Drug hypersensitivity reactions

Overview Of Drug hypersensitivity reactions

Drug hypersensitivity reactions are adverse immune-mediated responses to medications, ranging from mild skin rashes to life-threatening conditions like anaphylaxis or Stevens-Johnson syndrome (SJS). These reactions occur when the immune system mistakenly identifies a drug or its metabolites as harmful, triggering an inflammatory response. Drug hypersensitivity can be classified into immediate (Type I) or delayed (Type IV) reactions, depending on the timing and immune mechanisms involved. Common culprits include antibiotics (e.g., penicillins), nonsteroidal anti-inflammatory drugs (NSAIDs), and anticonvulsants. Accurate diagnosis and management are crucial to prevent recurrence and ensure patient safety.

Causes of Drug hypersensitivity reactions

• Drug hypersensitivity reactions are caused by an immune response to a medication or its metabolites. Key factors include:
• Type I (Immediate) reactions: - IgE-mediated, occurring within minutes to hours. - Examples: Anaphylaxis to penicillin or beta-lactam antibiotics.
• Type II (Cytotoxic) reactions: - IgG or IgM antibodies targeting drug-bound cells. - Examples: Hemolytic anemia caused by cephalosporins.
• Type III (Immune complex) reactions: - Deposition of drug-antibody complexes in tissues. - Examples: Serum sickness or drug-induced vasculitis.
• Type IV (Delayed) reactions: - T-cell-mediated, occurring days to weeks after exposure. - Examples: Maculopapular rash, SJS, or toxic epidermal necrolysis (TEN).
• Non-immune-mediated reactions: - Pseudoallergic reactions (e.g., NSAID-induced urticaria).

Risk Factors of Drug hypersensitivity reactions

• Several factors increase the risk of drug hypersensitivity reactions:
• Genetic predisposition: HLA alleles associated with specific reactions (e.g., HLA-B*15:02 and carbamazepine-induced SJS).
• Previous hypersensitivity: History of allergic reactions to medications.
• Route of administration: Intravenous or intramuscular routes are more likely to cause severe reactions.
• Drug properties: High molecular weight or protein-based drugs (e.g., biologics).
• Underlying conditions: Asthma, chronic urticaria, or viral infections (e.g., HIV, EBV).
• Polypharmacy: Use of multiple medications increases the risk of interactions.

Prevention of Drug hypersensitivity reactions

• Preventing drug hypersensitivity reactions involves:
• Patient education: Informing patients about potential risks and symptoms.
• Allergy testing: Identifying specific drug allergies before prescribing.
• Avoidance: Using alternative medications for patients with known hypersensitivity.
• Desensitization: For essential medications when no alternatives exist.
• Monitoring: Close observation during initial doses of high-risk medications.
• Documentation: Clearly recording drug allergies in medical records. These measures can help reduce the risk of hypersensitivity reactions.

Prognosis of Drug hypersensitivity reactions

• The prognosis for drug hypersensitivity reactions varies depending on the type and severity of the reaction. Mild reactions, such as maculopapular rashes, typically resolve with discontinuation of the drug and symptomatic treatment. Severe reactions, like anaphylaxis or SJS/TEN, have higher morbidity and mortality rates, particularly if not treated promptly. Long-term management involves identifying safe alternatives and educating patients about potential risks.

Complications of Drug hypersensitivity reactions

• Drug hypersensitivity reactions can lead to several complications, particularly if not managed appropriately:
• Anaphylaxis: Life-threatening systemic reaction requiring immediate intervention.
• Chronic skin conditions: Persistent rashes or scarring from severe reactions.
• Organ damage: Liver or kidney injury from immune complex deposition.
• Psychological impact: Anxiety or fear of medication use.
• Treatment limitations: Restricted options for future therapies due to cross-reactivity. Early diagnosis and comprehensive management are essential to prevent these complications.

Related Diseases of Drug hypersensitivity reactions

• Drug hypersensitivity reactions are often associated with other conditions, including:
• Allergic diseases: Asthma, allergic rhinitis, or atopic dermatitis.
• Autoimmune disorders: Lupus or vasculitis, which may mimic drug reactions.
• Infections: Viral infections like HIV or EBV, which increase susceptibility.
• Chronic urticaria: May be exacerbated by drug reactions.
• Eosinophilic disorders: Drug-induced eosinophilia or eosinophilic pneumonia. Understanding these related diseases can aid in comprehensive management of drug hypersensitivity.

Treatment of Drug hypersensitivity reactions

Treatment for drug hypersensitivity depends on the type and severity of the reaction: 1. **Immediate reactions**: - Anaphylaxis: Epinephrine, antihistamines, and corticosteroids. - Bronchospasm: Bronchodilators and oxygen therapy. 2. **Cutaneous reactions**: - Antihistamines and topical corticosteroids for mild rashes. - Systemic corticosteroids for severe reactions. 3. **SJS/TEN**: - Hospitalization in a burn unit. - Supportive care, including fluid management and wound care. 4. **Desensitization**: Gradual reintroduction of the drug under controlled conditions for essential medications. 5. **Avoidance**: Discontinuation of the offending drug and identification of safe alternatives.