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House dust mite allergy

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House dust mite allergy (Contd)

Reviewed by Dr Paul Klenerman, specialist and Professor Brian Lipworth, professor of allergies and respiratory medicine

Future prospects

If you are allergic to house dust mites, it is important that you don't expose yourself to the dust mite allergen because it increases your chances of developing asthma. The best remedy against house dust mites is described under the heading 'Good advice' above.

Your symptoms can be controlled by treatment, but you can't escape your hypersensitivity. If severe dust mite allergy is the only form of allergy you suffer from, your doctor may want to try hyposensitisation - a 'vaccination' against the allergen. This tolerance treatment involves regular allergen injections in increased doses over a period of five years, but is not routinely given and is not always successful.

What medicine is given?

Medicines for allergies include:

Antihistamine tablets or syrup (eg loratadine, cetirizine). These lessen the allergic reaction by blocking the actions of histamine. They relieve hayfever symptoms.

Nasal sprays or drops containing sodium cromoglicate, corticosteroids (eg beclometasone) or antihistamines (eg levocabastine). These can be used to reduce nasal inflammation and control symptoms in the nose.

Eye drops containing sodium cromoglicate, nedocromil, or antihistamines (eg azelastine) reduce eye inflammation and can be used if eye symptoms are a particular problem.

If the allergy causes asthmatic symptoms, some of the asthma medication below may be used

Relievers (bronchodilators): these are quick-acting medicines that relax the muscles of the airways. They are used when required to relieve shortness of breath.

Preventers: these act over a longer time and work by reducing the inflammation within the airways. They should be used regularly for maximum benefit. When the dosage and type of preventive medicine is correct, there will be little need for reliever medicines.

Relievers There are three groups of bronchodilators.

Beta-2 agonists Beta-2 agonists cause the airways to relax and widen. Examples of those which act for a short time (3 or 4 hours following a single dose) are salbutamol and terbutaline. These medicines are inhaled from a variety of delivery devices, the most familiar being the pressurised metered-dose-inhaler (MDI). When inhaled, these types of medicines work within minutes to open the airways, making breathing easier.

Longer-acting beta-2 agonists include salmeterol and formoterol. Their action lasts over 12 hours, making them suitable for twice daily dosage to keep the airways open.

Anticholinergics

One of the ways in which the size of the airways is naturally controlled is through nerves that connect to the muscles surrounding the airways. The nerve impulses cause the muscles to contract, thus narrowing the airway. Anticholinergic medicines such as ipratropium block this effect, allowing the airways to open. The size of this effect is fairly small, so it is most noticeable if the airways have already been narrowed by other conditions, such as chronic bronchitis.

Theophyllines and aminophylline

Theophylline and aminophylline are given by mouth and are less commonly used in Britain because they are more likely to produce side effects than inhaled treatment. They are still in very wide use throughout the world.

All three types of reliever can be combined if necessary.

Preventers

There are three main groups of anti-inflammatories.

Corticosteroids Corticosteroids (or 'steroids') work to reduce the amount of inflammation within the airways, reducing their tendency to contract. They are usually given as inhaled treatment, eg beclometasone, although sometimes oral steroid tablets may be required for severe attacks. Although steroids are powerful medicines with many potential side effects their safety in asthma has been well established. It is also important to balance the problems that arise from poorly treated asthma against the improvement in health which occurs when the condition is well treated.

Cromones

There are two kinds of cromones: sodium cromoglicate and nedocromil. They also act to reduce inflammation of the airways. They tend to be best for mild asthma symptoms and are more effective in children than adults. The medicines are given by inhalation and are usually very well tolerated.

Leukotriene receptor antagonists

Leukotriene receptor antagonists are compounds released by inflammatory cells within the lungs and which have a powerful constricting effect upon the airways. By blocking this effect with these antagonist medicines the constriction is reversed. There are two such medicines currently available: montelukast and zafirlukast.

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