Self-Administration of Burosumab in Children and Adults with X-Linked Hypophosphataemia in Two Open-Label, Single-Arm Clinical Studies

Introduction: X-linked hypophosphataemia (XLH) is a rare, genetic renal phosphate-wasting disease, resulting from excess fibroblast growth factor 23 (FGF23) activity, which has a progressive and profound impact on patients throughout life. The monoclonal anti-FGF23 antibody, burosumab, is a subcutaneous injection indicated for the treatment of XLH in children and adults. Originally, burosumab was approved to be administered by a healthcare professional (HCP), but the option of self-administration would enable patient independence and easier access to treatment. Two open-label, single-arm clinical trials, conducted in Japan and Korea, have assessed the safety and efficacy of self-administration of burosumab in both children and adults with XLH.

Methods: In KRN23-003 (n = 15 children aged 1-12 years) and KRN23-004 (n = 5 children aged 3-13 years, n = 4 adults aged 21-65 years), children initially received 0.8 mg/kg of burosumab every 2 weeks and adults initially received 1.0 mg/kg of burosumab every 4 weeks. Self-administration was permitted from Week 4, and patients or carers were provided with training to inject correctly.

Results: In both trials, burosumab had an acceptable safety profile with mainly mild-to-moderate adverse events. Following self-administration, no patients reported serious treatment-emergent adverse events ≥ grade 3, injection-site reactions or hypersensitivity reactions related to burosumab. Serum phosphate and active vitamin D levels increased from baseline in children and adults.

Conclusions: These results indicated that the efficacy and safety of burosumab when administered either by a carer or patient are similar to that when administered by an HCP and show that self-administration is a viable option for patients with XLH.

Trial registration numbers: NCT03233126 and NCT04308096.