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Avonex (Interferon Beta-1A) - Description and Clinical Pharmacology



AVONEX is a 166 amino acid glycoprotein with a molecular weight of approximately 22,500 daltons. It is produced by recombinant DNA technology using genetically engineered Chinese Hamster Ovary cells into which the human interferon beta gene has been introduced. The amino acid sequence of AVONEX is identical to that of natural human interferon beta.

Using the World Health Organization (WHO) International Standard for Interferon, AVONEX has a specific activity of approximately 200 million international units of antiviral activity per mg of interferon beta-1a determined specifically by an in vitro cytopathic effect bioassay using lung carcinoma cells (A549) and Encephalomyocarditis virus (ECM). AVONEX 30 micrograms contains approximately 6 million international units of antiviral activity using this method. The activity against other standards is not known. Comparison of the activity of AVONEX with other interferon betas is not appropriate, because of differences in the reference standards and assays used to measure activity.

AVONEX Lyophilized Powder Vial

A vial of AVONEX is a sterile, white to off-white lyophilized powder for intramuscular injection after reconstitution with supplied diluent (Sterile Water for Injection, USP). Each vial of reconstituted AVONEX contains 30 micrograms of interferon beta-1a; 15 mg Albumin (Human), USP; 5.8 mg Sodium Chloride, USP; 5.7 mg Dibasic Sodium Phosphate, USP; and 1.2 mg Monobasic Sodium Phosphate, USP, in 1.0 mL at a pH of approximately 7.3.

AVONEX Single-Use Prefilled Syringe

A prefilled syringe of AVONEX is a sterile liquid for intramuscular injection. Each 0.5 mL (30 microgram dose) of AVONEX in a prefilled glass syringe contains 30 micrograms of interferon beta-1a, 0.79 mg Sodium Acetate Trihydrate, USP; 0.25 mg Glacial Acetic Acid, USP; 15.8 mg Arginine Hydrochloride, USP; and 0.025 mg Polysorbate 20 in Water for Injection, USP at a pH of approximately 4.8.

AVONEX PEN Single-Use Prefilled Autoinjector

AVONEX PEN is a sterile liquid for intramuscular injection in a prefilled glass syringe surrounded by an autoinjector. Each 0.5 mL (30 microgram dose) in the AVONEX PEN contains 30 micrograms of interferon beta-1a, 0.79 mg Sodium Acetate Trihydrate, USP; 0.25 mg Glacial Acetic Acid, USP; 15.8 mg Arginine Hydrochloride, USP; and 0.025 mg Polysorbate 20 in Water for Injection, USP at a pH of approximately 4.8.


Mechanism of Action

The mechanism of action by which AVONEX exerts its effects in patients with multiple sclerosis is unknown.


Interferons (IFNs) are a family of naturally occurring proteins, produced by eukaryotic cells in response to viral infection and other biologic agents. Three major types of interferons have been defined: type I (IFN-alpha, beta, epsilon, kappa and omega), type II (IFN gamma) and type III (IFN-lambda). Interferon-beta is a member of the type I subset of interferons. The type I interferons have considerably overlapping but also distinct biologic activities. The bioactivities of all IFNs, including IFN-beta, are induced via their binding to specific receptors on the membranes of human cells. Differences in the bioactivites induced by the three major subtypes of IFNs likely reflect differences in the signal transduction pathways induced by signaling through their cognate receptors.

Interferon beta exerts its biological effects by binding to specific receptors on the surface of human cells. This binding initiates a complex cascade of intracellular events that leads to the expression of numerous interferon-induced gene products and markers. These include 2', 5'-oligoadenylate synthetase, β2-microglobulin, and neopterin. These products have been measured in the serum and cellular fractions of blood collected from patients treated with AVONEX.

Clinical studies conducted in multiple sclerosis patients showed that interleukin 10 (IL-10) levels in cerebrospinal fluid were increased in patients treated with AVONEX compared to placebo. Serum IL-10 levels maximally were increased by 48 hours after intramuscular injection of AVONEX and remained elevated for 1 week. However, no relationship has been established between absolute levels of IL-10 and clinical outcome in multiple sclerosis.


Pharmacokinetics of AVONEX in multiple sclerosis patients have not been evaluated. The pharmacokinetic and pharmacodynamic profiles of AVONEX in healthy subjects following doses of 30 micrograms through 75 micrograms have been investigated. Serum levels of AVONEX as measured by antiviral activity are slightly above detectable limits following a 30 microgram intramuscular dose, and increase with higher doses.

After an intramuscular dose, serum levels of AVONEX typically peak between 3 and 15 hours and then decline at a rate consistent with a 10 hour elimination half-life. Serum levels of AVONEX may be sustained after intramuscular administration due to prolonged absorption from the intramuscular site. Systemic exposure, as determined by AUC and Cmax values, is greater following intramuscular than subcutaneous (SC) administration.

