Clinical Pharmacology for Aralast NP
Mechanism Of Action
ARALAST NP administration is intended to inhibit serine proteases such as neutrophil elastase (NE), which is capable of degrading protein components of the alveolar walls and which is chronically present in the lung.
Alpha1-PI deficiency is an autosomal, co-dominant, hereditary disorder characterized by low serum and lung levels of Alpha1-PI.1,2,4,5 Severe forms of the deficiency are frequently associated with slowly progressive, moderate-to-severe panacinar emphysema that most often manifests in the third to fourth decades of life.1,2,3,5,6 However, an unknown percentage of individuals with severe Alpha1-PI deficiency are not diagnosed with or may never develop clinically evident emphysema during their lifetimes. Individuals with Alpha1-PI deficiency have little protection against NE released by neutrophils in their lower respiratory tract, resulting in a protease:protease inhibitor imbalance in the lung.2,7 This imbalance allows relatively unopposed destruction of the connective tissue framework of the lung parenchyma.7
There are a large number of phenotypic variants of this disorder.1,2,3 Individuals with the PiZZ variant typically have serum Alpha1-PI levels less than 35% of the average normal level.1,4 Individuals with the Pi(null)(null) variant have undetectable Alpha1-PI protein in their serum.1,2 Individuals with these low serum Alpha1-PI levels, i.e., less than 11 microΜ, have an increased risk of developing emphysema over their lifetimes. In addition, PiSZ individuals, whose serum Alpha1-PI levels range from approximately 9 to 23 microΜ,10are considered to have moderately increased risk for developing emphysema, regardless of whether their serum Alpha1-PI levels are above or below 11 microΜ. The risk of accelerated development and progression of emphysema in individuals with severe Alpha1-PI deficiency is higher in smokers than in ex-smokers or non-smokers.2
Not all individuals with severe genetic variants of Alpha1-PI deficiency have emphysema. Augmentation therapy with Alpha1-Proteinase Inhibitor (Human) is indicated only in patients with severe congenital Alpha1-PI deficiency who have clinically evident emphysema.
Augmenting the levels of functional Alpha1-proteinase inhibitor by intravenous infusion is an approach to therapy for patients with Alpha1-PI deficiency. However, the efficacy of augmentation therapy in affecting the progression of emphysema has not been demonstrated in randomized, controlled clinical trials. The intended theoretical goal is to provide protection to the lower respiratory tract by correcting the imbalance between neutrophil elastase and protease inhibitors. Whether augmentation therapy with ARALAST NP actually protects the lower respiratory tract from progressive emphysematous changes has not been evaluated. Although the maintenance of blood serum levels of Alpha1-PI (antigenically measured) above 11 microM has been historically postulated to provide therapeutically relevant anti-neutrophil elastase protection, this has not been proven. Individuals with severe Alpha1-PI deficiency have been shown to have increased neutrophil and neutrophil elastase concentrations in lung epithelial lining fluid compared to normal PiMM individuals, and some PiSZ individuals with Alpha1-PI above 11 microM have emphysema attributed to Alpha1-PI deficiency. These observations underscore the uncertainty regarding the appropriate therapeutic target serum level of Alpha1-PI during augmentation therapy. The clinical benefit of increased blood levels of Alpha1-PI at the recommended dose has not been established.
The clinical efficacy of ARALAST NP in influencing the course of pulmonary emphysema or the frequency, duration, or severity of pulmonary exacerbations has not been demonstrated in randomized, controlled clinical trials.
Pharmacodynamics
Chronic augmentation therapy with a weekly dose of ARALAST NP at 60 mg/kg body weight to patients with Alpha1-PI deficiency increases the level of the deficient protein in plasma and in the epithelial lining fluid (ELF) as determined by antigenic assay. Normal individuals have plasma levels of Alpha1-PI greater than 20 microM. The clinical benefit of increased blood and ELF levels of Alpha1-PI at the recommended dose has not been demonstrated in adequately powered, randomized, double-blind, placebo-controlled trials for any Alpha1-PI product.
Pharmacokinetics
The pharmacokinetic comparability of ARALAST NP and the predecessor product ARALAST was demonstrated in a randomized, double-blind, crossover trial in 25 subjects (median age: 59 years old; range: 20 to 75 years old) with severe Alpha1-PI deficiency who received a single infusion of 60 mg/kg body weight of each product. Figure 2 depicts the mean ± standard deviation (SD) plasma Alpha1-PI concentration-time profiles measured using an enzyme-linked immunosorbent assay (ELISA). Table 4 summarizes the pharmacokinetic parameters of ARALAST NP and ARALAST.
Mean (± SD) Plasma Alpha1-PI Concentration-Time Profiles After a Single Intravenous Infusion of ARALAST NP and ARALAST (60 mg/kg) in Subjects with Congenital Alpha1-PI Deficiency
Figure 2
Table 4: Pharmacokinetic Parameters for Plasma Antigenic Alpha1-PI in 25 Subjects Following a Single 60 mg/kg Dose of ARALAST NP or ARALAST
Pharmacokinetic
Parameter |
ARALAST NP
Mean (± SD) |
ARALAST
Mean (± SD) |
| Cmax |
1.6 (± 0.3) mg/mL |
1.7 (± 0.3) mg/mL |
| AUC0-35d/dose |
0.0837 (± 0.0212) day*kg/mL |
0.0897 (± 0.0204) day*kg/mL |
| Half-life |
4.7 (± 2.7) days |
4.8 (± 2.0) days |
| Cmax = Maximum increase in plasma Alpha1-PI concentration following infusion; AUC0-35d/dose = Area under the curve from time 0 to 35 days divided by dose; Half-life = terminal phase half-life determined using non-compartmental method |
The key pharmacokinetic parameter was AUC0-35d/dose. The 90% confidence interval (85.8% to 100.2%) for the geometric mean ratio of AUC0-35d/dose for ARALAST NP and ARALAST indicated that the 2 products are pharmacokinetically equivalent.
