cases. This technique of direct transfusion with ethacrynic acid is simple, and it may well replace exchange transfusion as a means of treating patients with anaemic heart failure.

Ethacrynic Acid

Ethacrynic acid, a chemically different diuretic, has been evaluated in 82 patients. The drug was remarkably potent when administered intravenously (0.5 to 1 mg./Kg.) or by mouth (doses to 50 mg. four times per day). It proved particularly effective in patients with refractory edema, and in edematous states accompanied by azotemia or electrolyte disturbances. Its natriuretic effects added to those of other diuretics and potentiation actually appeared to occur when it was combined with a carbonic-anhydrase inhibitor.

Renal clearance data indicated that ethacrynic acid has a unique mode of action. There was little effect on glomerular filtration or renal plasma flow and its major action was to block sodium and chloride reabsorption probably in both proximal and distal portions of the renal tubules.

Ion exchange mechanisms seemed little affected by the drug because it characteristically increased both hydrogen and potassium ion excretion. In general the degree of induced potassium loss correlated well with the rate of endogenous aldosterone secretion. Furthermore, ethacrynic acid did not cause potassium loss in one adrenalectomized subject nor in another subject pretreated with an aldosterone antagonist.

Diuresis induced by ethacrynic acid was often accompanied by the development of systemic metabolic alkalosis. Factors in the development of this alkalosis were (1) urinary K + loss with hypokalemia, (2) urinary H + loss, and (3) in edematous patients the rapid large loss of relatively HCO 3 - -free fluid from the extracellular fluid space. The systemic alkalosis was found to be accompanied by compensatory alveolar hypoventilation. These studies of the mechanisms of the alkalosis point to the occasional importance of the administration of chloride, of potassium, or of saline as corrective measures.

Diuresis with ethacrynic acid, like other diuretic agents, produced marked increases in the rate of aldosterone secretion of normal subjects. More variable effects were observed in patients with heart disease, possibly because improvement in their circulatory status operated to lower hormone secretion activity.

Ethacrynic acid had effects on urate excretion that resembled thiazide diuretics. Higher blood levels of intravenous administration were uricosuric. Lower blood levels of oral therapy caused renal urate retention and hyperuricemia.

Most of the problems associated with the use of ethacrynic acid appeared to be related more to its pharmacologic potency than to any truly toxic effect. Because of this it is suggested that the sensitivity and response pattern of each patient be determined in stepwise fashion. In most patients with edema an intermittent dosage schedule provides a more efficient diuretic response and allows time intervals for correction of any electrolyte imbalance. If used with a thorough understanding of its pharmacologic effects ethacrynic acid promises to be a most useful agent in the therapy of patients with difficult or refractory edema.