<prompt> All of the following are true regarding diuretics except: March 2008Spironolactone is a potassium sparing drugMannitol is an osmotic diureticThiazides act by inhibiting Sodium-potassiumchloride cotranspoAcetazolamide inhibits carbonic anhydrase enzyme  <response>: Ans. C: Thiazides act by inhibiting Sodium-potassium-chloride cotranspo High Efficacy diuretics: - High ceiling diureticsLoop diuretics, such as furosemide, inhibit the bodys 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 Weakadjunctive 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. 