A drug allergy occurs when your immune system overreacts to something in a medicine. This causes an allergic reaction. Although drug allergies can be life-threatening, most of them are mild, and symptoms go away within a few days after you stop using the medicine. Anaphylaxis, which is the most serious reaction. It is life-threatening, and you will need emergency treatment. Symptoms usually appear within 1 hour after you take the medicine and include hives, difficulty breathing, and shock.

 

What is a drug allergy?

A drug allergy occurs when your immune system overreacts to something in a medicine. This causes an allergic reaction. Although drug allergies can be life-threatening, most of them are mild, and symptoms go away within a few days after you stop using the medicine.

What are the symptoms of a drug allergy?

The symptoms of a drug allergy vary from mild to life-threatening and include:

• Hives or welts, rash, blisters, or eczema. These are the most common symptoms of drug allergies. See an illustration of skin reactions caused by drug allergies.
• Coughing, wheezing, runny nose, and difficulty breathing.
• Stomach cramps, feeling sick to the stomach, vomiting, and diarrhea.
• Anaphylaxis, which is the most serious reaction. It is life-threatening, and you will need emergency treatment. Symptoms usually appear within 1 hour after you take the medicine and include hives, difficulty breathing, and shock.

What medicines commonly cause an allergic reaction?

Any medicine can cause an allergic reaction. However, penicillin’s (such as nafcillin, ampicillin, and amoxicillin) cause most drug allergies. Sulfa medicines (sulfonamides), barbiturates, insulin, vaccines, anticonvulsants, and anti thyroid medications for hyperthyroidism also can cause drug allergies.

If you are allergic to one medicine, you may be allergic to a similar medicine. For example, if you are allergic to penicillin, you may also be allergic to similar antibiotics such as cephalosporins (cephalexin or cefuroxime, for example).

Symptoms

Symptoms of drug allergies can be mild or life-threatening and appear within 1 to 72 hours. They include:

• Hives or welts, rash, swelling, redness, and blisters, or eczema. These are the most common symptoms of drug allergies, and they may occur right after you take a medicine or several days later. See an illustration of skin reactions caused by drug allergies.
• Coughing, Wheezing, runny nose, skin color changes, and difficulty breathing.
• Stomach cramps, feeling sick to the stomach, vomiting, and diarrhea.
• Anaphylaxis, which is the most serious reaction. It is life-threatening, and you will need emergency treatment. Symptoms usually appear within 1 hour after you take the medicine and include hives, difficulty breathing, and shock.

A drug allergy can also affect the liver, kidneys, and lymph system. However, you usually do not have any symptoms in this case.

How is a drug allergy treated?

The best thing you can do for a drug allergy is avoid the medicine that causes it and know what to do if you have an allergic reaction.

• Your doctor may be able to give you another type of medicine.
• If you have a life-threatening allergic reaction, you may need to give yourself an epinephrine shot and seek emergency medical treatment. You may also need to take other medicines, such as antihistamines and corticosteroids, directly into your vein (intravenously).
• If you have a mild allergic reaction, over-the-counter antihistamines may help your symptoms. You may need prescription medicine if these do not help or if you have problems with side effects, such as drowsiness.