Is serum phosphorus control related to parathyroid hormone control in dialysis patients with secondary hyperparathyroidism?

Background: Elevated serum phosphorus (P) levels have been linked to increased morbidity and mortality in dialysis patients with secondary hyperparathyroidism (SHPT) but may be difficult to control if parathyroid hormone (PTH) is persistently elevated. We conducted a post hoc analysis of data from an earlier interventional study (OPTIMA) to explore the relationship between PTH control and serum P. Methods. The OPTIMA study randomized dialysis patients with intact PTH (iPTH) 300-799pg/mL to receive conventional care alone (vitamin D and/or phosphate binders [PB]; n=184) or a cinacalcet-based regimen (n=368). For patients randomized to conventional care, investigators were allowed flexibility in using a non-cinacalcet regimen (with no specific criteria for vitamin D analogue dosage) to attain KDOQI targets for iPTH, P, Ca and Ca x P. For those assigned to the cinacalcet-based regimen, dosages of cinacalcet, vitamin D sterols, and PB were optimized over the first 16weeks of the study, using a predefined treatment algorithm. The present analysis examined achievement of serum P targets (4.5 and 5.5mg/dL) in relation to achievement of iPTH 300pg/mL during the efficacy assessment phase (EAP; weeks 17-23). Results: Patients who achieved iPTH300pg/mL (or a reduction of 30% from baseline) were more likely to achieve serum P targets than those who did not, regardless of treatment group. Of those who did achieve iPTH300pg/mL, 43% achieved P 4.5mg/dL and 70% achieved P 5.5mg/dL, versus 21% and 46% of those who did not achieve iPTH300pg/mL. Doses of PB tended to be higher in patients not achieving serum P targets. Patients receiving cinacalcet were more likely to achieve iPTH 300pg/mL than those receiving conventional care (73% vs 23% of patients). Logistic regression analysis identified lower baseline P, no PB use at baseline and cinacalcet treatment to be predictors of achieving P 4.5mg/dL during EAP in patients above this threshold at baseline. Conclusions: This post hoc analysis found that control of serum P in dialysis patients was better when serum PTH levels were lowered effectively, regardless of treatment received. Trial registration. Clinicaltrials.gov identifier NCT00110890.