- Aust Prescr 2003;26:146-51
- 1 December 2003
- DOI: 10.18773/austprescr.2003.110
vials containing 150 mg as powder for reconstitution for injection
Approved indication: asthma
Australian Medicines Handbook section 14.1.4
Inflammation of the airways plays an important part in the pathogenesis of asthma. Allergens stimulate the production of IgE which then binds to mast cells resulting in the release of inflammatory mediators. Omalizumab is a recombinant monoclonal antibody which forms complexes with free IgE to prevent it binding to mast cells.
The concentration of free IgE is reduced within a few hours of a subcutaneous injection, even though it takes six to ten days for the drug to reach its peak plasma concentration. As well as slow absorption omalizumab has a slow clearance. Its half-life is approximately three weeks. Some patients may only need one injection a month depending on their weight and IgE concentration.
Two doses of intravenous omalizumab were compared with placebo injections in 317 patients who required corticosteroids for the control of allergic asthma. After a period of dose titration, patients were injected every two weeks for 20 weeks. In the later part of the study attempts were made to reduce the patients' doses of corticosteroids. Treatment reduced the patients' free IgE concentrations by 95% and resulted in a reduction of asthma symptoms. Half the patients given omalizumab were able to reduce their dose of inhaled steroids and 33-43% of those taking oral steroids were able to stop them. During the study period there were fewer exacerbations in the patients receiving omalizumab.1
Another study also found that subcutaneous omalizumab reduced exacerbations and enabled some patients to reduce or stop their inhaled corticosteroids.2
Omalizumab is generally well tolerated, but as it is a protein there is a risk of anaphylaxis and other allergic reactions. The most common adverse effects are reactions at the injection site.
Although omalizumab improves the symptoms of asthma it does not have a profound effect on lung function. In the trial of intravenous omalizumab FEV1 increased by approximately 2%, while subcutaneous omalizumab resulted in a 4% improvement.
Omalizumab is only approved for subcutaneous injection into patients with moderate allergic asthma who have a raised IgE concentration and are already taking steroids. It is therefore not indicated for the majority of patients with asthma who have a normal IgE concentration and no history of allergy. Childhood asthma often has an allergic component, however, although omalizumab has been studied in children3, it is not approved for patients less than 12 years old.