Oral Phosphate Binders: Phosphate Binding Capacity of Iron (III) Hydroxide Complexes Containing Saccharides; and Their Effect on the Urinary Excretion of Calcium and Phosphate in Rats

Abstract

Phosphate binders that contain aluminum or calcium are frequently prescribed to treat hyperphosphatemia in patients with end-stage renal disease (ESRD), but an accumulation of aluminum can lead to encephalopathy, aluminum related bone disease (ARBD) such as osteomalacia, anaemia, and resistance to erythropoietin, and calcium accumulation can lead to hyperculcaemia. High phosphate concentrations are reducd in vitro and in vivo by a phosphate adsorption pill, which is synthesized by hydrolyzing ferrous sulfate in the presence of saccharides, to form an iron (III)-saccharide complex that is acid resistant anti binds phosphate greater than iron (III) hydroxide alone. Under in vitro conditions, containing 3.26 mg P/dL, the iron (III)-sucrose complex showed the highest phosphate adsorption capacity at pH 2 with artificial gastric juice, 58.9 mg P/g binder. For the 7 day in vivo study, 0% (Group 1), 1% (Group 2), 4% (Group 3), and 8% (Group 4) iron (III)-sucrose complex was admixed into the rodent chow by weight and fed to 15 male Wistar rats. The weight and volume of the feces and urine, and the calcium, iron, and phosphorus excretions in the feces and urine samples were monitored for any signs of irregularity. Total urine outfrow was collected during a 24-h period to determine the amount of phosphate recovered, which indicates the ability of the phosphate binder to reduce gastrointestinal phosphate absorption. The fecal iron excretion was significantly effected by the amount of binder ingested throughout the study for Group 2 (p < 0.001), Group 3 (p < 0.01), and Group 4 (p < 0.001). The urinary calcium excretion (mg/rat/24-h) significantly increased by the 7th day for Group 2 (p < 0.05) and Group 4 (p < 0.01) in comparison to the control. Finally, after 7 days, there was a significant drop in the urinary phosphorus levels (mg P/rat/24-h) in a dose dependant manner for Group 2: from 7.82 ± 1.46 to 1.98 ± 0.10 mg P/rat/24-h (102 mg P/dL/24-h; p < 0.05); Group 3: from 6.70 ± 1.14 to 0.16 ± 0.09 mg P/rat/24-h (6.0 mg P/dL/24-h; p < 0.01); and Group 4: fiom 8.25 ± 0.67 to 0.04 ± 0.01 mg P/rat/24-h (0.9 mg P/dL/24-h; p < 0.01). The results show that this new adsorbent might provide an alternative to conventional aluminum and calcium containing phosphate-binding agents for combating hyperphosphataemia.

Key Words:

• Phosphate binder
• Hyperphosphatemia
• Saccharide
• Uremia