Allopurinol-Induced Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis

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Mappings

MONDO

MONDO:0044739 Stevens-Johnson syndrome/toxic epidermal necrolysis overlap syndrome

MONDO:0044739 specifically represents the 10-30% body-surface-area overlap band. This is a close rather than exact match because this allopurinol-triggered entry covers the full SJS, overlap, and TEN spectrum and adds an etiologic qualifier.

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Pathophysiology

6

Oxypurinol-HLA class I interaction with HLA-B*58:01 susceptibility

Oxypurinol forms a labile interaction with peptide/HLA complexes at the cell surface and can activate drug-reactive T cells without intracellular antigen processing. HLA-B*58:01 strongly favors this response but is not required in every affected patient.

CD8-positive cytotoxic T cell CL:0000625 keratinocyte CL:0000312

HLA-B hgnc:4932

antigen processing and presentation GO:0019882 ↑ INCREASED

Experimental models

Oxypurinol-stimulated patient PBMC model PRIMARY CELL CULTURE Models the labile oxypurinol interaction with peptide/HLA complexes.

Downstream

Drug-specific cytotoxic T-cell activation HLA-restricted presentation activates drug-specific cytotoxic T cells.

Show evidence (3 references)

PMID:28133001 SUPPORT Other

"acute TEN is considered a T-cell mediated, type IV hypersensitivity disorder. It mostly results from a cumulative effect of risks from the drug structure, drug metabolism, HLA alleles and T cell clonotypes."

Frames the SCAR trigger as a type IV hypersensitivity driven by drug, HLA alleles, and T-cell clonotypes, matching the module trigger node this disease conforms to. Evidence source is OTHER because this is a review.

PMID:15743917 SUPPORT Human Clinical

"The HLA-B*5801 allele was present in all (100%) 51 patients with allopurinol-SCAR, but only in 20 (15%) of 135 tolerant patients"

Human case-control data show the HLA-B*58:01 allele in all allopurinol-SCAR patients in the index Han Chinese cohort, identifying a strong population-specific HLA restriction element for the trigger.

PMID:37452515 SUPPORT In Vitro

"using in vitro drug-treated PBMCs isolated from both resolved ALP-induced SJS/TEN cases and drug-naïve healthy donors, we show that OXP is the driver of CD8+ T cell-mediated responses"

Patient-derived PBMC experiments directly identify oxypurinol as the driver of the CD8 T-cell response in resolved allopurinol-induced SJS/TEN.

Reduced renal oxypurinol clearance

Renal impairment delays oxypurinol clearance and sustains higher plasma exposure, providing a pharmacokinetic amplifier of the concentration-dependent drug-specific T-cell response.

Downstream

Drug-specific cytotoxic T-cell activation Sustained oxypurinol exposure amplifies the concentration-dependent generation of drug-specific T cells.

Show evidence (1 reference)

PMID:25115449 SUPPORT Human Clinical

"Poor renal function was significantly associated with the delayed clearance of plasma oxypurinol, and increased the risk of allopurinol-SCAR (p<0.001, OR (95% CI) 8.0 (3.9 to 17))."

The prospective cohort directly supports impaired renal clearance as an exposure-amplifying cofactor in allopurinol-SCAR.

Drug-specific cytotoxic T-cell activation

Oxypurinol-specific CD8 T cells are activated in a concentration-dependent response favored by HLA-B*58:01, then expand as the effector population that targets keratinocytes. NK cells also participate in the convergent SJS/TEN effector response.

CD8-positive cytotoxic T cell CL:0000625 natural killer cell CL:0000623

T cell activation GO:0042110 ↑ INCREASED

Experimental models

Oxypurinol-stimulated patient PBMC model PRIMARY CELL CULTURE Models oxypurinol-driven CD8 T-cell activation and clonal expansion.

Downstream

Keratinocyte death by cytotoxic mediators Activated cytotoxic lymphocytes release mediators that kill keratinocytes.

Fever Systemic immune activation contributes to the influenza-like febrile prodrome, although the intervening cytokine pathway is not specified here.

Show evidence (2 references)

PMID:24152157 SUPPORT In Vitro

"Allopurinol allergic patients are primarily sensitized to oxypurinol in a dose-dependent manner. TCL induction data show that both the presence of HLA-B*58:01 allele and high concentration of drug are important for the generation of drug-specific T cells."

In-vitro T-cell-line experiments support concentration-dependent oxypurinol sensitization and the amplifying contribution of HLA-B*58:01.

PMID:33341195 SUPPORT Other

"Drug-specific CD8 T-cells and natural killer cells are thought to be the major inducers of keratinocyte apoptosis via release of soluble cytotoxic mediators, including Fas ligand, perforin/granzyme, tumor necrosis factor, and granulysin."

Identifies drug-specific CD8 T cells and NK cells as the effector population driving keratinocyte death, matching the module amplifier node. Evidence source is OTHER because this is a review article.

Keratinocyte death by cytotoxic mediators

Activated lymphocytes release granulysin, Fas ligand, and perforin/granzyme, driving keratinocyte apoptosis and necroptosis — the central effector lesion of allopurinol SJS/TEN and the key conformance target of the SCAR module.

keratinocyte CL:0000312

T cell mediated cytotoxicity GO:0001913 ↑ INCREASED apoptotic process GO:0006915 ↑ INCREASED

Downstream

Epidermal necrolysis and detachment Confluent keratinocyte death produces full-thickness epidermal necrosis.

Show evidence (2 references)

PMID:25355273 SUPPORT Other

"With regard to keratinocyte death, several cell death mediators, such as FasL, granulysin and annexin A1, have been proposed as playing a role in SJS/TEN pathogenesis."

Names the cytotoxic mediators (FasL, granulysin) effecting keratinocyte death, matching the module central-effector node. Evidence source is OTHER because this is a review article.

PMID:28133001 SUPPORT Other

"Apoptosis or necroptosis causes keratinocytes to lose their shape and adhesion, and necrosis predominates within a few days."

Specifies apoptosis and necroptosis as the keratinocyte death modalities of SJS/TEN. Evidence source is OTHER because this is a review article.

Epidermal necrolysis and detachment

Confluent keratinocyte death produces full-thickness epidermal necrosis that separates the epidermis from the dermis, manifesting as the skin and mucosal detachment of allopurinol SJS/TEN.

keratinocyte CL:0000312

cell death GO:0008219 ↑ INCREASED

Downstream

Mucocutaneous failure Loss of the epidermal barrier produces systemic consequences.

Skin detachment Epidermal necrolysis directly manifests as skin detachment.

Abnormal blistering of the skin Dermo-epidermal separation manifests clinically as blistering.

Erosion of oral mucosa Mucosal epithelial necrolysis produces painful oral erosions.

Conjunctivitis Ocular-surface involvement produces acute conjunctival inflammation.

Genital mucosal erosion Genital mucosal epithelial injury produces erosions.

Show evidence (1 reference)

PMID:28133001 SUPPORT Other

"Total epidermal necrosis separates the epidermis from the dermis."

