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The U.S. Food and Drug Administration today approved Crysvita (burosumab), the first drug approved to treat adults and children ages 1 year and older with x-linked hypophosphatemia (XLH), a rare, inherited form of rickets. XLH causes low levels of phosphorus in the blood. It leads to impaired bone growth and development in children and adolescents and problems with bone mineralization throughout a patient’s life.
Most children with XLH experience bowed or bent legs, short stature, bone pain and severe dental pain. Some adults with XLH experience persistent discomfort or complications, such as joint pain, impaired mobility, tooth abscesses and hearing loss. The safety and efficacy of Crysvita were studied in four clinical trials. In the placebo-controlled trial, 94 percent of adults receiving Crysvita once a month achieved normal phosphorus levels compared to 8 percent of those receiving placebo.
In children, 94 to 100 percent of patients treated with Crysvita every two weeks achieved normal phosphorus levels. In both children and adults, X-ray findings associated with XLH improved with Crysvita therapy. Comparison of the results to a natural history cohort also provided support for the effectiveness of Crysvita. The most common adverse reactions in adults taking Crysvita were back pain, headache, restless leg syndrome, decreased vitamin D, dizziness and constipation. The most common adverse reactions in children were headache, injection site reaction, vomiting, decreased vitamin D and pyrexia (fever).
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