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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.

Commonest allergens administered worldwide
Indications

The Committee on Safety of Medicines have advised that hyposensitisation should only be used for the following indications:2

  • Seasonal allergic hay fever - that not responding to anti-allergy medication but not in asthmatic patients as this group are more likely to have a severe reaction.3
  • Hypersensitivity to wasp and bee venoms - asthmatics not excluded as the reaction is potentially life-threatening. Except for wasp and bee sting allergy, specific hyposensitisation with allergen extract vaccines has usually shown little benefit in asthma.

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.
Method
  • 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.
Investigations5

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.

Benefits and risks
  • 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

Contraindications

Desensitising vaccines should be avoided in:

  • Pregnant women
  • Children under five years old
  • In those taking beta-blockers (may render adrenaline ineffective in hypersensitivity)
  • Patients on ACEI - can develop severe anaphylactoid reactions

Adverse reactions

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

  • Itchiness
  • Swelling
  • Redness
Administration
  • The allergen is given subcutaneously
  • Recent studies have investigated the effects of sublingual allergen administration
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.


Document References
  1. Durham SR, Walker SM, Varga EM, et al; Long-term clinical efficacy of grass-pollen immunotherapy. N Engl J Med. 1999 Aug 12;341(7):468-75. [abstract]
  2. British National Formulary British Medical Association and Royal Pharmaceutical Society of Great Britain. London.
  3. Abramson MJ, Puy RM, Weiner JM; Allergen immunotherapy for asthma. Cochrane Database Syst Rev. 2003;(4):CD001186. [abstract]
  4. No authors listed; Immunotherapy. CMAJ. 2005 Sep 13;173(6 Suppl):S46-50.
  5. Douglass JA, O'Hehir RE; 1. Diagnosis, treatment and prevention of allergic disease: the basics. Med J Aust. 2006 Aug 21;185(4):228-33. [abstract]
  6. Weiner JM; Allergen injection immunotherapy. Med J Aust. 2006 Aug 21;185(4):234.
  7. Palma-Carlos AG, Santos AS, Branco-Ferreira M, et al; Clinical efficacy and safety of preseasonal sublingual immunotherapy with grass pollen carbamylated allergoid in rhinitic patients. A double-blind, placebo-controlled study. Allergol Immunopathol (Madr). 2006 Sep-Oct;34(5):194-8. [abstract]

Internet and Further Reading
  • No authors listed; Allergen immunotherapy: a practice parameter. American Academy of Allergy, Asthma and Immunology. American College of Allergy, Asthma and Immunology. Ann Allergy Asthma Immunol. 2003 Jan;90(1 Suppl 1):1-40.
  • Becker A, Lemiere C, Berube D, et al; Summary of recommendations from the Canadian Asthma Consensus guidelines, 2003. CMAJ. 2005 Sep 13;173(6 Suppl):S3-11.
AcknowledgementsEMIS is grateful to Dr Gurvinder Rull for writing this article. The final copy has passed scrutiny by the independent Mentor GP reviewing team. ©EMIS 2007.
DocID: 237
Document Version: 1
DocRef: bgp24948
Last Updated: 10 Aug 2007
Review Date: 9 Aug 2008

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