Describes the full-thickness epidermal necrosis with dermo-epidermal separation that defines TEN, matching the module effector node. Evidence source is OTHER because this is a review article.

Mucocutaneous failure

Extensive epidermal and mucosal detachment causes skin-barrier failure with high morbidity and mortality, the defining consequence of allopurinol SJS/TEN.

keratinocyte CL:0000312

cell death GO:0008219 ↑ INCREASED

Show evidence (1 reference)

PMID:33341195 SUPPORT Other

"immunologically mediated cutaneous adverse reaction characterized by mucous membrane and epidermal detachment, with a mortality ranging from 15% to 25%"

Documents the mucocutaneous detachment and high mortality that define the consequence of SJS/TEN. Evidence source is OTHER because this is a review.

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Histopathology

1

Full-thickness epidermal necrosis with dermo-epidermal separation

Confluent epidermal necrosis separates the epidermis from the dermis, providing the tissue-level correlate of clinical detachment.

Show evidence (1 reference)

PMID:28133001 SUPPORT Other

"Total epidermal necrosis separates the epidermis from the dermis."

The review directly describes the defining tissue lesion and plane of separation.

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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

6

Cardiovascular 1

Conjunctivitis HP:0000509

Show evidence (1 reference)

PMID:19243825 SUPPORT Human Clinical

"Acute conjunctivitis and oral and nail involvements were reported in all patients who remembered the details. Acute conjunctivitis occurred before the skin eruptions in 42 patients and simultaneously in 21 patients, whereas only 1 patient reported posteruption conjunctivitis."

This 94-patient clinical study directly documents acute conjunctivitis and its timing relative to the skin eruption among SJS/TEN patients selected for ocular complications; it is not used to infer population frequency.

Genitourinary 1

Genital mucosal erosion Genital ulcers HP:0003249

Show evidence (1 reference)

PMID:29188475 SUPPORT Other

"Nasopharyngeal, esophageal, and genital mucosal involvement with blisters, erosions as well as secondary development of strictures also play a role."

The review explicitly identifies genital mucosal erosions in SJS/TEN; the HPO genital-ulcer term is the closest available specific ontology binding.

Head and Neck 1

Erosion of oral mucosa HP:0031446

Show evidence (1 reference)

PMID:42482572 SUPPORT Other

"Stevens-Johnson syndrome and toxic epidermal necrolysis (SJS-TEN) and erythema multiforme (EM) often present with clinically similar features in the oral mucosa: classically widespread mucosal erosions or ulceration."

The 2026 expert consensus directly supports the specific oral-erosion phenotype without asserting an allopurinol-specific frequency.

Integument 2

Skin detachment HP:0032156

Show evidence (1 reference)

PMID:33341195 SUPPORT Other

"immunologically mediated cutaneous adverse reaction characterized by mucous membrane and epidermal detachment, with a mortality ranging from 15% to 25%"

Identifies mucous membrane and epidermal detachment as the defining feature. Evidence source is OTHER because this is a review article.

Abnormal blistering of the skin HP:0008066

Show evidence (1 reference)

PMID:35437717 SUPPORT Other

"severe mucocutaneous bullous disorders characterized by widespread skin and mucosal necrosis and detachment, which are most commonly triggered by medications"

Characterizes SJS/TEN as drug-triggered mucocutaneous bullous disorders. Evidence source is OTHER because this is a review article.

Metabolism 1

Fever HP:0001945

Show evidence (1 reference)

PMID:29188475 SUPPORT Other

"SJS/TEN manifest with an "influenza-like" prodromal phase (malaise, fever), followed by painful cutaneous and mucous membrane"

The review directly supports fever as a prodromal feature without importing an oxcarbazepine-specific frequency into this allopurinol entry.

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Genetic Associations

1

HLA-B*58:01 pharmacogenomic susceptibility (HLA-B*58:01 strongly predisposes to allopurinol-induced SCAR (SJS/TEN))

Gene: HLA-B hgnc:4932 relationship_type: RISK_FACTOR variant_origin: GERMLINE

Show evidence (3 references)

PMID:15743917 SUPPORT Human Clinical

"The HLA-B*5801 allele was present in all (100%) 51 patients with allopurinol-SCAR, but only in 20 (15%) of 135 tolerant patients"

Human case-control data establish HLA-B*58:01 as a strong genetic risk factor for allopurinol-induced SCAR.

PMID:25047754 SUPPORT Other

"the HLA-B5801 allele and renal impairment are strongly associated with SCARs"

Confirms the HLA-B*58:01 association (and renal impairment as a cofactor) with allopurinol SCAR. Evidence source is OTHER because this is a cost-effectiveness modeling study.

PMID:41160012 SUPPORT Human Clinical

"although HLA-B*58:01 was found to be associated with allopurinol-induced SCARs, generalizing findings from previous studies, the allele was absent in more than one-third of the patient cohort and is therefore an incomplete indicator of risk."

This small, mixed-phenotype US cohort confirms association while qualifying HLA-B*58:01 as an incomplete predictor across heterogeneous populations.

Variants (1)

HLA-B*58:01

Class I HLA allele present in essentially all allopurinol-SCAR patients in the index Han Chinese case-control study; the restricting element for drug-specific T-cell recognition.

Show evidence (1 reference)

PMID:15743917 SUPPORT Human Clinical

"The HLA-B*5801 allele was present in all (100%) 51 patients with allopurinol-SCAR, but only in 20 (15%) of 135 tolerant patients"

The index Han Chinese case-control study directly supports the stated population-specific allele observation.

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Medical Actions

2

Causative drug withdrawal and supportive care

Action: supportive care Ontology label: Supportive Care NCIT:C15747

Immediate withdrawal of allopurinol and multidisciplinary supportive care (often in an ICU or burn unit) are the cornerstone of management.

Show evidence (1 reference)

PMID:35437717 SUPPORT Other

"immediate withdrawal of causative agents, and critical multidisciplinary supportive care are key management of SJS/TEN"

Identifies causative-drug withdrawal and supportive care as key management of SJS/TEN. Evidence source is OTHER because this is a review article.

HLA-B*58:01 pre-prescription screening

Action: genetic testing Ontology label: Genetic Testing NCIT:C15709

Genotyping for HLA-B*58:01 before allopurinol in high-risk populations to avoid the drug in carriers and prevent SCAR.

Show evidence (2 references)

PMID:26399967 SUPPORT Human Clinical

"Prospective screening of the HLA-B*58:01 allele, coupled with an alternative drug treatment for carriers, significantly decreased the incidence of allopurinol induced SCARs in Taiwanese medical centres."

A national prospective cohort provides direct clinical evidence that pre-prescription screening plus allopurinol avoidance in carriers prevents allopurinol-induced SCAR in Han Chinese patients.

PMID:25047754 SUPPORT Other

"Recent American College of Rheumatology guidelines recommend that, prior to treatment with allopurinol, the HLA-B5801 genotype of gout patients at high risk for SCARs, including Korean patients with chronic renal insufficiency, should be determined."

