American Association of Clinical Endocrinoligist's (AACE) 23rd Annual Scientific and Clinical Congress:
Recombinant Human Parathyroid Hormone (rhPTH) as a Hormone Replacement to Treat Hypoparathryoidism
Hypoparathyroidism is the only endocrine disease without a hormone replacement approved by the U.S. Food and Drug Administration. It is a rare endocrine disorder characterized by low parathyroid hormone (PTH) levels, hypocalcemia (low serum calcium), hyperphosphatemia (abnormally high serum phosphate), and hypercalciura (excessive urinary calcium excretion). Current therapy for hypoparathryoidism includes high doses of oral calcium and activated Vitamin D.
Findings from a 24-week, double-blind, placebo-controlled Phase III study (REPLACE Study) of Natpara® showed that PTH is an effective therapy in maintaining serum calcium levels while significantly reducing dosing of oral calcium and active Vitamin D (calcitriol). Patients were invited to participate in the subsequent study—reported on here—from the REPLACE study and others (eg, RELAY and smaller studies).
The results of the recent study were presented during the 23rd Annual Scientific and Clinical Congress of the American Association of Clinical Endocrinology. EndocrineWeb spoke with Tamara J. Vokes, MD during her poster presentation, Long-term safety and efficacy of recombinant human parathyroid hormone, rhPTH(1-84), for the treatment of adults with hypoparathryoidism: One-year data from the RACE Study. Dr. Vokes summarized this Phase III open-label exception study.
This is an ongoing open label extension study. Fifty-three patients were enrolled, and 49 completed 52 weeks. All patients were started on 25 or 50 µg/d rhPTH(1-84) with titration up to 50, 75, and 100 µg/d if active Vitamin D and oral calcium could be further reduced. “The primary efficacy endpoint defined as ≥50% reduction in oral calcium and ≥50% reduction in active Vitamin D while maintaining a serum calcium level in the target range, was achieved by 74% of participants” stated Dr. Vokes.
Furthermore, Dr. Vokes told EndocrineWeb, “In practically all study participants both oral calcium and active Vitamin D were reduced. Approximately, 25% of patients are completely free of supplements; nearly one-third were able to discontinue oral calcium, and about two-thirds were able to discontinue active Vitamin D.”
- Mean baseline oral calcium and active Vitamin D doses were 2203±1708 mg/d and 0.7±0.5 µg/d, respectively, and by week 52 decreased by 67±34% and 73±44% respectively.
- Serum phosphate decreased by a mean of 0.73±0.79 mg/dL.
- Injection compliance was 80% or higher in 98% of patients.
- No patients left the study due to adverse events (AE).
- The most common AEs were muscle spasm, hypocalcemia, paresthesia, nausea, headache, arthralgia, and constipation.
In conclusion, over the course of 52-weeks, rhPTH(1-84) was efficacious and well-tolerated.
Vokes T, Levine M, Warren M, Shoback D, Bilezikian J. Mannstadt M, et al. Long-term safety and efficacy of recombinant human parathyroid hormone, rhPTH(1-84), for the treatment of adults with hypoparathryoidism: One-year data from the RACE Study. Abstract #1116. Presented at the American Association of Clinical Endocrinologists 23rd Annual Scientific and Clinical Congress, Las Vegas, NV. May 14-18, 2014.