DESCRIPTION

ENBREL® (etanercept) is a dimeric fusion protein consisting of the extracellular ligand-binding portion of the human 75 kilodalton (p75) tumor necrosis factor receptor (TNFR) linked to the Fc portion of human IgG1. The Fc component of etanercept contains the C _H 2 domain, the C _H 3 domain and hinge region, but not the C _H 1 domain of IgG1. Etanercept is produced by recombinant DNA technology in a Chinese hamster ovary (CHO) mammalian cell expression system. It consists of 934 amino acids and has an apparent molecular weight of approximately 150 kilodaltons.

ENBREL® is supplied in a single-use prefilled 1 mL syringe as a sterile, preservative-free solution for subcutaneous injection. The solution of ENBREL® is clear and colorless and is formulated at pH 6.3 ± 0.2. Each ENBREL® single-use prefilled syringe contains 0.98 mL of a 50 mg/mL solution of etanercept with 10 mg/mL sucrose, 5.8 mg/mL sodium chloride, 5.3 mg/mL L-arginine hydrochloride, 2.6 mg/mL sodium phosphate monobasic monohydrate and 0.9 mg/mL sodium phosphate dibasic anhydrous. Administration of one 50 mg/mL prefilled syringe of ENBREL® provides a dose equivalent to two 25 mg vials of lyophilized ENBREL®, when vials are reconstituted and administered as recommended.

ENBREL® multiple-use vial contains sterile, white, preservative-free, lyophilized powder. Reconstitution with 1 mL of the supplied Sterile Bacteriostatic Water for Injection (BWFI), USP (containing 0.9% benzyl alcohol) yields a multiple-use, clear, and colorless solution with a pH of 7.4 ± 0.3 containing 25 mg etanercept, 40 mg mannitol, 10 mg sucrose, and 1.2 mg tromethamine.

CLINICAL PHARMACOLOGY

General

Etanercept binds specifically to tumor necrosis factor (TNF) and blocks its interaction with cell surface TNF receptors. TNF is a naturally occurring cytokine that is involved in normal inflammatory and immune responses. It plays an important role in the inflammatory processes of rheumatoid arthritis (RA), polyarticular-course juvenile rheumatoid arthritis (JRA), and ankylosing spondylitis and the resulting joint pathology. In addition, TNF plays a role in the inflammatory process of plaque psoriasis. Elevated levels of TNF are found in involved tissues and fluids of patients with RA, psoriatic arthritis, ankylosing spondylitis (AS), and plaque psoriasis.

Two distinct receptors for TNF (TNFRs), a 55 kilodalton protein (p55) and a 75 kilodalton protein (p75), exist naturally as monomeric molecules on cell surfaces and in soluble forms. Biological activity of TNF is dependent upon binding to either cell surface TNFR.

Etanercept is a dimeric soluble form of the p75 TNF receptor that can bind to two TNF molecules. It inhibits the activity of TNF in vitro and has been shown to affect several animal models of inflammation, including murine collagen-induced arthritis. Etanercept inhibits binding of both TNF(alpha) and TNF(beta) (lymphotoxin alpha [LT(alpha)]) to cell surface TNFRs, rendering TNF biologically inactive. Cells expressing transmembrane TNF that bind ENBREL® are not lysed in vitro in the presence or absence of complement.

Etanercept can also modulate biological responses that are induced or regulated by TNF, including expression of adhesion molecules responsible for leukocyte migration (i.e., E-selectin and to a lesser extent intercellular adhesion molecule-1 [ICAM-1]), serum levels of cytokines (e.g., IL-6), and serum levels of matrix metalloproteinase-3 (MMP-3 or stromelysin).

Pharmacokinetics

After administration of 25 mg of ENBREL® by a single subcutaneous (SC) injection to 25 patients with RA, a mean ± standard deviation half-life of 102 ± 30 hours was observed with a clearance of 160 ± 80 mL/hr. A maximum serum concentration (Cmax) of 1.1 ± 0.6 mcg/mL and time to Cmax of 69 ± 34 hours was observed in these patients following a single 25 mg dose. After 6 months of twice weekly 25 mg doses in these same RA patients, the mean Cmax was 2.4 ± 1.0 mcg/mL (N = 23). Patients exhibited a two- to seven-fold increase in peak serum concentrations and approximately four-fold increase in AUC _{0-72 hr} (range 1 to 17 fold) with repeated dosing. Serum concentrations in patients with RA have not been measured for periods of dosing that exceed 6 months. The pharmacokinetic parameters in patients with plaque psoriasis were similar to those seen in patients with RA.

