CHICAGO—Hyperphosphatemia may be more difficult to manage in younger dialysis patients, study findings presented the American Society of Nephrology’s 2016 Kidney Week meeting suggest.

The findings, from a post hoc analysis of a phase 3 trial comparing sucroferric oxyhydroxide and sevelamer carbonate, also found that baseline phosphorus levels predicted treatment response to either medication.

For the initial trial, investigators randomly assigned 1059 dialysis patients to receive sucroferric oxyhydoxide 1.0–3.0 g/day or sevelamer carbonate 2.4–14.4 g/day for 12 weeks of dose titration, followed by 12 weeks of maintenance therapy. Treatment doses were titrated to achieve pre-defined serum phosphorus levels of 3.5 to 5.5 mg/dL. Following the initial 24-week safety and efficacy study, eligible patients were allowed entrance into a 28-week safety extension study, continuing on the same treatment and at the same dose.

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Jürgen Floege, MD, of RWTH University Hospital Aachen in Aachen, Germany, and colleagues performed the post hoc analysis using data for patients who had a serum phosphorus measurement available at week 52. Of the 1041 patients making up the full analysis set of the initial phase 3 study, 497 (48%) had a serum phosphorus measurement available at week 52 and were eligible for analysis: 302 responders (61%) and 195 non-responders (39%). The researchers defined responders as patients who achieved a serum phosphorus concentration of 5.5 mg/dL or less at week 52.

The mean age of responders was significant higher than that of non-responders (56.9 vs 53.4 years), Dr Floege’s team reported in a poster presentation. Mean baseline serum phosphorus levels were significantly lower among responders compared with non-responders (7.30 vs 7.85 mg/dL). Decreases in serum phosphorus from baseline to weeks 24 and 52 were greater among responders versus non-responders.

In addition, mean serum intact parathyroid hormone (iPTH) levels declined from baseline to week 24 in both subgroups, but, after 1 year of treatment, these initial reductions in iPTH were only maintained among the responders, with overall increases in iPTH levels observed in the non-responders. Mean serum fibroblast growth factor 23 (FGF-23) levels declined more from baseline in responders compared with non-responders, with significant differences observed between them at weeks 24 and 52, according to the investigators. The adherence rates to binder treatment over 1 year were 90.5% and 86.2% in the responder and non-responders groups, respectively, a non-significant difference.

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  1. Floege J, Sprague S, Rastogi A, et al. Characteristics of responders and non-responders to phosphate binder therapy: A post hoc analysis of a phase 3 study. Poster presented at the 2016 Kidney Week meeting in Chicago, Nov. 15-20. Poster TH-PO564.