Pharmacotherapeutic group: Drugs for obstructive airway diseases, other systemic drugs for obstructive airway diseases, ATC code: R03DX09.
Mechanism of action
Mepolizumab is a humanised monoclonal antibody (IgG1, kappa), which targets human interleukin‑5 (IL‑5) with high affinity and specificity. IL‑5 is the major cytokine responsible for the growth and differentiation, recruitment, activation and survival of eosinophils. Mepolizumab inhibits the bioactivity of IL‑5 with nanomolar potency by blocking the binding of IL‑5 to the alpha chain of the IL‑5 receptor complex expressed on the eosinophil cell surface, thereby inhibiting IL‑5 signalling and reducing the production and survival of eosinophils.
Pharmacodynamic effects
In patients with severe refractory eosinophilic asthma (adults/adolescents), following a dose of 100 mg administered subcutaneously every 4 weeks for 32 weeks, blood eosinophils were reduced from a geometric mean count at baseline of 290 to 40 cells/μL at week 32 (n=182), a reduction of 84% compared to placebo. This magnitude of blood eosinophils reduction was maintained in severe refractory eosinophilic asthma patients (n=998) treated for a median of 2.8 years (range 4 weeks to 4.5 years) in open-label extension studies.
In children aged 6 to 11 years old with severe refractory eosinophilic asthma administered mepolizumab subcutaneously every 4 weeks for 52 weeks, blood eosinophils were reduced from a geometric mean count at baseline to week 52 of 306 (n=16) to 48 (n=15) following 40 mg (for a weight < 40kg) and 331 to 44 cells/µL (n=10) following 100 mg (for a weight ≥ 40 kg), a reduction from baseline of 85% and 87%, respectively.
In adults, adolescents and children, this magnitude of reduction was observed within 4 weeks of treatment.
Immunogenicity
Consistent with the potentially immunogenic properties of protein and peptide therapeutics, patients may develop antibodies to mepolizumab following treatment. In the placebo-controlled trials, 15/260 (6%) of adults and adolescents with severe refractory eosinophilic asthma treated with 100 mg dose , subcutaneously had detectable anti-mepolizumab antibodies after having received at least one dose of mepolizumab.
The immunogenicity profile of mepolizumab in severe refractory eosinophilic asthma patients (n=998) treated for a median of 2.8 years (range 4 weeks to 4.5 years) was similar to that observed in the placebo-controlled studies.
In children aged 6 to 11 years old with severe refractory eosinophilic asthma following either 40 mg subcutaneously (for a weight < 40kg) or 100 mg subcutaneously (for a weight ≥ 40 kg), 2/35 (6%) had detectable anti-mepolizumab antibodies after having received at least one dose of mepolizumab during the initial short phase of the study. No children had detectable anti-mepolizumab antibodies during the long-term phase of the study. Neutralising antibodies were detected in one adult patient with severe refractory eosinophilic asthma. Anti-mepolizumab antibodies did not discernibly impact the pharmacokinetics and pharmacodynamics of mepolizumab in the majority of patients and there was no evidence of a correlation between antibody titres and change in blood eosinophil level.
Clinical efficacy
The efficacy of mepolizumab in the treatment of a targeted group of patients with severe refractory eosinophilic asthma was evaluated in 3 randomised, double-blind, parallel-group clinical studies of between 24-52 weeks duration, in patients aged 12 years and older. These patients either remained uncontrolled (at least two severe exacerbations in the previous 12 months) on their current standard of care, including at least high doses of inhaled corticosteroids (ICS) plus an additional maintenance treatment(s), or were dependent on systemic corticosteroids. Additional maintenance treatments included long-acting beta2 -adrenergic agonists (LABA), leukotriene modifiers, long-acting muscarinic antagonists (LAMA), theophylline, and oral corticosteroids (OCS).
The two exacerbations studies MEA112997 and MEA115588 enrolled a total of 1192 patients, 60% females, with a mean age of 49 years (range 12– 82). The proportion of patients on maintenance OCS was 31% and 24%, respectively. Patients were required to have a history of two or more severe asthma exacerbations requiring oral or systemic corticosteroid treatment in the past 12 months and reduced lung function at baseline (pre-bronchodilator FEV1<80% in adults and <90% in adolescents). The mean number of exacerbations in the previous year was 3.6 and the mean predicted pre-bronchodilator FEV1 was 60%. Patients continued to receive their existing asthma medicinal product during the studies.
For the oral corticosteroid-sparing study MEA115575, a total of 135 patients were enrolled (55% were female; mean age of 50 years) who were being treated daily with OCS (5-35 mg per day), and high-dose ICS plus an additional maintenance medicinal product.