In another study, serum concentration profiles at steady state were comparable among patients with RA treated with 50 mg ENBREL® once weekly and those treated with 25 mg ENBREL® twice weekly. The mean (± standard deviation) Cmax, Cmin, and partial AUC were 2.4 ± 1.5 mg/L, 1.2 ± 0.7 mg/L, and 297 ± 166 mg·h/L, respectively, for patients treated with 50 mg ENBREL® once weekly (N = 21); and 2.6 ± 1.2 mg/L, 1.4 ± 0.7 mg/L, and 316 ± 135 mg·h/L for patients treated with 25 mg ENBREL® twice weekly (N = 16).

Pharmacokinetic parameters were not different between men and women and did not vary with age in adult patients. No formal pharmacokinetic studies have been conducted to examine the effects of renal or hepatic impairment on ENBREL® disposition.

Patients with JRA (ages 4 to 17 years) were administered 0.4 mg/kg of ENBREL® twice weekly for up to 18 weeks. The mean serum concentration after repeated SC dosing was 2.1 mcg/mL, with a range of 0.7 to 4.3 mcg/mL. Limited data suggests that the clearance of ENBREL® is reduced slightly in children ages 4 to 8 years. Population pharmacokinetic analyses predict that administration of 0.8 mg/kg of ENBREL® once weekly will result in Cmax 11% higher, and Cmin 20% lower at steady state as compared to administration of 0.4 mg/kg of ENBREL® twice weekly. The predicted pharmacokinetic differences between the regimens in JRA patients are of the same magnitude as the differences observed between twice weekly and weekly regimens in adult RA patients. The pharmacokinetics of ENBREL® in children < 4 years of age have not been studied.

CLINICAL STUDIES

Adult Rheumatoid Arthritis

The safety and efficacy of ENBREL® were assessed in four randomized, double-blind, controlled studies. The results of all four trials were expressed in percentage of patients with improvement in RA using American College of Rheumatology (ACR) response criteria.

Study I eva luated 234 patients with active RA who were >/= 18 years old, had failed therapy with at least one but no more than four disease-modifying antirheumatic drugs (DMARDs; e.g., hydroxychloroquine, oral or injectable gold, methotrexate [MTX], azathioprine, D-penicillamine, sulfasalazine), and had >/= 12 tender joints, >/= 10 swollen joints, and either ESR >/= 28 mm/hr, CRP > 2.0 mg/dL, or morning stiffness for >/= 45 minutes. Doses of 10 mg or 25 mg ENBREL® or placebo were administered SC twice a week for 6 consecutive months. Results from patients receiving 25 mg are presented in Table 1.

Study II eva luated 89 patients and had similar inclusion criteria to Study I except that subjects in Study II had additionally received MTX for at least 6 months with a stable dose (12.5 to 25 mg/week) for at least 4 weeks and they had at least 6 tender or painful joints. Subjects in Study II received a dose of 25 mg ENBREL® or placebo SC twice a week for 6 months in addition to their stable MTX dose.

Study III compared the efficacy of ENBREL® to MTX in patients with active RA. This study eva luated 632 patients who were >/= 18 years old with early (</= 3 years disease duration) active RA; had never received treatment with MTX; and had >/= 12 tender joints, >/= 10 swollen joints, and either ESR >/= 28 mm/hr, CRP > 2.0 mg/dL, or morning stiffness for >/= 45 minutes. Doses of 10 mg or 25 mg ENBREL® were administered SC twice a week for 12 consecutive months. The study was unblinded after all patients had completed at least 12 months (and a median of 17.3 months) of therapy. The majority of patients remained in the study on the treatment to which they were randomized through 2 years, after which they entered an extension study and received open-label 25 mg ENBREL®. Results from patients receiving 25 mg are presented in Table 1. MTX tablets (escalated from 7.5 mg/week to a maximum of 20 mg/week over the first 8 weeks of the trial) or placebo tablets were given once a week on the same day as the injection of placebo or ENBREL® doses, respectively.

