Chapter 63: Cutaneous Drug Reactions¶
Chapter 63 | Cutaneous Drug Reactions: Incidence, Pathogenesis, and Management
KEY CLINICAL POINTS¶
- Cutaneous drug reactions account for 10–15% of adverse drug reactions, with morbilliform eruptions being the most common.
- Severe reactions like Stevens-Johnson syndrome (SJS)/toxic epidermal necrolysis (TEN) and drug-induced hypersensitivity syndrome (DIHS/DRESS) are life-threatening and require immediate intervention.
- Genetic factors (e.g., HLA-B57:01 for abacavir, HLA-B15:02 for carbamazepine) play a critical role in predisposing individuals to severe drug reactions.
1. DEFINITION & OVERVIEW¶
Cutaneous drug reactions encompass a spectrum of adverse skin manifestations triggered by medications. These include acute eruptions (e.g., urticaria, morbilliform rashes), delayed hypersensitivity (e.g., DIHS/DRESS), and severe systemic reactions (e.g., SJS/TEN).
Table 63-1: Revised Classification of Adverse Drug Reactions Based on Immune Pathway¶
| TYPE | KEY PATHWAY | KEY IMMUNE MEDIATORS | ADVERSE DRUG REACTION TYPE |
|---|---|---|---|
| Type I | IgE, immediate | IgE, B cells, T2, ILC2 (IL-4, IL-5, IL-9, IL-13) | Acute urticaria, angioedema, anaphylaxis |
| Type II | IgG-mediated cytotoxicity | IgG, B cells, IgM | Drug-induced cytopenia (e.g., hemolysis, thrombocytopenia) |
| Type III | Immune complexes | IgG + antigen (immune complexes) | Serum sickness, Arthus reaction, drug-induced vasculitis and lupus |
| Type IVa | T lymphocyte–mediated macrophage inflammation | T1 cells, ILC1, Tc1, NK (IFN-g, TNF-a, granzyme B, perforins) | SJS/TEN, erythema multiforme, fixed drug eruption |
| Type IVb | T lymphocyte–mediated eosinophil inflammation | T2 cells, ILC2, Tc2, NK-T (IL-4, IL-5, IL-9, IL-13) | DIHS/DRESS, morbilliform eruption |
| Type IVc | T lymphocyte–mediated neutrophil inflammation | TH17, ILC3, Tc17 (IL17, IL-22, IL-23, CXCL8, GM-CSF) | AGEP |
1.1 Common Cutaneous Drug Reactions¶
Morbilliform eruptions (maculopapular rashes), urticaria, and fixed drug eruptions are the most frequent. Severe reactions include SJS/TEN, DIHS/DRESS, and anaphylaxis.
1.2 Severe Cutaneous Reactions¶
SJS/TEN (epidermal necrolysis >30% BSA) and DIHS/DRESS (drug reaction with eosinophilia and systemic symptoms) are rare but life-threatening. They often involve mucosal involvement, systemic inflammation, and multiorgan failure.
2. EPIDEMIOLOGY¶
Acute cutaneous reactions affect 2.2–10 per 1000 hospitalized patients. Severe reactions (e.g., SJS/TEN, DIHS/DRESS) occur in 1 in 1000–2 per million users. Risk factors include immunocompromise, HLA associations, and prior drug exposure.
2.1 Incidence¶
Morbilliform rash (91%) and urticaria (6%) are most frequent in hospitalized patients. Severe reactions (e.g., SJS/TEN) occur in 1 in 1000–2 per million users.
2.2 Risk Factors¶
Immunocompromised patients (e.g., HIV, transplant recipients), elderly, and those with autoimmune diseases are at higher risk. HLA alleles (e.g., HLA-B57:01, HLA-B15:02) predispose to specific reactions.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Reactions arise from immune (IgE-mediated, T-cell–mediated) or non-immune (direct mast cell activation, photosensitivity) mechanisms. Genetic factors (HLA) and drug metabolism influence susceptibility.
