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Dermatitis, contact |
Dermatitis, pustular contact |
Drug rash, Tegretol |
Fixed drug eruption |
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Fixed drug eruption, bullous |
Fixed drug eruption on the cheek |
Drug rash on the back |
Antibodies |
Alternative
names
Allergic reaction - drug
(medication) Definition
A group
of symptoms caused by allergic reaction to a drug
(medication).
Causes
and risks 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 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. 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 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 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, 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, 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 known 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) and antihistamines (such
as diphenhydramine).
Symptoms
- hives (common)
- skin rash (common)
- itching of the skin
or eyes (common)
- wheezing
- swelling of the lips,
tongue, and/or face
- anaphylaxis, or severe
allergic reaction (see below)
Symptoms of anaphylaxis
include:
- difficulty breathing
with wheeze or hoarse voice
- hives over different
parts of the body
- fainting, light-headedness
- dizziness
- confusion
- rapid pulse
- sensation of feeling
the heart beat (palpitations)
- nausea, vomiting
- diarrhea
- abdominal pain or
cramping
Signs
and tests
An examination
of the skin and face may show hives, rash, or
angioedema (swelling of the lips, face, and/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 adequately
diagnostic for drug allergy. (No further testing
is required to demonstrate the allergy.)
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 prevent consequences
of a severe reaction, if present.
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, hospital personnel,
etc.) 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.
Prognosis
Most drug
allergies respond readily to treatment. A few
cases cause severe asthma or anaphylaxis. |
