How to assess the efficacy of phosphate binders.

BACKGROUND AND AIMS The efficacy of phosphate binders is difficult to be estimated clinically. This study analyzes the changes in serum phosphate and urinary phosphate excretion after the prescription of phosphate binders (PB) in patients with chronic kidney disease stage 4-5 pre-dialysis, and the usefulness of the ratio between total urinary phosphate and protein catabolic rate (Pu/PCR) for estimating the efficacy of PB. METHODS This retrospective observational cohort study included adult chronic kidney disease patients. Biochemical parameters were determined baseline and after 45-60 days on a low phosphate diet plus PB ("binder" subgroup=260 patients) or only with dietary advice ("control" subgroup=79 patients). RESULTS Phosphate load (total urinary excretion) per unit of renal function (Pu/GFR) was the best parameter correlated with serum phosphate levels (R2=0.61). Mean±SD level of Pu/PCR was 8.2±2.3mg of urinary phosphate per each g of estimated protein intake. After treatment with PB, serum phosphate levels decreased by 11%, urinary phosphate 22%, protein catabolic rate 7%, and Pu/PCR 15%. In the control subgroup, Pu/PCR increased by 20%. Urinary phosphate and urea nitrogen excretion correlated strongly, both baseline and after PB or dietary advice. CONCLUSIONS The proposed parameter Pu/PCR may reflect the rate of intestinal phosphate absorption, and therefore, its variations after PB prescription may be a useful tool for estimating the pharmacological efficacy of these drugs.