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Drug allergiesDefinition Drug allergies are a group of symptoms caused by allergic reaction to a drug (medication). Causes, incidence, and risk factors In general, adverse reactions to drugs are not uncommon, and almost any drug can cause an adverse reaction. Reactions range from irritating or mild side effects such as nausea and vomiting, to allergic reactions, including life-threatening anaphylaxis. Some drug reactions are idiosyncratic (unusual effects of the medication). For example, aspirin can cause nonallergic hives (no antibodies formed), or it may trigger asthma. Only a small proportion of these reactions are allergic in nature. Many individuals may confuse an uncomfortable but not serious side effect of a medicine, such as nausea, with a true drug allergy, which can be life-threatening. True drug allergies occur when there is an allergic reaction to a medication. This is caused by hypersensitivity of the immune system, leading to an incorrect response against a substance that is harmless in most people. The body becomes sensitized (the immune system is triggered) by the first exposure to the medication. The second or subsequent exposure causes an immune response, including the production of antibodies and release of histamine. Most drug allergies cause minor skin rashes and hives. However, other symptoms occasionally develop and life-threatening acute allergic reaction involving the whole body (anaphylaxis) can occur. Serum sickness is a delayed type of drug allergy that occurs a week or more after exposure to a medication or vaccine. Penicillin and related antibiotics are the most common cause of drug allergies. Other common allergy-causing drugs include sulfa drugs, anticonvulsants, insulin preparations (particularly animal sources of insulin), local anesthetics such as Novocain, and iodine (found in many x-ray contrast dyes). Symptoms
Symptoms of anaphylaxis include:
Signs and tests An examination of the skin and face may show hives, rash, or angioedema (swelling of the lips, face, or tongue). Decreased blood pressure, wheezing, and other signs may indicate an anaphylactic reaction. Skin testing may confirm allergy to penicillin-type medications. Testing may be ineffective (or in some cases, dangerous) for other medications. A history of allergic-type reaction after use of a medication is often considered proof enough of drug allergy -- no further testing is required. The same applies to other substances that are not considered drugs but are used in hospitals, such as x-ray contrast dyes. Treatment The treatment goal is relief of symptoms and preventing a severe reaction. Antihistamines usually relieve mild symptoms (rash, hives, itching). Topical (applied to a localized area of the skin) corticosteroids may also be recommended. Bronchodilators such as albuterol may be prescribed to reduce asthma-like symptoms (moderate wheezing or cough). Epinephrine by injection may be necessary to treat anaphylaxis. The offending medication should be avoided. Health care providers -- including dentists and hospital personnel -- should be advised of drug allergies before treating the allergic patient. Identifying jewelry or cards (such as Medic-Alert or others) may be advised. Occasionally, a penicillin allergy responds to desensitization (immunotherapy) in which increasing doses (each dose of the drug is slightly larger than the previous dose) are given to improve tolerance of the drug. This should only be done by a doctor. Expectations (prognosis) Most drug allergies respond readily to treatment. A few cases cause severe asthma, anaphylaxis, or death. Complications
Calling your health care provider Call your health care provider if you are taking a medication and seem to be having a reaction to it. Go to the emergency room or call the local emergency number (such as 911) if you have difficulty breathing or develop other symptoms of severe asthma or anaphylaxis (see above). These are emergency conditions! Prevention There is no known way to prevent development of a drug allergy. In people who have a known drug allergy, avoiding the medication is the best means to prevent an allergic reaction. In some cases, a doctor may recommend pre-treatment. The medication may be given safely after pre-treatment with corticosteroids (such as prednisone) and antihistamines (such as diphenhydramine). Illustrations
Page Content: Allergic reaction - drug (medication) |
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