Nephrol Dial Transplant (1992) 7: 822-828
© 1992 European Renal Association-European Dialysis and Transplant Association
research-article
Effect of chronic intravenous calcitriol on parathyroid function and set point of calcium in dialysis patients with refractory secondary hyperparathyroidism
Servizio Dialisi, Ospedale Maggiore, Lodi, Italy
Correspondence and offprint requests to: Correspondence and offprint requests to: Dr Fabio Malberti, Servizio Dialisi, Ospedale Maggiore, 20075 Lodi, Italy.
This study evaluates the effect of intravenous calcitriol on parathyroid function and ionized calcium–PTH sigmoidal curve obtained during lowand high–calcium haemodialysis in 10 patients with osteitis fibrosa whose secondary hyperparathyroidism was refractory to conventional therapy. After 4 months of intravenous calcitriol, serum ionized calcium increased from 1.28±0.08 to 1.37±0.11 mmol/1 (p<0.00l), serum phosphate from 1.54±0.18 to 1.79±0.4 mmol/1 (P NS), serum calcitriol from 16.7±9.9 to 34.3±6.4 pg/ml (p<0.001), while alkaline phosphatase decreased from 366±340 to226±180 IU/1 (p<0.05), osteocalcin from 46.4±20 to 34.5±15.3 ng/ml (p<0.05), and basal intact PTH from 1069±700 to 305±270 (p<0.01). Basal PTH started to decrease after 1 month of treatment prior to the increase in the ionized calcium. Because of hypercalcaemia the dialysate calcium was decreased from 1.75 to 1.5 mmol/1 in three of five patients on haemodialysis, and calcium–containing solutions were replaced by calcium–free fluids in four of five patients on haemodiafiltration. Calcitriol dose at the first month of therapy was 5.6±0.8 uµg/week, but it was successively decreased because of hypercalcaemia to a final dose of 3.6±1.3 uµg/week. After intravenous calcitriol the ionized calcium–PTH sigmoidal curve shifted to the left and downward. Maximally stimulated PTH and maximally inhibited PTH obtained during low– and high–calcium dialysis significantly decreased, as well as the ratio of basal PTH/PTHmax and the set point of calcium. Despite the marked decrease in baseline PTH, two patients were considered to be non—responders as the reduction in PTH was exclusively due to severe hypercalcaemia, and the set point of calcium and ionized calcium—PTH curve did not change. In conclusion, intravenous calcitriol is effective in. lowering PTH and shifting toward normal the ionized calcium—PTH curve in most patients whose secondary hyperparathyroidism is refractory to conventional therapy. To prevent the development of hypercalcaemia, particularly in patients treated with calcium salts as phosphate binders, the use of low—calcium dialysate is advisable. When, during intravenous calcitriol treatment, despite the decrease in baseline PTH, persistent hypercalcaemia or increased calcium–phosphate product develop and the ionized calcium–PTH curve does not shift toward left and downward, parathyroidectomy should be considered.
Keywords: secondary hyperparathyroidism; set point of calcium; ionized calcium-PTH sigmoidal curve; calcitriol therapy; dialysate calcium
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