New England Journal of Medicine SEPTEMBER 25, 2014

Oral Glucocorticoid-sparing Effect of Mepolizumab in Eosinophilic Asthma (SIRIUS)

Bel EH, Wenzel SE, Thompson PJ, et al. (The SIRIUS Investigators)

Bottom Line

In patients with severe eosinophilic asthma dependent on daily oral corticosteroids, mepolizumab significantly reduced the required glucocorticoid dose compared with placebo while improving asthma control and reducing exacerbation rates.

Key Findings

1. Mepolizumab was associated with a 2.39-fold greater likelihood of achieving a reduction in the oral corticosteroid (OCS) dose stratum compared to placebo (95% CI, 1.25 to 4.56; P=0.008).

2. Patients in the mepolizumab group achieved a median 50% reduction in their baseline daily OCS dose compared to 0% in the placebo group (P=0.007).

3. Despite lower OCS usage, the mepolizumab group experienced a 32% relative reduction in the annualized rate of clinically significant asthma exacerbations compared to the placebo group.

4. Mepolizumab treatment yielded a statistically significant improvement in asthma control, with a mean difference in the Asthma Control Questionnaire-5 (ACQ-5) score of -0.52 (P=0.004) versus placebo.

Study Design

Design

RCT

Double-Blind

Sample

135

Patients

Duration

24 wk

Median

Setting

Multicenter

Population Patients with severe eosinophilic asthma requiring daily oral corticosteroid maintenance therapy (5-35 mg/day) and high-dose inhaled corticosteroids plus at least one additional controller.

Intervention 100 mg of mepolizumab administered subcutaneously every 4 weeks.

Comparator Matching subcutaneous placebo administered every 4 weeks.

Outcome Percentage reduction of the daily oral corticosteroid dose during weeks 20-24 compared to the baseline dose determined during the optimization phase.

Study Limitations

• The study was limited by a relatively short 24-week duration, which does not fully capture the long-term OCS-sparing effects or the durability of clinical improvement.

• The sample size (n=135) was relatively small, potentially limiting the power to detect differences in secondary outcomes like complete OCS cessation.

• The stringent patient selection criteria (e.g., OCS dependence and specific eosinophil thresholds) may limit the generalizability of these findings to the broader asthma population.

• The study design utilized a dose-optimization phase prior to randomization, which may not reflect real-world clinical practice settings.

Clinical Significance

The SIRIUS trial established mepolizumab as a validated, steroid-sparing therapeutic option for patients with severe eosinophilic asthma. By enabling substantial reductions in systemic glucocorticoid use, this therapy mitigates the significant risk of serious long-term adverse effects associated with chronic OCS therapy, while simultaneously improving asthma-related quality of life and exacerbation outcomes.

Historical Context

Before the introduction of IL-5 antagonists like mepolizumab, treatment options for patients with severe, refractory eosinophilic asthma were limited, often forcing patients to rely on chronic high-dose systemic oral corticosteroids, which carry significant long-term morbidity. The SIRIUS trial provided the pivotal evidence required to demonstrate the clinical utility of targeting eosinophilic inflammation through IL-5 inhibition to effectively reduce reliance on systemic steroids.

Guided Discussion

High-yield insights from every perspective

Med Student

Medical Student

What is the biological rationale for targeting Interleukin-5 (IL-5) with mepolizumab specifically in patients with severe asthma who are dependent on oral corticosteroids (OCS)?

Key Response

IL-5 is the primary cytokine responsible for the maturation, recruitment, and survival of eosinophils. While corticosteroids induce eosinophil apoptosis, patients with severe eosinophilic asthma often require high systemic doses to maintain control, leading to significant morbidity. Mepolizumab acts as a targeted alternative by neutralizing IL-5, thereby reducing the eosinophilic airway inflammation that necessitates OCS use.

Resident

In the SIRIUS trial, what specific clinical and laboratory criteria defined the 'eosinophilic phenotype' required for enrollment, and how does this guide the selection of patients for mepolizumab in clinical practice?

Key Response

Participants were required to have a peripheral blood eosinophil count of at least 150 cells per microliter at screening or at least 300 cells per microliter in the preceding 12 months. This reflects the trial's finding that systemic eosinophil biomarkers are effective predictors of response to anti-IL-5 therapy, allowing residents to use simple CBC with differential to identify candidates for this biologic.