Table 63-3: Clinical Features of Severe Cutaneous Drug Reactions¶
| DIAGNOSIS | MUCOSAL LESIONS | TYPICAL SKIN LESIONS | FREQUENT SIGNS AND SYMPTOMS | MOST COMMON CULPRIT DRUGS |
|---|---|---|---|---|
| Stevens-Johnson syndrome (SJS) | Erosions usually of two or more sites | Dusky macules or atypical targets evolving into small blisters | Most cases involve fever | Trimethoprim-sulfam ethoxazole, allopurinol, anticonvulsants, b-lactam antibiotics, NSAIDs |
| Toxic epidermal necrolysis (TEN) | Erosions usually of two or more sites | Individual lesions like those in SJS evolving into confluent dusky erythema | Fever, leukopenia | Same as for SJS |
| Drug-induced hypersensitivity syndrome (DIHS/DRESS) | Mucositis reported in up to 30% | Diffuse, deep red morbilliform eruption with facial involvement | Fever, lymphadenopathy; eosinophilia, atypical lymphocytosis, hepatitis, nephritis, myocarditis | Anticonvulsants, sulfonamides, allopur, minocycline, vancomycin |
| DIAGNOSIS | MUCOSAL LESIONS | TYPICAL SKIN LESIONS | FREQUENT SIGNS AND SYMPTOMS | MOST COMMON CULPRIT DRUGS |
|---|---|---|---|---|
| Acute generalized exanthematous pustulosis (AGEP) | Oral erosions in perhaps 20% | Diffuse erythematous eruption; innumerable pinpoint pustules | High fever, leukocytosis (neutrophilia), hypocalcemia | b-Lactam antibiotics, macrolide antibiotics, calcium channel blockers, IV contrast |
| Serum sickness or serum sickness–like reaction | Absent | Urticarial rash, often serpiginous or polycyclic | Fever, arthralgias, lymphadenopathy | Antithymocyte globulin, anti-toxins, rituximab, monoclonal antibodies; cefaclor, penicillin, amoxicillin, trimethoprim-sulfam ethoxazole |
| Anticoagulant-induce d necrosis | Infrequent | Purpura and necrosis, especially of central, fatty areas | Ischemic pain in affected areas | Warfarin, heparin |
3.1 Immune Mechanisms¶
Type I (IgE-mediated) reactions (e.g., anaphylaxis), Type IV (T-cell–mediated) reactions (e.g., SJS/TEN, DIHS/DRESS), and immune complex-mediated reactions (e.g., serum sickness) are key pathways.
3.2 Genetic Predisposition¶
HLA associations include HLA-B57:01 (abacavir), HLA-B15:02 (carbamazepine), and HLA-B*58:01 (allopurinol). These alleles increase risk of severe reactions but are not sufficient alone.
4. CLINICAL FEATURES¶
Reactions vary from mild (urticaria) to severe (SJS/TEN). Symptoms include rash, fever, mucosal involvement, and systemic inflammation. Skin biopsy and lab tests aid diagnosis.
4.1 Common Presentations¶
Morbilliform eruptions (erythematous/maculopapular), urticaria, fixed drug eruptions, and photosensitivity reactions are typical. Severe cases may involve mucosal erosion and systemic symptoms.
4.2 Severe Reaction Features¶
SJS/TEN: epidermal detachment >30% BSA, mucosal involvement, systemic inflammation. DIHS/DRESS: fever, eosinophilia, multiorgan involvement. Anaphylaxis: hypotension, respiratory distress.
5. DIFFERENTIAL DIAGNOSIS¶
Distinguish between drug reactions, infections, autoimmune diseases, and malignancies. Consider viral exanthems, contact dermatitis, and drug-induced lupus.
5.1 Viral Exanthems¶
Differentiate from morbilliform drug eruptions using clinical context, timing, and absence of systemic symptoms.