Supports HLA-B*58:01 pre-prescription genotyping as a guideline-recommended preventive strategy. Evidence source is OTHER because this is a cost-effectiveness modeling study.

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Environmental Factors

2

Allopurinol exposure

Therapeutic exposure to allopurinol (for gout/hyperuricemia) is the precipitating exposure. In EuroSCAR, risk was concentrated in the first eight weeks and was higher at daily doses of at least 200 mg.

Show evidence (2 references)

PMID:15743917 SUPPORT Human Clinical

"Allopurinol, a commonly prescribed medication for gout and hyperuricemia, is a frequent cause of severe cutaneous adverse reactions (SCAR), which include the drug hypersensitivity syndrome, Stevens-Johnson syndrome, and toxic epidermal necrolysis."

Establishes allopurinol as a frequent cause of SCAR including SJS/TEN, the exposure that precipitates this disease.

PMID:17919772 SUPPORT Human Clinical

"Daily doses equal to or greater than 200 mg were associated with a higher risk (adjusted odds ratio = 36, 95% confidence interval: 17-76) than lower doses (adjusted odds ratio = 3.0, 95% confidence interval: 1.1-8.4). The risk was restricted to short-term use (<or=8 weeks)."

The multinational EuroSCAR case-control study supports the dose association and the early treatment-risk window specifically for allopurinol-associated SJS/TEN.

Mechanism Target:

TRIGGERS Oxypurinol-HLA class I interaction with HLA-B*58:01 susceptibility — Allopurinol itself is not the antigenic species. It is metabolized to oxypurinol, which is what engages peptide-HLA complexes at the cell surface, so the prescribed exposure reaches this node through its metabolite.

Show evidence (1 reference)

PMID:15743917 SUPPORT Human Clinical

"Allopurinol, a commonly prescribed medication for gout and hyperuricemia, is a frequent cause of severe cutaneous adverse reactions (SCAR), which include the drug hypersensitivity syndrome, Stevens-Johnson syndrome, and toxic epidermal necrolysis."

Establishes therapeutic allopurinol as a frequent cause of severe cutaneous adverse reactions including Stevens-Johnson syndrome and toxic epidermal necrolysis, the reaction this pathway produces.

Renal impairment

Poor renal function delays oxypurinol clearance, increasing exposure to the metabolite that drives the dose-dependent T-cell response and worsening prognosis in allopurinol-SCAR, including SJS/TEN.

Show evidence (1 reference)

PMID:25115449 SUPPORT Human Clinical

"Poor renal function was significantly associated with the delayed clearance of plasma oxypurinol, and increased the risk of allopurinol-SCAR (p<0.001, OR (95% CI) 8.0 (3.9 to 17)). Sustained high levels of oxypurinol after allopurinol withdrawal correlated with the poor prognosis of allopurinol-SCAR."

A prospective cohort directly links renal impairment to delayed oxypurinol clearance, increased allopurinol-SCAR risk, and worse prognosis.

Mechanism Target:

TRIGGERS Reduced renal oxypurinol clearance — Impaired renal function is the direct cause of the delayed oxypurinol clearance this node describes, sustaining the higher metabolite concentrations that drive the concentration-dependent T-cell response.

Show evidence (1 reference)

PMID:25115449 SUPPORT Human Clinical

"Poor renal function was significantly associated with the delayed clearance of plasma oxypurinol, and increased the risk of allopurinol-SCAR (p<0.001, OR (95% CI) 8.0 (3.9 to 17)). Sustained high levels of oxypurinol after allopurinol withdrawal correlated with the poor prognosis of allopurinol-SCAR."

Ties poor renal function directly to delayed plasma oxypurinol clearance and to an eightfold increased risk of allopurinol-induced severe cutaneous adverse reactions.

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Diagnosis

3

Clinical SJS/TEN spectrum classification with skin-biopsy histopathology

Diagnose epidermal necrolysis by clinical assessment together with compatible histopathology, and classify extent as SJS (<10% detached body surface area), overlap (10-30%), or TEN (>30%).

skin biopsy NCIT:C51692

Show evidence (1 reference)

PMID:29188475 SUPPORT Other

"The difference between SJS, SJS/TEN overlap, and TEN is defined by the degree of skin detachment: SJS is defined as skin involvement of < 10%, TEN is defined as skin involvement of > 30%, and SJS/TEN overlap as 10-30% skin involvement. The diagnosis of different degrees of epidermal necrolysis..."

This directly supports both the spectrum thresholds and the combined clinical-histopathologic diagnostic approach.

ALDEN culprit-drug causality assessment

Apply the Algorithm of Drug Causality for Epidermal Necrolysis (ALDEN) to assess whether allopurinol is the culprit rather than inferring attribution from exposure alone.

drug causality assessment

Show evidence (1 reference)

PMID:20375998 SUPPORT Human Clinical

"Being more sensitive than a general method, ALDEN, which correlates well with case-control analysis results, can be considered a reference tool in SJS/TEN."

The validation study supports ALDEN as a reference method for assigning culprit-drug causality in SJS/TEN.

SCORTEN severity and prognosis assessment

Use the Severity-of-Illness Score for Toxic Epidermal Necrolysis (SCORTEN) to assess SJS/TEN severity and prognosis after diagnosis.

SCORTEN severity score

Show evidence (1 reference)

PMID:29188475 SUPPORT Other

"severity-of-illness score for toxic epidermal necrolysis (SCORTEN) is available for SJS/TEN severity assessment."

The clinical review explicitly identifies SCORTEN for severity assessment across the SJS/TEN spectrum.

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Experimental Models

1

Oxypurinol-stimulated patient PBMC model PRIMARY_CELL_CULTURE

In-vitro oxypurinol stimulation of peripheral blood mononuclear cells from resolved allopurinol-induced SJS/TEN cases models the drug-reactive CD8 T-cell response and its oligoclonal TCR repertoire.

Organism

human NCBITaxon:9606

Cell source

Peripheral blood mononuclear cells from resolved cases and drug-naïve donors

Culture

In-vitro drug stimulation with paired alpha-beta TCR repertoire analysis

Publication

PMID:37452515

Pathograph links

Oxypurinol-HLA class I interaction with HLA-B*58:01 susceptibility Models the labile oxypurinol interaction with peptide/HLA complexes.

Show evidence (1 reference)

PMID:37452515 SUPPORT In Vitro

"this response supported the pharmacological interaction with immune receptors (p-i) concept by showcasing (i) the labile metabolite interaction with peptide/HLA complexes"

The experiment directly models the oxypurinol-peptide/HLA interaction.

Drug-specific cytotoxic T-cell activation Models oxypurinol-driven CD8 T-cell activation and clonal expansion.

Show evidence (1 reference)

PMID:37452515 SUPPORT In Vitro

"OXP is the driver of CD8+ T cell-mediated responses"

The experiment directly supports the modeled T-cell activation response.

Show evidence (1 reference)

PMID:37452515 SUPPORT In Vitro

"Examination of paired OXP-induced αβTCR repertoires highlighted an oligoclonal and private clonotypic profile in both resolved ALP-induced SJS/TEN cases and drug-naïve healthy donors."

