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What is a Loop Diuretic?
A diuretic is any drug which increases the output of urine. The mechanism, by which the drug accomplishes this, characterizes the drug into one of five classes: thiazides, potassium sparing, carbonic anhydrase inhibitors, osmotic diuretics or loop diuretics.1 Loop diuretics target the sodium-potassium-chloride co-transporter molecules on the thick ascending limb of the Loop of Henle region in the kidney nephron. The drug prevents the reabsorption of sodium from the blood filtrate at this location. This leads to an increased concentration of sodium within the distal convoluted tubule region of the nephron and reduces the hypertonicity of the interstitial fluid. A lesser amount of water is reabsorbed at the collecting duct region of the nephron, resulting in a much higher urine volume output. Common loop diuretics include furosemide, torsemide, bumetanide and ethacrynic acid.2 Each is administered orally or intravenously.
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Loop diuretics are prescribed to treat water imbalances associated with congestive heart failure and kidney failure. Symptoms include shortness of breath as a result of water retention in the lungs and swelling of lower extremities. Loop diuretics reduce blood volume and venous pressure, leading to increased capillary fluid reabsorption and decreased water retention.2
Loop diuretics can be used to treat high blood pressure for certain patients, such as those that have lost greater than 50% of kidney function.3 Otherwise, the side effects of loop diuretics would prevent its use for high blood pressure and thiazides would be prescribed for the vast majority of patients.
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Side Effects of Loop Diuretics
Loop diuretics remove water and electrolytes from the body. Potential side effects of loop diuretics include an extremely low blood volume which leads to dehydration and low blood pressure. The levels of sodium, potassium and magnesium in the blood decrease and the pH of the blood increase above the normal range. Patients taking loop diuretics may also experience hearing loss. Taking loop diuretics over a long period of time reduces the ability of arterial walls to resist blood flow.2
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Loop diuretics can interact negatively with other medications. Low potassium levels associated with loop diuretics increase the risk of digitalis toxicity, a medicine prescribed for congestive heart failure. Corticosteriods further reduce the levels of potassium in the blood. Antibiotics derived from aminoglycoside can increase the risk of hearing loss and kidney damage when taken with loop diuretics. Non-steroidal anti-inflammatory drugs such as aspirin and naproxen reduce the effect of loop diuretics.2
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1. http://www.nursereview.org/2007/11/pharmacology-kidney-drugs-nursing.html "Renal Pharmacology" Nurse Review. Nov. 2007. Web. 11 Apr. 2010.
2. http://www.cvpharmacology.com/diuretic/diuretics.htm Klabunde, Richard E. "Diuretics." Cardiovascular Pharmacology Concepts. 10 Jan. 2010. Web. 11 Apr. 2010.
3. http://www.merck.com/mmpe/sec07/ch071/ch071a.html#sec07-ch071-ch071a-404 Bakris, George L. "Drugs for Hypertension: Diuretics." The Merck Manuals Online Medical Library. Jan. 2010. Web 11 Apr. 2010.