5.2 Autoimmune Diseases¶
Drug-induced lupus (antinuclear antibodies) vs. systemic lupus erythematosus (SLE) requires serologic testing and clinical correlation.
6. INVESTIGATIONS & DIAGNOSIS¶
Diagnosis relies on clinical presentation, drug history, and lab tests (e.g., CBC, liver function, HLA typing). Skin biopsy and patch testing may confirm causality.
Table 63-2: Clinical and Laboratory Findings Suggestive of Severe Cutaneous Adverse Drug Reaction¶
| Cutaneous | General | Laboratory Results |
|---|---|---|
| Generalized rash | Fever | Eosinophil count >1000/mL |
| Dusky or target-like lesions | Enlarged lymph nodes | Leukopenia or leukocytosis with atypical lymphocytes |
| Purpura | Arthralgias or arthritis | Abnormal liver or kidney function tests |
| Blisters or epidermal detachment | Tachycardia, hypotension | |
| Skin pain | Shortness of breath, hoarseness, wheezing | |
| Skin necrosis | Swelling of the lips or tongue |
6.1 Laboratory Tests¶
CBC with eosinophilia, liver/kidney function, and HLA typing for suspected genetic associations. Serologic tests for drug-induced lupus (ANA, anti-histone).
6.2 Skin Biopsy¶
Histopathology reveals spongiosis, eosinophils, or necrosis depending on reaction type. Immunofluorescence may show immune complex deposition.
7. MANAGEMENT & TREATMENT¶
Immediate discontinuation of the culprit drug is critical. Supportive care, corticosteroids, and immunosuppressants are used for severe cases. Desensitization may be considered for essential medications.
7.1 Mild Reactions¶
Antihistamines (e.g., diphenhydramine), topical corticosteroids, and avoidance of the drug. Monitor for progression to severe reactions.
7.2 Severe Reactions¶
Systemic corticosteroids (prednisone 1.5–2 mg/kg/d), IV immunoglobulin, or cyclosporine. Supportive care includes fluid management, wound care, and monitoring for organ failure.
7.3 Desensitization¶
Used for essential drugs (e.g., penicillin, β -lactams). Requires close monitoring and may involve gradual dose escalation with premedication.
8. PROGNOSIS & COMPLICATIONS¶
Mild reactions are usually self-limiting. Severe reactions (SJS/TEN, DIHS/DRESS) may lead to mortality (up to 10%), organ failure, and long-term sequelae (e.g., scarring, ocular complications).
8.1 Mortality¶
SJS/TEN: 10% mortality (up to 20% in severe cases). DIHS/DRESS: 2% mortality. Anaphylaxis: 0.01–0.1% incidence.
8.2 Long-Term Effects¶
Scarring, ocular damage, nail changes, and chronic skin conditions. Some patients develop autoimmune sequelae (e.g., lupus, thyroiditis).
9. SPECIAL CONSIDERATIONS¶
Genetic testing for HLA alleles (e.g., HLA-B*57:01) is recommended for high-risk drugs. Cross-sensitivity and drug interactions must be considered in treatment planning.
9.1 Genetic Testing¶
HLA typing for abacavir (HLA-B57:01), carbamazepine (HLA-B15:02), and allopurinol (HLA-B*58:01) to prevent severe reactions.
9.2 Cross-Sensitivity¶
Avoid structurally related drugs (e.g., penicillins and cephalosporins) unless the risk is low. Cross-reactivity is rare (<2% for penicillin-cephalosporin).
10. KEY POINTS & CLINICAL PEARLS¶
- Discontinue the suspected drug immediately for severe reactions. 2. HLA testing is critical for high-risk drugs (e.g., abacavir, carbamazepine). 3. Monitor for systemic involvement in morbilliform eruptions. 4. Desensitization is an option for essential medications. 5. Document drug reactions in medical records to prevent future exposure.