Study in Patients with Established Hypoparathyroidism

The efficacy of NATPARA was evaluated in a 24-week, randomized, double-blind, placebo-controlled, multicenter trial. In this trial, patients with established hypoparathyroidism receiving calcium and active forms of vitamin D (vitamin D metabolite or analogs) were randomized (2:1) to NATPARA (n=84) or placebo (n=40). The mean age was 47 years (range, 19 to 74 years), 79.0% were females and 96.0% were Caucasian, 0.8% were Black, and 1.6% were Asian. Patients had hypoparathyroidism for on average 15 years and hypoparathyroidism was caused by post-surgical complications in 71% of cases, idiopathic hypoparathyroidism in 25%, DiGeorge Syndrome in 3%, and auto-immune hypoparathyroidism in 1%. Patients with hypoparathyroidism due to calcium-sensing receptor mutations were excluded from the trial. The mean eGFR at baseline was 97.4 mL/min/1.73 m2 and 45%, 10% and 0% had mild, moderate and severe renal impairment, respectively, at baseline.

Before randomization, participants entered a 2-16 weeks run-in phase. In this phase calcium supplement and active vitamin D doses were adjusted to target an albumin-corrected serum calcium concentration between 8.0 and 9.0 mg/dL and 25-hydroxyvitamin D was replaced in patients with insufficient stores. At randomization, baseline serum calcium was 8.6 mg and participants were receiving a median (interquartile range) daily oral calcium dose of 2000 (1250, 3000) mg and a median daily oral active vitamin D dose equivalent to 0.75 mcg (0.5, 1) of calcitriol.

At randomization, active forms of vitamin D were reduced by 50% and patients were randomized to NATPARA 50 mcg daily or placebo. Randomization was followed by a 12-week NATPARA titration phase and a 12-week NATPARA dose maintenance phase. During the titration phase NATPARA was increased by 25 mcg increments every four weeks up to a maximum of 100 mcg. Titration was indicated for patients who could not achieve independence from active vitamin D and who could not reduce oral calcium to 500 mg or less per day. At end of treatment, 56% of subjects randomized to NATPARA were receiving 100 mcg of NATPARA per day, 26% were receiving 75 mcg of NATPARA per day, and 18% were receiving 50 mcg of NATPARA per day. Doses of co-administered active forms of vitamin D and calcium were adjusted (reduced or increased) to maintain albumin-corrected serum calcium within a desired target range throughout the trial in both arms.

For the efficacy analysis, subjects that fulfilled three components of a three-part response criterion were considered responders. A responder was defined as an individual who had: at least a 50% reduction from baseline in the dose of active vitamin D, at least a 50% reduction from baseline in the dose of oral calcium supplementation and an albumin-corrected total serum calcium concentration between 7.5 mg/dL and 10.6 mg/dL.

At the end of treatment, significantly (p-value <0.001) more subjects treated with NATPARA [46/84 (54.8%)] compared to placebo [1/40 (2.5%)] met the response criterion. Forty-two percent (35/84) of subjects randomized to NATPARA were independent of active forms of vitamin D and were on no more than 500 mg of oral calcium, compared with 2.5% (1/40) of subjects randomized to placebo (p<0.001). There were no differences in the proportion of patients with a calcium level between 7.5 mg and 10.6 mg at end of treatment between subjects randomized to NATPARA and placebo.

Table 5 shows the proportion of individuals who, at the end of treatment, fulfilled the 3-part response criterion. Table 6 provides results on individual components of the response criterion.