Study IV eva luated 682 adult patients with active RA of 6 months to 20 years duration (mean of 7 years) who had an inadequate response to at least one DMARD other than MTX. Forty-three percent of patients had previously received MTX a mean of two years prior to the trial at a mean dose of 12.9 mg. Patients were excluded from this study if MTX had been discontinued for lack of efficacy or for safety considerations. The patient baseline characteristics were similar to those of patients in Study I (Table 3). Patients were randomized to MTX alone (7.5 to 20 mg weekly, dose escalated as described for Study III; median dose 20 mg), ENBREL® alone (25 mg twice weekly), or the combination of ENBREL® and MTX initiated concurrently (at the same doses as above). The study eva luated ACR response, Sharp radiographic score and safety.

Clinical Response

A higher percentage of patients treated with ENBREL® and ENBREL® in combination with MTX achieved ACR 20, ACR 50, and ACR 70 responses and Major Clinical Responses than in the comparison groups. The results of Studies I, II, and III are summarized in Table 1. The results of Study IV are summarized in Table 2.

The time course for ACR 20 response rates for patients receiving placebo or 25 mg ENBREL® in Studies I and II is summarized in Figure 1. The time course of responses to ENBREL® in Study III was similar.

Among patients receiving ENBREL®, the clinical responses generally appeared within 1 to 2 weeks after initiation of therapy and nearly always occurred by 3 months. A dose response was seen in Studies I and III: 25 mg ENBREL® was more effective than 10 mg (10 mg was not eva luated in Study II). ENBREL® was significantly better than placebo in all components of the ACR criteria as well as other measures of RA disease activity not included in the ACR response criteria, such as morning stiffness.

In Study III, ACR response rates and improvement in all the individual ACR response criteria were maintained through 24 months of ENBREL® therapy. Over the 2-year study, 23% of ENBREL® patients achieved a major clinical response, defined as maintenance of an ACR 70 response over a 6-month period.

The results of the components of the ACR response criteria for Study I are shown in Table 3. Similar results were observed for ENBREL®-treated patients in Studies II and III.

After discontinuation of ENBREL®, symptoms of arthritis generally returned within a month. Reintroduction of treatment with ENBREL® after discontinuations of up to 18 months resulted in the same magnitudes of response as patients who received ENBREL® without interruption of therapy based on results of open-label studies.

Continued durable responses were seen for over 60 months in open-label extension treatment trials when patients received ENBREL® without interruption. A substantial number of patients who initially received concomitant MTX or corticosteroids were able to reduce their doses or discontinue these concomitant therapies while maintaining their clinical responses.

A 24-week study was conducted in 242 patients with active RA on background methotrexate who were randomized to receive either ENBREL® alone or the combination of ENBREL® and anakinra. The ACR50 response rate was 31% for patients treated with the combination of ENBREL® and anakinra and 41% for patients treated with ENBREL® alone, indicating no added clinical benefit of the combination over ENBREL® alone. Serious infections were increased with the combination compared to ENBREL® alone (see WARNINGS ).

Physical Function Response

In Studies I, II, and III, physical function and disability were assessed using the Health Assessment Questionnaire (HAQ). ¹ Additionally, in Study III, patients were administered the SF-36 ² Health Survey. In Studies I and II, patients treated with 25 mg ENBREL® twice weekly showed greater improvement from baseline in the HAQ score beginning in month 1 through month 6 in comparison to placebo (p < 0.001) for the HAQ disability domain (where 0 = none and 3 = severe). In Study I, the mean improvement in the HAQ score from baseline to month 6 was 0.6 (from 1.6 to 1.0) for the 25 mg ENBREL® group and 0 (from 1.7 to 1.7) for the placebo group. In Study II, the mean improvement from baseline to month 6 was 0.6 (from 1.5 to 0.9) for the ENBREL® /MTX group and 0.2 (from 1.3 to 1.2) for the placebo/MTX group. In Study III, the mean improvement in the HAQ score from baseline to month 6 was 0.7 (from 1.5 to 0.7) for 25 mg ENBREL® twice weekly. All subdomains of the HAQ in Studies I and III were improved in patients treated with ENBREL®.

