Allergen immunotherapy (desensitisation treatment)

Allergen immunotherapy (sometimes called desensitisation treatment) is a treatment for allergy. It involves giving increasing doses of an allergen such as grass pollen, dust mite, or cat dander. 

The treatment can be given by injection (subcutaneous immunotherapy), or by drops placed under the tongue (oral immunotherapy). Unlike drug treatment which only suppresses symptoms, immunotherapy treatment works by re-programming the immune system to prevent allergy symptoms from developing in the first place.

• Allergic rhinitis
• Some stinging insects (such as wasps, bees)
• Severe hay fever
• Animal allergies  

• Food allergies
• Skin rashes – such as eczema

Immunotherapy treatment was first given by injection just under the skin and this treatment is still in use. It involves a series of these tiny injections. For example, hay fever treatment would require weekly or fortnightly doses given over 12–16 weeks in the first few months of the year. Clinical studies have shown that this form of treatment is helpful from year one, although it is usual to stop after three annual courses because most patients have by then acquired lasting benefit.

The main risk of immunotherapy is that the injections could cause a severe allergic reaction. Although this form of treatment is nowadays regarded as safe, such treatments should only be given in hospital clinics and a wait of one hour after each injection is recommended.

Oral (under the tongue) Immunotherapy has recently become the most widely practised form of desensitisation treatment in Europe although it has yet to become popular in the UK. In the treatment of hay fever, drops from a pipette are placed under the tongue and swallowed every day for a minimum of two months before, and then throughout, the grass pollen season. Clinical trials have demonstrated up to 60% reductions in symptom scores and medication requirements.

Other forms of allergic rhinitis and allergic asthma, for example due to cat or house dust mite allergy, can be treated in the same way and this form of treatment is backed by an extensive list of successful clinical trials and a World Health Organisation position paper.

Only minor side effects such as mouth itch or slight swelling have been reported. Neither severe reactions nor anaphylaxis have occurred. Even so, it is recommended that the first dose of any treatment course should be given in a specialist clinic, although the treatment can then be safely continued at home.

Copy written by Dr Michael Radcliffe, Consultant in Immunology & Allergy at Sarum Road Hospital.