Drug Allergy Overview

By : Dr Mohammad Baghaei

Pharmacist & Researcher

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. Any medication — over-the-

counter, prescription or herbal — is capable of inducing a drug allergy.

However, a drug allergy is more likely with certain medications.

A drug allergy is not the same as drug side effects, the known

possible reactions that are listed on a drug label. A drug allergy is

also distinct from drug toxicity caused by an overdose of

medication.

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.

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

Who are at greater risk for a severe allergic reaction to a medication?

The people who involved by:

heart disease

asthma

high blood pressure

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 Aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs) Chemotherapy drugs for treating cancer Medications for autoimmune diseases, such as rheumatoid arthritis Corticosteroid creams or lotions Medications for people with HIV or AIDS Bee pollen products Echinacea

The term drug allergy refers to a group of symptoms caused by allergic

reaction to a drug. Many drugs have side effects such as stomach upset or

headache; however, these symptoms do not indicate an allergic reaction.

As with other allergies, the symptoms may cause only mild discomfort, or

they may be severe and even life threatening.

Signs and symptoms of a drug allergy often occur within an hour after taking a drug. Less commonly, reactions 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 is a rare, life-threatening reaction to a drug allergy that causes the widespread dysfunction of body systems. Signs and symptoms of anaphylaxis include:

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

Anaphylaxis

Other conditions resulting from drug allergy

Less common drug allergy reactions occur 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 counts, general swelling, swollen lymph nodes and recurrence of dormant hepatitis infection

Inflammation in the kidneys (nephritis), which can cause fever, blood in the urine, general swelling, confusion and other symptoms

Nonallergic drug reactions

Sometimes a reaction to a drug can produce signs and symptoms virtually the same as those of a drug allergy, but it's not 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

Tests to Diagnose a Drug Allergy The first step in the diagnosis of drug allergy is a complete physical

examination. Your doctor will want to know if you have other allergies or

a family history of allergies. He or she will also want to know how long

you were using the drug before your reaction began and whether you had

used the drug before. You will be asked to describe your symptoms in

detail.

If possible, see your doctor while you are experiencing the reaction to a

drug. This will help your doctor make a diagnosis. If your doctor suspects

a drug allergy, they can perform several tests to confirm a diagnosis.

Skin Tests

For some drugs, an allergy skin test may determine whether or not you are

allergic to a substance. Depending on the drug, a doctor might perform a

skin-prick test or intradermal test.

During a skin-prick test, the doctor injects a small amount of the drug into

the skin—usually the back or forearm. If you are allergic, you will develop

redness, a bump, or other noticeable skin inflammation.

Intradermal tests can test for allergic reactions to penicillin and some other

antibiotics. During these tests, the doctor injects a small amount of the

allergen just under the skin, and monitors the site for a reaction.

Blood Tests

Blood tests can determine whether you are allergic to certain drugs. While

they are not as accurate as other test methods, a doctor might choose to do

Drug Allergy Treatments

There are several medications available to treat drug allergies.

Interventions for a drug allergy can be divided into two general

strategies:

• Treatment for the present allergy symptoms

• Treatment that may enable you to take an allergy-causing drug if

it's medically necessary

Treating current symptoms

The following interventions may be used to treat an allergic reaction to a drug:

Withdrawal of the drug. If your doctor determines that you have a drug allergy — or likely allergy — discontinuing the drug is the first step in treatment. In many cases, this may be the only intervention necessary.

Antihistamines. Your doctor may prescribe an antihistamine or recommend an over-the-counter antihistamine such as diphenhydramine (Benadryl) that can block immune system chemicals activated during an allergic reaction.

Corticosteroids. Either oral or injected corticosteroids may be used to treat inflammation associated with more-serious reactions.

Treatment of anaphylaxis. Anaphylaxis requires an immediate epinephrine injection as well as hospital care to maintain blood pressure and support breathing.

Antihistamines

For mild symptoms such as a rash, hives, and itching, over-the-counter

or first-generation antihistamines can be effective. These drugs may

cause drowsiness.

First generation antihistamines include:

brompheniramine

dimenhydrinate

diphenhydramine

doxylamine)

Second-generation antihistamines, which have fewer or no such effects,

are now recommended by many doctors. These include:

cetirizine

desloratadine

fexofenadine

loratadine

Bronchodilator

A bronchodilator can help when main symptoms include wheezing or

coughing. Examples of bronchodilators include:

albuterol

formoterol

salmeterol

theophylline

Corticosteroids

Corticosteroids can be taken by mouth, intravenous injection, or applied

directly to the skin. They act more slowly than antihistamines, but last

longer and can provide relief from some of the more serious symptoms of

a drug allergy. These include:

beclomethasone

fluticasone furoate

fluticasone propionate

mometasone

Epinephrine

In acute anaphylaxis cases, epinephrine should be taken by injection as

soon as possible. An emergency medical response team will be able to

administer an emergency dose of epinephrine.