This describes the principal clonotypic finding of the primary-cell model.

{ }

Source YAML

click to show

name: Allopurinol-Induced Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis
creation_date: "2026-06-24T00:00:00Z"
category: Complex
categories:
- Treatment-Related Disorder
- Cutaneous Toxicity
- Adverse Drug Reaction
synonyms:
- allopurinol-induced SJS/TEN
- allopurinol-induced severe cutaneous adverse reaction
- allopurinol SCAR
description: >-
  Allopurinol is a frequent cause of severe cutaneous adverse reactions (SCARs),
  including Stevens-Johnson syndrome and toxic epidermal necrolysis (SJS/TEN). The
  reaction is a T-cell-mediated, type IV hypersensitivity for which HLA-B*58:01 is
  a strong but incomplete risk marker. Oxypurinol can interact labilely with
  peptide/HLA complexes and activate drug-reactive cytotoxic T cells without
  intracellular antigen processing; the resulting effector response kills
  keratinocytes and produces epidermal necrolysis and detachment. This entry
  conforms to the conserved drug hypersensitivity (SCAR) mechanism module.
parents:
- Skin Disease
- Iatrogenic condition
disease_term:
  preferred_term: allopurinol-induced Stevens-Johnson syndrome/toxic epidermal necrolysis
  term:
    id: MONDO:0044739
    label: Stevens-Johnson syndrome/toxic epidermal necrolysis overlap syndrome
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0044739
      label: Stevens-Johnson syndrome/toxic epidermal necrolysis overlap syndrome
    mapping_predicate: skos:closeMatch
    mapping_source: MONDO
    mapping_justification: >-
      MONDO:0044739 specifically represents the 10-30% body-surface-area overlap
      band. This is a close rather than exact match because this
      allopurinol-triggered entry covers the full SJS, overlap, and TEN spectrum
      and adds an etiologic qualifier.
environmental:
- name: Allopurinol exposure
  influences_mechanisms:
  - target: Oxypurinol-HLA class I interaction with HLA-B*58:01 susceptibility
    environmental_effect: TRIGGERS
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Allopurinol itself is not the antigenic species. It is metabolized to
      oxypurinol, which is what engages peptide-HLA complexes at the cell
      surface, so the prescribed exposure reaches this node through its
      metabolite.
    evidence:
    - reference: PMID:15743917
      reference_title: "HLA-B*5801 allele as a genetic marker for severe cutaneous adverse reactions caused by allopurinol."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Allopurinol, a commonly prescribed medication for gout and hyperuricemia, is a frequent cause of severe cutaneous adverse reactions (SCAR), which include the drug hypersensitivity syndrome, Stevens-Johnson syndrome, and toxic epidermal necrolysis."
      explanation: >-
        Establishes therapeutic allopurinol as a frequent cause of severe
        cutaneous adverse reactions including Stevens-Johnson syndrome and
        toxic epidermal necrolysis, the reaction this pathway produces.
  description: >-
    Therapeutic exposure to allopurinol (for gout/hyperuricemia) is the
    precipitating exposure. In EuroSCAR, risk was concentrated in the first eight
    weeks and was higher at daily doses of at least 200 mg.
  evidence:
  - reference: PMID:15743917
    reference_title: "HLA-B*5801 allele as a genetic marker for severe cutaneous adverse reactions caused by allopurinol."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Allopurinol, a commonly prescribed medication for gout and hyperuricemia,
      is a frequent cause of severe cutaneous adverse reactions (SCAR), which
      include the drug hypersensitivity syndrome, Stevens-Johnson syndrome, and
      toxic epidermal necrolysis.
    explanation: >-
      Establishes allopurinol as a frequent cause of SCAR including SJS/TEN, the
      exposure that precipitates this disease.
  - reference: PMID:17919772
    reference_title: "Allopurinol is the most common cause of Stevens-Johnson syndrome and toxic epidermal necrolysis in Europe and Israel."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Daily doses equal to or greater than 200 mg were associated with a higher
      risk (adjusted odds ratio = 36, 95% confidence interval: 17-76) than lower
      doses (adjusted odds ratio = 3.0, 95% confidence interval: 1.1-8.4). The
      risk was restricted to short-term use (<or=8 weeks).
    explanation: >-
      The multinational EuroSCAR case-control study supports the dose association
      and the early treatment-risk window specifically for allopurinol-associated
      SJS/TEN.
- name: Renal impairment
  influences_mechanisms:
  - target: Reduced renal oxypurinol clearance
    environmental_effect: TRIGGERS
    causal_link_type: DIRECT
    description: >-
      Impaired renal function is the direct cause of the delayed oxypurinol
      clearance this node describes, sustaining the higher metabolite
      concentrations that drive the concentration-dependent T-cell response.
    evidence:
    - reference: PMID:25115449
      reference_title: "Insights into the poor prognosis of allopurinol-induced severe cutaneous adverse reactions: the impact of renal insufficiency, high plasma levels of oxypurinol and granulysin."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Poor renal function was significantly associated with the delayed clearance of plasma oxypurinol, and increased the risk of allopurinol-SCAR (p<0.001, OR (95% CI) 8.0 (3.9 to 17)). Sustained high levels of oxypurinol after allopurinol withdrawal correlated with the poor prognosis of allopurinol-SCAR."
      explanation: >-
        Ties poor renal function directly to delayed plasma oxypurinol
        clearance and to an eightfold increased risk of allopurinol-induced
        severe cutaneous adverse reactions.
  description: >-
    Poor renal function delays oxypurinol clearance, increasing exposure to the
    metabolite that drives the dose-dependent T-cell response and worsening
    prognosis in allopurinol-SCAR, including SJS/TEN.
  evidence:
  - reference: PMID:25115449
    reference_title: "Insights into the poor prognosis of allopurinol-induced severe cutaneous adverse reactions: the impact of renal insufficiency, high plasma levels of oxypurinol and granulysin."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Poor renal function was significantly associated with the delayed clearance
      of plasma oxypurinol, and increased the risk of allopurinol-SCAR (p<0.001,
      OR (95% CI) 8.0 (3.9 to 17)). Sustained high levels of oxypurinol after
      allopurinol withdrawal correlated with the poor prognosis of
      allopurinol-SCAR.
    explanation: >-
      A prospective cohort directly links renal impairment to delayed oxypurinol
      clearance, increased allopurinol-SCAR risk, and worse prognosis.
pathophysiology:
- name: Oxypurinol-HLA class I interaction with HLA-B*58:01 susceptibility
  conforms_to: "drug_hypersensitivity_scar#HLA-Restricted Drug Presentation to Drug-Specific T Cells"
  description: >-
    Oxypurinol forms a labile interaction with peptide/HLA complexes at the cell
    surface and can activate drug-reactive T cells without intracellular antigen
    processing. HLA-B*58:01 strongly favors this response but is not required in
    every affected patient.
  role: trigger
  biological_scale: MOLECULAR
  gene:
    preferred_term: HLA-B
    term:
      id: hgnc:4932
      label: HLA-B
  cell_types:
  - preferred_term: CD8-positive cytotoxic T cell
    term:
      id: CL:0000625
      label: CD8-positive, alpha-beta T cell
  - preferred_term: keratinocyte
    term:
      id: CL:0000312
      label: keratinocyte
  biological_processes:
  - preferred_term: antigen processing and presentation
    term:
      id: GO:0019882
      label: antigen processing and presentation
