Loop diuretics

Loop diuretics

Loop (high ceiling) diuretics are highly potent drugs. They include bumetanide, ethacrynic acid, and furosemide.

Pharmacokinetics

Loop diuretics are absorbed well in the GI tract and are rapidly distributed. These diuretics are highly protein bound. They under-go partial or complete metabolism in the liver, except for furo-semide, which is excreted primarily unchanged. Loop diuretics are excreted primarily by the kidneys.

Pharmacodynamics

Loop diuretics are the most potent diuretics available, producing the greatest volume of diuresis (urine production). Bumetanide— which is 40 times more potent than furosemide—is the shortest-acting diuretic. Loop diuretics also have a high potential for caus-ing severe adverse reactions. (See Loop diuretics warning.)

The scoop on the loop

Loop diuretics received their name because they act primarily on the thick, ascending loop of Henle (the part of the nephron re-sponsible for concentrating urine) to increase the secretion of sodium, chloride, and water. These drugs also inhibit sodium, chloride, and water reabsorption in the proximal tubule.

Pharmacotherapeutics

Loop diuretics are used to treat edema associated with renal dis-ease, hepatic cirrhosis, and heart failure, as well as to treat hyper-tension (usually with a potassium-sparing diuretic or potassium supplement to prevent hypokalemia).

Ethacrynic acid may also be used for the short-term manage-ment of ascites due to malignancy, idiopathic edema, or lym-phedema. Furosemide may be used with mannitol to treat cere-bral edema.

Drug interactions

Loop diuretics produce a variety of drug interactions:

§    The risk of ototoxicity (damage to the organs of hearing) in-creases when aminoglycosides and cisplatin are taken with loop diuretics (especially with high doses of furosemide). (See Adversereactions to loop diuretics.)

§    Loop diuretics reduce the hypoglycemic effects of oral antidia-betic drugs, possibly resulting in hyperglycemia.

§    These drugs may increase the risk of lithium toxicity.

§    The risk of electrolyte imbalances that can trigger arrhythmias increases when cardiac glycosides and loop diuretics are taken to-gether.

§     Use with digoxin may cause additive toxicity, increasing the risk

§    of digoxin toxicity and arrhythmias.