Drug allergy

Diagnosis

An accurate diagnosis is essential. Research has suggested that drug allergies may be overdiagnosed and that patients may report drug allergies that have never been confirmed. Misdiagnosed drug allergies may result in the use of less-appropriate or more-expensive drugs.

Your health care provider typically conducts a physical examination and ask you questions. Details about the onset of symptoms, the time you took medications, and improvement or worsening of symptoms are important clues for helping your provider make a diagnosis.

Your provider may order additional tests or refer you to an allergy specialist (allergist) for tests. These may include the following.

Skin tests

With a skin test, the allergist or nurse administers a small amount of a suspect drug to your skin either with a tiny needle that scratches the skin, an injection or a patch. A positive reaction to a test often causes a red, itchy, raised bump.

A positive result suggests you may have a drug allergy.

A negative result isn't as clear-cut. For some drugs, a negative test result usually means that you're not allergic to the drug. For other drugs, a negative result may not completely rule out the possibility of a drug allergy.

Blood tests

Your provider may order blood work to rule out other conditions that could be causing symptoms.

While there are blood tests for detecting allergic reactions to a few drugs, these tests aren't used often because of the relatively limited research on their accuracy. They may be used if there's concern about a severe reaction to a skin test.

Results of diagnostic work-up

After analyzing your symptoms and test results, your provider can usually reach one of the following conclusions:

• You have a drug allergy
• You don't have a drug allergy
• You may have a drug allergy — with varying degrees of certainty

These conclusions can help when making future treatment decisions.

Treatment

Interventions for a drug allergy can be divided into two general strategies:

• Treatment for 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 provider 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 provider may prescribe an antihistamine or recommend a nonprescription antihistamine such as diphenhydramine (Benadryl). An antihistamine can block immune system chemicals triggered 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. Hospital care also is necessary to maintain blood pressure and support breathing.

Taking allergy-causing drugs

If you have a confirmed drug allergy, your provider likely would not prescribe the drug unless it is necessary. In some cases — if the diagnosis of drug allergy is uncertain or there's no alternative treatment — your provider may use one of two strategies to use the suspect drug.

With either strategy, your provider provides careful supervision. Supportive care also is available in the event of an adverse reaction. These interventions are generally not used if drugs have caused severe, life-threatening reactions in the past.

Graded challenge

If the diagnosis of a drug allergy is uncertain and your provider judges that an allergy is unlikely, a graded drug challenge may be an option. With this procedure, you receive 2 to 5 doses of the drug, starting with a small dose and increasing to the desired dose.

If you reach the therapeutic dose with no reaction, then your provider may recommend that you take the drug as prescribed.

Drug desensitization

If it's necessary for you to take a drug that has caused an allergic reaction, your provider may recommend a treatment called drug desensitization. With this treatment, you receive a very small dose and then progressively larger doses every 15 to 30 minutes over several hours or days. If you can reach the desired dosage with no reaction, then you can continue the treatment.

Clinical trials

Explore Mayo Clinic studies testing new treatments, interventions and tests as a means to prevent, detect, treat or manage this condition.

Preparing for your appointment

See your health care provider if you experience symptoms that may be related to a drug you recently started taking or take regularly. Be prepared to answer the following questions. These details are important in helping to determine the cause of your symptoms.

• What symptoms did you experience? Don't leave out details even if they seem unrelated.
• When did the symptoms start? Be as specific as possible.
• How long did the symptoms last?
• What new drug have you taken?
• When did you take it?
• Have you stopped taking the new drug?
• What other nonprescription or prescription drugs do you take?
• What herbal medications, vitamins or other dietary supplements do you take?
• At what time of day do you take your other medications or supplements?
• Have you increased the dosage of any regular drug or supplement?
• Have you stopped taking your regular medications or supplements?
• Did you take anything to treat your symptoms, and what was the effect?
• Have you had a reaction to a drug in the past? If so, what drug was it?
• Do you have hay fever, food allergy or other allergies?
• Is there a history of drug allergies in your family?

You may want to take pictures of any condition, such as a rash or swelling, to show your provider. These may help if symptoms have subsided by the time of your appointment.