Drug Allergy

What is a drug allergy?

A drug allergy is a reaction by your immune system to a medicine you have taken. If you are allergic to a drug, even a small amount can trigger a reaction. These reactions range from mild to life-threatening.

How does it occur?

When you have an allergic reaction to a drug, your immune system treats the drug as a foreign substance and tries to protect you from it. The drugs most likely to cause these problems are:

• antibiotics, such as penicillin
• anti-seizure medicines
• contrast dyes used for some X-rays
• some heart and cancer drugs
• local anesthetics (pain killers), such as lidocaine

What are the symptoms?

The most common symptoms are:

• itching
• redness of the skin or a red rash
• swelling of the skin
• hives.

Symptoms of a drug allergy can happen within minutes of taking the first dose, or they may start several days after taking the drug. About half of all allergic reactions occur 1 week after starting a drug. 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 anaphylaxis include:

• skin rash or hives
• swelling of the lips, face, or throat
• trouble breathing, often with wheezing
• a hoarse voice
• lightheadedness
• fast or pounding heartbeat
• nausea and vomiting
• fainting

How is it diagnosed?

Your healthcare provider will ask about your symptoms and the drugs you have taken. Tell your provider about all your medicines, including prescription and nonprescription drugs, supplements, natural remedies, herbs, and vitamins.

If you have a severe allergic reaction or anaphylaxis and there is a question about the cause of the reaction, your provider may recommend that you see an allergy specialist for testing.

How is it treated?

Anaphylaxis is life-threatening. If you think you are having a severe allergic reaction, go to the emergency room or call 911 for help. A severe or life-threatening reaction usually requires:

• a shot of epinephrine (also called adrenaline) and
• a shot of antihistamine, such as Benadryl (diphenhydramine)

Often a steroid medicine, such as hydrocortisone, is also needed.

You may be observed in the emergency room to make sure the medicines stop the allergic reaction. Usually you are sent home with medicine to take to keep the reaction from happening again over the next several hours. Sometimes a reaction may be so severe that you need to stay in the hospital for a day or two to make sure the swelling and your breathing and blood pressure all go back to normal.

A mild allergic reaction may be treated with just an antihistamine. You may also be given a shot or a prescription for steroids to be taken for the next few days. The steroids should be taken exactly as prescribed.

How long will the effects last?

The effects of an allergic reaction last from several minutes to hours, depending on how much of the drug you took and the severity of your allergy.

How can I take care of myself?

Follow your healthcare provider's instructions if you were given medicine to take at home. If you have had anaphylaxis, your provider may prescribe EpiPen. EpiPen is a single-dose injection kit of epinephrine to be used if you have another reaction. With the kit you can give yourself a shot of medicine to counteract the allergic reaction while you wait for medical help to arrive. You should check the expiration date on your EpiPen and replace it as needed to make sure the one you are carrying will work.

Wear a bracelet or necklace that warns of your allergy and tells what to do in case of an emergency.

How can I prevent allergic reactions?

• Avoid taking drugs that have caused you to have an allergic reaction. Be sure to check the label for the names of drugs you are allergic to before taking any medicine or natural remedy. Because many drugs are made by different companies and some are brand-name and some are generic, the same drug may be available in different shapes and colors. Do not depend on how a drug looks to determine whether it's the one you're allergic to.
• 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 past allergic reactions you have had.

Disclaimer: This content is reviewed periodically and is subject to change as new health information becomes available. The information provided is intended to be informative and educational and is not a replacement for professional medical evaluation, advice, diagnosis or treatment by a healthcare professional.

HIA File alli3107.htm Release 13/2010