Effects on calcium homeostasis of changing PTH replacement therapy of postoperative hypoparathyroidism from intact PTH to teriparatide: a case series.

Abstract

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