    modifier: INCREASED
  evidence:
  - reference: PMID:28133001
    reference_title: "A Review of the Pathogenesis of Toxic Epidermal Necrolysis."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      acute TEN is considered a T-cell mediated, type IV hypersensitivity
      disorder. It mostly results from a cumulative effect of risks from the drug
      structure, drug metabolism, HLA alleles and T cell clonotypes.
    explanation: >-
      Frames the SCAR trigger as a type IV hypersensitivity driven by drug, HLA
      alleles, and T-cell clonotypes, matching the module trigger node this
      disease conforms to. Evidence source is OTHER because this is a review.
  - reference: PMID:15743917
    reference_title: "HLA-B*5801 allele as a genetic marker for severe cutaneous adverse reactions caused by allopurinol."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The HLA-B*5801 allele was present in all (100%) 51 patients with
      allopurinol-SCAR, but only in 20 (15%) of 135 tolerant patients
    explanation: >-
      Human case-control data show the HLA-B*58:01 allele in all allopurinol-SCAR
      patients in the index Han Chinese cohort, identifying a strong
      population-specific HLA restriction element for the trigger.
  - reference: PMID:37452515
    reference_title: "The allopurinol metabolite, oxypurinol, drives oligoclonal expansions of drug-reactive T cells in resolved hypersensitivity cases and drug-naïve healthy donors."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      using in vitro drug-treated PBMCs isolated from both resolved ALP-induced
      SJS/TEN cases and drug-naïve healthy donors, we show that OXP is the driver
      of CD8+ T cell-mediated responses
    explanation: >-
      Patient-derived PBMC experiments directly identify oxypurinol as the driver
      of the CD8 T-cell response in resolved allopurinol-induced SJS/TEN.
  downstream:
  - target: Drug-specific cytotoxic T-cell activation
    causal_link_type: DIRECT
    description: >-
      HLA-restricted presentation activates drug-specific cytotoxic T cells.
    evidence:
    - reference: PMID:37452515
      reference_title: "The allopurinol metabolite, oxypurinol, drives oligoclonal expansions of drug-reactive T cells in resolved hypersensitivity cases and drug-naïve healthy donors."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        OXP is the driver of CD8+ T cell-mediated responses
      explanation: >-
        The patient-derived PBMC study directly supports the oxypurinol-to-CD8
        T-cell activation edge.
- name: Reduced renal oxypurinol clearance
  description: >-
    Renal impairment delays oxypurinol clearance and sustains higher plasma
    exposure, providing a pharmacokinetic amplifier of the concentration-dependent
    drug-specific T-cell response.
  role: amplifier
  biological_scale: ORGANISM
  evidence:
  - reference: PMID:25115449
    reference_title: "Insights into the poor prognosis of allopurinol-induced severe cutaneous adverse reactions: the impact of renal insufficiency, high plasma levels of oxypurinol and granulysin."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Poor renal function was significantly associated with the delayed clearance
      of plasma oxypurinol, and increased the risk of allopurinol-SCAR (p<0.001,
      OR (95% CI) 8.0 (3.9 to 17)).
    explanation: >-
      The prospective cohort directly supports impaired renal clearance as an
      exposure-amplifying cofactor in allopurinol-SCAR.
  downstream:
  - target: Drug-specific cytotoxic T-cell activation
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Sustained oxypurinol exposure amplifies the concentration-dependent
      generation of drug-specific T cells.
    evidence:
    - reference: PMID:24152157
      reference_title: "Allopurinol hypersensitivity is primarily mediated by dose-dependent oxypurinol-specific T cell response."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Allopurinol allergic patients are primarily sensitized to oxypurinol in a
        dose-dependent manner.
      explanation: >-
        In-vitro evidence establishes the concentration-dependent response that
        sustained oxypurinol exposure can amplify.
- name: Drug-specific cytotoxic T-cell activation
  conforms_to: "drug_hypersensitivity_scar#Drug-Specific Cytotoxic T-Cell and NK-Cell Activation"
  description: >-
    Oxypurinol-specific CD8 T cells are activated in a concentration-dependent
    response favored by HLA-B*58:01, then expand as the effector population that
    targets keratinocytes. NK cells also participate in the convergent SJS/TEN
    effector response.
  role: amplifier
  biological_scale: CELLULAR
  cell_types:
  - preferred_term: CD8-positive cytotoxic T cell
    term:
      id: CL:0000625
      label: CD8-positive, alpha-beta T cell
  - preferred_term: natural killer cell
    term:
      id: CL:0000623
      label: natural killer cell
  biological_processes:
  - preferred_term: T cell activation
    term:
      id: GO:0042110
      label: T cell activation
    modifier: INCREASED
  evidence:
  - reference: PMID:24152157
    reference_title: "Allopurinol hypersensitivity is primarily mediated by dose-dependent oxypurinol-specific T cell response."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Allopurinol allergic patients are primarily sensitized to oxypurinol in a
      dose-dependent manner. TCL induction data show that both the presence of
      HLA-B*58:01 allele and high concentration of drug are important for the
      generation of drug-specific T cells.
    explanation: >-
      In-vitro T-cell-line experiments support concentration-dependent
      oxypurinol sensitization and the amplifying contribution of HLA-B*58:01.
  - reference: PMID:33341195
    reference_title: "Diagnosis and management of Stevens-Johnson syndrome/toxic epidermal necrolysis."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Drug-specific CD8 T-cells and natural killer cells are thought to be the
      major inducers of keratinocyte apoptosis via release of soluble cytotoxic
      mediators, including Fas ligand, perforin/granzyme, tumor necrosis factor,
      and granulysin.
    explanation: >-
      Identifies drug-specific CD8 T cells and NK cells as the effector population
      driving keratinocyte death, matching the module amplifier node. Evidence
      source is OTHER because this is a review article.
  downstream:
  - target: Keratinocyte death by cytotoxic mediators
    causal_link_type: DIRECT
    description: >-
      Activated cytotoxic lymphocytes release mediators that kill keratinocytes.
    evidence:
    - reference: PMID:33341195
      reference_title: "Diagnosis and management of Stevens-Johnson syndrome/toxic epidermal necrolysis."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Drug-specific CD8 T-cells and natural killer cells are thought to be the
        major inducers of keratinocyte apoptosis via release of soluble cytotoxic
        mediators
      explanation: >-
        The review directly supports the activated cytotoxic-cell to
        keratinocyte-death edge.
  - target: Fever
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Systemic immune activation contributes to the influenza-like febrile
      prodrome, although the intervening cytokine pathway is not specified here.
- name: Keratinocyte death by cytotoxic mediators
  conforms_to: "drug_hypersensitivity_scar#Cytotoxic Mediator Release and Keratinocyte Death"
  description: >-
    Activated lymphocytes release granulysin, Fas ligand, and perforin/granzyme,
    driving keratinocyte apoptosis and necroptosis — the central effector lesion
    of allopurinol SJS/TEN and the key conformance target of the SCAR module.
  role: central_effector
  biological_scale: CELLULAR
