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Oral sodium phosphate bowel purgatives and acute phosphate nephropathy

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Clinical Nephrotoxins

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Within both the kidney and the small intestine, phosphate absorption occurs mainly via sodium-dependent phosphate cotransporter proteins that are members of the SLC34 gene family [2-3]. NaPi-IIa (SLC34A1) and NaPi-IIc (SLC34A3) are expressed in the brush border of the proximal tubule and their expression is down regulated by increases in serum phosphate and parathyroid hormone (PTH). As such, NaPi-IIa knock-out mice have significant hyperphosphaturia and develop early and severe nephrocalcinosis [4]. NaPi-IIb (SLC34A2) has a broader distribution that includes the brush border of the small intestine and levels of this protein increase in response to hypophosphatemia and vitamin D. While expression of NaPi-IIa is acutely controlled over short time periods (i.e. minutes), NaPi-IIb expression in the intestine is slower, requiring days to respond to physiologic changes. Interestingly, recent studies have shown that there is a direct signaling axis by which intestinal phosphate absorption rapidly increases fractional phosphate excretion in the kidney. This effect is apparent within 10 minutes of phosphate ingestion and is independent of serum phosphate concentration or PTH [5].

In the usual state, between 60-80% of ingested phosphate is absorbed in the small intestine. In the kidney, phosphate is freely filtered at the level of the glomerulus. Approximately 80% of phosphate is reabsorbed in the proximal tubule, with smaller amounts reabsorbed in the distal tubule and collecting duct [6-7]. Oral phosphate ingestion has the potential to increase serum levels when the intake is at higher than usual levels or occurs over short periods of time. Similarly hyperphosphatemia may follow phosphate ingestion when it occurs in the setting of impaired gastrointestinal motility leading to increased absorption or with renal dysfunction leading to decreased excretion. Hyperphosphatemia may also result from massive intracellular phosphate release in the setting of tumor lysis syndrome or rhabdomyolysis.

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  1. College of Physicians and Surgeons, Department of Pathology, Columbia University, 630 West 168th Street, VC14-224, New York, NY, 10032, USA

    Glen S. Markowitz

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Editors and Affiliations

  1. Laboratory of Pathophysiology Universiteitsplein 1, University of Antwerp, Wilrijk, B-2610, Belgium

    Marc E. De Broe

  2. Division of Nephrology, Hypertension and Clinical Pharmacology, Oregon Health Sciences University, 3181 SW Sam Jackson Park Road, Portland, OR, 97201, USA

    George A. Porter

  3. Legacy Good Samaritan Hospital, 1015 NW 22nd Avenue, W004, Portland, OR, 97201, USA

    William M. Bennett

  4. Groupe Hôspitalier Pitié Salpétrière Service De Néphrologie 83, Boulevard de l′Hôpital, Paris, F-75013, France

    Gilbert Deray

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Markowitz, G.S. (2008). Oral sodium phosphate bowel purgatives and acute phosphate nephropathy. In: De Broe, M.E., Porter, G.A., Bennett, W.M., Deray, G. (eds) Clinical Nephrotoxins. Springer, Boston, MA. https://doi.org/10.1007/978-0-387-84843-3_26

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