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Drug Allergies
| Definition |
| A group of symptoms caused by allergic
reaction to a drug (medication). |
| Alternative names |
| allergic reaction to a drug
(medication) |
| Causes, incidence, and risk factors |
Drug allergies occur when there is an
allergic reaction to a medication. This is caused by hypersensitivity of
the immune system, leading to a misdirected response against a substance
that does not cause a response 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.
Reactions to drugs are uncommon, but almost any drug can cause an
adverse reaction. Reactions range from irritating or mild side effects
(such as nausea and vomiting), to allergic response 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.
"True" drug allergies involve the production of antibodies and
the release of histamine and other chemicals. 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,
barbiturates, anticonvulsants, insulin preparations (particularly animal
sources of insulin), local anesthetics such as Novocain, and iodine
(found in many X-ray contrast dyes). |
| Prevention |
| There is no known way to prevent
development of a drug allergy. In people who have a drug allergy,
avoiding the medication is the best means to prevent an allergic
reaction. In some cases, the medication may be given safely after
pre-treatment with corticosteroids (such as prednisone), antihistamines
(such as diphenhydramine), and/or epinephrine. |
| Symptoms |
- hives (common)
- skin rash (common)
- itching of the skin or eyes
(common)
- wheezing
- swelling of the lips or conductive
Symptoms of anaphylaxis include:
- nasal congestion
- difficulty breathing
- cough
- blueness of the skin (cyanosis),
including the lips or nail beds
- fainting, lightheadedness
- dizziness
- anxiety
- confusion
- slurred speech
- rapid pulse
- sensation of feeling the heart beat
(palpitations)
- nausea, vomiting
- diarrhea
- abdominal pain or cramping
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| Signs and tests |
An examination of the skin may show
hives, skin rash, or angioedema. Difficulty breathing, wheezing, and
other symptoms may indicate 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 adequately diagnostic for drug allergy. (No further testing
is required to demonstrate the allergy.) |
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