In Study III, patients treated with 25 mg ENBREL® twice weekly showed greater improvement from baseline in SF-36 physical component summary score compared to ENBREL® 10 mg twice weekly and no worsening in the SF-36 mental component summary score. In open-label ENBREL® studies, improvements in physical function and disability measures have been maintained for up to 4 years.

In Study IV, median HAQ scores improved from baseline levels of 1.8, 1.8, and 1.8 to 1.1, 1.0, and 0.6 at 12 months in the MTX, ENBREL®, and ENBREL®/MTX combination treatment groups, respectively (combination versus both MTX and ENBREL®, p < 0.01). Twenty-nine percent of patients in the MTX alone treatment group had an improvement of HAQ of at least one unit versus 40% and 51% in the ENBREL® alone and the ENBREL®/MTX combination treatment groups, respectively.

Radiographic Response

In Study III, structural joint damage was assessed radiographically and expressed as change in total Sharp score (TSS) and its components, the erosion score and joint space narrowing (JSN) score. Radiographs of hands/wrists and forefeet were obtained at baseline, 6 months, 12 months, and 24 months and scored by readers who were unaware of treatment group. The results are shown in Table 4. A significant difference for change in erosion score was observed at 6 months and maintained at 12 months.

Patients continued on the therapy to which they were randomized for the second year of Study III. Seventy-two percent of patients had x-rays obtained at 24 months. Compared to the patients in the MTX group, greater inhibition of progression in TSS and erosion score was seen in the 25 mg ENBREL® group, and in addition, less progression was noted in the JSN score.

In the open-label extension of Study III, 48% of the original patients treated with 25 mg ENBREL® have been eva luated radiographically at 5 years. Patients had continued inhibition of structural damage, as measured by the TSS, and 55% of them had no progression of structural damage. Patients originally treated with MTX had further reduction in radiographic progression once they began treatment with ENBREL®.

In Study IV, less radiographic progression (TSS) was observed with ENBREL® in combination with MTX compared with ENBREL® alone or MTX alone at month 12 (Table 5). In the MTX treatment group 55% of patients experienced no radiographic progression (TSS change </= 0.0) at 12 months compared to 63% and 76% in the ENBREL® alone and the ENBREL®/MTX combination treatment groups, respectively.

Once Weekly Dosing

The safety and efficacy of 50 mg ENBREL® (two 25 mg SC injections) administered once weekly were eva luated in a double-blind, placebo-controlled study of 420 patients with active RA. Fifty-three patients received placebo, 214 patients received 50 mg ENBREL® once weekly, and 153 patients received 25 mg ENBREL® twice weekly. The safety and efficacy profiles of the two ENBREL® treatment groups were similar.

Polyarticular-Course Juvenile Rheumatoid Arthritis (JRA)

The safety and efficacy of ENBREL® were assessed in a two-part study in 69 children with polyarticular-course JRA who had a variety of JRA onset types. Patients ages 4 to 17 years with moderately to severely active polyarticular-course JRA refractory to or intolerant of methotrexate were enrolled; patients remained on a stable dose of a single nonsteroidal anti-inflammatory drug and/or prednisone (</= 0.2 mg/kg/day or 10 mg maximum). In part 1, all patients received 0.4 mg/kg (maximum 25 mg per dose) ENBREL® SC twice weekly. In part 2, patients with a clinical response at day 90 were randomized to remain on ENBREL® or receive placebo for four months and assessed for disease flare. Responses were measured using the JRA Definition of Improvement (DOI), ³ defined as >/= 30% improvement in at least three of six and >/= 30% worsening in no more than one of the six JRA core set criteria, including active joint count, limitation of motion, physician and patient/parent global assessments, functional assessment, and ESR. Disease flare was defined as a >/= 30% worsening in three of the six JRA core set criteria and >/= 30% improvement in not more than one of the six JRA core set criteria and a minimum of two active joints.

