Drug Allergies

Overview

Drug allergies occur when the immune system identifies a certain prescription, herbal, or over-the-counter drug as harmful. This identification leads the immune system to produce antibodies, called immunoglobulin E (IgE), that remain on the alert for that drug. When you are exposed to the drug again, these antibodies attack the “invader” by releasing immune system chemicals such as histamine, which cause allergy symptoms.

People can develop allergies to any drug, although some drug allergies are more common than others.

Common symptoms of drug allergies include rashes, hives, or fever. In some people, drug allergies can cause a serious and life-threatening allergic reaction called anaphylaxis, which is characterized by throat constriction and trouble breathing, a rapid pulse, or a loss of consciousness.

Your doctor can administer tests to identify possible drug allergies, prescribe emergency medications to treat anaphylaxis, and help set up a long-term plan to avoid drugs that cause your allergic reactions.

If you are experiencing symptoms of anaphylaxis, call 911 or seek emergency medical treatment immediately.

Drug allergy causes

Drug allergies occur when your immune system identifies a specific drug as a dangerous invader. When your immune system makes this identification, it leads cells to release antibodies called immunoglobulin E (IgE), which remain on the alert for that drug. When you are exposed to the dug again, these antibodies attack the “invader” by releasing immune system chemicals such as histamine, which cause allergy symptoms.

Some drugs, however, may cause allergic reactions the first time you are exposed to them.

The most common drugs that can cause allergies include:

• Antibiotics such as penicillin
• Pain-relievers such as ibuprofen, aspirin, and naproxen sodium
• Chemotherapy drugs
• Medications that treat autoimmune diseases

Drug allergy risk factors

You may be more likely to develop a drug allergy if you have:

• Other existing allergies
• A family history of drug allergies
• High exposure to a certain drug, such as through high doses or repeated use
• Illnesses such as HIV or Epstein-Barr virus infection

Drug allergy symptoms

Symptoms of severe drug allergies typically begin within an hour of taking the drug. Some symptoms can occur days or weeks after beginning the medication, such as rashes.

Common symptoms of drug allergies include:

• Hives or skin rashes
• Itching
• Swelling
• Fever
• Shortness of breath
• Wheezing
• Watery, itchy eyes

Severe drug allergies can cause anaphylaxis, a life-threatening reaction. Symptoms of anaphylaxis include:

• A tightening of the airways or a swollen throat that restricts breathing
• Shock, and a dramatic blood pressure drop
• A rapid pulse
• Feeling lightheaded, dizzy, or losing consciousness

People experiencing symptoms of anaphylaxis must seek immediate emergency medical treatment.

Drug allergy complications

Some drug allergy reactions can cause less-common symptoms that may last for some time even after you cease taking the drug. Such symptoms may include:

• Serum sickness, which can include symptoms such as nausea, swelling, fever and joint pain.
• Anemia, which can lead to symptoms such as fatigue, shortness of breath, and irregular heartbeats.
• Drug rash with eosinophilia and systemic symptoms (DRESS), which includes symptoms such as swelling, swollen lymph nodes, a high white blood cell count, and a rash.
• Kidney inflammation (nephritis), which can lead to swelling, confusion, fever, and blood in the urine.

Drug allergy diagnosis

When diagnosing a possible drug allergy, your doctor may:

• Conduct a physical examination and assess symptoms
• Review your medications to assess which drugs may be causing problems
• Ask about any family history of allergies to specific drugs
• Administer a skin test. In a skin test, a doctor or nurse will prick your skin to expose you to small amounts of the potentially problematic drugs. If you are allergic, you will likely develop a raised bump, or hive, at the injection site on your skin.
• Perform a blood test to measure your immune system response to various drugs

Drug allergy treatment

If you are experiencing current symptoms from an allergic reaction, your doctor may provide the following treatments:

• Ceasing use of the possible problem drug
• Prescribe antihistamines or recommend over-the-counter options to alleviate symptoms
• Provide corticosteroids to reduce inflammation
• Administer an epinephrine injection in the case of anaphylaxis

While drug allergies cannot be cured, the following measures can prevent your exposure to the problem drug:

• Communicate your drug allergy to all health care providers from whom you are receiving treatment
• Make sure your allergies are specified in your medical records.
• Wear a medical alert bracelet or necklace stating your allergy in the event of a reaction that compromises your ability to communicate

When to seek care

Call your doctor if you think you are experiencing an allergic reaction to a drug.

If you are experiencing symptoms of anaphylaxis, call 911 or seek emergency medical treatment immediately.

Next Steps

Identifying a drug allergy will inform future treatment practices that avoid the problem drug.