Population Pharmacokinetics and Pharmacodynamics of Burosumab in Adult and Pediatric Patients With X-linked Hypophosphatemia

Nivolumab and ipilimumab population pharmacokinetics in support of pediatric dose recommendations-Going beyond the body-size effect

Body size has historically been considered the primary source of difference in the pharmacokinetics (PKs) of monoclonal antibodies (mAbs) between children aged greater than or equal to 2 years and adults. The contribution of age-associated differences (e.g., ontogeny) beyond body-size differences in the pediatric PKs of mAbs has not been comprehensively evaluated. In this study, the population PK of two mAbs (nivolumab and ipilimumab) in pediatric oncology patients were characterized. The effects of age-related covariates on nivolumab or ipilimumab PKs were assessed using data from 13 and 10 clinical studies, respectively, across multiple tumor types, including melanoma, lymphoma, central nervous system tumors (CNSTs), and other solid tumors. Clearance was lower in pediatric patients (aged 1-17 years) with solid tumors or CNST than in adults after adjusting for other covariates, including the effect of body size. In contrast, clearance was similar in pediatric patients with lymphoma to that in adults with lymphoma. The pediatric effects characterized have increased the accuracy of the predictions of the model, facilitating its use in subsequent exposure comparisons between pediatric and adult patients, as well as for exposure-response analyses to inform pediatric dosing. This study approach may be applicable to the optimization of pediatric dosing of other mAbs and possibly other biologics.

Real-world data of Brazilian adults with X-linked hypophosphatemia (XLH) treated with burosumab and comparison with other worldwide cohorts

BACKGROUND

Disease-related variants in PHEX cause XLH by an increase of fibroblast growth factor 23 (FGF23) circulating levels, resulting in hypophosphatemia and 1,25(OH)2 vitamin D deficiency. XLH manifests in early life with rickets and persists in adulthood with osseous and extraosseous manifestations. Conventional therapy (oral phosphate and calcitriol) improves some symptoms, but evidence show that it is not completely effective, and it can lead to nephrocalcinosis (NC) and hyperparathyroidism (HPT). Burosumab (anti-FGF23 antibody) has shown to be effective and safety in the clinical trials.

METHODS

The current real-world collaborative study evaluated genetic, clinical and laboratory data of XLH Brazilian adult patients treated with burosumab.

RESULTS

Nineteen unrelated patients were studied. Patients reported pain, limb deformities and claudication, before burosumab initiation. 78% of them were previously treated with conventional therapy. The severity of the disease was moderate to severe (15 patients with score >5). At the baseline, 3 patients presented NC (16.7%) and 12 HPT (63%). After 16 ± 8.4 months under burosumab, we observed a significant: increase in stature (p = 0.02), in serum phosphate from 1.90 ± 0.43 to 2.67 ± 0.52 mg/dL (p = 0.02); in TmP/GFR from 1.30 ± 0.46 to 2.27 ± 0.64 mg/dL (p = 0.0001), in 1,25 (OH)2 D from 50.5 ± 23.3 to 71.1 ± 19.1 pg/mL (p = 0.03), and a decrease in iPTH from 86.8 ± 37.4 pg/mL to 66.5 ± 31.1 (p = 0.002). Nineteen variants were found (10 novel). HPT tended to develop in patients with truncated PHEX variants (p = 0.06).

CONCLUSIONS

This study confirms the efficacy and safety of burosumab on XLH adult patients observed in clinical trials. Additionally, we observed a decrease in iPTH levels in patients with moderate to severe HPT at the baseline.

Effects of Burosumab Treatment on Mineral Metabolism in Children and Adolescents With X-linked Hypophosphatemia

CONTEXT

Burosumab has been approved for the treatment of children and adults with X-linked hypophosphatemia (XLH). Real-world data and evidence for its efficacy in adolescents are lacking.

OBJECTIVE

To assess the effects of 12 months of burosumab treatment on mineral metabolism in children (aged <12 years) and adolescents (aged 12-18 years) with XLH.

DESIGN

Prospective national registry.

SETTING

Hospital clinics.

PATIENTS

A total of 93 patients with XLH (65 children, 28 adolescents).

MAIN OUTCOME MEASURES

Z scores for serum phosphate, alkaline phosphatase (ALP), and renal tubular reabsorption of phosphate per glomerular filtration rate (TmP/GFR) at 12 months.

RESULTS

At baseline, patients showed hypophosphatemia (-4.4 SD), reduced TmP/GFR (-6.5 SD), and elevated ALP (2.7 SD, each P < .001 vs healthy children) irrespective of age, suggesting active rickets despite prior therapy with oral phosphate and active vitamin D in 88% of patients. Burosumab treatment resulted in comparable increases in serum phosphate and TmP/GFR in children and adolescents with XLH and a steady decline in serum ALP (each P < .001 vs baseline). At 12 months, serum phosphate, TmP/GFR, and ALP levels were within the age-related normal range in approximately 42%, 27%, and 80% of patients in both groups, respectively, with a lower, weight-based final burosumab dose in adolescents compared with children (0.72 vs 1.06 mg/kg, P < .01).

CONCLUSIONS

In this real-world setting, 12 months of burosumab treatment was equally effective in normalizing serum ALP in adolescents and children, despite persistent mild hypophosphatemia in one-half of patients, suggesting that complete normalization of serum phosphate is not mandatory for substantial improvement of rickets in these patients. Adolescents appear to require lower weight-based burosumab dosage than children.

Osteomalacia in Adults: A Practical Insight for Clinicians

The term osteomalacia (OM) refers to a series of processes characterized by altered mineralization of the skeleton, which can be caused by various disorders of mineral metabolism. OM can be genetically determined or occur due to acquired disorders, among which the nutritional origin is particularly relevant, due to its wide epidemiological extension and its nature as a preventable disease. Among the hereditary diseases associated with OM, the most relevant is X-linked hypophosphatemia (XLH), which manifests in childhood, although its consequences persist into adulthood where it can acquire specific clinical characteristics, and, although rare, there are XLH cases that reach the third or fourth decade of life without a diagnosis. Some forms of OM present very subtle initial manifestations which cause both considerable diagnosis and treatment delay. On occasions, the presence of osteopenia and fragility fractures leads to an erroneous diagnosis of osteoporosis, which may imply the prescription of antiresorptive drugs (i.e., bisphosphonates or denosumab) with catastrophic consequences for OM bone. On the other hand, some radiological features of OM can be confused with those of axial spondyloarthritis and lead to erroneous diagnoses. The current prevalence of OM is not known and is very likely that its incidence is much higher than previously thought. Moreover, OM explains part of the therapeutic failures that occur in patients diagnosed with other bone diseases. Therefore, it is essential that clinicians who treat adult skeletal diseases take into account the considerations provided in this practical review when focusing on the diagnosis and treatment of their patients with bone diseases.