The potential of a microencapsulated urease-zeolite oral sorbent for the removal of urea in uremia.

Abstract

Although successful in reducing urea levels, the use of oral microcapsules containing a urease-silica adduct and a zirconium phosphate ion exchanger result in a number of problems, including a negative calcium balance. In this study, it is demonstrated that the use of microcapsules containing a urease-zeolite preparation may be a potential route to urea removal. The use of zeolite ion exchangers, and zeolite W in particular, can alleviate the problems encountered with zirconium phosphate. Unlike zirconium phosphate, zeolite W is nonselective toward calcium ions and is stable at the high pH found in the intestinal tract. Zeolite W, when present in the sodium form, has a high ammonium capacity of 3.6 mEq NH4+/g zeolite under simulated intestinal conditions; its reactivity to ammonium is also higher. The application of enzyme envelopes to zeolite particles is a novel immobilization procedure that does not involve the use of colloidal silica and can reduce the amount of ingested material by as much as 25%. The current in vitro study shows that cellulose acetate butyrate microcapsules, containing a urease-zeolite preparation, remove up to 80% of urea in less than 1 hour. These microcapsules can be dried and retain activity when sealed in a jar at 4 degrees C.