Comparison of Phosphate Binding Capacities of PA21, A Novel Phosphate Binder, with those of other Phosphate Binders in vitro and in vivo

Purpose: The phosphate binding capacity of PA21, a novel phosphate binder, was compared with those of other phosphate binders in vitro and in vivo. Methods: 1) For in vitro studies, PA21, sevelamer hydrochloride, lanthanum carbonate hydrate, calcium carbonate, and ferric citrate hydrate were incubated with a phosphate solution at 37 degrees C for 2h. Phosphate binding capacity was assessed at simulated gastrointestinal tract pH levels of 2, 5, and 8 for estimation of clinical effects, and the quantity of phosphate adsorbed by each phosphate binder was determined. 2) For in vivo studies, rats were orally administered various phosphate binders after the oral administration of phosphate solution (100mg/kg) adjusted to pH 2, 5, or 8, and the effects of PA21 and other phosphate binders on the serum phosphorus level of the rats were investigated. Results: 1) The in vitro studies revealed that PA21 and sevelamer hydrochloride adsorbed phosphate better at all tested pH levels than lanthanum carbonate hydrate, calcium carbonate, and ferric citrate hydrate, and PA21 showed the most potent phosphate binding capacity among the tested compounds. 2) The in vivo studies showed that PA21 dose-dependently inhibited the increase in the serum phosphorus level after the administration of phosphate solution and no difference in the extent of inhibition by PA21 was observed at the different pH levels (in contrast to other phosphate binders). Conclusion: These results indicated that PA21 has a phosphate binding capacity over the entire pH range of the GI tract.