Intravenous 1,25(OH)2 Vitamin D3 Therapy in Haemodialysis Patients: Evaluation of Direct and Calcium-Mediated Short-Term Effects on Serum Parathyroid Hormone Concentration

Abstract

Eleven patients on chronic haemodialysis treatment thrice weekly received 1 μg 1,25(OH)2D3 i.v. after each dialysis for 3 weeks. Phosphate binders were mainly CaCO3, supplemented in a few patients by moderate amounts of A1(OH)3. Ionised calcium was measured by ion-selective electrode, normal values being 1.28-1.42mmol/l. PTH was estimated by an N-terminalsensitive assay; normal values are <0.25μg/ml. Results before and after 1,25(OH)2D3 were: ionised calcium before haemodialysis, 1.19±0.12and 1.17±0.14; ionised calcium after haemodialysis, 1.33±0.07 and 1.30±0.09; PTH before haemodialysis, 1.39±0.71 and 1.38±0.69; PTH after haemodialysis, 0.64±0.22 and 0.60 ±0.17; Phosphate before haemodialysis, 1.85±0.48 and 2.18±0.43 (P<0.05). No change of PTH concentration and ionised calcium before and after haemodialysis treatment could be documented after i.v. 1,25(OH)2D3 treatment. Mild and severe hyperparathyroidism were indistinguishable. Increased serum calcium concentrations therefore appear to be required for the suppression of PTH secretion by i.v. 1,25(OH)2D3 therapy