Efficacy of a single weekly bolus of intravenous calcitriol in severe secondary hyperparathyroidism

Intermittent intravenous calcitriol administration lowes serum PTH. This ha s been attributed to higher peak concentration and greater occupancy of the parathyroid cell vit D receptors. However, the optimal interval between do ses has not been worked out We compared two time intervals between doses of IV calcitriol in dialysis patients with secondary hyperparathyroidism. Twenty two chronic hemodialysis patients with secondary hyperparathyroidism (PTH > 450 pg/ml) were randomized into two groups (GI and GII). There were no differences in sex, age ad time of treatment on hemodialysis. GI (n = I I): intact PTH: 1,299 +/- 588 pg/ml, serum calcium (Ca): 10.5 +/- 1.2; phos phate (P): 5.6 +/- 1.3 (mg/dl) alkaline phosphatase (AP): 268 +/- 93.2 UI/I . GII (n = 11): PTH: 1,087 +/- 467 pg/ml, Car 10.6 +/- 6.1; P: 5.2 +/- 1.4 (mg/dl), AP: 302.2 +/- 129 UI/I (NS). Dialysate calcium was 3 mEq/I and CaC O3 was used as phosphate binder up to 3 g/d; Al (OH)(2) was added if serum phosphate was still too high. Calcitriol IV was administered in doses of 3 mu g at the end on midweek dialysis to Gi and I mu g at the end of each dia lysis session to GII. Calcitriol and phosphate binders were modified for ea ch patient according to PTH levels to mantain calcium levels below 11.5 mg/ dl and calcium-phosphate product below 70. The dose of calcitriol ranged fr om 3 to 9 mu g per week for each patient. Serum total calcium, phosphate an d alkaline phosphatase were measured weekly and PTH monthly After 12 weeks of IV calcitriol treatment GI showed a decrease in serum concentrations of PTH of 74% and Gli of 39.5% (p < 0.05). In the severe casas (PTH > 1,000 pg /ml; GI: n = 7 GII: n = 7;) the response was better in GI: all patients of CI showed a decrease in serum PTH levels (mean = 76.2%) and in only 4 patie nts of GII were serum PTH levels reduced (mean: 33.5%). Final serum concent rations in the two groups were: GI: PTH: 332 +/- 169 pg/ml, Ca: 11.5 +/- 1. 4, P: 5.73 +/- 1.9 (mg/dl) AP: 208 +/- 51 UI/I. GII: PTH: 657 +/- 650 pg/ml , Ca: 11.5 +/- 1.5, P: 7.5 +/- 3.7 (mg/dl), AP: 322 +/- 201 UI/I (NS). In conclusion, a single weekly dose of intravenous calcitriol administratio n was as efficacious as three to suppress PTH secretion and more effective in severe cases. It could be a useful therapy for the treatment of severe h yperparathyroidism in patients on dialysis.