You should report any abnormal drug
reaction to your doctor. They will want to determine the underlying cause of
your symptoms in order to know whether your reaction is allergic or nonallergic.
According to the World
Allergy Organization (WAO), if you react to a drug with a noticeable
symptom, there is about a one in 10 chance that it is an allergic reaction. It
is important to know whether your reaction is allergic or nonallergic because
an allergic reaction may develop into life-threatening anaphylaxis in the
A nonallergic reaction might be a
side effect of the drug. A side effect is any secondary action of the drug that
might occur in a healthy person. These reactions can be either adverse or
beneficial. Most side effects are known before a drug is prescribed. (Your
doctor should tell you about any known side effects before prescribing a
Sometimes, a lower dose can reduce
or eliminate any negative side effects.
A nonallergic reaction can be an
idiosyncratic (unusual and unpredictable) reaction. This can occur after your
first exposure to a drug. Idiosyncratic reactions are not a typical side
effect, and are often due to a genetic or metabolic abnormality.
In some cases, your reaction to a
drug may closely mimic an allergic reaction. This is called a pseudoallergy or
sensitivity. In some cases, this is a known side effect of a medication. This
can occur during first use of a drug. For example, many people who take
narcotic pain relievers such as codine experience hives.
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.
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
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
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 a blood
test if there is concern that you will have an anaphylactic reaction to the
drug. Because the blood is tested outside your body there is no risk of an
You may experience some pain at the site where the blood is drawn. A
blood test can detect allergies to only a few specific drugs, such as some
antibiotics, muscle relaxants, and insulin.
In a provocation test, increasing doses of the drug are
given at planned intervals. You may take the drug orally or under the skin. Any
reaction indicates possible allergy or sensitivity to the drug. If the reaction
is mild, or if there is no reaction, the drug may be a safe treatment for the
patient. The risks of provocation tests include a severe reaction, potentially
even anaphylaxis. This test is used only in special cases and is usually
performed only at specialized allergy centers.