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Furosemide (Lasix)

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Furosemide (Lasix)





Actions:

Loop diuretic. Furosemide inhibits the coupled Na+/K+/2Cl- transport system in the luminal membrane of the thick ascending limb of the loop of Henle. Thus the loop diuretics reduce the reabsorption of NaCl and also diminish the normal lumen-positive potential that derives from K+ recycling.

Therapeutic Effects:

Lowers blood pressure by depleting body sodium stores. Initially, blood volume and cardiac output declines; after 6-8 weeks, cardiac output returns toward normal while peripheral vascular resistance declines.

Decreases calcium reabsorption causing hypercalciuria.

Decreases potassium reabsorption.

Reduces accumulation of edema.

Nontherapeutic Effects and Toxicities:

Hypokalemia and hypomagnesemia. Can be readily reversed by administration of oral K+ and Mg++ preparations.

Hypovolemia, hyponatremia if increased water intake.

GI disturbances. Anorexia, nausea, vomiting, diarrhea.

Ototoxicity. The loop diuretics can cause dose-relatd hearing loss that is usually reversible. Most common in patients who have diminished renal function.

Allergic reactions. Skin rash, pruritus, photosensitivity.

Decreased libido.

Indications:

Hypertension. Thiazides are preferable to loop diuretics, however when a patient has renal impairment or significant volume overload, the more potent loop diuretics may be needed.

Edema. Treatment of edema in Na+-retaining states such as CHF, chronic renal failure, acute renal failure, and hepatic cirrhosis.

Pulmonary edema. IV furosemide is used when rapid diuresis is required, such as acute CHF.

Hypercalcemia. Furosemide is useful in the acute treatment of hypercalcemia.

Hyperkalemia. In mild hyperkalemia, loop diuretics can signifcantly enhance urinary excretion of K+ as a means of reducing total body K+ stores.

Contraindications and Precautions:

Sulfonamide sensitivity. Furosemide may demonstrate cross-reactivity in patients who are sensitive to other sulfonamides.

Overzealous use of any diuretic is dangerous in:

Hepatic cirrhosis.

Borderline renal failure.

CHF.

Drug Interactions:

Nonsteroidal anti-inflammatory drugs. NSAIDs decrease diuretic, natriuretic and antihypertensive response to furosemide, due to prostaglandin inhibition.

Propranolol. Furosemide causes decreased metabolism of propranolol.

Miscellaneous

Owing to the large NaCl absorptive capacity of the loop of Henle, loop agents are the most efficacious diuretic agents available.

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