The U.S. Food and Drug Administration has approved Natpara (parathyroid horomone) to control hypocalcemia (low blood calcium levels) in patients with hypoparathyroidism, a rare disease that affects approximately 60,000 people in the United States.
Hypoparathyroidism occurs when the body secretes abnormally low levels of parathyroid hormone, which helps regulate calcium and phosphorus levels in the body.
Hypoparathyroidism is caused by loss of function of the parathyroid glands and occurs most commonly as a result of surgical removal of the parathyroid glands and more rarely as a result of autoimmune or congenital diseases. Patients with hypoparathyroidism can experience numbness, tingling, muscle twitching, spasms or cramps, abnormal heart rhythm, and seizures as a consequence of low blood calcium levels.
Hypoparathyroidism is also associated with long-term complications such as kidney damage, kidney stones, development of cataracts and calcification of soft tissues.
Natpara, a hormonal injection administered once daily, helps to regulate the body’s calcium levels. The FDA granted Natpara orphan drug designation because it is intended to treat a rare disease.
“People with hypoparathyroidism have limited treatment options and face challenging symptoms that can severely impact their quality of life,” said Jean-Marc Guettier, M.D., director of the Division of Metabolism and Endocrinology Products in the FDA’s Center for Drug Evaluation and Research. “This product offers an alternative to patients whose calcium levels cannot be controlled on calcium supplementation and active forms of vitamin D.”
The safety and effectiveness of Natpara were evaluated in a clinical trial of 124 participants who were randomly assigned to receive Natpara or a placebo. The trial was designed to determine whether Natpara can be used as a substitute for, or be used to help reduce the amount of, active forms of vitamin D or oral calcium taken by participants.
Results showed 42 percent of Natpara-treated participants achieved normal blood calcium levels on reduced doses of calcium supplements and active forms of vitamin D, compared to three percent of placebo-treated participants.
Natpara carries a boxed warning that bone cancer (osteosarcoma) has been observed in rat studies with Natpara. It is unknown whether Natpara causes osteosarcoma in humans, but because of a potential risk of osteosarcoma, Natpara is only recommended for use in patients whose hypocalcemia cannot be controlled on calcium supplementation and active forms of vitamin D, and for whom the potential benefits are considered to outweigh this potential risk. Natpara is only available through a restricted program under a Risk Evaluation and Mitigation Strategy (REMS).
The most common side effects observed in Natpara-treated participants were sensations of tingling, tickling, pricking, or burning of the skin (paraesthesia); low blood calcium; headache; high blood calcium; and nausea.
Natpara is manufactured by NPS Pharmaceuticals, Inc., based in Bedminster, New Jersey.