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Drug allergy is the term for a group of symptoms caused by an allergic
reaction. An allergic reaction occurs when your immune system mistakes
the drug for a harmful substance and mounts an inflammatory response
that actually harms rather than protects you. Any medication — over-the-
counter, prescription or herbal — is capable of inducing a drug allergy.
However, a drug allergy is more likely with certain medications.
A drug allergy is not the same as drug side effects, the known
possible reactions that are listed on a drug label. A drug allergy is
also distinct from drug toxicity caused by an overdose of
medication.
When a harmful substance, such as a virus or bacteria, enters your body,
your immune system creates antibodies to fight off the invading infection.
An antibody is a special protein that’s programmed to destroy one specific
substance.
Antibodies are also called immunoglobulins. There are different kinds of
immunoglobulins. For example, immunoglobulin A (IgA) concentrates in
tears and saliva and helps to guard these entrances to the body. IgM is very
effective at marking bacteria as invaders and telling cells to kill them.
The immunoglobulin most often responsible for the symptoms of an
allergy is IgE. IgE tells your white blood cells to release histamine, which
in turn causes many of your symptoms.
Once your immune system has programmed antibodies to recognize and
defend against a specific substance, those antibodies are always ready to
multiply quickly and go to action whenever the substance is detected. This
is how you develop immunity to specific illnesses. It’s also how you
develop allergies to specific substances, such as a particular drug.
Anyone can develop an allergy to a drug or other substance. It can happen
at any age. You might become allergic to a drug you’ve used many times
before without any adverse reactions. The reasons why people develop
drug allergies are not fully understood. However, the following factors can
increase your risk:
a weakened immune system from conditions such as HIV/AIDS or
Epstein-Barr virus
other allergies
taking several drugs at the same time
taking frequent doses of the same medication
taking a drug that is similar to one you’ve previously had an allergic
reaction to
Who are at greater risk for a severe allergic reaction to a medication?
The people who involved by:
heart disease
asthma
high blood pressure
Drugs commonly linked to allergies
Although any drug can cause an allergic reaction, some drugs are more commonly associated with allergies. These include:
Antibiotics, such as penicillin Aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs) Chemotherapy drugs for treating cancer Medications for autoimmune diseases, such as rheumatoid arthritis Corticosteroid creams or lotions Medications for people with HIV or AIDS Bee pollen products Echinacea
The term drug allergy refers to a group of symptoms caused by allergic
reaction to a drug. Many drugs have side effects such as stomach upset or
headache; however, these symptoms do not indicate an allergic reaction.
As with other allergies, the symptoms may cause only mild discomfort, or
they may be severe and even life threatening.
Signs and symptoms of a drug allergy often occur within an hour after taking a drug. Less commonly, reactions can occur hours, days or weeks later.
Drug allergy symptoms may include:
Skin rash Hives Itching Fever Swelling Shortness of breath Wheezing Runny nose Itchy, watery eyes
Anaphylaxis is a rare, life-threatening reaction to a drug allergy that causes the widespread dysfunction of body systems. Signs and symptoms of anaphylaxis include:
Tightening of the airways and throat, causing trouble breathing Nausea or abdominal cramps Vomiting or diarrhea Dizziness or lightheadedness Weak, rapid pulse Drop in blood pressure Seizure Loss of consciousness
Anaphylaxis
Other conditions resulting from drug allergy
Less common drug allergy reactions occur days or weeks after exposure to a drug and may persist for some time after you stop taking the drug. These conditions include:
Serum sickness, which may cause fever, joint pain, rash, swelling and nausea
Drug-induced anemia, a reduction in red blood cells, which can cause fatigue, irregular heartbeats, shortness of breath and other symptoms
Drug rash with eosinophilia and systemic symptoms (DRESS), which results in rash, high white blood cell counts, general swelling, swollen lymph nodes and recurrence of dormant hepatitis infection
Inflammation in the kidneys (nephritis), which can cause fever, blood in the urine, general swelling, confusion and other symptoms
Nonallergic drug reactions
Sometimes a reaction to a drug can produce signs and symptoms virtually the same as those of a drug allergy, but it's not triggered by immune system activity. This condition is called a nonallergic hypersensitivity reaction or pseudoallergic drug reaction.
Drugs that are more commonly associated with this condition include:
Aspirin Dyes used in imaging tests (radiocontrast media) Opiates for treating pain Local anesthetics
Tests to Diagnose a Drug Allergy The first step in the diagnosis of drug allergy is a complete physical
examination. Your doctor will want to know if you have other allergies or
a family history of allergies. He or she will also want to know how long
you were using the drug before your reaction began and whether you had
used the drug before. You will be asked to describe your symptoms in
detail.
If possible, see your doctor while you are experiencing the reaction to a
drug. This will help your doctor make a diagnosis. If your doctor suspects
a drug allergy, they can perform several tests to confirm a diagnosis.
Skin Tests
For some drugs, an allergy skin test may determine whether or not you are
allergic to a substance. Depending on the drug, a doctor might perform a
skin-prick test or intradermal test.
During a skin-prick test, the doctor injects a small amount of the drug into
the skin—usually the back or forearm. If you are allergic, you will develop
redness, a bump, or other noticeable skin inflammation.
Intradermal tests can test for allergic reactions to penicillin and some other
antibiotics. During these tests, the doctor injects a small amount of the
allergen just under the skin, and monitors the site for a reaction.
Blood Tests
Blood tests can determine whether you are allergic to certain drugs. While
they are not as accurate as other test methods, a doctor might choose to do
Drug Allergy Treatments
There are several medications available to treat drug allergies.
Interventions for a drug allergy can be divided into two general
strategies:
• Treatment for the present allergy symptoms
• Treatment that may enable you to take an allergy-causing drug if
it's medically necessary
Treating current symptoms
The following interventions may be used to treat an allergic reaction to a drug:
Withdrawal of the drug. If your doctor determines that you have a drug allergy — or likely allergy — discontinuing the drug is the first step in treatment. In many cases, this may be the only intervention necessary.
Antihistamines. Your doctor may prescribe an antihistamine or recommend an over-the-counter antihistamine such as diphenhydramine (Benadryl) that can block immune system chemicals activated during an allergic reaction.
Corticosteroids. Either oral or injected corticosteroids may be used to treat inflammation associated with more-serious reactions.
Treatment of anaphylaxis. Anaphylaxis requires an immediate epinephrine injection as well as hospital care to maintain blood pressure and support breathing.
Antihistamines
For mild symptoms such as a rash, hives, and itching, over-the-counter
or first-generation antihistamines can be effective. These drugs may
cause drowsiness.
First generation antihistamines include:
brompheniramine
dimenhydrinate
diphenhydramine
doxylamine)
Second-generation antihistamines, which have fewer or no such effects,
are now recommended by many doctors. These include:
cetirizine
desloratadine
fexofenadine
loratadine
Bronchodilator
A bronchodilator can help when main symptoms include wheezing or
coughing. Examples of bronchodilators include:
albuterol
formoterol
salmeterol
theophylline
Corticosteroids
Corticosteroids can be taken by mouth, intravenous injection, or applied
directly to the skin. They act more slowly than antihistamines, but last
longer and can provide relief from some of the more serious symptoms of
a drug allergy. These include:
beclomethasone
fluticasone furoate
fluticasone propionate
mometasone