Polycation as an alternative osmotic agent and phosphate binder in peritoneal dialysis.

We have previously shown that polyanions can be utilized to achieve balanced removal of sodium and water during peritoneal dialysis. The excessive binding of potassium, calcium, and magnesium to anionic polymers proves undesirable. The present study was designed to demonstrate the reversibility of cation binding by using a polycation (polyethylenimine) as the osmotic agent, thus favoring the removal of undesirable excess phosphate anions via peritoneal dialysis. Polyethylenimine shows a measurable affinity for phosphorus when present as dialysate in an in vitro system simulating peritoneal dialysis. The polycation also stimulates ultrafiltration across the rat peritoneum when present in dialysate. The polymer is toxic to the rat and light microscopy reveals gross morphological tissue alterations of the visceral mesothelium and associated organs. We have demonstrated that a polycation can give ultrafiltration with enhanced removal of phosphate. Although the polymer we chose as a prototype is toxic to the rat, other polycations should be studied.