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Drug Allergy

What is a drug allergy?

A drug allergy is a reaction by your immune system to a medicine you have taken. The immune system is your body’s defense against infection. Sometimes, the immune system reacts to something other than an infection. This is how allergic reactions happen. If you are allergic to a medicine, even a small amount can trigger a reaction. The reaction can range from mild to life-threatening.

What is the cause?

When you have an allergic reaction to a medicine, your immune system treats the drug as a foreign substance and tries to protect you from it. Any medicine can cause an allergic reaction. The medicines most likely to cause allergic reactions are:

  • Antibiotics, such as penicillin
  • Anti-seizure medicines
  • Aspirin and non-steroidal anti-inflammatory drugs (NSAIDS) such as Advil, Motrin or Aleve
  • Contrast dyes used for some X-rays
  • Some heart and cancer drugs
  • Local anesthetics (pain medicines), such as lidocaine or novocaine
  • Sulfa drugs

What are the symptoms?

The most common symptoms are:

  • Itching
  • Hives (a red skin rash)
  • Swelling of the lips, mouth, or skin

Symptoms of a drug allergy can happen within minutes or within a few days after you start taking the medicine. Most symptoms go away 3 to 5 days after you stop taking the drug.

Anaphylaxis is a life-threatening allergic reaction. The reaction is sudden and severe and involves the whole body. Symptoms of a severe reaction may include:

  • Rash or hives
  • Swelling or itching of the lips, face, or throat
  • Trouble swallowing
  • Trouble breathing, often with wheezing
  • Lightheadedness
  • Fast or pounding heartbeat
  • Nausea, vomiting, or diarrhea
  • Fainting
  • Feeling very nervous or confused

How is it diagnosed?

Your healthcare provider will ask about your symptoms and medical history and examine you. Tell your provider about all of the medicines you are taking. This includes prescription and nonprescription drugs, supplements, natural remedies, herbs, and vitamins.

If you have a severe allergic reaction you may need to see an allergy specialist for evaluation and tests.

How is it treated?

Several kinds of medicines may be used to treat allergies:

  • Antihistamines block the effect of histamine and help reduce your symptoms. Histamine is a chemical your body makes when you have an allergic reaction. Do not give antihistamines to children under the age of 4. If your child is between the ages of 4 and 6, ask your healthcare provider before giving antihistamines.
  • Steroid pills or nasal sprays help reduce the irritation and swelling in your body. By lessening the swelling, you will have fewer symptoms and be able to breathe better. Take steroid medicine exactly as your healthcare provider prescribes. Don’t take more or less of it than prescribed by your provider and don’t take it longer than prescribed. Don’t stop taking a steroid without your provider's approval. You may have to lower your dosage slowly before stopping it.
  • A severe allergic reaction is life-threatening and needs to be treated with a shot of epinephrine. Epinephrine relaxes the muscles in your airways, reduces swelling, and helps keep blood pressure from getting too low. You may be kept in the emergency room for a while to make sure your treatment stops the allergic reaction. Sometimes a reaction may be so severe that you need to stay in the hospital for a while to make sure the swelling, your breathing, and your blood pressure all go back to normal.

How can I take care of myself?

  • Follow your healthcare provider's instructions if you were given medicine to take at home.
  • If you had a severe reaction, your provider may prescribe an epinephrine emergency kit, such as EpiPen or Twinject. You will need to carry the kit with you at all times. It contains a ready-to-use syringe of epinephrine. If you have a severe allergic reaction, a shot of this medicine can counteract allergy symptoms until you get emergency medical care. You or someone with you can give you the shot and call 911 or emergency medical services.
    • You should check the expiration date for this medicine and replace it as needed to make sure it will work. It should not be stored at extreme heat or cold or in direct sunlight.
    • Sometimes 1 dose of epinephrine is not enough, so you may need more than 1 epinephrine pen. If so, follow your healthcare provider’s instructions.
    • Ask your healthcare provider or pharmacist if you have any questions about safe use.
  • Wear a bracelet or necklace that warns of your allergy and tells what to do in case of an emergency. Tell your family, friends, and co-workers what they should do if you have a severe reaction.

How can I help prevent allergic reactions?

  • Avoid taking medicine that you have had an allergic reaction to. Check medicine labels for the names of drugs you are allergic to before taking any medicine or natural remedy. A medicine may be available in different shapes and colors. Don’t depend on how a medicine looks to know whether it’s the one you’re allergic to. If you have questions, ask your provider or pharmacist
  • Write down the name of any medicines you have reacted to and what your reaction was. Carry this information with you.
  • Tell all healthcare providers who treat you, including pharmacists and dentists, about all known allergies you have.
Developed by RelayHealth.
Adult Advisor 2015.1 published by RelayHealth.
Last modified: 2014-10-15
Last reviewed: 2014-10-15
This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.
Copyright ©1986-2015 McKesson Corporation and/or one of its subsidiaries. All rights reserved.
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