Subcutaneous administration of AVONEX should not be substituted for intramuscular administration. Subcutaneous and intramuscular administration have been observed to have non-equivalent pharmacokinetic and pharmacodynamic parameters following administration to healthy volunteers.

Biological response markers (e.g., neopterin and β2-microglobulin) are induced by AVONEX following parenteral doses of 15 micrograms through 75 micrograms in healthy subjects and treated patients. Biological response marker levels increase within 12 hours of dosing and remain elevated for at least 4 days. Peak biological response marker levels are typically observed 48 hours after dosing. The relationship of serum AVONEX levels or levels of these induced biological response markers to the mechanisms by which AVONEX exerts its effects in multiple sclerosis is unknown.


Carcinogenesis, Mutagenesis, and Impairment of Fertility

Carcinogenesis: The carcinogenic potential of AVONEX has not been tested in animals.

Mutagenesis: Interferon beta was not mutagenic when tested in an in vitro bacterial reverse mutation (Ames) test or in an in vitro cytogenetic assay in human lymphocytes.

Impairment of Fertility: In monkeys administered interferon beta by subcutaneous injection (8 to 15 doses of 1.25 mcg/kg or 50 mcg/kg) over the course of one menstrual cycle, menstrual irregularities, anovulation, and decreased serum progesterone levels were observed at the higher dose. These effects were reversible after discontinuation of drug. The no-effect dose (1.25 mcg/kg) is approximately 2 times the recommended weekly dose in humans (30 mcg) on a mg/m2 basis.


The clinical effects of AVONEX in patients with relapsing forms of multiple sclerosis (MS) were studied in two randomized, multicenter, double-blind, placebo-controlled studies in patients with MS (Studies 1 and 2). Safety and efficacy of treatment with AVONEX beyond 3 years is not known.

In Study 1, 301 patients received either 30 micrograms of AVONEX (n=158) or placebo (n=143) by intramuscular injection once weekly. Patients received injections for up to 2 years, and continued to be followed until study completion. Two hundred eighty-two patients completed 1 year on study, and 172 patients completed 2 years on study. There were 144 patients treated with AVONEX for more than 1 year, 115 patients for more than 18 months and 82 patients for 2 years.

All patients had a definite diagnosis of multiple sclerosis of at least 1 year duration and had at least 2 exacerbations in the 3 years prior to study entry (or 1 per year if the duration of disease was less than 3 years). At entry, study participants were without exacerbation during the prior 2 months and had Kurtzke Expanded Disability Status Scale (EDSS3) scores ranging from 1.0 to 3.5. The EDSS is a scale that quantifies disability in patients with MS and ranges from 0 (normal neurologic exam) to 10 (death due to MS). Patients with chronic progressive multiple sclerosis were excluded from this study.


The primary outcome assessment was time to progression in disability, measured as an increase in the EDSS score of at least 1 point that was sustained for at least 6 months. An increase in EDSS score reflects accumulation of disability. This endpoint was used to help distinguish permanent increase in disability from a transient increase due to an exacerbation.

As shown in Figure 1, the time to onset of sustained progression in disability was significantly longer in AVONEX-treated patients than in placebo-treated patients in Study 1 (p = 0.02). The percentage of patients progressing by the end of 2 years was 35% for placebo-treated patients and 22% for AVONEX-treated patients. This represents a 37% relative reduction in the risk of accumulating disability in the AVONEX-treated group compared to the placebo-treated group.

Figure 1: Time to Onset of Sustained Disability Progression in Patients with MS in Study 1 1

1 Kaplan-Meier Methodology; Disability progression was defined as at least a 1 point increase in EDSS score sustained for at least 6 months.

The distribution of confirmed EDSS change from study entry (baseline) to the end of the study is shown in Figure 2. There was a statistically significant difference between the AVONEX and placebo groups in confirmed change for patients with at least 2 scheduled visits (p = 0.006).

Figure 2: Confirmed Change in EDSS from Study Entry to End of Study 1


The rate and frequency of MS exacerbations were secondary outcomes. For all patients included in the study, irrespective of time on study, the annual exacerbation rate was 0.67 per year in the AVONEX-treated group and 0.82 per year in the placebo-treated group (p = 0.04).

AVONEX treatment significantly decreased the frequency of exacerbations in the subset of patients who were enrolled in the study for at least 2 years (87 placebo-treated patients and 85 AVONEX-treated patients; p = 0.03; see Table 3).

MRI Results

Gadolinium (Gd)-enhanced and T2-weighted magnetic resonance imaging (MRI) scans of the brain were obtained in most patients at baseline and at the end of 1 and 2 years of treatment. Secondary outcomes included Gd-enhanced lesion number and volume, and T2-weighted lesion volume. Gd-enhancing lesions seen on brain MRI scans represent areas of breakdown of the blood brain barrier thought to be secondary to inflammation. AVONEX-treated patients demonstrated significantly lower Gd-enhanced lesion number after 1 and 2 years of treatment than placebo-treated patients (p ≤ 0.05; see Table 3). The volume of Gd-enhanced lesions showed similar treatment effects in the AVONEX and placebo groups (p ≤ 0.03). Percentage change in T2-weighted lesion volume from study entry to Year 1 was significantly lower in AVONEX-treated than placebo-treated patients (p = 0.02). A significant difference in T2-weighted lesion volume change was not seen between study entry and Year 2 in the AVONEX and placebo groups.

