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Drug Allergies


Drug allergies are a group of symptoms caused by an allergic reaction to a drug (medication).

What is the difference between a drug allergy and an adverse drug reaction?

Adverse reactions to drugs are common, and almost any drug can cause them.  Adverse reactions range from irritating or mild side effects such as nausea and vomiting to life-threatening anaphylaxis.

A true drug allergy ellicits an immune response within the body that produce the allergic reaction to a medication.

Only 6% to 10% of adverse drug reactions are allergic or immunologic in nature*.

Drug allergies can take two different paths:

  1. The first time you take the medicine, you have no reactions, but your body’s immune system produces an antibody called IgE against that drug. The next time you take the drug, the IgE recognizes that drug and triggers an immune response  which causes allergy symptoms.
  2. A drug allergy may also occur without your body producing IgE, but this is not well understood.

Most side effects of drugs are not due to an allergic reaction. Some drugs such as aspirin can cause nonallergic hives or trigger asthma. Some drug reactions are considered “idiosyncratic”. This  means the reaction is an unusual effect of the medication, not due to a predictable chemical effect of the drug. Many people confuse an uncomfortable, but not serious, side effect of a medicine (such as nausea) with a true drug allergy, which can be life threatening.

What drugs are people most commonly allergic to?

Penicillin and related antibiotics are the most common cause of drug allergies.  Other common allergy-causing drugs include:

  • Sulfa drugs
  • Anticonvulsants
  • Insulin preparations (particularly animal sources of insulin)
  • Iodinated (containing iodine) x-ray contrast dyes (these can cause allergy-like anaphylaxis reactions)

What are the symptoms of a drug allergy?

The most common symptoms are skin rash, hives and itching of the skin or eyes.  Other symptoms include:

  • Angioedema (swelling of the lips, tongue, or face)
  • Wheezing
  • Anaphylaxis symptoms
    • Abdominal pain or cramping
    • Confusion
    • Diarrhea
    • Difficulty breathing with wheeze or hoarse voice
    • Dizziness
    • Fainting
    • Lightheadedness
    • Hives over different parts of the body
    • Nausea and  vomiting
    • Rapid pulse
    • Heart palpitations

Serum sickness is a delayed type of drug allergy that occurs a week or more after exposure to a medication or vaccine.

How is a drug allergy diagnosed?

Skin testing may help diagnose allergy to penicillin-type medications. Unfortunately, there are no good skin or blood tests to help diagnose other drug allergies. If you have had allergy-like symptoms after taking a medicine or receiving contrast (dye) before getting an x-ray, your physician will often tell you that this is proof that you have a drug allergy. No further testing is required.

Who is at risk for a drug allergy?

Anyone can develop an allergic reaction to a drug, but there are a few factors that can increase your risk. These include:

  • Having an allergic reaction to a similar drug in the past.
  • Having a health condition that weakens your immune system, such as the Epstein-Barr virus or HIV/AIDS.
  • Having hay fever or other allergies.


Treatment is determined on an individual basis as prescribed by your physician.  Please contact our office to schedule an appointment with one of our allergy and asthma specialists.

Is there a cure for a drug allergy?

Although there is no cure for drug allergy, immunotherapy may reduce or eliminate symptoms.

What are the possble complications of a drug allergy?

Complications of serious drug reactions can include:

  • Anaphylaxis
  • Drug-induced anemia due to an immune system reaction that destroys blood cells
  • Serum sickness which can cause serious symptoms and lead to organ damage. Signs and symptoms include fever, rash and joint pain, usually starting two to four weeks after you begin taking a drug.

Those with drug allergies may have to take alternative drugs that may be less effective or  cause long-term, bothersome side effects.

How can you prevent drug allergy reactions?

  • Avoid the offending drug and similar drugs in its class.
  • Make sure all your health care providers, including physicians and dentists, know about any drug allergies that you or your children have.
  • Wear identifying medical alert  jewelry or cards.

*Gruchalla R. Understanding drug allegies. J Allergy Clin Immunol 2000;105:S637-44.

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