Dose-ranging efficacy MEA112997 (DREAM) study
In MEA112997, a randomised, double-blind, placebo-controlled, parallel-group, multi-centre study of 52 weeks duration in 616 patients with severe refractory eosinophilic asthma, mepolizumab significantly reduced clinically significant asthma exacerbations (defined as worsening of asthma requiring use of oral/systemic corticosteroids and/or hospitalisation and/or emergency department visits) when administered in doses of 75 mg, 250 mg or 750 mg intravenously compared to placebo (see Table 1).
Table 1: Frequency of clinically significant exacerbations at week 52 in the intent to treat population
| | Intravenous mepolizumab | Placebo |
| 75mg n=153 | 250mg n=152 | 750mg n=156 | n= 155 |
| Exacerbation rate/year | 1.24 | 1.46 | 1.15 | 2.40 |
| Percent reduction | 48% | 39% | 52% | |
| Rate ratio (95% CI) | 0.52 (0.39, 0.69) | 0.61(0.46, 0.81) | 0.48 (0.36, 0.64) | |
| p-value | <0.001 | <0.001 | <0.001 | - |
Exacerbation reduction MEA115588 (MENSA) study
MEA115588 was a randomised, double-blind, placebo-controlled, parallel-group, multi-centre study which evaluated the efficacy and safety of mepolizumab as add-on therapy in 576 patients with severe refractory eosinophilic asthma defined as peripheral blood eosinophils greater than or equal to 150 cells/μL at initiation of treatment or greater than or equal to 300 cells/μL within the past 12 months.
Patients received mepolizumab 100 mg administered subcutaneously, mepolizumab 75 mg administered intravenously or placebo treatment once every 4 weeks over 32 weeks. The primary endpoint was the frequency of clinically significant exacerbations of asthma and the reductions for both mepolizumab treatment arms compared to placebo were statistically significant (p<0.001). Table 2 provides the results of the primary and secondary endpoints for patients treated with subcutaneous mepolizumab or placebo.
Table 2: Results of primary and secondary endpoints at week 32 in the intent to treat population (MEA115588)
| | Mepolizumab 100 mg (subcutaneous) N= 194 | Placebo N= 191 |
| Primary endpoint |
| Frequency of clinically significant exacerbations |
| Exacerbation rate per year | 0.83 | 1.74 |
| Percent reduction Rate ratio (95% CI) | 53% 0.47 (0.35, 0.64) | - |
| p-value | <0.001 | |
| Secondary endpoints |
| Frequency of exacerbations requiring hospitalisations/emergency room visits |
| Exacerbation rate per year | 0.08 | 0.20 |
| Percent reduction Rate ratio (95% CI) | 61% 0.39 (0.18, 0.83) | _ |
| p-value | 0.015 | |
| Frequency of exacerbations requiring hospitalisation |
| Exacerbations rate per year | 0.03 | 0.10 |
| Percent reduction Rate ratio (95% CI) | 69% 0.31 (0.11, 0.91) | _ |
| p-value | 0.034 | |
| Pre-bronchodilator FEV1 (mL) at week 32 |
| Baseline (SD) | 1730 (659) | 1860 (631) |
| Mean change from baseline (SE) | 183 (31) | 86 (31) |
| Difference (mepolizumab vs. placebo) | 98 | |
| 95% CI | (11, 184) | |
| p-value | 0.028 | |
| St. George's Respiratory Questionnaire (SGRQ) at week 32 |
| Baseline (SD) | 47.9 (19. 5) | 46.9 (19.8) |
| Mean change from baseline (SE) | -16.0 (1.1) | -9.0 (1.2) |
| Difference (mepolizumab vs. placebo) | -7.0 | |
| 95% CI | (-10.2, -3.8) | |
| p-value | <0.001 | |
Reduction of exacerbation rate by baseline blood eosinophil count
Table 3 shows the results of a combined analysis of the two exacerbation studies (MEA112997 and MEA115588) by baseline blood eosinophil count. The rate of exacerbations in the placebo arm increased with increasing baseline blood eosinophil count. The reduction rate with mepolizumab was greater in patients with higher blood eosinophil counts.
