Drugs used to prevent and treat allergic conditions and allergic reactions
Antiallergy drugs are used in the treatment of a variety of allergic disorders, such as allergic conjunctivitis, hay fever (see Allergic rhinitis), and atopic eczema. Antiallergy drugs can be used to prevent an allergic response from occurring or to relieve the symptoms of allergy, such as sneezing.
Several groups of drugs are used to treat allergic reactions. The most commonly used are antihistamines, mast cell stabilizers, corticosteroids, leukotriene antagonists, allergen extracts, and the drug epinephrine (adrenaline).
These drugs are most commonly used to relieve the symptoms of hay fever, to treat allergic rashes such as urticaria, and to relieve itching due to insect bites. They block the action of histamine, a chemical that is released by the body in an allergic reaction.
These may be prescribed to prevent allergic reactions. The drugs block the release of histamine, a chemical that is stored in mast cells (a type of white blood cell present in blood and most body tissues). Histamine is released from these cells in allergic reactions. The most commonly used mast cell stabilizer is sodium cromoglicate, which is given for allergic conjunctivitis, hay fever, asthma in children, and exercise-induced asthma in adults. Since these drugs cannot be absorbed when taken orally, they are used topically as eyedrops, nasal sprays, or inhalers. The drugs are taken as preventive treatment; they do not relieve symptoms.
These drugs reduce inflammation caused by allergic reactions. They may be included in skin creams used to treat atopic eczema (see Topical corticosteroids) and in nasal sprays to relieve the symptoms of hay fever (see Corticosteroids for respiratory disease). For severe or persistent allergies, corticosteroids may be given orally or intravenously.
When used with corticosteroids, these drugs help to prevent asthma attacks. They block the action of leukotrienes, chemicals that cause airway inflammation in asthma.
Substances that can cause allergic reactions, such as bee venom or grass pollen, are called allergens. Tiny amounts of an allergen may be used to desensitize a person who has a severe allergy to that substance. The treatment is usually given as a series of weekly injections containing gradually increasing doses. Treatment may last for several months. Allergen extracts can themselves cause life-threatening allergic reactions and are given only where emergency treatment is available.
This drug is used to treat anaphylaxis, a life-threatening allergic reaction. The drug reverses the swelling of the throat, narrowing of the airways, and drop in blood pressure that occurs in anaphylaxis. Epinephrine is injected in repeated doses until the condition improves. If you are at risk of anaphylaxis because of a severe allergy, you should carry a syringe prefilled with epinephrine for emergency treatment (see Emergency aid for anaphylaxis).
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.