Hyposensitisation

Synonyms: desensitisation, allergen immunotherapy

During hyposensitisation the aim is to expose a patient with sensitivity to a known allergen, to progressively larger doses of the allergen so that the severity of their hypersensitive response is reduced or even abolished. There is evidence that immunotherapy is effective for hay fever and it has been shown that grass-pollen immunotherapy for 3-4 years is still effective 3 years after therapy being discontinued.¹ However, safety concerns mean there are limitations and restrictions to the use of immunotherapy.

• House dust mite
• Grass and tree pollen
• Animal dander (cat or dog)
• Wasp and bee venom

Points to note regarding the use of allergen immunotherapy

• There is inadequate evidence of the benefit from desensitisation to other allergens such as house dust, house dust mite, animal danders and foods and these are thus not recommended at present.
• Allergen immunotherapy is not effective in the treatment of atopic dermatitis, urticaria, or headaches and is potentially dangerous if used for food or antibiotic allergies.

• Allergen immunotherapy (also called allergy vaccine therapy) involves the administration of gradually increasing quantities of specific allergens to patients with IgE-mediated conditions until a dose is reached that is effective in reducing disease severity from natural exposure.⁴
• Progressive exposure to the allergen leads to IgG production rather than the IgE production which occurs in type 1 allergic responses.⁵
• Safe administration of allergen immunotherapy requires the immediate availability of a health care professional capable of recognising and treating anaphylaxis and the presence of cardiopulmonary resuscitation facilities.
• An observation period of one hour after injection is mandatory. If the patient develops any symptoms even if mild, they need to be observed until these completely resolve.
• Patients should not be taking beta-adrenergic blocking agents or ACEI when receiving immunotherapy because these drugs may mask early signs and symptoms of anaphylaxis and may make the treatment of anaphylaxis more difficult.⁶

Patients need to be referred to a specialist in immunotherapy. Diagnostic skin tests alone are unreliable and should only be used in conjunction with a detailed history of allergen exposure.

• Hyposensitisation may be effective in allergic rhinitis if sensitisation to a particular allergen can be proven.
• The benefit of hyposensitisation needs to be balanced against the significant risk of anaphylaxis, particularly in patients with asthma.
• An Australian review estimated the risk of mild effects at 1 in 1500 injections; near-fatal anaphylaxis one per million injections and death at one in 2.5 million injections.⁸

These mostly relate to the site of injection e.g.

• Itchiness
• Swelling
• Redness

• The allergen is given subcutaneously
• Recent studies have investigated the effects of sublingual allergen administration

There have been a number of studies that have observed the effects of sublingual grass pollen. For example, a randomised, double blind, placebo controlled trial testing sublingual grass pollen was associated with a significant decrease in symptoms and reduced the frequency of other treatment usage e.g. steroids.^7,9,10 There were no significant adverse events associated with this product.

A preparation called Grazax® to use in immunotherapy for grass pollen allergy is now licensed in the UK. The first dose is usually administered in clinic and can then continue unsupervised. It is taken for three to four months before the pollen season and therapy should continue (for up to 3 years). Adverse effects have been described and include oral itching and mild swelling.¹¹ Other sub-lingual preparations are undergoing further research, for example in food allergies.¹²