Allergic reactions


Allergic reactions are sensitivities to a specific substance, called an allergen, which is contacted through the skin, inhaled into the lungs, swallowed, or injected. They are fairly common; approximately 50 million Americans suffer from some form of allergic disease, and the incidence is increasing.
Some allergic reactions may be mild enough to treat at home while others are severe and life-threatening. First time exposure to a potential allergen may only produce a mild reaction, but once a person is sensitized, repeated exposure may lead to more severe reactions.
An allergic reaction may be a side effect of drugs, certain foods or drinks, various chemicals or environmental factors, which involves immunologic mechanisms (the immune system's distinction of self from nonself). Common allergens may include: plants, pollens, animal danders, bee stings, insect bites, medications, nuts and shellfish.
Certain agents are most often responsible for allergic reactions in surgical patients. These include neuromuscular blocking agents, latex, colloids, hypnotics, antibiotics, benzodiazepines (anti-anxiety agents), opioids (often used to treat pain or for sleep induction), local anesthetics, intravenous (IV) contrast media (a diagnostic tool), and blood products. The antibiotics most commonly associated with allergic reactions are the sulfonamides, penicillins, and cephalosporins.
Anaphylaxis is the most severe form of allergic reaction. It can present as an acute, life-threatening reaction with multiple organ system involvement or it can be more localized in appearance. Approximately 1 in every 2,700 hospitalized patients experience drug-induced anaphylaxis. If antibodies are not involved in the process, the reaction is termed anaphylactoid. However, it is not possible to distinguish between anaphylactic and anaphylactoid reactions through clinical observation.

Related Terms

Allergen, allergy, anaphylactoid, anaphylaxis, antibody, bronchospasm, chemotactic factors, cytotoxic reaction, histamine, hives, IgE, IgG, IgM, immune complex, immunoglobulin, latex allergy, penicillin allergy.

classification of allergic reactions

Allergic reactions can be classified into four immunopathologic categories using various classification systems. These classifications are based on the immune system's response to the allergen, not on the severity of the reaction.
Type I: This classification involves a certain immunoglobulin (antibody), known as IgE, which is specific for the drug, antigen, or other allergen that initiates the allergic reaction. The allergen binds to the immunoglobulin on specific immune cells known as basophils and mast cells. This binding results in the release of chemicals that cause inflammation in the body within 30 minutes of the allergen, such as histamine, serotonin, proteases, bradykinin generating factor, chemotactic factors from various immune cells, leukotrienes, prostaglandins and thromboxanes. This type of allergic reaction is often seen with penicillin, latex, blood products and vaccines, among other allergens.
Type II: This classification is known as a cytotoxic reaction, involving destruction of the host cells. An antigen associated with a specific cell initiates cytolysis of the cell by an antigen-specific antibody, such as IgG or IgM. This reaction often involves blood elements such as red blood cells, white blood cells, and platelets. It often occurs within five to twelve hours of the allergen, which may include penicillin, quinidine, phenylbutazone, thiouracils, sulfonamides, or methyldopa.
Type III: This category involves the formation of an antigen-antibody immune complex, which deposits on blood vessel walls and activates cell components known as complements. This causes a serum-sickness like syndrome, involving fever, swelling, skin rash, and enlargement of the lymph nodes, in about three to eight hours. It may be caused by a variety of allergens, including penicillins, sulfonamides, intravenous (IV) contrast media, and hydantoins.
Type IV: This classification involves delayed cell mediated reactions. Antigens on the allergen release inflammatory mediators in 24 to 48 hours. This type of reaction is seen with graft rejection, latex contact dermatitis, and tuberculin reaction.