Drug Allergy - Symptoms

Introduction Causes Symptoms Treatments

The symptoms of a drug allergy can range from mild to very serious. They include:

  • Symptoms of drug allergies can be mild or life-threatening and usually appear within 1 to 72 hours.
  • Hives or welts, a rash, blisters, or a skin problem called eczema. These are the most common symptoms of drug allergies.
  • Coughing, wheezing, a runny nose, and trouble breathing.
  • A fever.
  • A serious skin condition that makes your skin blister and peel. This problem is called toxic epidermal necrolysis, and it can be deadly if it is not treated.
  • Anaphylaxis, which is the most dangerous reaction. It can be deadly, and you will need emergency treatment.
  • Symptoms, such as hives and trouble breathing, usually appear within 1 hour after you take the medicine. Without quick care, you could go into shock.
A drug allergy can also affect the liver, kidneys, and lymph system. But you usually do not have any symptoms in this case.

Medicines commonly cause an allergic reaction

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

  • Penicillins (such as nafcillin, ampicillin, or amoxicillin). These types of medicines cause the most drug allergies.
  • Sulfa medicines.
  • Barbiturates.
  • Insulin.
  • Vaccines.
  • Anticonvulsants.
  • Medicines for hyperthyroidism.

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

People with AIDS or lupus may be allergic to many types of medicines. The reactions usually aren't dangerous, but they can make it hard to treat the disease.

Some people-especially those with asthma-have reactions to common pain relievers such as aspirin and ibuprofen. These seem like allergic reactions but they are not, because they do not affect the immune system. But these reactions can be severe in people who have asthma.

Diagnosing a drug allergy

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. He or she will do a physical exam.

If this doesn't tell your doctor whether you have a drug allergy, then he or she may do skin tests. Or your doctor may have you take small doses of a medicine to see if you have a reaction. In some cases, you may need a blood test or other type of testing.

When to Call a Doctor

Call911or other emergency services right away if:

  • You develop hives and have trouble breathing or other symptoms of anaphylaxis. If you have an epinephrine shot, give it to yourself while you have someone else call 911.

Call your doctor if:

  • Your face, tongue, or lips are swollen, even if you are not having trouble breathing and the swelling is not getting worse.
  • You develop a skin rash, itching, a feeling of warmth, or hives.
  • Home treatment does not help and symptoms get worse.


Exams and Tests

Your doctor will diagnose a drug allergy by asking you questions about the medicines you are or have recently been taking, your past health, and your symptoms ( medical history) and by doing a physical exam. To find out which medicine is causing your allergic reaction, your doctor will consider:
Your medicine. Some medicines are more likely to cause an allergic reaction than others.
Whether you have a drug allergy or another adverse reaction to medication. You have more treatment options if you have an adverse reaction that does not involve the immune system.
How many medicines you are taking. If you take several medicines, the medicine you began taking most recently is often the cause.

Your doctor probably will ask you to stop taking the medicine that is most likely to be causing the reaction. If this does not help, your doctor may ask you to stop taking other medicines, until you can find which medicine is causing the allergic reaction.

If your doctor cannot find out which medicine is causing the reaction, he or she may suggest a skin test. In a skin test, your doctor will place a small amount of medicine on or under your skin to see if your body reacts to it. But a skin test does not work for all medicines, and you risk having a severe reaction.