Effect of calcitriol and age on recovery from hypocalcemia in hemodialysispatients

Calcitriol is used to treat hyperparathyroidism in hemodialysis patients. C alcitriol treatment, either through a reduction in parathyroid hormone (PTH ) levels or direct effect on bone, decreases the osteoblast and osteoclast surface and bone formation rate. Our study of 13 hemodialysis patients was designed to evaluate whether calcitriol treatment changed the rate of spont aneous recovery from hypocalcemia induced by a low-calcium dialysis. Calcit riol treatment decreased basal PM levels from 614 +/- 84 to 327 +/- 102 pg/ mL (P < 0.001) and maximal PTH levels from 1,282 +/- 157 to 789 +/- 161 pg/ mL (P < 0.001), but the rate of serum ionized calcium recovery from hypocal cemia did not change. When the 13 patients were separated based on the medi an age of 64 years, the predialysis serum ionized calcium revel was less in the younger (group I, 44 +/- 6 years; n = 6) than older (group II, 68 +/- 1 years; n = 7) patients (1.05 +/- 0.03 v 1.22 +/- 0.03 mmol/L, respectivel y; P < 0.01) despite similar basal (group I, 595 +/- 122 pg/mL v group II, 629 +/- 96 pg/mL) and maximal (group I, 1,114 +/- 299 pg/mL v group II, 1,4 25 +/- 141 pg/mL) PTH levels. Before calcitriol treatment, the rate of seru m ionized calcium recovery from induced hypocalcemia was greater (P < 0.05) for similar PM levels in the older than younger patients. After calcitriol treatment, despite a similar reduction in PTH levels, the rate of calcium recovery increased (P < 0.05) in the younger patients but did not change in the older patients. We also observed that toward the end of the low-calciu m hemodialysis, PTH values decreased even though serum ionized calcium leve l continued to decline when the rate of calcium reduction slowed. In additi on, hysteresis, defined as a lower PTH value during the recovery from hypoc alcemia than during the induction of hypocalcemia for the same serum calciu m concentration, was present during the spontaneous recovery from hypocalce mia. In conclusion, in the hemodialysis patient: (1) age appeared to affect the bone response to PTH and calcitriol treatment, (2) the PTH response to hypocalcemia was affected by a deceleration in the rate of calcium decreas e, and (3) hysteresis of the PTH response to hypocalcemia occurred during t he spontaneous recovery from hypocalcemia. (C) 1999 by the National Kidney Foundation, Inc.