Specific Allergen Immunotherapy (SIT), also known as ‘desensitisation’:

• is the process of injecting gradually increasing quantities of an allergen extract, which modifies the immune response
• can improve asthma control by reducing airway inflammation and bronchial hyper-responsiveness
• should be used in conjunction with allergen avoidance and appropriate use of medication
• should be initiated and supervised by a doctor with appropriate expertise such as an allergy specialist
• should be administered according to established guidelines and precautions
• is a long term (3-5 years) approach for selected patients.

Efficacy

Immunotherapy by injection has been shown to benefit selected individuals with asthma.¹¹⁸ This pertains to people with asthma who are allergic to house dust mite, cat and grass pollen.^{<LE I>} There is limited evidence for some weed and tree pollen and the mould Cladosporium.^{<LE 2>} Most patients with asthma have allergic rhinitis and SIT is also of proven efficacy in allergic rhinitis.^{<LE I>}

Other routes of immunotherapy such as high dose sublingual-swallow immunotherapy may provide some clinical benefits in selected subjects. However, the magnitude and duration of the effects compared to conventional subcutaneous immunotherapy, the benefit for asthma and the effects on the underlying immunological mechanisms remain to be determined. This form of treatment is not currently recommended.

Indications

All the following criteria need to be met for immunotherapy in asthma:

• A particular aeroallergen is confirmed to precipitate symptoms from the history and allergy testing.
• Asthma is stable and well controlled.
• An effective allergen extract is available.
• Patients or parents/guardians give informed consent.
• Further allergen exposure is unavoidable or only partially reducible.
• When there is significant allergic upper airway or ocular disease this strengthens the indication.

Contraindications

• Concomitant administration of beta blockers.
• Lack of expertise in immunotherapy and/or asthma management and/or equipment to manage acute asthma and/or anaphylaxis.
• Previous anaphylaxis to immunotherapy.
• Poorly controlled or brittle asthma.

Safety

Asthma needs to be monitored prior to, during and after immunotherapy. Spirometry or peak flow monitoring must be performed prior to and 30 minutes after injection. If it is less than 80% of the best recent reading for that patient the injection should be deferred.

Patients should be monitored for at least 30 minutes after immunotherapy.

Adverse reactions

Local reactions at the injection site are common. Systemic reactions are uncommon, but range from urticaria to bronchospasm and/or anaphylaxis (including hypotension, upper airway edema and collapse). The onset of a reaction is usually within 30 minutes of injection although delayed reactions may occur. Rarely, deaths have occurred as a consequence of SIT. These have usually occurred in individuals with asthma, with use of highly purified and potent aqueous extracts or where there has been a divergence from recommended protocols.

The administration of non-sedating antihistamines 1-2 hours before injections has been shown to reduce the risk of adverse reactions to immunotherapy. Nevertheless, dangerous reactions can still occur.

For more detailed information refer to the TSANZ and ASCIA position statement on Immunotherapy and asthma.¹¹⁸

Content Updated March 2005