Abstract
Cinacalcet, a calcimimetic agent, binds to the calcium-sensing receptor (CaSR) and effectively decreases parathyroid hormone (PTH) secretion. CaSR is expressed in organs such as the parathyroid, kidneys, and bone. In the kidneys, it is expressed in the thick ascending limb (TAL) and the distal tubule (DT). In the TAL, activation of CaSR inhibits magnesium and calcium resorption by direct or indirect mechanisms. It also inhibits recycling of potassium back into the lumen by potassium channels. Peritoneal dialysis (PD) is thought to preserve the residual renal function (RRF) longer than hemodialysis. RRF is thus an important prognostic factor for PD patients. We investigated the effects on electrolyte balance and safety of cinacalcet. Six PD patients with RRF received once-daily oral cinacalcet at 25mg for two months. We examined the changes in levels of serum iPTH, and serum and urinary excretion of phosphorus, calcium, magnesium, and potassium for two months. Median (interquatile range: IQR) serum iPTH levels decreased significantly from 427.2 (351.2~1,313.3) pg/mL to 234.4 (86.0~721.3) pg/mL. Serum phosphorus levels and urinary excretion of phosphorus also decreased significantly. In contrast, concentrations of serum calcium, magnesium, and potassium, and urinary excretion of calcium, magnesium, and potassium did not change significantly. Serum levels of magnesium and potassium were not significantly altered, and were within the normal ranges (before, median 2.2 (IQR: 1.9~2.3) mg/dL, after, median 2.0 (IQR: 1.8~2.5) mg/dL for Mg; and before, median 4.5 (IQR: 4.4~5.2) mEq/L to 4.6 (IQR: 4.2~4.8) mEq/L for K). Based on these findings regarding the potassium and magnesium balance, cinacalcet appears to be useful and safe for the treatment of secondary hyperparathyroidism in PD patients with RRF.
