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Drug Allergies

Condition Basics

What is a drug allergy?

A drug allergy occurs when your immune system overreacts to something in a medicine. Your body's immune system fights back by setting off an allergic reaction. Most drug allergies are mild, and the symptoms go away within a few days after you stop using the medicine. But some drug allergies can be very serious.

Some drug allergies go away with time. But after you have an allergic reaction to a drug, you will probably always be allergic to that drug. You can also be allergic to other drugs that are like it.

A drug allergy is one type of unwanted, or adverse, drug reaction. There are other kinds of adverse drug reactions. Symptoms and treatments of different kinds of adverse reactions vary. So your doctor will want to find out if you have a true drug allergy or if you have side effects that are not as serious.

What causes it?

Any medicine can cause an allergic reaction. A few of the most common ones are:

  • Penicillins (such as ampicillin or amoxicillin).
  • Sulfa medicines.
  • Anesthesia.
  • Aspirin and other nonsteroidal anti-inflammatory drugs.

If you are allergic to one medicine, you may be allergic to others like it. For example, if you are allergic to penicillin, there is a chance that you may also be allergic to similar medicines, such as amoxicillin.

What are the symptoms?

The symptoms of a drug allergy can range from mild to very serious. Most of the time they appear within 1 to 72 hours. They include:

  • Hives, a rash, and itchy skin.
  • Coughing, wheezing, a runny nose, and trouble breathing.
  • A fever.
  • Serious skin conditions that make your skin blister and peel. These include toxic epidermal necrolysis and Stevens-Johnson syndrome.
  • Anaphylaxis, which is the most dangerous reaction. It can be deadly, and you will need emergency treatment. Symptoms include hives all over your body, trouble breathing, nausea or vomiting, swelling of the throat or mouth, and/or feeling very lightheaded. These usually appear within 1 hour after you take the medicine. Without emergency care, you could die.

How is it diagnosed?

Your doctor will diagnose a drug allergy by asking you questions about the medicines you take and about any medicines you have taken in the recent past. Your doctor will also ask about your past health and your symptoms. Your doctor may do a physical exam.

If this doesn't tell your doctor whether you have a drug allergy, you may need skin tests. Or your doctor may have you take small doses of a medicine to see if you have a reaction.

How is a drug allergy treated?

If you have severe drug allergies, your doctor may give you an epinephrine auto-injector. Your doctor will teach you how to use it. If you have a serious allergic reaction, you may need to give yourself the shot and get emergency medical treatment.

Inject epinephrine into the thigh muscle if you have signs of a severe allergic reaction, such as trouble breathing, having hives all over your body, or feeling faint. Call 911 right away.

If you have a mild allergic reaction, over-the-counter (OTC) antihistamines may help your symptoms. Mild symptoms include sneezing or an itchy or runny nose; an itchy mouth; a few hives or mild itching; and mild nausea or stomach discomfort. You may need prescription medicine if OTC antihistamines don't help or if you have problems with side effects, such as drowsiness. Not all OTC antihistamines cause drowsiness.

The best thing you can do for a drug allergy is to stop taking the medicine that causes it. Talk to your doctor to see if you can take another type of medicine.

If you can't change your medicine, your doctor may try a method called desensitization. This means that you will start to take small amounts of the medicine that caused your reaction. Under your doctor's supervision, you will then slowly increase how much you take. This lets your immune system "get used to" the medicine. After this, you may no longer have an allergic reaction.

Be sure to wear a medical alert bracelet or other jewelry that lists your drug allergies. If you are in an emergency, this can save your life.

How can you care for yourself?

To take care of yourself at home:

  • Know which medicines you're allergic to, and avoid taking these medicines.
  • Keep a list of all medicines you are taking.
  • Talk with your doctor or pharmacist about any new medicines you are prescribed. Make sure they are not similar to those that can cause a reaction.
  • Don't use someone else's medicines or share yours.

If you do have a mild reaction, take steps to relieve symptoms such as itching. Take cool showers, or apply cool compresses. Wear light clothing that doesn't bother your skin. Stay away from strong soaps and detergents, which can make itching worse.

Credits

Current as of: February 10, 2021

Author: Healthwise Staff
Medical Review:
Adam Husney MD - Family Medicine
E. Gregory Thompson MD - Internal Medicine
Martin J. Gabica MD - Family Medicine
Kathleen Romito MD - Family Medicine
Anne C. Poinier MD - Internal Medicine

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