  cell_types:
  - preferred_term: keratinocyte
    term:
      id: CL:0000312
      label: keratinocyte
  biological_processes:
  - preferred_term: T cell mediated cytotoxicity
    term:
      id: GO:0001913
      label: T cell mediated cytotoxicity
    modifier: INCREASED
  - preferred_term: apoptotic process
    term:
      id: GO:0006915
      label: apoptotic process
    modifier: INCREASED
  evidence:
  - reference: PMID:25355273
    reference_title: "Immunological response in Stevens-Johnson syndrome and toxic epidermal necrolysis."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      With regard to keratinocyte death, several cell death mediators, such as
      FasL, granulysin and annexin A1, have been proposed as playing a role in
      SJS/TEN pathogenesis.
    explanation: >-
      Names the cytotoxic mediators (FasL, granulysin) effecting keratinocyte
      death, matching the module central-effector node. Evidence source is OTHER
      because this is a review article.
  - reference: PMID:28133001
    reference_title: "A Review of the Pathogenesis of Toxic Epidermal Necrolysis."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Apoptosis or necroptosis causes keratinocytes to lose their shape and
      adhesion, and necrosis predominates within a few days.
    explanation: >-
      Specifies apoptosis and necroptosis as the keratinocyte death modalities of
      SJS/TEN. Evidence source is OTHER because this is a review article.
  downstream:
  - target: Epidermal necrolysis and detachment
    causal_link_type: DIRECT
    description: >-
      Confluent keratinocyte death produces full-thickness epidermal necrosis.
    evidence:
    - reference: PMID:28133001
      reference_title: "A Review of the Pathogenesis of Toxic Epidermal Necrolysis."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Total epidermal necrosis separates the epidermis from the dermis.
      explanation: >-
        The review directly supports keratinocyte necrosis progressing to
        dermo-epidermal separation.
- name: Epidermal necrolysis and detachment
  conforms_to: "drug_hypersensitivity_scar#Epidermal Necrolysis and Detachment"
  description: >-
    Confluent keratinocyte death produces full-thickness epidermal necrosis that
    separates the epidermis from the dermis, manifesting as the skin and mucosal
    detachment of allopurinol SJS/TEN.
  role: effector
  biological_scale: TISSUE
  cell_types:
  - preferred_term: keratinocyte
    term:
      id: CL:0000312
      label: keratinocyte
  biological_processes:
  - preferred_term: cell death
    term:
      id: GO:0008219
      label: cell death
    modifier: INCREASED
  evidence:
  - reference: PMID:28133001
    reference_title: "A Review of the Pathogenesis of Toxic Epidermal Necrolysis."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Total epidermal necrosis separates the epidermis from the dermis.
    explanation: >-
      Describes the full-thickness epidermal necrosis with dermo-epidermal
      separation that defines TEN, matching the module effector node. Evidence
      source is OTHER because this is a review article.
  downstream:
  - target: Mucocutaneous failure
    causal_link_type: DIRECT
    description: >-
      Loss of the epidermal barrier produces systemic consequences.
    evidence:
    - reference: PMID:33341195
      reference_title: "Diagnosis and management of Stevens-Johnson syndrome/toxic epidermal necrolysis."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        cutaneous adverse reaction characterized by mucous membrane and
        epidermal detachment, with a mortality ranging from 15% to 25%
      explanation: >-
        Mucous-membrane and epidermal detachment support the transition from
        tissue necrolysis to life-threatening mucocutaneous failure.
  - target: Skin detachment
    causal_link_type: DIRECT
    description: Epidermal necrolysis directly manifests as skin detachment.
  - target: Abnormal blistering of the skin
    causal_link_type: DIRECT
    description: Dermo-epidermal separation manifests clinically as blistering.
  - target: Erosion of oral mucosa
    causal_link_type: DIRECT
    description: Mucosal epithelial necrolysis produces painful oral erosions.
  - target: Conjunctivitis
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Ocular-surface involvement produces acute conjunctival inflammation.
  - target: Genital mucosal erosion
    causal_link_type: DIRECT
    description: Genital mucosal epithelial injury produces erosions.
- name: Mucocutaneous failure
  conforms_to: "drug_hypersensitivity_scar#Mucocutaneous Failure and Systemic Complications"
  description: >-
    Extensive epidermal and mucosal detachment causes skin-barrier failure with
    high morbidity and mortality, the defining consequence of allopurinol SJS/TEN.
  role: consequence
  biological_scale: ORGANISM
  cell_types:
  - preferred_term: keratinocyte
    term:
      id: CL:0000312
      label: keratinocyte
  biological_processes:
  - preferred_term: cell death
    term:
      id: GO:0008219
      label: cell death
    modifier: INCREASED
  evidence:
  - reference: PMID:33341195
    reference_title: "Diagnosis and management of Stevens-Johnson syndrome/toxic epidermal necrolysis."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      immunologically mediated cutaneous adverse reaction characterized by mucous
      membrane and epidermal detachment, with a mortality ranging from 15% to 25%
    explanation: >-
      Documents the mucocutaneous detachment and high mortality that define the
      consequence of SJS/TEN. Evidence source is OTHER because this is a review.
genetic:
- name: HLA-B*58:01 pharmacogenomic susceptibility
  gene_term:
    preferred_term: HLA-B
    term:
      id: hgnc:4932
      label: HLA-B
  association: HLA-B*58:01 strongly predisposes to allopurinol-induced SCAR (SJS/TEN)
  relationship_type: RISK_FACTOR
  variant_origin: GERMLINE
  notes: >-
    HLA-B*58:01 is a clinically actionable pharmacogenomic risk allele, but its
    sensitivity varies across populations and a negative result does not exclude
    risk. The 2025 US study included only 16 adjudicated allopurinol-SCAR cases
    and combined SJS/TEN with DRESS, so its additional HLA-A*34:02 association
    requires replication before being modeled as an established SJS/TEN risk
    factor here.
  variants:
  - name: HLA-B*58:01
    description: >-
      Class I HLA allele present in essentially all allopurinol-SCAR patients in
      the index Han Chinese case-control study; the restricting element for
      drug-specific T-cell recognition.
    evidence:
    - reference: PMID:15743917
      reference_title: "HLA-B*5801 allele as a genetic marker for severe cutaneous adverse reactions caused by allopurinol."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The HLA-B*5801 allele was present in all (100%) 51 patients with
        allopurinol-SCAR, but only in 20 (15%) of 135 tolerant patients
      explanation: >-
        The index Han Chinese case-control study directly supports the stated
        population-specific allele observation.
  evidence:
  - reference: PMID:15743917
    reference_title: "HLA-B*5801 allele as a genetic marker for severe cutaneous adverse reactions caused by allopurinol."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The HLA-B*5801 allele was present in all (100%) 51 patients with
      allopurinol-SCAR, but only in 20 (15%) of 135 tolerant patients
    explanation: >-
      Human case-control data establish HLA-B*58:01 as a strong genetic risk
      factor for allopurinol-induced SCAR.
  - reference: PMID:25047754
    reference_title: "Cost-effectiveness analysis of HLA-B5801 genotyping in the treatment of gout patients with chronic renal insufficiency in Korea."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      the HLA-B5801 allele and renal impairment are strongly associated with
