Drug allergy refers to a type of drug hypersensitivity reaction (DHR) that is caused by an immunological mechanism, specifically involving drug-specific antibodies (IgE) or T cells. True drug hypersensitivity is uncommon, but many children are mislabeled as “allergic,” particularly to antibiotics, leading to suboptimal treatment and increased resistance. When drug allergy is diagnosed, the implicated drug should be avoided, and an appropriate alternative should be identified. Since this can pose a significant burden not only to the patient but also to society, accurate evaluation and diagnosis are essential.
Types of Drug Allergy
Drug hypersensitivity reactions present with a wide range of clinical manifestations and may involve the skin, respiratory tract, gastrointestinal system, or lead to systemic symptoms.
1. Immediate-type reactions
These occur within 1 hour of drug administration (up to 6 hours in IgE-mediated cases) and include localized urticaria, angioedema, rhinitis, conjunctivitis, bronchospasm, gastrointestinal symptoms such as vomiting, diarrhea, and abdominal pain, as well as anaphylaxis. Most immediate reactions are mediated by immunoglobulin E (IgE), but non-IgE-mediated mechanisms can also occur.
2. Delayed-type reactions
These appear more than 1 hour after drug administration and can develop even weeks to months later. Clinical features include delayed urticaria, maculopapular rashes, fixed drug eruptions, vasculitis, and severe cutaneous adverse reactions such as toxic epidermal necrolysis (TEN), Stevens-Johnson syndrome (SJS), drug reaction with eosinophilia and systemic symptoms (DRESS), acute generalized exanthematous pustulosis (AGEP), and symmetrical drug-related intertriginous and flexural exanthema. Internal organ involvement may occur either alongside skin symptoms or independently, manifesting as hepatitis, renal failure, interstitial pneumonia, anemia, neutropenia, or thrombocytopenia.
* Severe cutaneous adverse drug reaction, SCAR
Severe cutaneous adverse drug reaction(SCAR) is a delayed-type reaction mediated by CD4+CD8+ T cells. Although rare, it can cause permanent damage to the affected mucosa or skin, leading to severe long-term complications and a high mortality rate.
A. Stevens-Johnson Syndrome (SJS)
Stevens-Johnson Syndrome (SJS) is a rare, severe mucocutaneous reaction, typically triggered by medications or infections. It is characterized by widespread skin detachment and erosions involving less than 10% of the body surface area. Patients often present with fever, malaise, and painful red or purplish skin lesions. Mucosal involvement, especially in the eyes, mouth, and genital area, is common.
B. Toxic Epidermal Necrolysis (TEN)
Toxic Epidermal Necrolysis (TEN) is the most severe form of drug-induced skin reaction, considered a spectrum with SJS. It involves widespread epidermal necrosis and detachment affecting more than 30% of the body surface. Symptoms include high fever, extensive skin peeling, and mucosal damage, often requiring intensive care or burn unit management. Mortality rates are high, and early withdrawal of the offending drug is critical.
C. Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS)
Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS) is a potentially life-threatening hypersensitivity reaction that usually appears 2–6 weeks after drug exposure. It features fever, rash, lymphadenopathy, eosinophilia, and multi-organ involvement (commonly liver, kidney, or lungs). It has a delayed onset and may worsen even after discontinuing the drug. Systemic corticosteroids are often required for treatment.