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Old 05-22-2015
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Default Comments on Carbonic Anhydrase inhibitors and urine pH

First Aid states that Carbonic Anhydrase inhibitors are used for urine alkalization, but it also associates carbonic anhydrase inhibitors to Type 2 Renal Tubular Acidosis, which is associated with low urine pH (pH<5.5). Anyone have any comments/explanations for this? Thanks
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Old 05-22-2015
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The reduction in HCO3- reabsorption leads to an increase in bicarbonate loss in the urine. Remember that a loss of a single bicarbonate ion is akin to adding one hydrogen ion to the plasma, therefore this bicarbonate loss in the urine leads to increased hydrogen ion concentration and a subsequent reduction in arterial pH.

Usually about 90% of the filtered HCO3- is absorbed by the proximal tubule, the rest is absorbed by the distal nephrons. In the setting of proximal impairment of HCO3- , the distal nephrons become overwhelmed by an increase in HCO3- delivery and cannot compensate for the loss in proximal function. However as urinary HCO3- loss progresses, plasma HCO3- drops to 15-18 meq/L. This causes the level of filtered HCO3- to fall and thus there is reduced delivery of HCO3- ions to the distal nephrons. At that point, the distal nephrons are no longer overwhelmed and can regain function, leading to a reduction in bicarbonaturia and a urine which can now be acidic. This is in contrast to type 1 RTA, where urine acidification is limited to a minimum urinary pH of 5.5.

Now since acetazolamide acts by inhibiting Carbonic Anhydrase and will result into no reabsorbtion of HCO3- so it can be associated with RTA Type II

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