Drug allergy - Symptoms and causes (2024)

Overview

A drug allergy is the reaction of the immune system to a medicine. Any medicine — nonprescription, prescription or herbal — can provoke a drug allergy. However, a drug allergy is more likely with certain medicines.

The most common symptoms of drug allergy are hives, rash or fever. But a drug allergy also may cause serious reactions. This includes a severe, life-threatening condition known as anaphylaxis.

A drug allergy is not the same as a drug side effect. A side effect is a known possible reaction to a medicine. Side effects to medicines are listed on their drug labels. A drug allergy also is different from drug toxicity. Drug toxicity is caused by an overdose of medicine.

Symptoms

Symptoms of a serious drug allergy often occur within an hour after taking a drug. Other reactions, particularly rashes, can occur hours, days or weeks later.

Drug allergy symptoms may include:

• Skin rash
• Hives
• Itching
• Fever
• Swelling
• Shortness of breath
• Wheezing
• Runny nose
• Itchy, watery eyes

Anaphylaxis

Anaphylaxis is a rare, life-threatening reaction to a drug allergy that causes the widespread dysfunction of body systems. Symptoms of anaphylaxis include:

• Tightening of the airways and throat, causing trouble breathing
• Nausea or abdominal cramps
• Vomiting or diarrhea
• Dizziness or lightheadedness
• Weak, fast pulse
• Drop in blood pressure
• Seizure
• Loss of consciousness

Other conditions resulting from drug allergy

Less-common drug allergy reactions happen days or weeks after exposure to a drug and may persist for some time after you stop taking the drug. These conditions include:

• Serum sickness, which may cause fever, joint pain, rash, swelling and nausea
• Drug-induced anemia, a reduction in red blood cells, which can cause fatigue, irregular heartbeats, shortness of breath and other symptoms
• Drug rash with eosinophilia and systemic symptoms (DRESS), which results in rash, high white blood cell count, general swelling, swollen lymph nodes and recurrence of dormant hepatitis infection
• Inflammation in the kidneys, also called nephritis, which can cause fever, blood in the urine, general swelling, confusion and other symptoms

When to see a doctor

Call 911 or emergency medical help if you experience signs of a severe reaction or suspected anaphylaxis after taking a medication.

If you have milder symptoms of a drug allergy, see your health care provider as soon as possible.

Causes

A drug allergy occurs when your immune system mistakenly identifies a drug as a harmful substance, such as a virus or bacterium. Once your immune system detects a drug as a harmful substance, it develops an antibody specific to that drug. This can happen the first time you take a drug, but sometimes an allergy doesn't develop until there have been repeated exposures.

The next time you take the drug, these specific antibodies flag the drug and direct immune system attacks on the substance. Chemicals released by this activity cause the symptoms associated with an allergic reaction.

You may not be aware of your first exposure to a drug, however. Some evidence suggests that trace amounts of a drug in the food supply, such as an antibiotic, may be sufficient for the immune system to create an antibody to it.

Some allergic reactions may result from a somewhat different process. Researchers believe that some drugs can bind directly to a certain type of immune system white blood cell called a T cell. This event causes the release of chemicals that can result in an allergic reaction the first time you take the drug.

Drugs commonly linked to allergies

Although any drug can cause an allergic reaction, some drugs are more commonly associated with allergies. These include:

• Antibiotics, such as penicillin
• Pain relievers, such as aspirin, ibuprofen (Advil, Motrin IB, others) and naproxen sodium (Aleve)
• Chemotherapy drugs for treating cancer
• Medicines for autoimmune diseases, such as rheumatoid arthritis

Nonallergic drug reactions

Sometimes a reaction to a drug can produce symptoms virtually the same as those of a drug allergy. However, a drug reaction isn't triggered by immune system activity. This condition is called a nonallergic hypersensitivity reaction or pseudoallergic drug reaction.

Drugs that are more commonly associated with this condition include:

• Aspirin
• Dyes used in imaging tests (radiocontrast media)
• Opiates for treating pain
• Local anesthetics

Risk factors

While anyone can have an allergic reaction to a drug, a few factors can increase your risk. These include:

• A history of other allergies, such as food allergy or hay fever
• A personal or family history of drug allergy
• Increased exposure to a drug, because of high doses, repeated use or prolonged use
• Certain illnesses commonly associated with allergic drug reactions, such as HIV infection or the Epstein-Barr virus

Prevention

If you have a drug allergy, the best prevention is to stop using the problem drug. Steps you can take to protect yourself include the following:

• Inform health care workers. Be sure that your drug allergy is clearly identified in your medical records. Inform other health care providers, such as your dentist or any medical specialist.
• Wear a bracelet. Wear a medical alert bracelet that identifies your drug allergy. This information can ensure proper treatment in an emergency.