Diuretics are medications that are used to treat hypertension, and edema due to heart failure, liver failure, certain renal disorders, and some drug therapies. Specific classes of diuretics work differently, targeting different segments of the nephron, except for the osmotic diuretics, which work throughout the nephron. The most important thing to remember is that diuretics affect fluid and electrolyte balance, so it’s critical to monitor intake and output, weight, and electrolyte levels – especially potassium – closely. Let’s take a closer look at the classes of diuretics and how they work, and what nurses need to know.
Loop diuretics have their effects in the ascending limb of the loop of Henle. They are first-line therapy for acute relief of pulmonary and peripheral edema due to heart failure but are also used to treat edema associated with liver cirrhosis, and renal disease, including nephrotic syndrome. The most well-known agent is furosemide. Other drugs in this class include bumetanide, torsemide, and ethacrynic acid. Many loop diuretics are available in both oral and IV forms.
Loop diuretics are generally well tolerated. Diuretic-associated hypokalemia can lead to cardiac arrhythmias in patients with coronary or cardiac insufficiency, and loop diuretics are also associated with dose-related ototoxicity (co-administration with aminoglycosides should be avoided.)
Thiazide diuretics inhibit sodium chloride reabsorption in the distal convoluted tubule. They are first-line agents for the treatment of hypertension and are often used together with loop diuretics for their synergistic diuretic effects in heart failure. They are administered orally.
Hydrochlorothiazide is an example of a thiazide diuretic. In addition to its effects on renal electrolyte handling, hydrochlorothiazide decreases glucose tolerance and may unmask diabetes in patients at risk for impaired glucose metabolism. Hydrochlorothiazide should be taken several times a day. A longer acting thiazide, chlorthalidone, can be taken once a day.
Thiazide diuretics should not be administered concurrently with antiarrhythmic agents that prolong the QT interval (i.e., quinidine, sotalol), due to the risk of torsades de pointes; this may be related to thiazide-induced hypokalemia, which increases the potential for cardiac arrhythmias. Patients should also be monitored for symptoms of acute pancreatitis.
Carbonic anhydrase inhibitors decrease sodium and bicarbonate reabsorption in the proximal tubule. While considered diuretics, these drugs are also used for glaucoma, idiopathic intracranial hypertension, altitude sickness, and epilepsy, among other diseases. Acetazolamide is an example of a carbonic anhydrase inhibitor; it may be used as an adjunctive therapy to treat edema due to heart failure. It is available in both an oral and IV form.
Potassium-sparing diuretics increase nephron reabsorption of potassium by interrupting sodium reabsorption in the collecting duct. They are typically used with a thiazide or loop diuretic to enhance its action, as potassium-sparing diuretics have weak diuretic and antihypertensive effects when used alone. Examples are spironolactone, amiloride, and triamterene. In contrast to the other classes of diuretics, the risk of hyperkalemia is increased.
Osmotic diuretics increase urinary flow by osmotic retention of water throughout the nephron. Mannitol is used to decrease intracranial pressure and cerebral edema. It is given by IV injection (intermittent bolus preferred), and preferably via a large central vein, as it is a vesicant.
As with any medication, it’s important for nurses to be familiar with the specific diuretic(s) a patient is taking, including indication, dosage and administration, contraindications, interactions, and adverse effects. Below are some general considerations related to diuretics.
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