Effectiveness, safety, and pharmacokinetics of burosumab in Chinese children with X-linked hypophosphatemia: an open-label, single-arm phase 4 study

Burosumab has shown benefits in treating X-linked hypophosphatemia (XLH), a rare genetic bone disorder that causes rickets among pediatric patients. However, data in Chinese children with XLH are lacking. Therefore, we evaluated the effectiveness, safety, and pharmacokinetics of burosumab among Chinese children (aged 1-12 yr) with XLH in this open-label, multi-center, single-arm, phase 4 study. Of the 28 patients enrolled (12 male, 16 female), 27 completed the study. All patients received s.c. injections of burosumab at a starting dose of 0.8 mg/kg every 2 wk for 64 wk. The mean ± SD patient age was 5.68 ± 3.07 yr. Burosumab treatment increased the serum phosphorus level by 0.96 ± 0.27 mg/dL from baseline during the burosumab dose cycles (average of Week 2, 4, 8, 12, 16, 24, 32, 40, 52, and 64). The improvement from baseline (2.33 ± 0.24 mg/dL) to Week 64 (3.29 ± 0.30 mg/dL) was significant (p < .05). The Radiograph Global Impression of Change was significantly improved at Week 64 (1.90 ± 0.48; p < .0001 vs baseline), and the percentage predicted 6-min walking test among patients aged ≥5 yr with post-baseline values (n = 16) was significantly increased from 67.32% ± 8.27% at baseline to 71.91% ± 8.25% at Week 64 (p < .05). All patients experienced treatment-emergent adverse events; most were mild to moderate. In conclusion, burosumab treatment in Chinese children with XLH corrected serum phosphorus levels and improved clinical parameters with tolerable safety profiles.