Table 3: Combined analysis of the rate of clinically significant exacerbations by baseline blood eosinophil count in patients with severe refractory eosinophilic asthma
| | Mepolizumab 75 mg IV/100 mg SC N=538 | Placebo N=346 |
| MEA112997+MEA115588 |
| <150 cells/μL | | |
| n | 123 | 66 |
| Exacerbation rate per year | 1.16 | 1.73 |
| Mepolizumab vs. placebo | | |
| Rate ratio (95% CI) | 0.67 (0.46,0.98) | --- |
| 150 to <300 cells/μL | | |
| n | 139 | 86 |
| Exacerbation rate per year | 1.01 | 1.41 |
| Mepolizumab vs. placebo | | |
| Rate ratio (95% CI) | 0.72 (0.47,1.10) | --- |
| 300 to <500 cells/μL | | |
| n | 109 | 76 |
| Exacerbation rate per year | 1.02 | 1.64 |
| Mepolizumab vs. placebo | | |
| Rate ratio (95% CI) | 0.62 (0.41,0.93) | --- |
| ≥500 cells/μL | | |
| n | 162 | 116 |
| Exacerbation rate per year | 0.67 | 2.49 |
| Mepolizumab vs. placebo | | |
| Rate ratio (95% CI) | 0.27 (0.19,0.37) | --- |
Oral corticosteroid reduction study MEA115575 (SIRIUS)
MEA115575 evaluated the effect of mepolizumab 100 mg administered subcutaneously on reducing the requirement for maintenance oral corticosteroids (OCS) while maintaining asthma control in subjects with severe refractory eosinophilic asthma. Patients had a blood eosinophil count of ≥150/μL at baseline or a blood eosinophil count of ≥300/μL in the 12 months prior to screening. Patients were administered mepolizumab or placebo treatment once every 4 weeks over the treatment period. Patients continued to receive their existing asthma medicinal product during the study with the exception of their OCS dose which was reduced every 4 weeks during the OCS reduction phase (Weeks 4-20), as long as asthma control was maintained.
A total of 135 patients were enrolled: mean age was 50 years, 55% were female, and 48% had been receiving oral steroid therapy for at least 5 years. The baseline mean prednisone equivalent dose was approximately 13 mg per day.
The primary endpoint was the percent reduction in daily OCS dose (weeks 20-24), whilst maintaining asthma control by defined dose reduction categories (see Table 4). Predefined categories included percent reductions ranging from 90-100% reduction, to no decrease in the prednisone dose from the end of the optimisation phase. The comparison between mepolizumab and placebo was statistically significant (p=0.008).
Table 4: Results of the primary and secondary endpoints in MEA115575
| | ITT Population |
| | Mepolizumab 100 mg (subcutaneous) N= 69 | Placebo N= 66 |
| Primary endpoint |
| Percent reduction in OCS from baseline (weeks 20-24) |
| 90% - 100% 75% - <90% 50% - <75% >0% - <50% No decrease in OCS/lack of asthma control/ withdrawal from treatment | 16 (23%) 12 (17%) 9 (13%) 7 (10%) 25 (36%) | 7(11%) 5 (8%) 10 (15%) 7 (11%) 37 (56%) |
| Odds ratio (95% CI) | 2.39 (1.25, 4.56) | |
| p-value | 0.008 | |
| Secondary endpoints (weeks 20-24) |
| Reduction in the daily OCS dose to 0 mg/d | 10 (14%) | 5 (8%) |
| Odds ratio (95% CI) | 1.67 (0.49, 5.75) | |
| p-value | 0. 414 | |
| Reduction in the daily OCS dose to ≤5mg/day | 37 (54%) | 21 (32%) |
| Odds ratio (95% CI) | 2.45 (1.12, 5.37) | |
| p-value | 0.025 | |
| Median % reduction in daily OCS dose from baseline (95% CI) | 50.0 (20.0, 75.0) | 0.0 (-20.0, 33.3) |
| Median difference (95% CI) | -30.0 (-66.7, 0.0) | |
| p-value | 0.007 | |
Open-label extension studies in severe refractory eosinophilic asthma MEA115666 (COLUMBA), MEA115661 (COSMOS) and 201312 (COSMEX)
The long-term efficacy profile of mepolizumab in severe refractory eosinophilic asthma patients (n=998) treated for a median of 2.8 years (range 4 weeks to 4.5 years) in open-label extension studies MEA115666, MEA115661 and 201312 was generally consistent with the 3 placebo-controlled studies.
Paediatric population
In MEA115588 and in the double-blind placebo-controlled study 200862, there were 34 adolescents (12 to 17 years old). Of these 34 subjects: 12 received placebo, 9 received mepolizumab 75 mg intravenously, and 13 received 100 mg subcutaneously. In a combined analysis of these studies, a 40% reduction in clinically significant exacerbations was observed in adolescents following mepolizumab treatment compared to placebo (rate ratio 0.60; 95% CI: 0.17, 2.10).