antihistamines

Definition

Antihistamines are drugs used to treat the symptoms of allergies and allergic rhinitis by blocking the action of histamine, a chemical released by the immune system in allergic reactions.

Description

Antihistamines are used to treat the sneezing, runny nose, and itchy eyes of allergies and allergic rhinitis, as well as allergic skin reactions and anaphylactic reactions to insect stings and certain foods. Antihistamines are available as prescription and over-the-counter tablets, topical preparations, nasal sprays, and eye drops.

Antihistamines work by blocking the effects of histamine, a chemical released by mast cells during an allergic response to an allergen. Histamine irritates and inflames the airways to produce sneezing and mucus production. Antihistamines attach to the areas on cells that histamines attach to, thereby blocking the allergic response.

Antihistamines are most effective when taken before exposure to an allergen. When used over time as an allergy treatment, antihistamines reduce the amount of histamine released by cells and decrease the likelihood that an allergic reaction will occur.

General use

Antihistamines are prescribed or recommended for infants, children, and adolescents with allergies and allergic rhinitis. Depending on the type of allergy, oral antihistamines may be taken regularly or seasonally to combat responses to allergens. Common allergens include dog and cat hair, dust mites, grass and tree pollen, and molds and mildew. For allergies that produce nasal symptoms, an antihistamine nasal spray may be used. For itchy eyes, antihistamine eye drops may be used.

Antihistamine tablets and topical creams, gels, sprays, or ointments are used to treat skin hives related to food allergies and itching and hives associated with allergic contact dermatitis and insect bites and stings.

In addition to treating allergies, some antihistamines have side effects that are used to treat other conditions. The strong sedating effect of some antihistamines is used to treat insomnia and difficulties in falling asleep. Some antihistamines also help inhibit nausea and vomiting and reduce motion sickness.

Commonly used antihistamines include the following:

• diphenhydramine (Benadryl)
• loratadine (Claritin)
• cetirizine (Zyrtec)
• fexofenadine (Allegra)
• clemastine fumarate (Tavist)
• chlorpheniramine (Chlor Trimeton)
• brompheniramine (Dimetapp)

Content licensed from:

Author Info: Jennifer E. Sisk MA, Thomson Gale, Gale, Detroit, Gale Encyclopedia of Children's Health, 2006

This feature is for informational purposes only and should not be used to replace the care and information received from your healthcare provider. Please consult a healthcare professional with any health concerns you may have.