Loop diuretics act on the Na+ ,K+, 2Cl- symporter in the thick ascending limb of the loop of Henle. The medullary thick ascending limb is mostly impermeable to water.
Loop diuretics act on the Na+ ,K+, 2Cl- transporter in the thick ascending limb of the loop of Henle. They inhibit sodium and chloride reabsorption by competing for the Cl- binding site. Loop diuretics prevent the generation of a hypertonic renal medulla which prevents urine from being concentrated and leads to increased urine production.
Furosemide (Lasix) contains a sulfonamide group and can cause an allergic reaction in patients with a sulfa allergy. Patients with hypersensitivies to sulfa drugs may be prescribed ethacrynic acid (Edecrin) which is a loop diuretic without a sulfur component. Ethacrynic acid should be remembered because it has a greater risk of ototoxicity compared to Furosemide.
Furosemide is the generic name for a commonly prescribed potent loop diuretic. Other loop diuretics include torsemide (Diuver), bumetanide (Bumex), and ethacrynic acid (Edecrin).
Lasix is the brand name of Furosemide and is one of the most commonly used loop diuretics.
Ototoxicity (damage to the ear) is a serious but rare adverse effect of loop diuretics. Symptoms may be limited to tinnitus and vertigo but serious cases can result in hearing loss.
High levels of uric acid in the blood is the underlying cause of gout. This can occur for a number of reasons including diet, medications, genetics, or underexcretion of urate from the kidneys. Diuretics have been associated with hyperuricemia and gout.
Excessive use of diuretics may cause hypovolemia which may manifest as dehydration with skin tenting and excessive thirst and also low blood pressure.
Inhibition of the Na+, K+, 2Cl transporter causes a failure of reabsorption of calcium which may cause hypocalcemia. Hypocalcemia may manifest as ECG changes, muscle spasms, or tetany. Remember Chvostek sign and Trousseau's sign are indicators of hypocalcemia.
Because loop diuretics prevent reabsorption of sodium and chloride ions in the loop of Henle, there is an increased amount of sodium and water that passes through the collecting tubules. This causes a reflex secretion of potassium into the urine by increased aldosterone secretion. Also, volume depletion due to increased urine output causes increased secretion of aldosterone which further increases the secretion of potassium into the collecting duct and into the urine, leading to hypokalemia.
Hypokalemia may manifest as ECG changes, muscle tingling or weakness, fatigue and constipation.
Orthostatic hypotension occurs when a person’s blood pressure suddenly falls when standing up or stretching. Educate the patient to rise slowly or dangle their feet off the bed before standing.
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