A recently approved agent, burosumab (Crysvita), was better than placebo across a range of efficacy outcomes for 14 predefined subgroups of adults with X-linked hypophosphatemia (XLH), new research shows.
The authors analyzed data from the initial 24-week randomized blinded phase of the pivotal phase 3 trial that led to regulatory approval of this drug in the United States in 2018 for XLH, a rare form of rickets characterized by low serum phosphorus levels, skeletal defects, pain, and stiffness.
As in the main analysis, in the subgroups, among patients who received burosumab, serum phosphorus levels were improved, and outcomes were better on the following measures: Western Ontario and McMaster Universities Arthritis Index (WOMAC) stiffness scale, the WOMAC physical function measure, and the Brief Pain Inventory (BPI), which were the main efficacy outcomes. Improvements were seen for many other outcomes as well.
Maria-Luisa Brandi, MD, Careggi University Hospital, Florence, Italy, presented the new subanalysis during the virtual American Society of Bone and Mineral Research (ASBMR) 2020 annual meeting.
The subgroup results were consistent with the overall trial findings, “showing a favorable direction of effect of burosumab relative to placebo” except for results in patients recruited in Asia and non-White patients; those results were considered inconclusive because there were too few participants in those categories, she told Medscape Medical News,.
Lorenz Hofbauer, MD, scientific chair of the ASBMR meeting, said that the take-away message is that the drug “works to reduce pain and disability” in adults with XLH with more severe/less severe symptoms, and “it provides new hope for many patients suffering from this disease,” he told Medscape Medical News.
Burosemab also appears superior to what has previously been considered standard therapy for XLH, phosphate/calcitriol, the experts say.
‘Rare is relative,’ burosumab is a ‘transformative therapy’
“The disease prevalence is 1 to 9 in a million,” Brandi said. “Undiagnosed adults are treated by the doctor that makes the diagnosis, usually a nephrologist or a rheumatologist or a bone doctor; this depends on the prevalent complications in a given patient. The endocrinologist who treats this patient is the one expert in bone disorders.”
Hofbauer noted, however, that “[r]are is relative. If you run a bone clinic, you will see four to five patients with XLH; if you are a regional center, 20 to 30 patients. People with rare disease travel more than 1000 miles to see experts.”
The US Food and Drug Administration approved burosumab for use in children and adults with XLH 2 years ago. The European Medicines Agency (EMA) approved it for use in children.
The drug is expected to be approved by the EMA for adults with XLH some time this year, said Hofbauer, who is from Dresden Technical University, Dresden, Germany.
Burosumab is a “game changer” with respect to previous treatments, he stressed.
This study is one of the top five clinical abstracts of the ASBMR meeting, which are selected on the basis of “scientific content/novelty, making a difference in clinical practice,” Hofbauer explained. He noted that “new drugs that work are always in the top ranks.”
Craig Munns, PhD, who was senior author of a recent review about burosumab, agrees.
“Burosumab is transformative, as it is a paradigm shift in the way we manage XLH,” he told Medscape Medical News.
“Standard therapy for children is with oral phosphate and calcitriol, and many adults do not receive any therapy,” said Munns, from the University of Sydney, Sydney, Australia.
“Phosphate and calcitriol need to be taken multiple times per day, is an incomplete therapy, and has many complications. Burosumab offers a 2-weekly (children) or 4-weekly (adult) dosing regime with superior outcomes compared to no treatment or phosphate/calcitriol,” he emphasized.