Safety and Efficacy of Recombinant Human Parathyroid Hormone in Adults With Hypoparathyroidism Randomly Assigned to Receive Fixed 25-μg or 50-μg Daily Doses.

Purpose: The present study examined the efficacy and safety of a lower rhPTH(1-84) dose.

Methods: RELAY was a dose-blinded, multicenter, 8-week study of patients with hypoparathyroidism randomized to fixed 25- or 50-μg/d doses of subcutaneous rhPTH(1-84). The primary end point was the percentage of patients at week 8 with supplement reductions in calcium to ≤500 mg/d and in calcitriol to ≤0.25 μg/d, while maintaining serum calcium levels between 1.875 mmol/L and the upper limit of normal. The secondary end point was the percentage of patients at week 8 with a ≥50% reduction in calcium and calcitriol doses, while maintaining serum calcium levels between 1.875 mmol/L and the upper limit of normal.

Findings: Forty-two patients were randomized (25-μg group, n = 19; 50-μg group, n = 23). At week 8, the primary end point was achieved by 4 (21%; 95% CI, 6%-46%) and 6 (26%; 95% CI, 10%-48%) of the patients receiving 25 and 50 μg/d of rhPTH(1-84), respectively. The secondary end point was achieved by 2 (11%; 95% CI, 1%-33%) and 6 (26%; 95% CI, 10%-48%) of the patients receiving 25 and 50 μg/d of rhPTH(1-84), respectively. Treatment-emergent adverse events were reported by 11 (58%) patients in the 25-μg group and 17 (74%) patients in the 50-μg group.

Implications: Doses as low as 25 µg/d of rhPTH(1-84) are well tolerated and may be effective for a subset of patients. ClinicalTrials.gov identifier: NCT01268098.