Objectives: the current study evaluated the effectiveness of intravenous (i. v.) calcitriol in 6 patients with severe hyperparathyroidism -[parathyroid hormone(PTH) > 1000 pg/ml]. Methods: 12 weeks of i. v. calcitriol was given in doses from 2 to 7 µg. PTH was measured by using immunoradiometric assay (CIS int.). Bone isoenzyme of alkaline phosphatase was measured by using an automated analyzer after inactivation with the wheat germ lectin. Tartrate resistant acid phosphatase was measured by using a colorimetric method. Results: There was a decrease of PTH levels from 1113 pg/ml to 950 pg/ml after 12 weeks. Alkaline phosphatase decreased from 354 to 324 IU/l but levels of acid phosphatase remained unchanged. Serum calcium increased from 8.86 to 10.36 mg/dl, phosphorus remained unchanged. Calcium set point decreased from 1.258 to 1.197 mmol/l and the slope of the curve increased from -1845 to -1523 mmol/pg. Conclusion: patients with severe hyperparathyroidism resistant to oral calcitriol therapy may have a good response to i.v. calcitriol therapy, provided that phosphatemia and calcemia is controlled.

Keywords: intravenous calcitriol, severe hyperparathyreoidism