Open-label extension of a randomized trial investigating safety and efficacy of rhPTH(1–84) in hypoparathyroidism

Hypoparathyroidism is a rare disease, often inadequately controlled by conventional treatment. PARALLAX was a mandatory post-marketing trial assessing pharmacokinetics and pharmacodynamics of different dosing regimens of recombinant human parathyroid hormone 1–84 (rhPTH[1–84]) for treating hypoparathyroidism. The present study (NCT03364738) was a Phase 4, 1-year open-label extension of PARALLAX. Patients received only two doses of rhPTH(1–84) in PARALLAX and were thus considered treatment-naive at the start of the current study. rhPTH(1–84) was initiated at 50 μg once daily, with doses adjusted based on albumin-corrected serum calcium levels. Albumin-corrected serum calcium (primary outcome measure), health-related quality of life (HRQoL), adverse events, and healthcare resource utilization (HCRU) were assessed. The mean age of the 22 patients included was 50.0 years; 81.8% were women, and 90.9% were White. By end of treatment (EOT), 95.5% of patients had albumin-corrected serum calcium values in the protocol-defined primary endpoint range of 1.88 mmol/L to the upper limit of normal. Serum phosphorus was within the healthy range, and albumin-corrected serum calcium-phosphorus product was below the upper healthy limit throughout, while mean 24-hour urine calcium excretion decreased from baseline to EOT. Mean supplemental doses of calcium and active vitamin D were reduced from baseline to EOT (2402–855 mg/day and 0.8–0.2 μg/day, respectively). Mean serum bone turnover markers, bone-specific alkaline phosphatase, osteocalcin, procollagen type I N-terminal propeptide, and type I collagen C-telopeptide increased 2–5 fold from baseline to EOT. HCRU, disease-related symptoms and impact on HRQoL improved numerically between baseline and EOT. Nine patients (40.9%) experienced treatment-related adverse events; no deaths were reported. Treatment with rhPTH(1–84) once daily for 1 year improved HRQoL, maintained eucalcemia in 95% of patients, normalized serum phosphorus, and decreased urine calcium excretion. The effects observed on urine calcium and the safety profile are consistent with previous findings.