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 was still effective 3 years after being discontinued.¹ However, safety concerns led the UK Committee on the Safety of Medicines to make recommendations which have seriously limited and restricted the use of immunotherapy.

• House dust mite
• Grass pollen
• Cat
• Animal dander
• Wasp and bee venom

Points to note from CSM

• 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.
• 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.
• Safe administration of allergen immunotherapy requires the immediate availability of a health care professional capable of recognizing and treating anaphylaxis and 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 when receiving immunotherapy because these drugs may mask early signs and symptoms of anaphylaxis and may make the treatment of anaphylaxis more difficult.

Patients need to be referred to a specialist in immunotherapy. Unfortunately at present there are few consultants in this field. 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.⁶

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 recent randomized, 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.^7,5There were no significant adverse events associated with this product. This may well become a commonly used administration method - but further research is currently required.