      SCARs
    explanation: >-
      Confirms the HLA-B*58:01 association (and renal impairment as a cofactor)
      with allopurinol SCAR. Evidence source is OTHER because this is a
      cost-effectiveness modeling study.
  - reference: PMID:41160012
    reference_title: "HLA-B*58:01 and Risk of Allopurinol-Induced Severe Cutaneous Adverse Reactions in the US."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      although HLA-B*58:01 was found to be associated with allopurinol-induced
      SCARs, generalizing findings from previous studies, the allele was absent
      in more than one-third of the patient cohort and is therefore an incomplete
      indicator of risk.
    explanation: >-
      This small, mixed-phenotype US cohort confirms association while qualifying
      HLA-B*58:01 as an incomplete predictor across heterogeneous populations.
phenotypes:
- name: Skin detachment
  description: >-
    Widespread epidermal and mucosal detachment, the defining feature of SJS/TEN.
  phenotype_term:
    preferred_term: Skin detachment
    term:
      id: HP:0032156
      label: Skin detachment
  evidence:
  - reference: PMID:33341195
    reference_title: "Diagnosis and management of Stevens-Johnson syndrome/toxic epidermal necrolysis."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      immunologically mediated cutaneous adverse reaction characterized by mucous
      membrane and epidermal detachment, with a mortality ranging from 15% to 25%
    explanation: >-
      Identifies mucous membrane and epidermal detachment as the defining feature.
      Evidence source is OTHER because this is a review article.
- name: Abnormal blistering of the skin
  description: >-
    Mucocutaneous bullae preceding epidermal detachment.
  phenotype_term:
    preferred_term: Mucocutaneous blistering
    term:
      id: HP:0008066
      label: Abnormal blistering of the skin
  evidence:
  - reference: PMID:35437717
    reference_title: "Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis in the Era of Systems Medicine."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      severe mucocutaneous bullous disorders characterized by widespread skin and
      mucosal necrosis and detachment, which are most commonly triggered by
      medications
    explanation: >-
      Characterizes SJS/TEN as drug-triggered mucocutaneous bullous disorders.
      Evidence source is OTHER because this is a review article.
- name: Erosion of oral mucosa
  description: >-
    Widespread oral mucosal erosions or ulceration are a characteristic component
    of the SJS/TEN mucocutaneous presentation.
  phenotype_term:
    preferred_term: Erosion of oral mucosa
    term:
      id: HP:0031446
      label: Erosion of oral mucosa
  evidence:
  - reference: PMID:42482572
    reference_title: "Expert consensus on oral management in autoimmune bullous diseases, erythema multiforme and SJS/TEN."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Stevens-Johnson syndrome and toxic epidermal necrolysis (SJS-TEN) and
      erythema multiforme (EM) often present with clinically similar features in
      the oral mucosa: classically widespread mucosal erosions or ulceration.
    explanation: >-
      The 2026 expert consensus directly supports the specific oral-erosion
      phenotype without asserting an allopurinol-specific frequency.
- name: Conjunctivitis
  description: >-
    Acute ocular-surface inflammation may accompany the mucocutaneous eruption;
    ocular disease can also produce important long-term sequelae.
  phenotype_term:
    preferred_term: Conjunctivitis
    term:
      id: HP:0000509
      label: Conjunctivitis
  evidence:
  - reference: PMID:19243825
    reference_title: "Diagnosis and treatment of Stevens-Johnson syndrome and toxic epidermal necrolysis with ocular complications."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Acute conjunctivitis and oral and nail involvements were reported in all
      patients who remembered the details. Acute conjunctivitis occurred before
      the skin eruptions in 42 patients and simultaneously in 21 patients,
      whereas only 1 patient reported posteruption conjunctivitis.
    explanation: >-
      This 94-patient clinical study directly documents acute conjunctivitis and
      its timing relative to the skin eruption among SJS/TEN patients selected
      for ocular complications; it is not used to infer population frequency.
- name: Genital mucosal erosion
  description: >-
    Genital mucous-membrane erosions may accompany oral and ocular involvement.
  phenotype_term:
    preferred_term: Genital ulcers
    term:
      id: HP:0003249
      label: Genital ulcers
  evidence:
  - reference: PMID:29188475
    reference_title: "Current Perspectives on Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Nasopharyngeal, esophageal, and genital mucosal involvement with blisters,
      erosions as well as secondary development of strictures also play a role.
    explanation: >-
      The review explicitly identifies genital mucosal erosions in SJS/TEN; the
      HPO genital-ulcer term is the closest available specific ontology binding.
- name: Fever
  description: >-
    Fever occurs in the influenza-like prodrome before the painful cutaneous and
    mucous-membrane lesions.
  phenotype_term:
    preferred_term: Fever
    term:
      id: HP:0001945
      label: Fever
  evidence:
  - reference: PMID:29188475
    reference_title: "Current Perspectives on Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      SJS/TEN manifest with an "influenza-like" prodromal phase (malaise, fever),
      followed by painful cutaneous and mucous membrane
    explanation: >-
      The review directly supports fever as a prodromal feature without importing
      an oxcarbazepine-specific frequency into this allopurinol entry.
histopathology:
- name: Full-thickness epidermal necrosis with dermo-epidermal separation
  finding_term:
    preferred_term: Full-thickness epidermal necrosis
    term:
      id: NCIT:C36184
      label: Necrosis
  description: >-
    Confluent epidermal necrosis separates the epidermis from the dermis, providing
    the tissue-level correlate of clinical detachment.
  evidence:
  - reference: PMID:28133001
    reference_title: "A Review of the Pathogenesis of Toxic Epidermal Necrolysis."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Total epidermal necrosis separates the epidermis from the dermis.
    explanation: >-
      The review directly describes the defining tissue lesion and plane of
      separation.
diagnosis:
- name: Clinical SJS/TEN spectrum classification with skin-biopsy histopathology
  description: >-
    Diagnose epidermal necrolysis by clinical assessment together with compatible
    histopathology, and classify extent as SJS (<10% detached body surface area),
    overlap (10-30%), or TEN (>30%).
  diagnosis_term:
    preferred_term: skin biopsy
    term:
      id: NCIT:C51692
      label: Skin Biopsy
  evidence:
  - reference: PMID:29188475
    reference_title: "Current Perspectives on Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The difference between SJS, SJS/TEN overlap, and TEN is defined by the
      degree of skin detachment: SJS is defined as skin involvement of < 10%, TEN
      is defined as skin involvement of > 30%, and SJS/TEN overlap as 10-30% skin
      involvement. The diagnosis of different degrees of epidermal necrolysis is
      based on the clinical assessment in conjunction with the corresponding
      histopathology.
    explanation: >-
      This directly supports both the spectrum thresholds and the combined
      clinical-histopathologic diagnostic approach.
- name: ALDEN culprit-drug causality assessment
