Source: European Medicines Agency (EU) Revision Year: 2018 Publisher: Genzyme Europe B.V., Gooimeer 10, 1411 DD Naarden, The Netherlands
Pharmacotherapeutic group: Other alimentary tract and metabolism products enzymes
ATC code: A16AB04
Fabry disease is an inherited heterogeneous and multisystemic progressive disease, that affects both males and females. It is characterised by the deficiency of ฮฑ-galactosidase. Reduced or absent ฮฑgalactosidase activity results in the accumulation of GL-3 in the lysosomes of many cell types including the endothelial and parenchymal cells, ultimately leading to life-threatening clinical deteriorations as a result of renal, cardiac and cerebrovascular complications.
The rationale for enzyme replacement therapy is to restore a level of enzymatic activity sufficient to clear the accumulating substrate in the organ tissues; thereby, preventing, stabilizing or reversing the progressive decline in function of these organs before irreversible damage has occurred.
After intravenous infusion, agalsidase beta is rapidly removed from the circulation and taken up by vascular endothelial and parenchymal cells into lysosomes, likely through the mannose-6 phosphate, mannose and asialoglycoprotein receptors.
Efficacy and safety of Fabrazyme was evaluated in two studies with children, one dose-finding study, two double-blind placebo-controlled studies, and one open-label extension study in both male and female patients.
In the dose finding study, the effects of 0.3, 1.0 and 3.0 mg/kg once every 2 weeks and 1.0 and 3.0 mg/kg once every 2 days were evaluated. A reduction in GL-3 was observed in kidney, heart, skin and plasma at all doses. Plasma GL-3 was cleared in a dose dependent manner, but was less consistent at the dose of 0.3 mg/kg. In addition, infusion-associated reactions were dose dependent.
In the first placebo-controlled clinical trial, Fabrazyme was effective in clearing GL-3 from the vascular endothelium of the kidney after 20 weeks of treatment. This clearance was achieved in 69% (20/29) of the Fabrazyme treated patients, but in none of the placebo patients (p<0.001). This finding was further supported by a statistically significant decrease in GL-3 inclusions in kidney, heart and skin combined and in the individual organs in patients treated with agalsidase beta compared to placebo patients (p<0.001). Sustained clearance of GL-3 from kidney vascular endothelium upon agalsidase beta treatment was demonstrated further in the open label extension of this trial. This was achieved in 47 of the 49 patients (96%) with available information at month 6, and in 8 of the 8 patients (100%) with available information at the end of the study (up to a total of 5 years of treatment). Clearance of GL-3 was also achieved in several other cell types from the kidney. Plasma GL-3 levels rapidly normalised with treatment and remained normal through 5 years.
Renal function, as measured by glomerular filtration rate and serum creatinine, as well as proteinuria, remained stable in the majority of the patients. However, the effect of Fabrazyme treatment on the kidney function was limited in some patients with advanced renal disease.
Although no specific study has been conducted to assess the effect on the neurological signs and symptoms, the results also indicate that patients may achieve reduced pain and enhanced quality of life upon enzyme replacement therapy.
Another double-blind, placebo-controlled study of 82 patients was performed to determine whether Fabrazyme would reduce the rate of occurrence of renal, cardiac, or cerebrovascular disease or death. The rate of clinical events was substantially lower among Fabrazyme-treated patients compared to placebo-treated patients (risk reduction = 53% intent-to-treat population (p=0.0577); risk reduction = 61% per-protocol population (p=0.0341)). This result was consistent across renal, cardiac and cerebrovascular events.
The results of these studies indicate that Fabrazyme treatment at 1 mg/kg every other week provides clinical benefit on key clinical outcomes in patients with early and advanced Fabry disease. Because this condition is slowly progressive, early detection and treatment is critical to achieve the best outcomes.
In an additional study, 21 male patients were enrolled to follow GL3 clearance in kidney and skin tissues at an alternative dosing regimen. Following treatment with 1 mg/kg every other week for 24 weeks, a dose regimen of 0.3 mg/kg every 2 weeks for 18 months was able to maintain the clearance of cellular GL-3 in the capillary endothelium of the kidney, other kidney cell types and skin (superficial skin capillary endothelium) in the majority of patients. However, at the lower dose, IgG antibodies may play a role with respect to GL-3 clearance in some patients. Due to the limitations of the study design (small number of patients), no definitive conclusion regarding the dose maintenance regimen can be drawn, but these findings suggest that, after an initial debulking dose of 1.0 mg/kg every 2 weeks, 0.3 mg/kg every 2 weeks may be sufficient in some patients to maintain clearance of GL-3.
