Drug Allergy Causes

Written by the Healthline Editorial Team | Published on July 30, 2014
Medically Reviewed by Kenneth R. Hirsch, MD on July 30, 2014

Drug Allergy Overview

Drug allergy is the term for a group of symptoms caused by an allergic reaction. An allergic reaction occurs when your immune system mistakes the drug for a harmful substance and mounts an inflammatory response that actually harms rather than protects you.

How Does the Immune System Work?

When a harmful substance, such as a virus or bacteria, enters your body, your immune system creates antibodies to fight off the invading infection. An antibody is a special protein that’s programmed to destroy one specific substance.

Antibodies are also called immunoglobulins. There are different kinds of immunoglobulins. For example, immunoglobulin A (IgA) concentrates in tears and saliva and helps to guard these entrances to the body. IgM is very effective at marking bacteria as invaders and telling cells to kill them.

The immunoglobulin most often responsible for the symptoms of an allergy is IgE. IgE tells your white blood cells to release histamine, which in turn causes many of your symptoms.

Once your immune system has programmed antibodies to recognize and defend against a specific substance, those antibodies are always ready to multiply quickly and go to action whenever the substance is detected. This is how you develop immunity to specific illnesses. It’s also how you develop allergies to specific substances, such as a particular drug.

Why Do Some People Develop Drug Allergies and Others Don’t?

Anyone can develop an allergy to a drug or other substance. It can happen at any age. You might become allergic to a drug you’ve used many times before without any adverse reactions. The reasons why people develop drug allergies are not fully understood. However, the following factors can increase your risk:

  • a weakened immune system from conditions such as HIV/AIDS or Epstein-Barr virus
  • other allergies
  • taking several drugs at the same time
  • taking frequent doses of the same medication
  • taking a drug that is similar to one you’ve previously had an allergic reaction to

You are at greater risk for a severe allergic reaction to a medication if you have

  • heart disease
  • asthma
  • high blood pressure

Which Drugs Cause Allergic Reactions?

You can develop an allergy to almost any drug. Some drugs are involved in allergic reactions more often than others. These include:

  • penicillin and antibiotics similar to penicillin (such as ampicillin and amoxicillin)
  • sulfa drugs
  • insulin (especially if from an animal source)
  • cephalosporins (another type of antibiotic)
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