The BTS/SIGN guideline recommends that people with asthma who require treatment with high dose ICS or the addition of a fourth medicine for their asthma symptoms are referred to specialist services. 

Severe asthma is defined as asthma that does not get better even when the patient takes their usual medicines regularly and correctly and when other causes and triggers for the symptoms have been ruled out. Between five and 10 per cent of people with asthma have severe, difficult-to-control asthma. Specialist treatments include:

1. Omalizumab, a humanised monoclonal antibody which reduces the levels of free serum IgE. It is given by subcutaneous injection and is licensed for people over six years old 
2. Mepolizumab, an anti-interleukin-5 humanised monoclonal antibody which reduces circulating eosinophils 
3. Reslizumab, an interlukin-5 inhibitor which reduces eosinophil numbers and activity 
4. Immunosuppressants, such as methotrexate, ciclosporin and oral gold, which may be trialled once other treatments have been unsuccessful, as there is no evidence of persisting beneficial effect after stopping them and there is marked variability in response 
5. Bronchial thermoplasty, a procedure where heat is applied using radiofrequency to the inside of the airways, reducing the thickness of smooth muscle tissue.

The aim of these treatments is to reduce the patient’s steroid requirements. The side effect profiles of these treatments are much better than that of long-term exposure to steroid tablets, which can cause obesity, diabetes and osteoporosis.