FDA Approves First Therapy for Rare Form of Osteomalacia

The headquarters of the U.S. Food and Drug Administration (FDA) is seen in Silver Spring, Md., on Nov. 4, 2009. Jason Reed/AP-File

The Food and Drug Administration (FDA) has approved an injectable drug for a rare illness that causes low phosphate blood levels and bone softening, according to a notice on June 18.

FDA approved Crysvita (burosumab-twza), an injectable drug to treat tumor-induced osteomalacia (TIO) for patients above two years.

TIO is a rare disease that causes tumors that weaken and soften bones and releases FGF23, a hormone-like substance that lowers phosphate levels. Phosphate levels maintain bones, nerve function, and energy production by cells. Lower phosphate levels causes osteomalacia or the softening and weakening of bones.

“Treatment for TIO focuses on identifying and removing the tumor that causes the disease. However, when that is not possible, Crysvita can help increase the levels of phosphate in the blood,” said Theresa E. Kehoe, the acting director of the Division of General Endocrinology in the FDA’s Center for Drug Evaluation and Research in a statement.

FDA also approved Crysvita for treating children six months and older with the medical condition, X-linked hypophosphatemia which can’t be cured with Vitamin-D supplementation and leads to bone deformities including bow-leggedness and short stature.

“As the first FDA-approved therapy to treat this debilitating disease, today’s action is an important step in finding treatment options for patients living with TIO whose tumor cannot be found or removed,” said Kehoe.

About 500-1000 people in the United States live with TOI and the evaluation of Crysvita was done in two studies involving 27 adults with TIO. The first study was done in 14 adults in the United States for 144 weeks and the second was done on 13 adult patients in Japan and South Korea.

The approval to produce the drug was granted to Ultragenyx Pharmaceutical Inc.

“For approximately half of all individuals with TIO, surgical removal of the tumors is not possible, leaving these patients with no other treatment options. The FDA approval of Crysvita marks the first treatment option that addresses the cause of the severe hypophosphatemia and osteomalacia resulting from these rare tumors,” said Camille L. Bedrosian, M.D., Chief Medical Officer of Ultragenyx in a statement.

Adverse Effects

The evaluation studies on the drug also found the drug to cause hypersensitivity reactions like rash and hives.

“If serious hypersensitivity reactions occur, patients should stop taking Crysvita and talk with their health care provider about further medical treatment,” said FDA.

The agency said higher levels of phosphorus may increase the risk of nephrocalcinosis, a medical condition that involves too much calcium deposits in the kidneys.

According to the FDA, the common side effects of Crysvita are tooth abscess (infection), muscle spasms, dizziness, constipation, injection site reaction, rash, and headaches.

It warned patients with severe kidney impairment, those taking oral phosphate, and those who have serum phosphate levels within or above the normal range for their age to not take Crysvita.