The pathophysiology of drug hypersensitivity

The pathophysiology of drug hypersensitivity | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 16 October 2025 V1 Latest version Share on The pathophysiology of drug hypersensitivity Authors : Michael Rieder 0000-0003-3079-2873 [email protected] and Abdelbaset Elzagallaai 0000-0002-4036-9123 Authors Info & Affiliations https://doi.org/10.22541/au.176060171.10861959/v1 257 views 186 downloads Contents Abstract Supplementary Material Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Drug Hypersensitivity reactions (DHRs) - either Immediate or Delayed – are among the most feared adverse effects of drug therapy. While DHRs are perhaps one-sixth of all ADRs, they are among the most problematic given that they are unpredictable, often severe and are major disruptors of therapy both currently and in the future. A key problem with addressing DHRs is the lack of a clear understanding of their pathophysiology, which appears quitomplex. The immune system in a clearly a key mediator of DHRs, but while IgE has been identified as a core element in the pathophysiology of immediate DHRs, much less is known for delayed DHRs. The classical hypotheses for the pathophysiology are the Hapten Hypothesis, the Pharmacologic Interference Hypothesis and the Danger Hypothesis. More recently the Altered Peptide Repertoire Hypothesis has been suggested. Recent work demonstrating the potential contributions of viral infection and inflammasome activation have led us to propose the Cross-Reactivity Hypothesis as a unifying platform bring the hypotheses together and to help understand potential role(s) other factors in the dysregulated immune activation resulting in delayed DHRs. Hence delayed DHRs may begin with metabolism of the drug to a reactive metabolite with haptenation and activation of the immune system not as a solitary players but rather as part of a proinflammatory milieu driven by pathogen or danger signals. There is an urgent need for research to better define the pathophysiology of delayed DHRs to inform best approaches to diagnose, treat and ideally prevent these serious ADRs. Introduction and Classification of Adverse Drug Reactions Adverse drug reactions (ADRs) are a major issue in healthcare, being among the top six causes of death in most high-income countries and an increasingly issue for middle- and low-iincome countries not only in terms of mortality but in terms of morbidity and cost to the health care system (1-3). ADRs are part of a wide range of adverse drug effects and have classically been largely grouped into two distinct classifications, Type A (Predictable) and Type B (Unpredictable) (4). Type A reactions can be predicted from the drug’s pharmacology and include issues such as side effects, secondary effects and interactions, while Type B reactions include issues such as idiosyncratic reactions and allergy. Drug hypersensitivity reactions (DHRs) are classified as Type B reactions and are defined as “ objectively reproducible symptoms of signs initiated by exposure to a defined stimulus at a dose tolerated by normal subjects ” (5). This is a fairly broad definition which includes events with a clearly defined immunological mechanism such as penicillin allergy or events in which an immunological mechanism has not been defined (6). DHRs have classically been grouped into immediate and delayed reactions and were classically considered to be dose-independent and unpredictable as opposed to Type A reactions which display clear dose dependency and have clinical manifestations that were predicated on the drug’s known pharmacology. However, this has been brought into question as there is clearly a threshold dose required for immune system recognition/activation and there have been a series of genetic markers identified which can with some accuracy predict individuals at risk for a DHR, suggesting a degree of overlap between Type A and B ADRs (7-10). While classified as a Type B ADR, DHRs can be further classified into sub-types based on the system of Gell and Coombs, which uses the putative mechanism of immune activation and response to group immune-mediated events into Types I – IV (11, 12). Type I reactions are mediated by antibodies, primarily IgE, and clinically include drug and environmental allergy (13). Type IV reactions are T-cell mediated and include a range of clinical manifestations such as Stevens-Johnson Syndrome (SJS), Serum-Sickness Like Reactions (SSLR) and Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS) (14,15). There are key mechanistic differences in the pathophysiology of Type I versus Type IV reactions that significantly impact their clinical presentations, course and outcomes. Taken collectively DHRs represent a minority of ADRs, with estimates that in total they represent at most 15% of ADRs (16). However, the overall unpredictable nature of these reactions and the potential severity of their clinical expression – which can range from a mild self-limited rash to a life-threatening condition such as SJS – have made them among the most concerning types of ADRs and have resulted in circumstances which in the extreme can amount to therapeutic nihilism. Immediate Onset DHRs Immediate onset DHRs represent what many clinicians and patients view as the classical form of drug allergy (18). The pathophysiology of these reactions is reasonably well understood and frequently involves the development of drug-specific IgE (19-21). The initial pathogenesis in the case of the commonest manifestations of drug allergy involves the metabolism of a fraction of the dose – often a small fraction – to a reactive intermediate