HYPERCALCEMIA DURING PULSE VITAMIN-D3 THERAPY IN CAPD PATIENTS TREATED WITH LOW-CALCIUM DIALYSATE - THE ROLE OF THE DECREASING SERUM PARATHYROID-HORMONE LEVEL

Oral pulse therapy with vitamin D is effective in suppressing parathyr oid hormone (PTH) secretion in continuous ambulatory peritoneal dialys is patients with secondary hyperparathyroidism (2'hpt). However, this treatment often leads to hypercalcemia. The goals of the study were: ( 1) to examine whether the incidence of hypercalcemia decreases when di alysate calcium is reduced from 1.25 to 1.0 mmol/L; (2) to determine t he relative role of the factors involved in the pathogenesis of hyperc alcemia; and (3) to study the efficacy of a low oral pulse dose of alf acalcidol in preventing the recurrence of 2'hpt. Fourteen continuous a mbulatory peritoneal dialysis patients with 2'hpt were treated with pu lse oral alfacalcidol and calcium carbonate and dialyzed with a 1.0-mm ol (n = 7) or a 1.25-mmol (n = 7) dialysate calcium. The response rate (87%) and the incidence (71%) and severity of hypercalcemia were simi lar in both groups. In the early response stage, PTH decreased by 70% in both groups, and serum ionized calcium (iCa) increased from 1.18 +/ - 0.02 to 1.27 +/- 0.04 mmol/L (P < 0.005) in the 1.0 group and from 1 .19 +/- 0.02 to 1.29 +/- 0.02 mmol/L in the 1.25 group (P < 0.005). Ni ne of the 12 responders had a further decrease in serum PTH, which was associated with an additional increase in iCa from 1.28 +/- 0.02 to 1 .47 +/- 0.04 (P < 0.005). Multivariate analysis showed that the early increase in iCa was positively correlated with alfacalcidol dosage (r = 0.69). In contrast, the late increase in iCa was mostly accounted fo r by the decrease in serum PTH (r = -0.93). This occurred while calciu m carbonate, alfacalcidol dosage, and serum 1,25 hydroxy D3 remained u nchanged compared with the early response stage. Finally, an alfacalci dol dose of 1 mu g twice weekly was unable to maintain serum PTH at an adequate level in the long term. These data show that a reduction in dialysate calcium from 1.25 to 1.0 mmol does not reduce the occurrence of hypercalcemia and suggest that lowering serum PTH reduces the abil ity of the bone to handle a calcium load within a few weeks, thus caus ing hypercalcemia.