All of the following are true regarding diuretics except: March 2008
Ans. C: Thiazides act by inhibiting Sodium-potassium-chloride cotranspo High Efficacy diuretics: - High ceiling diuretics/Loop diuretics, such as furosemide, inhibit the body's ability to reabsorb sodium (by inhibiting sodium-potassium-chloride cotranspo) at the ascending loop in the kidney which leads to a retention of water in the urine as water normally follows sodium back into the extracellular fluid (ECF). Other examples of high ceiling loop diuretics include ethacrynic acid, torasemide and bumetanide. Medium efficacy diuretics: - Thiazide-type diuretics such as hydrochlorothiazide, Clopamide, act on the distal convoluted tubule and inhibit the sodium-chloride sympoer leading to retention of water in the urine, as water normally follows penetrating solutes. The sho-term anti-hypeensive action is based on the fact that thiazides decrease preload, decreasing blood pressure. On the other hand the long-term effect is due to an unknown vasodilator effect that decreases blood pressure by decreasing resistance. - Thiazide like diuretics includes chlohalidone, metolazone, xipamide, indapamide Weak/adjunctive drugs: - Carbonic Anhydrase Inhibitors inhibit the enzyme carbonic anhydrase which is found in the proximal convoluted tubule. This results in several effects including bicarbonate retention in the urine, potassium retention in urine and decreased sodium absorption. Drugs in this class include acetazolamide and methazolamide. - Potassium-sparing diuretics do not promote the secretion of potassium into the urine; thus, potassium is spared and not lost as much as in other diuretics. The term "potassium-sparing" refers to an effect rather than a mechanism or location; nonetheless, the term almost always refers to two specific classes that have their effect at similar locations: Aldosterone antagonists: spironolactone, which is a competitive antagonist of aldosterone. Aldosterone normally adds sodium channels in the principal cells of the collecting duct and late distal tubule of the nephron. Spironolactone prevents aldosterone from entering the principal cells, preventing sodium reabsorption. A similar agent is potassium canreonate. Epithelial sodium channel blockers: amiloride and triamterene. Osmotic diuretics as mannitol are filtered in the glomerulus, but cannot be reabsorbed. Their presence leads to an increase in the osmolarity of the filtrate. To maintain osmotic balance, water is retained in the urine.
Spironolactone is a potassium sparing drug
Mannitol is an osmotic diuretic
Thiazides act by inhibiting Sodium-potassiumchloride cotranspo
Acetazolamide inhibits carbonic anhydrase enzyme