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Drug Toxicity: Allergic Reactions

Drug Toxicity: Allergic Reactions

Drug-related allergies are immune-mediated responses triggered by the administration of pharmacological agents. These hypersensitivity reactions are classified based on the immune mechanisms involved. The four primary types—Type I, II, III, and IV—are mediated by different immunological pathways and exhibit distinct clinical manifestations.Type I Hypersensitivity/ IgE-Mediated Reactions: Immunoglobulin E (IgE) immediately mediates Type I hypersensitivity reactions. Upon initial exposure to a...

Hypersensitivity Reactions: Delayed Hypersensitivity Reactions

Hypersensitivity Reactions: Delayed Hypersensitivity Reactions

Delayed-Type Hypersensitivity (DTH), or Type IV hypersensitivity, is a cell-mediated immune response. It occurs when T cells, rather than antibodies, mediate a reaction to specific antigens. It is characterized by a delayed onset (1-2 days) and involves the recruitment of macrophages to the inflammation site.The initiation of a DTH response begins with the sensitization of T cells. During this phase, which lasts at least 1-2 weeks, antigen-specific T cells are activated, clonally expanded, and...

Allergic Drug Reactions

Allergic Drug Reactions

Allergic reactions related to drugs are hypersensitivity responses driven by the immune system and bear no connection to the drug's therapeutic action. While drugs in isolation do not trigger an immune response, they can interact with endogenous proteins to form antigens. These antigens stimulate lymphocytes to produce antibodies. IgE-type antibodies attach themselves to mast cells. Upon subsequent exposure to the same stimulus, the antigen-antibody interaction is initiated, unleashing numerous...

Hypersensitivities

Hypersensitivities

Hypersensitivity, also known as a hypersensitivity reaction or allergic reaction, is a condition where the body's immune system reacts abnormally to a foreign substance. Such substances, that cause hypersensitivity are referred to as an allergen, could be something typically harmless to most people, like pollen or certain foods.
Types of Hypersensitivities
Hypersensitivity reactions are categorized into four types: Type 1, Type 2, Type 3, and Type 4. Each type has a distinct mechanism...

Hypersensitivity Reactions: Immune-Complex Reactions

Hypersensitivity Reactions: Immune-Complex Reactions

Type III hypersensitivity reactions occur when antigen–antibody complexes form and activate the complement system. Normally, these complexes help the clearance of antigens by phagocytes and red blood cells. However, when large numbers of immune complexes are present, they can deposit in tissues—particularly in the walls of blood vessels—leading to inflammation and tissue injury. These deposits trigger complement activation and neutrophil recruitment, resulting in serum sickness, a systemic...

Allergic Reactions: Anaphylaxis

Allergic Reactions: Anaphylaxis

Anaphylaxis is a severe, life-threatening hypersensitivity reaction mediated by Immunoglobulin E (IgE) antibodies. When IgE binds to allergens, it triggers the release of mediators– histamine, leukotrienes, and prostaglandins from mast cells and basophils. These mediators cause vasodilation, edema, and inflammation, leading to various symptoms.The primary allergens causing anaphylaxis include food items (e.g., peanuts, shellfish), drugs (e.g., penicillin, asparaginase, corticotropin, heparin),...

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Related Experiment Video

Updated: Jul 14, 2026

Trans-vivo Delayed Type Hypersensitivity Assay for Antigen Specific Regulation

Trans-vivo Delayed Type Hypersensitivity Assay for Antigen Specific Regulation

Published on: May 2, 2013

Delayed drug hypersensitivity reactions - new concepts.

S J Posadas¹, W J Pichler

¹Division Allergology, Clinic for Rheumatology and Clinical Immunology/Allergology, Bern, Switzerland.

Clinical and Experimental Allergy : Journal of the British Society for Allergy and Clinical Immunology

|June 22, 2007

Summary

Drug hypersensitivity reactions involve delayed T cell responses, classified by T cell activation pathways (IVa, IVb, IVd) and cytotoxic functions (IVc). The p-i concept explains how drugs directly stimulate T cells, leading to rapid reactions.

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Last Updated: Jul 14, 2026

Trans-vivo Delayed Type Hypersensitivity Assay for Antigen Specific Regulation

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Published on: May 2, 2013

Induction and Monitoring of Active Delayed Type Hypersensitivity (DTH) in Rats

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Published on: July 19, 2007

Basophil Activation Test for Investigation of IgE-Mediated Mechanisms in Drug Hypersensitivity

Basophil Activation Test for Investigation of IgE-Mediated Mechanisms in Drug Hypersensitivity

Published on: September 16, 2011

Area of Science:

Immunology
Pharmacology
Dermatology

Background:

Drug hypersensitivity reactions (DHRs) manifest through immediate or delayed immune responses.
Delayed DHRs involve drug-specific T cells recognizing antigens in a MHC-dependent manner.

Purpose of the Study:

To elucidate the mechanisms underlying delayed drug hypersensitivity reactions.
To subclassify Type IV hypersensitivity reactions based on T cell effector functions.
To introduce the pharmacological-interaction (p-i) concept for drug-TCR binding.

Main Methods:

Immunohistochemical and functional studies of drug-reactive T cells.
Analysis of T cell-derived cytokines and chemokines.
Investigation of drug-TCR and drug-MHC interactions.

Main Results:

Distinct T cell functions correlate with specific clinical phenotypes in DHRs.
Type IV reactions can be subclassified into IVa (monocyte), IVb (eosinophil), IVd (neutrophil), and IVc (cytotoxic).
The p-i concept proposes direct drug-TCR binding, potentially activating pre-existing T cells, explaining rapid DHRs.

Conclusions:

Delayed DHRs are T cell-mediated and can be subclassified based on effector mechanisms.
The p-i concept provides a novel framework for understanding DHR pathogenesis, including rapid-onset reactions.
This model helps explain the prevalence of skin manifestations in drug hypersensitivity.