Clinical Studies
A clinical trial (ARALAST versus PROLASTIN trial) was conducted to compare the predecessor product ARALAST to a commercially available preparation of Alpha1-PI (PROLASTIN) in 28 subjects with congenital Alpha1-PI deficiency and emphysema, who had not received Alpha1-PI augmentation therapy within the preceding six months.
Subjects were randomized to receive either ARALAST or PROLASTIN, 60 mg/kg intravenously per week for 10 consecutive weeks. Following their first 10 weekly infusions, the subjects who were receiving PROLASTIN were switched to ARALAST while those who already were receiving ARALAST continued to receive it. Table 5 summarizes the mean serum antigenic and functional Alpha1-PI trough levels measured prior to infusion at steady state (Weeks 8 through 11).
Table 5: Steady-State Serum Antigenic and Functional Alpha1-PI Trough Levels Following Intravenous Augmentation Therapy with ARALAST or PROLASTIN
|
ARALAST
Mean ± SD
(Range of means)
(No. of Subjects = 13) |
PROLASTIN
Mean ± SD
(Range of means)
(No. of Subjects = 13) |
| Antigenic Alpha1-PI |
15.3 ± 2.5
(14.7 to 15.5) microM |
16.9 ± 2.3
(16.2 to 17.2) microM |
| Functional Alpha1-PI |
15.3 ± 2.4
(14.8 to 15.6) microM |
15.7 ± 2.6
(14.4 to 16.4) microM |
Following weekly augmentation therapy with ARALAST or PROLASTIN, a gradual increase in peak and trough serum Alpha1-PI levels was noted, with stabilization after several weeks. The metabolic half-life of ARALAST was 5.9 days. Serum ANEC trough levels rose substantially in all subjects by Week 2, and by Week 3, serum ANEC trough levels exceeded 11 microM in the majority of subjects. With few exceptions, levels in both treatment groups remained above this level in individual subjects for the duration of the period Weeks 3 through 24. Although only five of fourteen subjects (35.7%) receiving ARALAST had BALs meeting acceptance criteria for analysis at both baseline and Week 7, a statistically significant increase in the antigenic level of Alpha1-PI in epithelial lining fluid (ELF) was observed. No statistically significant increase in the ANEC in the ELF was detected.
It was concluded that at a dose of 60 mg/kg administered intravenously once weekly, ARALAST and PROLASTIN had similar effects in maintaining target serum Alpha1-PI trough levels and increasing antigenic levels of Alpha1-PI in the ELF with maintenance augmentation therapy.
The pharmacokinetic comparability of ARALAST NP and the predecessor product ARALAST was demonstrated in a randomized, double-blind, crossover trial in 25 subjects with severe Alpha1-PI deficiency [see Pharmacokinetics].
Another clinical trial (BAL TRIAL) was conducted to determine the effects of open-label, weekly intravenous augmentation therapy with 60 mg/kg ARALAST NP on ELF levels of Alpha1-PI, ANEC, and Alpha1-PI: human neutrophil elastase (HNE) complexes in subjects with severe, congenital Alpha1-PI deficiency. A total of 13 subjects completed 8 weekly infusions of ARALAST NP at a median dose of 63 (range: 58 to 67) mg/kg body weight at an infusion rate of 0.2 mL/kg/min. Of the 13 subjects, 12 had both baseline and post-treatment bronchoalveolar lavage samples. ARALAST NP augmentation therapy resulted in a significant increase (p<0.0001; n=12) in the mean plasma of antigenic Alpha1-PI levels, from a median baseline level of 4.0 (range: 3.1 to 6.3) microM to a median post-treatment level of 14.6 (range: 11.1 to 18.1) microM. Post-treatment values of plasma Alpha1-PI were above 11 microM in all 12 subjects. Median plasma functional Alpha1-PI (ANEC) levels also increased significantly (p<0.0001; n=12) from a median baseline level of 2.5 (range: 1.6 to 3.0) microM to a median post-treatment level of 11.4 (range: 7.8 to 16.9) microM. While antigenic Alpha1-PI levels in the ELF also increased significantly (p=0.0195; n=10) (Figure 3), only 4 out of 12 subjects were observed to have measurable ELF ANEC level in either or both lung lobes following 8 weekly infusions of ARALAST NP and the difference from baseline among these subjects did not reach statistical significance. Changes in the ELF analytes free and total human neutrophil elastase, Alpha1-PI:HNE complexes, IL-8, and TNF alpha were either not statistically significant, or could not be analyzed due to limited data.
Changes in ELF Alpha1-PI (AAT) Levels Following Intravenous Treatment with ARALAST NP (60 mg/kg/week) for 8 Weeks in Subjects with Severe Congenital Alpha1-PI Deficiency
Figure 3
The clinical efficacy of ARALAST NP or any Alpha1-PI product in influencing the clinical course of pulmonary emphysema in Alpha1-PI deficiency has not been conclusively demonstrated in adequately powered, randomized, controlled clinical trials.
REFERENCES
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