  description: >-
    Apply the Algorithm of Drug Causality for Epidermal Necrolysis (ALDEN) to
    assess whether allopurinol is the culprit rather than inferring attribution
    from exposure alone.
  diagnosis_term:
    preferred_term: drug causality assessment
  evidence:
  - reference: PMID:20375998
    reference_title: "ALDEN, an algorithm for assessment of drug causality in Stevens-Johnson Syndrome and toxic epidermal necrolysis: comparison with case-control analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Being more sensitive than a general method, ALDEN, which correlates well
      with case-control analysis results, can be considered a reference tool in
      SJS/TEN.
    explanation: >-
      The validation study supports ALDEN as a reference method for assigning
      culprit-drug causality in SJS/TEN.
- name: SCORTEN severity and prognosis assessment
  description: >-
    Use the Severity-of-Illness Score for Toxic Epidermal Necrolysis (SCORTEN) to
    assess SJS/TEN severity and prognosis after diagnosis.
  diagnosis_term:
    preferred_term: SCORTEN severity score
  evidence:
  - reference: PMID:29188475
    reference_title: "Current Perspectives on Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      severity-of-illness score for toxic epidermal necrolysis (SCORTEN) is
      available for SJS/TEN severity assessment.
    explanation: >-
      The clinical review explicitly identifies SCORTEN for severity assessment
      across the SJS/TEN spectrum.
treatments:
- name: Causative drug withdrawal and supportive care
  description: >-
    Immediate withdrawal of allopurinol and multidisciplinary supportive care
    (often in an ICU or burn unit) are the cornerstone of management.
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:35437717
    reference_title: "Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis in the Era of Systems Medicine."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      immediate withdrawal of causative agents, and critical multidisciplinary
      supportive care are key management of SJS/TEN
    explanation: >-
      Identifies causative-drug withdrawal and supportive care as key management
      of SJS/TEN. Evidence source is OTHER because this is a review article.
- name: HLA-B*58:01 pre-prescription screening
  description: >-
    Genotyping for HLA-B*58:01 before allopurinol in high-risk populations to
    avoid the drug in carriers and prevent SCAR.
  treatment_term:
    preferred_term: genetic testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  evidence:
  - reference: PMID:26399967
    reference_title: "Use of HLA-B*58:01 genotyping to prevent allopurinol induced severe cutaneous adverse reactions in Taiwan: national prospective cohort study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Prospective screening of the HLA-B*58:01 allele, coupled with an alternative
      drug treatment for carriers, significantly decreased the incidence of
      allopurinol induced SCARs in Taiwanese medical centres.
    explanation: >-
      A national prospective cohort provides direct clinical evidence that
      pre-prescription screening plus allopurinol avoidance in carriers prevents
      allopurinol-induced SCAR in Han Chinese patients.
  - reference: PMID:25047754
    reference_title: "Cost-effectiveness analysis of HLA-B5801 genotyping in the treatment of gout patients with chronic renal insufficiency in Korea."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Recent American College of Rheumatology guidelines recommend that, prior to
      treatment with allopurinol, the HLA-B5801 genotype of gout patients at high
      risk for SCARs, including Korean patients with chronic renal insufficiency,
      should be determined.
    explanation: >-
      Supports HLA-B*58:01 pre-prescription genotyping as a guideline-recommended
      preventive strategy. Evidence source is OTHER because this is a
      cost-effectiveness modeling study.
experimental_models:
- name: Oxypurinol-stimulated patient PBMC model
  description: >-
    In-vitro oxypurinol stimulation of peripheral blood mononuclear cells from
    resolved allopurinol-induced SJS/TEN cases models the drug-reactive CD8 T-cell
    response and its oligoclonal TCR repertoire.
  experimental_model_type: PRIMARY_CELL_CULTURE
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  conditions:
  - resolved allopurinol-induced SJS/TEN
  - oxypurinol exposure
  cell_source: Peripheral blood mononuclear cells from resolved cases and drug-naïve donors
  culture_system: In-vitro drug stimulation with paired alpha-beta TCR repertoire analysis
  publication: PMID:37452515
  modeled_mechanisms:
  - target: Oxypurinol-HLA class I interaction with HLA-B*58:01 susceptibility
    description: Models the labile oxypurinol interaction with peptide/HLA complexes.
    evidence:
    - reference: PMID:37452515
      reference_title: "The allopurinol metabolite, oxypurinol, drives oligoclonal expansions of drug-reactive T cells in resolved hypersensitivity cases and drug-naïve healthy donors."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        this response supported the pharmacological interaction with immune
        receptors (p-i) concept by showcasing (i) the labile metabolite
        interaction with peptide/HLA complexes
      explanation: >-
        The experiment directly models the oxypurinol-peptide/HLA interaction.
  - target: Drug-specific cytotoxic T-cell activation
    description: Models oxypurinol-driven CD8 T-cell activation and clonal expansion.
    evidence:
    - reference: PMID:37452515
      reference_title: "The allopurinol metabolite, oxypurinol, drives oligoclonal expansions of drug-reactive T cells in resolved hypersensitivity cases and drug-naïve healthy donors."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        OXP is the driver of CD8+ T cell-mediated responses
      explanation: >-
        The experiment directly supports the modeled T-cell activation response.
  evidence:
  - reference: PMID:37452515
    reference_title: "The allopurinol metabolite, oxypurinol, drives oligoclonal expansions of drug-reactive T cells in resolved hypersensitivity cases and drug-naïve healthy donors."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Examination of paired OXP-induced αβTCR repertoires highlighted an
      oligoclonal and private clonotypic profile in both resolved ALP-induced
      SJS/TEN cases and drug-naïve healthy donors.
    explanation: >-
      This describes the principal clonotypic finding of the primary-cell model.
review_notes: >-
  Publication-readiness review (2026-08-04): the generic SJS/TEN Falcon research
  artifact and current literature were cross-checked against this drug-specific
  entry. The 2025 US association with HLA-A*34:02 was reviewed but not promoted to
  a separate genetic assertion because it derives from only 16 mixed SJS/TEN and
  DRESS cases and needs phenotype-specific replication. Recent all-cause SJS/TEN
  single-cell studies were not promoted because they do not establish an
  allopurinol-specific mechanism; no allopurinol-specific interventional trial or
  validated animal/computational disease model was identified. Generic acute
  immunomodulatory management, including systemic steroids, IVIG, cyclosporine,
  and TNF inhibition, is curated in the parent Stevens-Johnson_Syndrome entry and
  is not duplicated here; culprit-drug withdrawal and supportive care are retained
  because they directly apply to allopurinol attribution. Oxcarbazepine-series
  frequency snippets were removed from the phenotype section rather than
  generalized to allopurinol cases.

Allopurinol-Induced Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis

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