Fellow

The SIRIUS trial observed a reduction in OCS dose despite a relatively modest improvement in FEV1. How should this discrepancy influence the management of expectations when transitioning a patient to mepolizumab?

Key Response

Mepolizumab primarily impacts exacerbation frequency and OCS requirements rather than being a potent bronchodilator. The SIRIUS data show that while asthma control (ACQ-5) and OCS doses improved, the effect on FEV1 was not the primary driver of success. Fellows should counsel patients that the goal of therapy is 'stability and steroid reduction' rather than immediate or dramatic improvements in daily lung function tests.

Attending

Given the successful OCS tapering achieved in SIRIUS, what clinical vigilance is required regarding adrenal insufficiency and the potential unmasking of comorbid conditions like Eosinophilic Granulomatosis with Polyangiitis (EGPA)?

Key Response

SIRIUS demonstrated that OCS can be reduced by a median of 50%, but this rapid reduction can reveal underlying HPA-axis suppression or systemic vasculitides (like EGPA) that were previously controlled by high-dose steroids. Attendings must monitor for 'steroid withdrawal' symptoms and consider morning cortisol testing or a slower taper than the trial protocol might suggest in real-world, high-risk patients.

Scholarly Review

Critical appraisal through the lens of expert reviewers and guideline development

PhD

Critique the use of a 'forced' steroid-reduction algorithm as the primary endpoint in SIRIUS; how might this design choice introduce bias compared to a clinician-led, flexible tapering schedule?

Key Response

A standardized algorithm ensures internal validity by removing investigator discretion, but it may artificially inflate or deflate the steroid-sparing effect. If the algorithm is too aggressive, it might lead to more 'failures' (exacerbations), whereas if it is too conservative, it might underestimate the true potential for OCS elimination. The PhD researcher would look at the sensitivity of the 'failure' criteria used to stop a taper.

Journal Editor

What is the editorial significance of the 2.39 odds ratio for OCS reduction in the mepolizumab group, and how does the choice of a rank-based OCS reduction scale impact the 'clinical meaningfulness' of the study's primary conclusion?

Key Response

Editors look for more than just statistical significance. The use of an ordinal scale for OCS reduction (categorized percentage decreases) is a robust way to handle non-normal data distribution in tapering trials. However, a reviewer would flag whether the 'reduction' resulted in a total dose low enough to actually reduce the long-term risk of osteoporosis or metabolic syndrome (e.g., getting below 5-7.5mg/day).

Guideline Committee

Based on the SIRIUS findings, how should the strength of recommendation for anti-IL-5 therapy be adjusted in GINA Step 5 for OCS-dependent patients compared to other 'add-on' therapies like tiotropium?

Key Response

Current GINA guidelines emphasize biologics for patients with a demonstrated type-2 inflammatory phenotype. SIRIUS provides high-level (Level A) evidence that mepolizumab is specifically effective for OCS sparing, a benefit not robustly shared by tiotropium. This evidence justifies prioritizing biologics earlier in the Step 5 pathway for patients specifically to mitigate the cumulative toxicity of systemic steroids.

Clinical Landscape

Noteworthy Related Trials

2014

MENSA Trial

n = 576 · NEJM

Tested

Mepolizumab 75mg IV or 100mg SC

Population

Patients with severe eosinophilic asthma

Comparator

Placebo

Endpoint

Annualized rate of clinically significant asthma exacerbations

Key result: Mepolizumab significantly reduced the rate of clinically significant exacerbations compared to placebo.

2014

ZEST Trial

n = 385 · Lancet Respir Med

Tested

Mepolizumab 75mg IV

Population

Patients with severe eosinophilic asthma requiring maintenance OCS

Comparator

Placebo

Endpoint

Reduction in daily OCS dose

Key result: Patients receiving mepolizumab achieved greater reductions in maintenance oral corticosteroid dose compared to those receiving placebo.

2017

CALIMA Trial

n = 1356 · Lancet

Tested

Benralizumab 30mg SC

Population

Patients with severe, uncontrolled asthma

Comparator

Placebo

Endpoint

Annual asthma exacerbation rate

Key result: Benralizumab significantly reduced exacerbations and improved lung function in patients with blood eosinophil counts of 300 cells per microliter or greater.

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