The exact relationship between MRI findings and the clinical status of MS patients is unknown. The prognostic significance of MRI findings in these studies has not been evaluated.

Summary of Effects of Clinical and MRI Endpoints in Study 1

A summary of the effects of AVONEX on the clinical and MRI endpoints of this study is presented in Table 3.

Table 3: Clinical and MRI Endpoints in Patients with MS in Study 1

Note: (N:,) denotes the number of evaluable placebo and AVONEX patients, respectively.

1 Patient data included in this analysis represent variable periods of time on study.

2 Analyzed by Mantel-Cox (logrank) test. 3 Analyzed by Mann-Whitney rank-sum test.

4 Analyzed by Cochran-Mantel-Haenszel test. 5 Analyzed by likelihood ratio test.

Endpoint Placebo AVONEX P-Value
Time to sustained progression
in disability (N: 143, 158)1                     ---See Figure 1 --- 0.022
Percentage of patients progressing
in disability at 2 years
(Kaplan-Meier estimate)1 35% 22%
Mean confirmed change in EDSS
from study entry to end of study
(N: 136, 150)1 0.50 0.20 0.0063
Number of exacerbations in subset
completing 2 years (N: 87, 85)
     0 26% 38% 0.033
     1 30% 31%
     2 11% 18%
     3 14% 7%
     ≥4 18% 7%
Percentage of patients exacerbation-
free in subset completing 2 years
(N: 87, 85) 26% 38% 0.104
Annual exacerbation rate
(N: 143, 158)1 0.82 0.67 0.045
Number of Gd-enhanced lesions:
At study entry (N: 132, 141)
     Mean (Median) 2.3 (1.0) 3.2 (1.0)
     Range 0-23 0-56
Year 1 (N: 123, 134)
     Mean (Median) 1.6 (0) 1.0 (0) 0.023
     Range 0-22 0-28
Year 2 (N: 82, 83)
     Mean (Median) 1.6 (0) 0.8 (0) 0.053
     Range 0-34 0-13
T2 lesion volume:
Percentage change from study
entry to Year 1 (N: 116, 123)
     Median -3.3% -13.1% 0.023
Percentage change from study
entry to Year 2 (N: 83, 81)
     Median -6.5% -13.2% 0.363

In Study 2, 383 patients who had recently experienced an isolated demyelinating event involving the optic nerve, spinal cord, or brainstem/cerebellum, and who had lesions typical of multiple sclerosis on brain MRI, received either 30 micrograms of AVONEX (n = 193) or placebo (n = 190) by intramuscular injection once weekly. Patients were enrolled into the study over a two-year period and followed for up to three years or until they developed a second clinical exacerbation in an anatomically distinct region of the central nervous system.


In Study 2, the primary outcome measure was time to development of a second exacerbation in an anatomically distinct region of the central nervous system. Time to development of a second exacerbation was significantly delayed in AVONEX-treated compared to placebo-treated patients (p = 0.002). The Kaplan-Meier estimates of the percentage of patients developing an exacerbation within 24 months were 39% in the placebo group and 21% in the AVONEX group (see Figure 3). The relative rate of developing a second exacerbation in the AVONEX group was 0.56 of the rate in the placebo group (95% confidence interval 0.38 to 0.81).

Figure 3: Time to onset of a Second Exacerbation in Study 2 1

1 Kaplan-Meier Methodology

MRI Findings

Secondary outcomes were brain MRI measures, including the cumulative increase in the number of new or enlarging T2 lesions, T2 lesion volume at baseline compared to results at 18 months, and the number of Gd-enhancing lesions at 6 months. See Table 4 for the MRI results.

Table 4: Brain MRI Results in Study 2

1 P value <0.001

2 P value <0.03

* P value from a Mann-Whitney rank-sum test

AVONEX Placebo
Actual Change (mm3)1*
Median (25th%, 75th%) 28 (-576, 397) 313 (5, 1140)
Percentage Change1*
Median (25th%, 75th%) 1 (-24, 29) 16 (0, 53)
T2 LESIONS AT 18 MONTHS 1*: N (%) N (%)
0 62 (47) 22 (18)
1-3 41 (31) 47 (40)
≥4 29 (22) 50 (42)
Mean (SD) 2.13 (3.2) 4.97 (7.7)
LESIONS AT 6 MONTHS 2*: N (%) N (%)
0 115 (70) 93 (61)
1 27 (16) 16 (11)
>1 23 (14) 43 (28)
Mean (SD) 0.87 (2.3) 1.49 (3.1)

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