In part 1 of the study, 51 of 69 (74%) patients demonstrated a clinical response and entered part 2. In part 2, 6 of 25 (24%) patients remaining on ENBREL® experienced a disease flare compared to 20 of 26 (77%) patients receiving placebo (p = 0.007). From the start of part 2, the median time to flare was >/= 116 days for patients who received ENBREL® and 28 days for patients who received placebo. Each component of the JRA core set criteria worsened in the arm that received placebo and remained stable or improved in the arm that continued on ENBREL®. The data suggested the possibility of a higher flare rate among those patients with a higher baseline ESR. Of patients who demonstrated a clinical response at 90 days and entered part 2 of the study, some of the patients remaining on ENBREL® continued to improve from month 3 through month 7, while those who received placebo did not improve.

The majority of JRA patients who developed a disease flare in part 2 and reintroduced ENBREL® treatment up to 4 months after discontinuation re-responded to ENBREL® therapy in open-label studies. Most of the responding patients who continued ENBREL® therapy without interruption have maintained responses for up to 48 months.

Studies have not been done in patients with polyarticular-course JRA to assess the effects of continued ENBREL® therapy in patients who do not respond within 3 months of initiating ENBREL® therapy, or to assess the combination of ENBREL® with methotrexate.

Psoriatic Arthritis

The safety and efficacy of ENBREL® were assessed in a randomized, double-blind, placebo-controlled study in 205 patients with psoriatic arthritis. Patients were between 18 and 70 years of age and had active psoriatic arthritis (>/= 3 swollen joints and >/= 3 tender joints) in one or more of the following forms: (1) distal interphalangeal (DIP) involvement (N = 104); (2) polyarticular arthritis (absence of rheumatoid nodules and presence of psoriasis; N = 173); (3) arthritis mutilans (N = 3); (4) asymmetric psoriatic arthritis (N = 81); or (5) ankylosing spondylitis-like (N = 7). Patients also had plaque psoriasis with a qualifying target lesion >/= 2 cm in diameter. Patients on MTX therapy at enrollment (stable for >/= 2 months) could continue at a stable dose of </= 25 mg/week MTX. Doses of 25 mg ENBREL® or placebo were administered SC twice a week during the initial 6-month double-blind period of the study. Patients continued to receive blinded therapy in an up to 6-month maintenance period until all patients had completed the controlled period. Following this, patients received open-label 25 mg ENBREL® twice a week in a 12-month extension period.

Compared to placebo, treatment with ENBREL® resulted in significant improvements in measures of disease activity (Table 6).

Among patients with psoriatic arthritis who received ENBREL®, the clinical responses were apparent at the time of the first visit (4 weeks) and were maintained through 6 months of therapy. Responses were similar in patients who were or were not receiving concomitant methotrexate therapy at baseline. At 6 months, the ACR 20/50/70 responses were achieved by 50%, 37%, and 9%, respectively, of patients receiving ENBREL®, compared to 13%, 4%, and 1%, respectively, of patients receiving placebo. Similar responses were seen in patients with each of the subtypes of psoriatic arthritis, although few patients were enrolled with the arthritis mutilans and ankylosing spondylitis-like subtypes. The results of this study were similar to those seen in an earlier single-center, randomized, placebo-controlled study of 60 patients with psoriatic arthritis.

The skin lesions of psoriasis were also improved with ENBREL®, relative to placebo, as measured by percentages of patients achieving improvements in the Psoriasis Area and Severity Index (PASI). ⁴ Responses increased over time, and at 6 months, the proportions of patients achieving a 50% or 75% improvement in the PASI were 47% and 23%, respectively, in the ENBREL® group (N = 66), compared to 18% and 3%, respectively, in the placebo group (N = 62). Responses were similar in patients who were or were not receiving concomitant methotrexate therapy at baseline.

Radiographic Response

Radiographic changes were also assessed in the psoriatic arthritis study. Radiographs of hands and wrists were obtained at baseline and months 6, 12, and 24. A modified Total Sharp Score (TSS), which included distal interphalangeal joints (i.e., not identical to the modified TSS used for rheumatoid arthritis) was used by readers blinded to treatment group to assess the radiographs. Some radiographic features specific to psoriatic arthritis (e.g., pencil-and-cup deformity, joint space widening, gross osteolysis and ankylosis) were included in the scoring system, but others (e.g., phalangeal tuft resorption, juxta-articular and shaft periostitis) were not.

