The quality of evidence is downgraded by study limitations (unclear allocation concealment and blinding).
A Cochrane review (abstract , review [Abstract]) included 25 studies with a total of 6 382 subjects with asthma. 19 studies considered the efficacy of subcutaneous anti-IgE treatment as an adjunct to treatment with corticosteroids.
Treatment with subcutaneous omalizumab resulted in fewer exacerbations overall (table T1). This effect was maintained during the steroid stable and steroid reduction phases of the included trials but with much greater uncertainty when only participants with severe disease were considered. In participants with severe asthma and receiving background inhaled plus oral steroid therapy, subcutaneous omalizumab did not reduce exacerbations compared with placebo (OR 1.65, 95% CI 0.66 to 4.13; 1 study, n=95). Subcutaneous omalizumab reduced hospitalisations during steroid stable phase; no separate data on hospitalisations were available for the severe asthma subgroup.
| Outcomes | Relative effect(95% CI) | Assumed risk (control) | Corresponding risk (omalizumab) | Participants (studies) |
|---|---|---|---|---|
| Participants with at least one exacerbation (all asthmatic participants; 16 to 60 weeks) | OR 0.55 (0.46 to 0.65) | 262 per 1000 | 163 per 1000(130 to 176) | 3 261(10 studies) |
| Participants with at least one exacerbation (moderate to severe asthma; 16 to 60 weeks) | OR 0.5 (0.42 to 0.6) | 274 per 1000 | 159 per 1000(137 to 185) | 2 889(7 studies) |
| Participants with at least one exacerbation (severe asthma; 16 to 32 weeks) | OR 1 (0.5 to 1.99) | 145 per 1000 | 145 per 1000(78 to 252) | 277(2 studies) |
| Mortality (16 to 60 weeks) | OR 0.19 (0.02 to 1.67) | 2 per 1000 | 0 per 1000(0 to 3) | 4 245(9 studies) |
| Hospitalisations (28 to 60 weeks) | OR 0.16 (0.06 to 0.42) | 31 per 1000 | 5 per 1000(2 to 13) | 1 824(4 studies) |
| Serious adverse events (16 to 60 weeks) | OR 0.72 (0.57 to 0.91) | 64 per 1000 | 47 per 1000(37 to 58) | 5 713(15 studies) |
Participants treated with subcutaneous omalizumab were significantly more likely to be able to withdraw their ICS completely than those treated with placebo (table T2). However, no significant difference between omalizumab and placebo treatment groups was seen in the number of participants who were able to withdraw from oral corticosteroid therapy (OR 1.18, 95% CI 0.53 to 2.63; 1 study, n=95).
| Outcomes | Relative effect(95% CI) | Assumed risk (control) | Corresponding risk (omalizumab) | Participants (studies) |
|---|---|---|---|---|
| *Moderate asthma; no trials included participants with severe asthma that contributed to this outcome. | ||||
| Number of participants achieving complete inhaled steroid withdrawal (28 to 32 weeks) | OR 2.5 (2 to 3.13) | 212 per 1000 | 402 per 1000(350 to 457) | 1 634(4 studies) |
| >50% reduction in inhaled steroid usage (28 to 32 weeks) | OR 2.5 (2.02 to 3.1) | 560 per 1000 | 761 per 1000(720 to 798) | 1 634(4 studies) |
| Exacerbations requiring hospitalisation (28 weeks)* | OR 0.11 (0.03 to 0.48) | 20 per 1000 | 3 per 1000(1 to 11) | 1 405(3 studies) |
Participants treated with subcutaneous omalizumab as an adjunct to treatment with corticosteroids required a small but significant reduction in rescue beta2-agonist medication compared with placebo (MD -0.39 puffs per day, 95% CI -0.55 to -0.24 puffs per day; 9 studies, n=3524). This benefit was observed in both the moderate to severe and severe asthma subgroups. However, no significant difference was noted for this outcome in participants with severe asthma who were receiving a background therapy of inhaled plus oral corticosteroids.
Significantly fewer serious adverse events were reported in participants assigned to subcutaneous omalizumab than in those receiving placebo (table T1), but more injection site reactions were observed (5.6% with placebo and 9.1% with omalizumab).
Many studies included participants with moderate asthma, and omalizumab is not licenced for this group. More studies need to focus on whether omalizumab is effective in people with the most severe asthma; evidence for efficacy in this group is poor.
Very few studies have explored efficacy in children with moderate to severe asthma.
It is not clear whether there is a threshold level of baseline serum IgE for optimum efficacy of omalizumab.
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