Lanthanum carbonate lowers serum phosphorus without altering body phosphorus burden in maintenance peritoneal...

Many studies show that intestinal phosphate binders reduce serum phosphorus concentrations in hyperphosphatemic patients with chronic kidney failure. To our knowledge, there are virtually no studies of the effect of these binders on fecal phosphate or body phosphate.

This study examined the hypothesis that phosphate binders increase fecal phosphate and reduce body phosphorus burden.

Seven adult patients undergoing maintenance peritoneal dialysis underwent full metabolic balance studies for phosphorus in a research ward while they ate a constant phosphorus diet. Patients were studied during a baseline period without phosphate binders and while they received, in random order, 3 doses of lanthanum carbonate (La₂(CO₃)₃), 1.5, 3.0, and 4.5 g/d, in 3 divided daily doses for ∼12-14 d each. The total duration of study was 47-49 d in each patient. Dialysate, urine, and feces were collected continuously and serum intermittently for phosphorus measurements.

Serum phosphorus concentrations fell progressively and significantly as the La₂(CO₃)₃ dose was increased (r = -0.47, P < 0.001). Fecal phosphorus concentrations rose progressively as La₂(CO₃)₃ increased (r = 46.4, P < 0.001). However, there was a negative correlation between both dialysate (r = -17.2, P = 0.002) and urine (r = -18.5, P < 0.001) phosphorus and La₂(CO₃)₃ dose. This decline in dialysate and urine phosphorus correlated with the fall in serum phosphorus concentration as the La₂(CO₃)₃ dose increased. As the La₂(CO₃)₃ dose rose, the increase in fecal phosphorus concentration was essentially counterbalanced by the fall in dialysate and urine phosphorus. Hence, body phosphorus balance did not change with increasing La₂(CO₃)₃ doses.

La₂(CO₃)₃ treatment lowered serum phosphorus concentration but did not change body phosphorus content. This trial was registered at clinicaltrials.gov as NCT01581996.