Most patients showed little or no change in the modified TSS during this 24-month study (median change of 0 in both patients who initially received ENBREL® or placebo). More placebo-treated patients experienced larger magnitudes of radiographic worsening (increased TSS) compared to ENBREL® treatment during the controlled period of the study. At 12 months, in an exploratory analysis, 12% (12 of 104) of placebo patients compared to none of the 101 ENBREL®-treated patients had increases of 3 points or more in TSS. Inhibition of radiographic progression was maintained in patients who continued on ENBREL® during the second year. Of the patients with one-year and two-year x-rays, 3% (2 of 71) had increases of 3 points or more in TSS at one and two years.

Physical Function Response

In the psoriatic arthritis study, physical function and disability were assessed using the HAQ Disability Index (HAQ-DI) ¹ and the SF-36 ² Health Survey. Patients treated with 25 mg ENBREL® twice weekly showed greater improvement from baseline in the HAQ-DI score (mean decreases of 54% at both months 3 and 6) in comparison to placebo (mean decreases of 6% at both months 3 and 6) (p <0.001). At months 3 and 6, patients treated with ENBREL® showed greater improvement from baseline in the SF-36 physical component summary score compared to patients treated with placebo, and no worsening in the SF-36 mental component summary score. Improvements in physical function and disability measures were maintained for up to 2 years through the open-label portion of the study.

Ankylosing Spondylitis

The safety and efficacy of ENBREL® were assessed in a randomized, double-blind, placebo-controlled study in 277 patients with active ankylosing spondylitis. Patients were between 18 and 70 years of age and had ankylosing spondylitis as defined by the modified New York Criteria for Ankylosing Spondylitis. ⁵ Patients were to have evidence of active disease based on values of >/= 30 on a 0-100 unit Visual Analog Scale (VAS) for the average of morning stiffness duration and intensity, and 2 of the following 3 other parameters: a) patient global assessment, b) average of nocturnal and total back pain, and c) the average score on the Bath Ankylosing Spondylitis Functional Index (BASFI). Patients with complete ankylosis of the spine were excluded from study participation. Patients taking hydroxychloroquine, sulfasalazine, methotrexate or prednisone (</= 10 mg/day) could continue these drugs at stable doses for the duration of the study. Doses of 25 mg ENBREL® or placebo were administered SC twice a week for 6 months.

The primary measure of efficacy was a 20% improvement in the Assessment in Ankylosing Spondylitis (ASAS) response criteria. ⁶ Compared to placebo, treatment with ENBREL® resulted in improvements in the ASAS and other measures of disease activity (Figure 2 and Table 7).

At 12 weeks, the ASAS 20/50/70 responses were achieved by 60%, 45%, and 29%, respectively, of patients receiving ENBREL®, compared to 27%, 13%, and 7%, respectively, of patients receiving placebo (p </= 0.0001, ENBREL® vs. placebo). Similar responses were seen at week 24. Responses were similar between those patients receiving concomitant therapies at baseline and those who were not. The results of this study were similar to those seen in a single-center, randomized, placebo-controlled study of 40 patients and a multi-center, randomized, placebo-controlled study of 84 patients with ankylosing spondylitis.

Plaque Psoriasis

The safety and efficacy of ENBREL® were assessed in two randomized, double-blind, placebo-controlled studies in adults with chronic stable plaque psoriasis involving >/= 10% of the body surface area, a minimum PASI of 10 and who had received or were candidates for systemic anti-psoriatic therapy or phototherapy. Patients with guttate, erythrodermic, or pustular psoriasis and patients with severe infections within 4 weeks of screening were excluded from study. No concomitant major anti-psoriatic therapies were allowed during the study.

Study I eva luated 672 patients who received placebo or ENBREL® SC at doses of 25 mg once a week, 25 mg twice a week or 50 mg twice a week for 3 months. After 3 months, patients continued on blinded treatments for an additional 3 months during which time, patients originally randomized to placebo began treatment with blinded ENBREL® at 25 mg twice weekly (designated as placebo/ENBREL® in Table 8); patients originally randomized to ENBREL® continued on the originally randomized dose (designated as ENBREL®/ENBREL® groups in Table 8).

Study II eva luated 611 patien