Effects on Calcium Homeostasis of Changing PTH Replacement Therapy of Postoperative Hypoparathyroidism from Intact PTH to Teriparatide: A Case Series

The objective of this study was to assess the effect on calcium homeostasis of changing PTH replacement therapy (PTH-RT) from intact PTH (PTH1-84) to teriparatide (PTH1-34). This study is a consecutive case series. All patients with postoperative hypoparathyroidism who changed medication from PTH1-84 (100 A mu g) to PTH1-34 (20 A mu g) were included. Plasma ionized calcium, daily dose of 1 alpha-hydroxylated-vitamin D metabolites alfacalcidol, calcium, TSH and PTH was collected. Eight patients (women = 88 %) with a mean age of 54 +/- A 12 years and a duration of hypoPT of 13 +/- A 6 years were included. Before initiation of PTH1-84, the mean daily dose of alfacalcidol was 1.9 +/- A 1.1 A mu g/d and calcium supplements were 1,550 +/- A 705 mg. Alfacalcidol dose was reduced with 88 +/- A 29 % (p < 0.01) after 6 months of PTH1-84 treatment and terminated in six patients. Calcium levels were reduced with 78 +/- A 36 % (p = 0.02) to 273 +/- A 353 mg/d and stopped in five patients. Six patients received 100 A mu g PTH1-84 daily, the seventh 2 out of 3 days and the last every second day. When changing from PTH1-84 to PTH1-34, plasma ionized calcium initially dropped and the demand for supplements increased. Alfacalcidol was resumed in five patients; mean daily dose increased to 1.50 +/- A 1.56 A mu g/d, (p = 0.02) and calcium increased to 329 +/- A 368 mg/d, (p = 0.72). Five patients received 20 A mu g PTH1-34 a day, two patients twice-a-day and one 20/40 A mu g/d alternately. Compared with PTH1-34, PTH1-84 has a longer plasma half-life and a higher calcemic response. We have shown a need for higher doses of alfacalcidol and calcium supplements to maintain normal serum calcium when treated with PTH1-34 compared to PTH1-84 and in some a need for more than one daily PTH1-34 dose.