Maj Christensen and Dr. Ott are physicians at Eglin Air Force Hospital in Valparasio, Florida.
Author disclosures The authors report no actual or potential conflicts of interest with regard to this article.
Disclaimer The opinions expressed herein are those of the authors and do not necessarily reflect those of Federal Practitioner, Frontline Medical Communications Inc., the U.S. Government, or any of its agencies. This article may discuss unlabeled or investigational use of certain drugs. Please review the complete prescribing information for specific drugs or drug combinations—including indications, contraindications, warnings, and adverse effects—before administering pharmacologic therapy to patients.
Recent asthma research has been focused on disrupting the inflammatory cascade. Both GINA and ERS/ATS divide asthma into allergic vs nonallergic endotypes. Allergic asthma usually is manifested by sputum eosinophilia and high serum eosinophil counts, whereas other endotypes include aspirin-sensitive and exercise-induced asthmas that present with a neutrophilic predominance. Nonallergic asthma is more severe typically and has been linked to steroid resistance.17 Many differentphenotypes have been identified, but the main categories include eosinophilic, neutrophilic, mixed, and paucigranulocytic.18
Mast cells, bronchial epithelium, and macrophages are involved in asthma progression. Targeting the cytokines produced by these pathways can be achieved through direct and indirect modulation. Interleukin (IL)-13 is central to development of AHR, and its effect is mediated through binding to its receptor and IL-4 receptor α complexes.19 Patients with severe asthma with an eosinophilic phenotype can benefit with the use of the new biologics, which decrease the amount of eosinophilia in lung tissue by blocking specific receptors for IL-5.
Omalizumab, an anti-immunoglobulin E (IgE) antibody, has been shown to be helpful in treating patients with allergic asthma. Omalizumab is a 95% humanized IgE monoclonal antibody (MAB) that binds to the IgE molecule at the fc region and prevents IgE from binding to cell-surface receptors. In a humanized MAB, only the hypervariable regions are from mouse origin vs the newer completely human MABs. Omalizumab forms small, biologically inert IgE+ anti-IgE complexes that cannot activate the complement cascade. The serum free IgE level is decreased.20 Approved in 2003 for those aged ≤ 12 years, its use is restricted to patients with severe asthma, allergic sensitization (positive allergen skin testing), and an elevated serum IgE level (30-700 IU/mL). It is administered subcutaneously every 2 to 4 weeks, based on body weight and serum IgE levels.
For those with baseline eosinophil counts > 300 µL, addition of omalizumab most likely has been shown to improve quality of life (QOL) and reduce exacerbations, the use of rescue medications, ICS dosages, and ED visits.21-26 The most dangerous adverse effect (AE) was found to be an anaphylaxis rate of 0.09%, most frequently occurring in the first 2 hours after the first dose. Therefore, the patient must be monitored for 2 hours after the first dose and 30 minutes after subsequent doses. Epinephrine injection also should be prescribed. Although a 5-year prospective cohort study and retrospective pooled analysis of more than 10,000 patients did not support any relationship with malignancy.27,28 A higher incidence of cardiovascular and cerebrovascular AEs has been observed, and the FDA issued a safety announcement regarding this finding.29
Both ERS/ATS and GINA 2016 recommended that a therapeutic trial of omalizumab should be performed in all patients with severe confirmed IgE dependent allergic asthma.4,5 If there is no response in 4 months, it is unlikely that further administration would be beneficial.
Mepolizumab
Interleukin-5 is a key cytokine in the eosinophil life pathway. There are receptors for IL-5 on eosinophils, basophils, and β cells.30 Mepolizumab is an anti-IL-5 antibody for those with refractory eosinophilic asthma and a history of continued exacerbations. It has beneficial effects in the management of persistent airways eosinophilia among corticosteroid-resistant subjects. In a 2009 study, rates of exacerbations at 50 weeks were significantly lower than with placebo (2.0 vs 3.4 mean exacerbations per subject, 95% confidence interval [CI], 0.32-0.92; P = .002) as were eosinophil counts in blood and sputum (P < .001 and P = .002 respectively.31 A 2014 randomized, double-blind trial by Ortega and colleagues demonstrated reduction in rate of asthma exacerbations (primary outcome) to 47% (95% CI, 29-61) among patients receiving IV dosing and 53% (95% CI, 37-65) in the oral mepolizumab group (P < .001 for both groups, n = 576).32
In addition, there is significant data to show that even if the patient did not respond to omalizumab, he or she might still respond to mepolizumab. Data were collected from 2 randomized, double-blind, placebo-controlled studies with rate of exacerbation and percentage reduction in oral corticosteroid dose as the primary outcomes. In one of the studies (n = 576), the subjects were noted to have prior omalizumab use but still decreased exacerbation rate by 57%.33
Reslizumab
Reslizumab also is an FDA-approved anti-IL-5 antibody. It binds directly to IL-5 and prevents it from binding to eosinophils.34 For adults with severe eosinophilic asthma and refractory exacerbations, the goal of reslizumab therapy is to reduce eosinophil maturation, recruitment, and activation. Reslizumab is delivered in a weight-based IV dose (3 mg/kg) every 4 weeks. The FDA has issued a boxed warning for a 0.3% anaphylaxis rate.35 The most common AEs are elevated creatinine kinase, musculoskeletal pain, and oropharyngeal pain. Use of reslizumab resulted in greater reduction in sputum eosinophils, improvements in airway function, and a trend toward greater asthma control compared with that of placebo.34
