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Updated on September 26, 2022

Drug Allergies

What are Drug Allergies?

All drugs have side effects. You can find them on the list of possible side effects provided with any medication you take. 

Some side effects are considered helpful, while others are not desirable. The undesirable side effects are also known as adverse drug reactions (ADR).

An ADR can present in different ways and might mimic an allergic reaction. However, side effects are just expected actions of the drug, like nausea. Allergic reactions are mediated by the immune system response.

Drug allergies are allergic reactions to a medication. They are pretty rare, with only 5 to 10 percent of adverse reactions caused by a true allergy to the medication. 

These allergies can be life-threatening if left unchecked, like any allergic reaction. This is why it’s essential to know everything about them and be prepared.  

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Why Do Drug Allergies Occur?

To understand why drug allergies occur, you need to know why allergic reactions happen:

The Immune System

Allergic reactions start with the immune system. 

Your body’s immune system is in charge of protecting it from possible infections. If you have an allergic reaction, it means your immune system is overreacting to specific allergens.

This causes your immune cells to produce antibodies. These antibodies are responsible for the allergic symptoms you experience. Depending on many factors, the symptoms can range from mild to severe. 

Allergic Reaction to Medication

Drug allergies occur when your immune system overreacts to medication and attacks it. This leads to inflammation and other symptoms.

Risk Factors

Many factors have been linked to an increased drug allergy risk. Some of these include:

  • Age and gender
  • A history of drug allergy in the family (genetics)
  • A history of other personal allergies such as food
  • HIV or other viral infections

Drug allergy risk is also more common in young and middle-aged adults, and it affects women more than men.

Common Drug Allergy Triggers

Some medications are known to cause allergic reactions more often than others. Some of these include: 

  • Chemotherapy drugs
  • Horse antisera
  • Penicillin and other antibiotics
  • Insulin
  • Anticonvulsants
  • Aspirin 
  • Ibuprofen
  • Naproxen
  • HIV treatment drugs
  • Drugs for autoimmune diseases
  • Monoclonal antibody therapy

The more you take a specific medication, the higher the chance you have of becoming allergic to it. Applying the medicine on your skin or through injection raises this risk as well. 

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Symptoms of a Drug Allergy 

In some cases, it can be hard to find out if the symptoms are caused by an ADR or by a true drug allergy. For example, you can take drugs to inhibit blood pressure, which can cause facial swelling. However, this does not necessarily mean that it is an allergic reaction.

The most common symptoms of a drug allergy include: 

  • Difficulty breathing
  • Skin rash and itchiness
  • Facial swelling

These symptoms are generally mild, but you should still seek treatment right away if you experience them.

A rarer but more severe symptom of a drug allergy is called anaphylaxis (an-a-fi-LAK-sis). It involves more than one system of the body and is characterized by severe swelling, hives, lowered blood pressure, and shock.

Anaphylactic shock must be treated promptly. It’s a life-threatening drug reaction.

Some symptoms can occur after taking a drug for a long time. These include:

  • Kidney inflammation
  • Drug-induced anemia
  • Drug rash with eosinophilia
  • Serum sickness

When is an Allergic Reaction Serious? 

An allergic reaction becomes extremely serious if you have trouble breathing, or if you go into anaphylactic shock. This is a severe reaction that can escalate quickly, so once you see signs, you must act immediately. 

The signs you should look out for to spot anaphylaxis include:

  • Dizziness 
  • Lightheadedness
  • Weakness
  • Rapid pulse
  • Heart palpitations 
  • Fainting
  • Difficulty breathing

Remember that anaphylaxis symptoms vary among people. Even a person who has experienced it before likely won’t have the exact same symptoms the next time they do. 

The most challenging part of dealing with a drug allergy is finding a replacement for the drug you are allergic to. This can delay you from receiving proper treatment. 

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How are Drug Allergies Diagnosed?

Because drug allergies often share symptoms with other drug-related conditions, they can be hard to diagnose. In order to diagnose a drug allergy properly, you need to tell your doctor about your complete history regarding drug allergies.

In most cases, your doctor will ask you:

  • To describe your symptoms
  • What drug you think caused your allergic reaction
  • When you started experiencing symptoms
  • How long after taking the medication the symptoms began
  • How long your symptoms lasted, and what you did to treat them
  • What medications you have taken, especially any new or changed medications

Furthermore, you may undergo the following:

  • Skin test (for penicillin)
  • Laboratory test
  • Drug challenge

If you suspect that you have a drug allergy, make sure to consult with an allergist to get the best diagnosis and treatment. 

Treatment for Drug Allergies (By Type)

There are two types of drug allergies: acute and severe. The treatment for them depends on the type you have.

However, in both types of drug allergies, the immediate treatment is to stop drug use. 

Acute Drug Allergy

If you are experiencing symptoms such as skin rashes and facial swelling, you have a mild allergic reaction. In these cases, you will be prescribed antihistamines or corticosteroids.

Antihistamines come in a liquid, pill, or nasal spray. Various antihistamines are available by prescription or over-the-counter (OTC).

On the other hand, corticosteroids are a medication used to reduce inflammation and inhibit the immune system. They come in many forms, such as:

  • Injections
  • Tablets
  • Inhalers
  • Creams

Severe Drug Allergy

In rare cases, you may be experiencing anaphylaxis, which is a life threatening reaction to a drug. This condition requires emergency care and treatment, including an epinephrine injection

Epinephrine is an injection-based medicine that treats a serious allergic reaction. It’s often supplied in an epinephrine auto injector to be administered into the thigh.

Additionally, you will receive treatments to help regulate your blood pressure, breathing, and symptoms. 

Drug Desensitization

If you exhibit an allergic reaction to a particular drug, your doctor will prescribe you another option. 

If there are no other options for your medication, but you need it, you can go through the desensitization process. In this treatment, you are safely given the drug in small doses to avoid an adverse reaction from your immune system.

Over time, the dosage is increased until you reach the required amount.

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  1. Abrams, Elissa  M., and David  A. Khan. “Diagnosing and Managing Drug Allergy.” CMAJ : Canadian Medical Association Journal = Journal De L'Association Medicale Canadienne, Joule Inc., 30 Apr. 2018
  2. Allergic Reactions.” American Academy of Allergy Asthma & Immunology
  3. Drug Allergies: Overview.” InformedHealth.org [Internet]., U.S. National Library of Medicine, 7 May 2020 
  4. Drug Allergy.” American Academy of Allergy Asthma & Immunology
  5. Immune System Defined.” American Academy of Allergy Asthma & Immunology
  6. Thong, Bernard, and Daniel Vervloet . “Drug Allergies.” WAO, Jan. 2007Warrington, Richard, and Fanny Silviu-Dan. “Drug Allergy - Allergy, Asthma & Clinical Immunology.” BioMed Central, BioMed Central, 10 Nov. 2011