High frequency of marked hyperphosphatemia during intravenous calcitriol therapy in hemodialysis patients with refractory hyperparathyroidism.

Efficacy and safety of intermittent intravenous calcitriol therapy were studied in 8 chronic hemodialysis patients with marked hyperparathyroidism refractory to oral therapy with calcium salts and daily vitamin D. They were followed for 20 weeks (32 weeks for 2 patients). At the start of the study, serum calcium was < 2.65 mmol/l and phosphate levels were controlled with calcium-based binders only. The phosphate content of the prescribed diet (< 1 g/day) remained unchanged during the study, and a low-calcium dialysate was used (1.38 mmol/l). The initial postdialysis calcitriol dose was 1 microgram and was increased to 2 micrograms in 6 patients. Intravenous calcitriol effectively improved hyperparathyroidism in 7 patients, with a significant decrease of the intact parathyroid hormone level from 650 +/- 433 to 195 +/- 208 pg/ml (p < 0.05). Hypercalcemia > 2.7 mmol/l occurring in 3 patients was observed in only 11% of the weekly laboratory controls and always resolved rapidly. In contrast, hyperphosphatemia > or = 2.0 mmol/l was observed in 7 patients and in 40% of the weekly laboratory controls. In 15% of the cases the phosphate values even exceeded 2.4 mmol/l. The phosphate binder therapy had to be intensified accordingly, not only by increasing the dose of calcium-based binders, but also by introducing aluminum salts in 6 patients. In summary, our data show that intravenously administered calcitriol is effective in the treatment of severe hyperparathyroidism in most hemodialysis patients resistant to oral therapy. However, its usefulness seems to be limited by frequency and severity of hyperphosphatemia, frequently necessitating additional prescription of aluminum-based binders. These undesirable secondary events may thus limit the long-term utility of intravenously administered calcitriol.