Diuretics and drugs that increase cardiac muscle strength (digitalis) are the main drug treatment for congestive heart failure. There are few randomized clinical trials that show diuretic treatment affects mortality rates of patients with congestive heart failure. Clinical experience shows their importance, however close monitoring is essential to avoid toxicity. This essay aims to discuss briefly yet comprehensively diuretics to treat congestive heart failure.
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The essence of heart failure has changed from Corvisart (1812) who considered the basic heart failure phenomenon as increased heart size pressing on the lungs. In 1830, Hope introduced the backpressure theory which has been elaborated by other scientists (as Lewis, Mackenzie, and Starling) and upheld till today. The fundamental abnormality in heart failure is the inability of the heart to deliver enough blood supply to the tissues under all conditions.
In all forms (right-sided, or left-sided), the cardiac output is subnormal, the so-called reduced cardiac reserve (Scott, 1975). Congestive heart failure is a progressively disabling disease with survival rates worse than cancer prostate and cancer breast in many countries (National Prescribing Centre, 2001). Many studies show that proper drug therapy reduces the frequency of hospital admissions and improves survival rates (National Prescribing Centre, 2001). Causes of heart failure are variable, in western countries the commonest cause is coronary artery disease while in developing countries rheumatic valvular heart disease is the commonest (Chau, 2006).
However, heart failure is largely independent of its underlying cause, and likewise, the treatment follows general principles which can be applied independently of the cause (Scott, 1975). The aims of treating cases of heart failure are to improve patients’ symptoms as dyspnea, easy fatigability, and edema or at least hold up their worsening. The second is to decrease the number of cardiac asthma events and according to the number of hospital admissions. The third is to reduce disease mortality and avoid drugs’ toxic effects (National Prescribing Centre, 2001).
Diuretics have a recognized role in every heart failure drug treatment protocol. There are few randomized controlled trials that suggest their significance in improving the mortality rate. Yet, clinical experience suggests they are the most rapid and reliable way to improve patients’ symptoms (National Prescribing Centre, 2001). Further, it is important to improve body volume condition before administering other drugs like beta-blockers and Angiotensin-converting enzyme inhibitors (Chau, 2006). This essay will focus on diuretics to treat congestive heart failure as regards mechanisms of action and toxic effects, assessment of patients’ response, and the question of resistance to diuretics and how to overcome it.
Why diuretics, types and toxic effects of diuretics
The basic reason for using diuretics in cases of congestive heart failure is to reduce edema and relieve lung congestion accompanying heart failure. Diuretics drugs commonly prescribed are thiazide diuretics as hydrochlorothiazide working on the distal convoluted tubule decreasing the water and electrolytes reabsorption. Loop diuretics as furosemide and ethacrynic acid, which act by blocking sodium, potassium, and chloride ions cotransporters in the lumen of the ascending limb of the loop of Henle.
Potassium-sparing diuretics like spironolactone work on the collecting tubules and are used mainly when there is a chronic liver disease associated with heart failure. The toxic effects of diuretics are mainly because of electrolyte depletion and excessive water loss. Weakness, malaise, muscle cramps, and vomiting are important symptoms of toxicity. Drug-drug interaction (probenecid and thiazides) may decrease the efficacy (Scott, 1975).
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Assessment of patients’ response
Diuretics can be used intravenously in the early treatment of acute congestive heart failure with dyspnea, edema, and elevated jugular reflex (collectively called manifestations of fluid volume overload). The patient often shows improvement before a significant increase in urinary output, intravenous administration calls for closer monitoring. In many centers, monitoring is done by observing the urine output amount, and a protocol-guided strategy to adjust diuretic therapy often results in better diuresis and a shorter period of hospitalization.
The basic difference between the usual patient care and the protocol-guided study is putting fluid restriction into effect and the diuretic dose is then adjusted according to the fluid intake and urine output. When the condition is relieved, a shift to oral diuretic treatment is advised before discharge (Dipiro and others, 2008).
Resistance to diuretics
It means that patients fail to improve manifestations of fluid volume overload despite having high doses of diuretics. Resistance to diuretics may take place secondary to delayed oral absorption because of splanchnic congestion. In the case of loop diuretics, decreased excretion through the tubule lumen takes place secondary to renal congestion and this may lead to resistance (Dipiro and others, 2008). The question remains, what strategy to use to overcome the problem of resistance. Increasing the diuretic dose or its frequency of administration can be an effective strategy particularly in the case of furosemide whose duration of action is only six hours, so patients on once daily or twice daily treatment may suffer resistance problems.
Adding another diuretic, like a thiazide to furosemide, can also be effective as they act on different areas of the loop of Henle, therefore, a synergistic action develops. In these conditions, close observation of potassium levels is crucial as potassium depletion may result in serious cardiac arrhythmias and neuromuscular disorders. Finally, re-hospitalization and administering diuretics through the intravenous route may be needed. In this case, clinical trials showed that a loading dose followed by closely observed continuous infusion can be more safe and effective than giving a bolus dose (Dipiro and others, 2008).
Congestive heart failure affects 2% of the US population with 1 million hospital admissions every year. This put a health cost of $ 60 billion US every year (Heart failure resource center at <http://www.medscape.com>). In a hospital or an outpatient setting, diuretics are well established as lines of treatment. Treatment with diuretics has shown efficacy based on clinical experience, however close observation and full patient awareness of their side effect is a must to avoid life-threatening complications. It is an interesting group of drugs that I wanted to learn about because of the diversity of their mechanisms of action, the variability of administration methods, and the problems encountered during treatment are not only those of side effects.
Chau, E. MC. (2006). Treatment of Congestive Cardiac Failure. Medical Bulletin, 11(7), 22-24.
Dipiro, J T., Katzke, G R., Posey, L M., Talbert, R L., et al (2008). Pharmacotherapy: A Pathophysiologic Approach. New York: McGraw-Hill Medical.
National Prescribing Centre (NHS) (2001). The diagnosis and drug treatment of heart failure. MeRec Briefing, 15, 1-8.
Sir R. B. Scott (1975). Price’s Textbook of the Practice of Medicine. London: The English Language Book Society and Oxford University Press.