Drug Allergy: Causes, Classification, Symptoms and Treatment

Drug Allergy: Causes, Classification, Symptoms and Treatment

Drug allergy is an adverse drug reaction (ADR) that occurs through the body’s immune system. It is a type B ADR, meaning it is not dose-related.

# Mechanism of Drug Allergy:

Drug allergy occurs when the body’s immune system reacts to the drug, its metabolites or non-drug components. This reaction is mediated by IgE antibodies and T cells, leading to the release of inflammatory mediators and allergic symptoms.

# Distinguishing Drug Allergy from Pseudoallergic Reactions:

Pseudoallergic reactions have similar manifestations to drug allergies, but are not related to an immune response. Instead, they are caused by the release of chemical mediators from mast cells and basophils due to the physical or pharmacological effect of the drug.

# Classification of Drug Allergy by Onset Time:

• Acute allergy: Occurs within 1 hour after taking the drug, manifested by anaphylaxis, urticaria, angioedema, and asthma.

• Subacute allergy: Occurs within the first day after taking the drug.

• Late allergy: Occurs days to weeks after taking the drug, manifested by serum sickness, allergic vasculitis, purpura, and arthritis.

# Classification of Drug Allergy by Mechanism:

Drug allergy is classified into 4 types based on the immune mechanism:

1. Type I: Anaphylactic-like reaction:

• Mechanism: Mediated by IgE, the IgE-antigen complex causes mast cell degranulation, releasing chemical mediators.

• Time: Rapid, usually within 24 hours.

• Manifestations: Manifestations on the digestive, skin, respiratory, and circulatory systems.

• Allergic drugs: Beta-lactam antibiotics.

2. Type II: Cytotoxic reaction:

• Mechanism: Mediated by IgM, IgG, antigen-antibody complexes activate complement, causing target cell lysis. Target cells are often blood cells.

• Time: Usually after 7 days of high-dose drug use.

• Manifestations: On the hematopoietic system: hemolysis (hemolytic anemia), thrombocytopenia, neutropenia, pancytopenia.

• Allergic drugs: Cephalosporin, Penicillin, NSAIDs.

3. Type III: Immune complex reaction:

• Mechanism: Mediated by IgG, antigen-antibody complexes deposit in the vascular endothelium.

• Time: Usually occurs 7-21 days after taking the drug.

• Manifestations: Manifestations on the pericardium, pleura, skin, joints, capillaries.

• Allergic drugs: Beta-lactams, Sulfonamides, Streptomycin, antiepileptics.

4. Type IV: Delayed-type cell-mediated reaction:

• Mechanism: Antigen-sensitized T lymphocytes cause direct toxicity or release lymphokin/cytokines, leading to inflammatory reactions and systemic damage.

• Time: Usually appears 24-72 hours later.

• Manifestations: Skin manifestations, from mild to severe.

• Allergic drugs: Sulfonamides, Streptomycin, Phenothiazine derivatives, Tetracyclines, Penicillin.

# Symptoms of Drug Allergy:

• Immediate, rapid-onset reaction: Occurs within 1 hour after taking the drug, manifested by:

• Erythema, urticaria, or angioedema and hypotension and/or bronchospasm.

• Urticaria or angioedema and no systemic clinical signs.

• Asthma attacks.

• Late, non-systemic reaction: Occurs 6-10 days after taking the drug or 3 days after the second dose, manifested by:

• Generalized rash, erythema.

• Fixed drug eruption.

# DRESS and DHS Syndrome:

• Onset time: Usually 2-10 weeks after the first dose of the drug or 3 days after the second dose.

• Manifestations:

• Generalized rash, papules or erythema.

• Fever.

• Lymphadenopathy.

• Liver failure.

• Eosinophilia.

# TEN and Stevens-Johnson Syndrome:

• Onset time: Usually 7-14 days after the first dose of the drug or 3 days after the second dose.

• Manifestations:

• Rash with pain and fever.

• Skin and mucous membrane ulcers.

• Bullous (peeling) epidermal detachment, blisters, bullae localized in natural orifices. At least 2 lesions in natural orifices.

• Polymorphic or morbilliform rash.

• Pneumonia, liver and kidney dysfunction.

# Drugs that are prone to allergy:

• Antibiotics.

• Vitamins.

• NSAIDs.

• Anesthetics, anesthetics, muscle relaxants.

• Hormones.

• Infusion solutions.

• Vaccines, sera.

• Iodinated contrast agents.

# Treatment of Drug Allergy:

• Withdrawal of the allergic drug.

• Symptom management:

• Corticosteroids: Immunosuppressive, potent anti-inflammatory agents. Used to treat anaphylaxis, early injection is needed to prevent delayed hypersensitivity reactions.

• Antihistamines (H1): Used in acute allergies.

• Adrenaline: Used in anaphylaxis, angioedema, cardiopulmonary resuscitation. Caution should be exercised in diabetic patients, hypertensive patients, elderly patients, and patients with coronary heart disease. Route of administration: IV>IM>SC.

• Noradrenaline: Only use IV, not IM, SC as it causes vasoconstriction, necrosis at the injection site.

• Enhance liver and kidney function: Through appropriate infusion solutions or medications.

• Anti-infection: If any.

• Support the patient’s health.

# Prevention of Drug Allergy:

• Be aware of drug allergy history.

• Limit combination of drugs.

• Understand the treatment process for drug allergy and anaphylaxis.

• Skin testing before taking medication.

Note: This article is for informational purposes only. If you suspect you have a drug allergy, consult a doctor for timely diagnosis and treatment.