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Drug allergy

 

This is an immune response caused by medicines. In a person with a drug allergy, the immune response overreacts to the drug. When the immune system sees the drug as an allergen, it causes an allergic response. Chemicals such as histamines are released. These chemicals can lead to allergy symptoms.

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Causes

Common allergy-causing drugs are:

  • Contrast used for medical imaging
  • Surgery or anesthesia medications
  • Pain medicines, like opioids and non-steroidal anti-inflammatory drugs (NSAIDs).
  • Penicillin and related antibiotics
  • Sulfa drugs

You can have side effects to drugs that are not because of an allergic reaction. Many people confuse side effects of a medicine with a drug allergy. Side effects that may not be because of an allergy are:

  • Nausea
  • Vomiting
  • Diarrhea

Symptoms

Most drug allergies cause minor skin rashes or hives. These can start within minutes, while others may be delayed. Some can take hours, days, or weeks to start.

These can be:

  • Hives or rash
  • Itching
  • Swelling of the lips, tongue, or face
  • Wheezing
  • Abdominal pain or cramping, nausea, vomiting, diarrhea
  • Difficulty breathing with wheezing or hoarse voice
  • Dizziness, fainting, lightheadedness

Exams and tests

  • If you have had allergy-like symptoms after taking a medicine, sometimes this is all that is needed to diagnose a drug allergy. You may not need more testing.
  • It may be not safe to test you so there may not be any testing that can be done.
  • If you can have testing, there are some tests that can be done:
  • Skin testing
    • Skin testing may help diagnose an allergy to penicillin medicines.
    • There are other skin or blood tests to help diagnose other drug allergies, but they are not as reliable as the skin test for penicillin.
    • However, some allergy clinics may skin test other drugs when they can.
  • Drug challenge
    • You could have a drug challenge if there is not skin test.
    • This is only for people who are not likely to have a severe reaction.
    • Drug challenges can take medicines off your allergy list.
    • A drug challenge is done only in a medical clinic. This is a safe place to test your ability to take a certain drug.
    • You must stay in the clinic during the entire time of the challenge. There is the risk that you will have an allergic reaction.
  • Desensitization
    • You will be given very small doses. Then you will get larger and larger doses of a medicine to give you more tolerance of the drug.
    • Only an allergist should do this when there is no other drug for you to take.
    • This will be often be done in a hospital as an inpatient.

Treatment

  • The goal of treating a drug allergy is to relieve symptoms.
  • Do not take the medicine that caused symptoms. Do not take any similar drugs.
  • Make sure all your health care team knows about your drug allergies.
  • Talk to your health care team about your drug allergies so they can be labeled correctly if they are a true drug allergy.

Treatment can be:

  • Antihistamines
  • H2-blockers. These are used to block histamine
  • Corticosteroids
  • Epinephrine by injection
  • Inhaled medicine to help you breathe

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