What is drug allergy?

A drug allergy occurs when your immune system overreacts to something in a medicine. This causes an allergic reaction. You may have skin problems, such as hives, a rash, or itching. Your lips, mouth, and throat may swell. You may have trouble breathing. And you may have belly pain, nausea, vomiting, or diarrhea. A reaction can range from mild to deadly.

After you have a reaction to a medicine, you may always be allergic to that medicine and to others like it. But some drug allergies go away with time.

Drug allergies are different than side effects and drug interactions. Side effects are reactions to medicines that aren't caused by the immune system. Drug interactions occur when two or more medicines that you take don't work well together in your body.

The symptoms of a drug allergy can range from mild to very serious, and can even cause death. Symptoms may appear within an hour or they could take days or weeks to appear. They include:

• Hives or welts, a rash, and itchy skin.
• Coughing, wheezing, a runny nose, and trouble breathing.
• A fever.
• Swelling of the throat, mouth, lips, or tongue.
• 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, belly pain, nausea or vomiting, swelling of the throat or mouth, and feeling very lightheaded. These usually appear within 1 hour after you take the medicine.

If you have severe drug allergies, your doctor may give you an epinephrine auto-injector. Inject epinephrine into the thigh muscle if you have signs of a severe allergic reaction, such as trouble breathing, hives all over your body, or fainting. Call 911 right away.

If you have a mild allergic reaction, over-the-counter (OTC) antihistamines may help your symptoms. You may need prescription medicine if OTC antihistamines don't help or if you have problems with side effects.

The best thing you can do for a drug allergy is to stop taking the medicine that causes it. Your doctor may give you another type of medicine instead.

If you can't change your medicine, your doctor may try giving you small amounts of the medicine that caused your reaction (desensitization therapy). 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.

Your doctor will ask about the medicines you have taken. You'll be asked about your health and symptoms. Your doctor may do a physical exam. You may need skin tests or blood tests. Or your doctor may have you take small doses of a medicine to see if you have a reaction.

• Your doctor may prescribe a shot of epinephrine to carry in case your child has a severe reaction. Learn how to give your child the shot, and keep it with you at all times. Make sure it has not expired. Teach your child how to give a shot if your child is old enough. Be sure your older child always carries it.
• Go to the emergency room every time your child has a severe reaction. Go even if you have used the shot of epinephrine and your child is feeling better. Symptoms can come back after a shot.
• If your child was given a medicine for an allergic reaction, give it exactly as directed. Call your doctor if you think your child is having a problem with a medicine.
• Avoid giving your child medicines like the one that caused the allergy. Ask your doctor or pharmacist if you think your child may be taking a similar medicine.
• If your child has a mild skin rash or itching from the allergy:
  • Dress your child in light clothing that does not irritate the skin.
  • Use calamine lotion. Or ask the doctor about giving your child a nondrowsy antihistamine, such as loratadine (Claritin). Be safe with medicines. Read and follow all instructions on the label.
  • Give your child a cool shower or bath.
  • Do not use strong soaps, detergents, and other chemicals. They can make itching worse.
• Have your child wear medical alert jewelry that lists their allergies. You can buy this at most drugstores.
• Be sure that anyone treating your child for any health problem knows that your child is allergic to this medicine.

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

• Penicillins (such as ampicillin or amoxicillin).
• Sulfa medicines.
• Anesthesia.
• Aspirin and other nonsteroidal anti-inflammatory drugs.
• Some medicines used to treat seizures.
• Some medicines used to treat cancer.

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.

A drug allergy occurs when your immune system overreacts to something in a medicine. It causes an allergic reaction. This response can range from mild symptoms to a severe whole-body reaction that can be deadly.