Polystyrene sulfonate (Kayexalate) is used in renal failure to:
A. Correct acidosis.
B. Reduce serum phosphate levels.
C. Exchange potassium for sodium.
D. Prevent constipation from sorbitol use.
Correct Answer: C. Exchange potassium for sodium.
In renal failure, patients become hyperkalemic because they can’t excrete potassium in the urine. Polystyrene sulfonate acts to excrete potassium by pulling potassium into the bowels and exchanging it for sodium. Sodium polystyrene sulfonate helps by removing extra potassium from the body. Due to its slow onset of action, it is a second-line agent in emergent situations. Data on the non-FDA approved use of this drug is limited. This drug can also help to remove excess calcium, sodium from solutions in technical applications.
Option A: Sodium polystyrene sulfonate (SPS) is an insoluble polymer cation-exchange resin. After ingestion of oral formulation or application through the rectal route, this resin exchanges sodium with potassium ions from the intestinal cells. Then the potassium binds with SPS, continues to move through the gastrointestinal tract, and is finally eliminated in the feces. But sodium polystyrene sulfonate is not selective for potassium; it may bind with calcium and magnesium.
Option B: The exchange capacity of SPS is approximately 33% or 1 mEq of potassium per 1 gram of resin, and this number is not constant. It may be as low as 0.4 to 0.8 mEq/gram of SPS resin. Competition from other cations, especially sodium, calcium, and magnesium, contributes to this reduction of this exchange capacity.
Option D: Clinicians should not use SPS in patients who have abnormal bowel functions, such as bowel obstruction, Ileus, and postoperative patients. Using SPS in these patients may increase the risk of bowel ischemia, necrosis, and serious constipation.
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