Allergic Reactions to Medication

Definition and Characteristics

A true allergic reaction is defined as a hypersensitivity response initiated by specific immunological mechanisms when exposed to a substance at a dose normally tolerated by most people, according to the European Academy of Allergy and Clinical Immunology 1, 2
Key characteristics of true allergic reactions include an immune-mediated response, involving the immune system, typically through immunoglobulin E (IgE) antibodies or T-cell dependent mechanisms, as stated by the American Academy of Allergy, Asthma, and Immunology 1
True allergic reactions also involve reproducible symptoms, occurring consistently upon exposure to the specific allergen, as noted by the Clinical Microbiology and Infection society 2
The timing of true allergic reactions usually occurs within minutes to hours after exposure for immediate-type reactions, or within days for delayed-type reactions, according to the Annals of Oncology 1

Immediate-type reactions, typically IgE-mediated, occur within 1-6 hours after drug administration and may include hives, swelling, respiratory symptoms, or anaphylaxis, as reported by the American College of Clinical Pharmacy 1, 3
Non-immediate reactions, often T-cell mediated, can occur from 1 hour to many days after drug administration and often involve skin manifestations like rashes, according to the European Journal of Clinical Pharmacology 1

True allergic reactions typically present with one or more symptoms, including skin manifestations, such as hives, itching, flushing, swelling of lips/tongue/uvula, as stated by the Clinical Microbiology and Infection society 2, 3
Respiratory symptoms, such as difficulty breathing, wheezing, cough, throat tightness, are also common, as reported by the American Thoracic Society 3
Cardiovascular symptoms, including low blood pressure, rapid heartbeat, dizziness, may occur, according to the American Heart Association 3
In severe cases, anaphylaxis, a life-threatening reaction involving multiple organ systems, may occur, as noted by the World Allergy Organization 1, 3

To determine if a reaction is a true allergy, multiple symptoms, timing, reproducibility, and severity should be considered, as stated by the Clinical Microbiology and Infection society 1, 2
True allergies typically affect multiple body systems, such as skin, respiratory, and cardiovascular systems, according to the American Academy of Allergy, Asthma, and Immunology 2

Accurate reporting of symptoms to healthcare providers is crucial, as over 90% of patients with medication "allergy" labels don't actually have true allergies, as reported by the Clinical Microbiology and Infection society 4
Incorrect allergy labels may lead to use of less effective alternative medications, according to the European Academy of Allergy and Clinical Immunology 4
Proper documentation of specific symptoms, timing, and circumstances of the reaction is essential, as stated by the American Medical Association 4

The American College of Allergy, Asthma, and Immunology recommends that true drug allergies are immune-mediated reactions that require prior exposure to develop, involving IgE antibodies or T-cell dependent mechanisms 5, 6, 7

The National Comprehensive Cancer Network suggests that certain clinical situations, such as reintroduction of platinum chemotherapy agents after a period without exposure, can increase the risk of developing hypersensitivity to previously tolerated medications 5, 6
The risk of developing an allergy to carboplatin increases with the number of previous exposures, with approximately 16% of patients experiencing hypersensitivity reactions 5, 6

The National Comprehensive Cancer Network recommends that for mild reactions to previously tolerated drugs, the infusion should be stopped immediately, and symptoms should be treated with antihistamines 6
For moderate to severe reactions, an allergist should be consulted before any rechallenge, and desensitization protocols may be appropriate if the drug is essential and no acceptable alternative exists 5, 6, 7

The Journal of Allergy and Clinical Immunology notes that penicillin is the most common cause of drug-induced anaphylaxis, but approximately 90% of patients with a history of penicillin allergy have negative skin tests, meaning they are no longer allergic 7
The Annals of Oncology reports that rituximab causes infusion reactions in 77% of patients on first administration, decreasing with subsequent infusions, and cetuximab can cause anaphylactic reactions due to pre-existing IgE antibodies against specific sugar molecules on the drug 8
The Journal of the National Comprehensive Cancer Network : JNCCN states that reactions with paclitaxel and docetaxel tend to occur during the first few cycles, though they can occur during any infusion regardless of previous tolerance, and are often infusion reactions rather than true allergies 6