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 medicines.

A healthcare professional typically does a physical exam and asks you questions. Details about when symptoms started, the time you took the medicine, and improvement or worsening of symptoms are important clues for helping your health professional make a diagnosis.

Your health professional may order more tests or refer you to an allergy specialist, called an allergist, for tests. These may include the following.

Skin test

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

A positive result suggests that you may have a drug allergy.

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

Blood tests

A healthcare professional may order blood tests to rule out other conditions that could be causing symptoms.

While there are blood tests for detecting allergic reactions to a few medicines, 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 serious reaction to a skin test.

Results of diagnostic work-up

After looking at your symptoms and test results, a healthcare professional 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

Treatments 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 medicine if it's medically necessary.

Treating current symptoms

The following treatments may be used to treat an allergic reaction to a medicine:

• Stopping the medicine. If a healthcare professional determines that you have a drug allergy — or likely allergy — stopping the medicine is the first step in treatment. For many people, this may be the only intervention necessary.
• Antihistamines. Your health professional 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. Corticosteroids given as a shot or taken by mouth may be used to treat symptoms associated with more-serious reactions.
• Treatment of anaphylaxis. Anaphylaxis requires an immediate epinephrine shot. Hospital care also is needed to maintain blood pressure and support breathing.

Taking allergy-causing medicines

If you have a confirmed drug allergy, a healthcare professional likely would not prescribe the medicine that causes a reaction unless it is necessary. Sometimes — if the diagnosis of drug allergy is uncertain or there's no other treatment — your health professional may use one of two strategies to give you the suspect medicine.

With either strategy, your health professional provides careful supervision. Supportive care also is available in the event of an adverse reaction. These treatments are generally not used if medicines have caused serious, life-threatening reactions in the past.

Graded challenge

If the diagnosis of a drug allergy is uncertain and a healthcare professional 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 medicine, starting with a small dose and increasing to the desired dose, also called the therapeutic dose.

If you reach the therapeutic dose with no reaction, then your health professional may recommend that you take the medicine as prescribed.

Drug desensitization

If it's necessary for you to take a medicine that has caused an allergic reaction, your care professional may recommend a treatment called drug desensitization. With this treatment, you receive a very small dose and then increasingly larger doses every 15 to 30 minutes over several hours or days. If you can reach the desired dose 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 a healthcare professional if you have symptoms that may be related to a medicine you recently started taking or take regularly. Be prepared to answer the following questions. These details are important in helping determine the cause of your symptoms.

• What symptoms did you experience? Don't leave out details even if they seem not related.
• When did the symptoms start? Be as specific as possible.
• How long did the symptoms last?
• What new medicine have you taken?
• When did you take it?
• Have you stopped taking the new medicine?
• What other nonprescription or prescription medicines do you take?
• What herbal medicines, vitamins or other dietary supplements do you take?
• At what time of day do you take your other medicines or supplements?
• Have you increased the dosage of any regular medicine or supplement?
• Have you stopped taking your regular medicines or supplements?
• Did you take anything to treat your symptoms, and if so, what was the effect?
• Have you had a reaction to a medicine in the past? If so, what medicine was it?
• Do you have hay fever, food allergies 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 healthcare team. These may help if symptoms have eased by the time of your appointment.