In the postmarketing setting, experience was gained in patients who initiated treatment at a dose of 1 mg/kg every 2 weeks and subsequently received a reduced dose for an extended period. In some of these patients, an increase of some of the following symptoms was spontaneously reported: pain, paraesthesia and diarrhoea, as well as cardiac, central nervous system and renal manifestations. These reported symptoms resemble the natural course of Fabry disease.
In one open-label paediatric study, sixteen patients with Fabry disease (8-16 years old; 14 males, 2 females) had been treated for one year at 1.0 mg/kg every 2 weeks. Clearance of GL-3 in the superficial skin vascular endothelium was achieved in all patients who had accumulated GL-3 at baseline. The 2 female patients had little or no GL-3 accumulation in the superficial skin vascular endothelium at baseline, making this conclusion applicable in male patients only.
In an additional 5-year open-label paediatric study, 31 male patients aged 5 to 18 years were randomized prior to the onset of clinical symptoms involving major organs and treated with two lower dose regimens of agalsidase beta, 0.5 mg/kg every 2 weeks or 1.0 mg/kg every 4 weeks. Results were similar between the two treatment groups. Superficial skin capillary endothelium GL-3 scores were reduced to zero or maintained at zero at all time points post-baseline upon treatment in 19/27 patients completing the study without a dose increase. Both baseline and 5-year kidney biopsies were obtained in a subset of 6 patients: in all, kidney capillary endothelium GL-3 scores were reduced to zero but highly variable effects were observed in podocyte GL-3, with a reduction in 3 patients. Ten (10) patients met per protocol dose increase criteria, two (2) had a dose increase to the recommended dose of 1.0 mg/kg every 2 weeks.
Following an intravenous administration of agalsidase beta to adults at doses of 0.3 mg, 1 mg and 3 mg/kg body weight, the AUC values increased more than dose proportional, due to a decrease in clearance, indicating a saturated clearance. The elimination half-life was dose independent and ranged from 45 to 100 minutes.
After intravenous administration of agalsidase beta to adults with an infusion time of approximately 300 minutes and at a dose of 1 mg/kg body weight, biweekly, mean Cmax plasma concentrations ranged from 2000-3500 ng/ml, while the AUCinf ranged from 370-780 ยตg min/ml. Vss ranged from 8.3-40.8 l, plasma clearance from 119-345 ml/min and the mean elimination half-life from 80-120 minutes.
Agalsidase beta is a protein and is expected to be metabolically degraded through peptide hydrolysis. Consequently, impaired liver function is not expected to affect the pharmacokinetics of agalsidase beta in a clinically significant way. Renal elimination of agalsidase beta is considered to be a minor pathway for clearance.
Fabrazyme pharmacokinetics was also evaluated in two paediatric studies. In one of these studies, 15 paediatric patients with available pharmacokinetics data, aged 8.5 to 16 years weighing 27.1 to 64.9 kg were treated with 1.0 mg/kg every 2 weeks. Agalsidase beta clearance was not influenced by weight in this population. Baseline CL was 77 ml/min with a Vss of 2.6 l; half-life was 55 min. After IgG seroconversion, CL decreased to 35 ml/min, Vss increased to 5.4 l, and half-life increased to 240 min. The net effect of these changes after seroconversion was an increase in exposure of 2- to 3-fold based on AUC and Cmax. No unexpected safety issues were encountered in patients with an increase in exposure after seroconversion.
In another study with 30 paediatric patients with available pharmacokinetics data, aged 5 to 18 years, treated with two lower dose regimens of 0.5 mg/kg every 2 weeks and 1.0 mg/kg every 4 weeks, mean CL was 4.6 and 2.3 ml/min/kg, respectively, mean Vss was 0.27 and 0.22 l/kg, respectively, and mean elimination half-life was 88 and 107 minutes, respectively. After IgG seroconversion, there was no apparent change in CL (+24% and +6%, resp.), while Vss was 1.8 and 2.2 fold higher, with the net effect being a small decrease in Cmax (up to -34% and -11%, resp.) and no change in AUC (-19% and -6%, resp.).
Non-clinical data reveal no special hazard for humans based on studies of safety pharmacology, single dose toxicity, repeated dose toxicity and embryonal/foetal toxicity. Studies with regard to other stages of the development have not been carried out. Genotoxic and carcinogenic potential are not expected.
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