which associates as a hapten with protein, leading to recognition of the hapten-protein complex as non-self by an antigen-presenting cell such as a macrophage or a dendritic cell (21). The antigen is then processed as the cell migrates to a regional lymph node where the antigen is presented to a naïve T cell. At this point an important distinction occurs; in individuals with an allergic diathesis the T cell response will be driven towards differentiation into Th2 cells while there is a simultaneous internalization of the antigen by B cells and processing via the Major Histocompatibility Comples (MHC) class II pathway. Presentation of the antigen-MHC II complex to Th2 cells and binding of B cell surface CD40 with CD40L on the Th2 cell then results in the release of cytokines and B cell activation with isotype switching from IgM to IgE, a process further driven by cytokine release (21-24). The sum of these events is the production of isotype-specific IgE against the drug in question, with any subsequent exposure leading to cross-linking of the specific IgE on mast cells and basophils with the release of key mediators such as histamine leading to the clinical expression of drug allergy (23). The clinical expression of a classical Type I DHR is driven by the pathophysiologic mechanism. Typically, there is an initial or priming exposure during which the person tolerates therapy with no adverse events but during which drug exposure leads to immune processing and activation. On a subsequent exposure the presence of drug-specific IgE leads to rapid development of symptoms, typically with hours of the initiation of therapy and characterized by manifestations of IgE mediated immune system activation including angioedema, urticaria, pruritis and bronchospasm which can progress to anaphylaxis and death (24-26). This potentially dire sequence of events has led, notably in the case of the beta-lactam antibiotics, to well recognized mislabelling of patients, with many health care systems recording a 10% rate of penicillin allergy when the actual rate is probably nearer 1% (25, 27-29). Strategies to address this substantial gap between perception and reality – given the known risks of mislabeling – include structured oral challenges and a series of in vitro and in vivo assessments including skin tests and determination of drug-specific antibodies (22, 23, 30, 31). Delayed Onset DHRs The situation with delayed onset DHRs is much more complex and much less understood. As the name implies, the clinical presentation of these reactions is delayed after the initiation of therapy, often between 4 – 5 days to 14 days after the start of therapy, although it may take up to six weeks for symptoms to manifest themselves (32-35). There are a wide range of clinical presentations, suggesting in turn a possible wide range of pathophysiological mechanism(s). These include a number of cutaneous presentations ranging from maculopapular rashes to more serious conditions such as SJS, toxic epidermal necrolysis (TEN), Fixed Drug Eruption, acute generalized exanthematous pustulosis (AGEP), and DRESS (15, 17, 32). In the case of blistering and exfoliating cutaneous manifestations such as SJS and TEN they are not only severe but are associated with a mortality risk of between 5 and 30%, depending on a series of known risk factors (36, 37). The highly variable clinical presentations, course and outcomes of delayed onset DHRs suggests that there may be considerable heterogeneity in their underlying pathophysiology. There are, however, some elements that are likely to be common to all delayed DHRs. The time of onset, manifestations and course of these reactions all point to the centrality of immune dysregulation as a mechanistic underpinning for these adverse events, more specifically to the likely key role of T cells in the development and progression of delayed onset DHRs (15, 38-42). The evolutionary development of the immune system as an essential element in the survival of multi-cellular organisms in environments where threats to longevity and existence are abundant involved the key ability to differentiate between self and non-self, which is accomplished by recognition of large molecules such as proteins (43). The immune system is thus able to address threats such as bacteria or tumours while preserving tolerance to endogenous molecules and large molecular complexes. Thus small molecular weight drugs – of note, until recently the vast majority of drugs had molecular weights less than 1000 daltons – would ordinarily not be recognized by the immune system and thus should not trigger an immune response. However the pathogenesis of immediate DHRs via IgE mediated mechanisms provides insights into how this may be possible and how this may in turn lead to a T-cell mediated response manifested clinically as delayed drug hypersensitivity. While work in this area has been hampered by the lack of compelling animal models for delayed DHRs, several hypotheses based on in vitro work and observations from other lines of research have been advanced as to the pathophysiology and underlying mechanisms responsible for drug hypersensitivity (15, 40, 42). These will be considered in turn (Table 1, Figure 1). The Hapten and Reactive Metabolite Hypothesis . Karl Landsteiner first advanced the concept of haptens in 1935 as an outcome of his work exploring contact sensitization to small molecular weight compounds in animals (44). He postulated that a small molecule could become immunogenic by association with a larger molecule – the small molecule being a “hapten” – from the Greek haptein , “to fasten”. It is now appreciated that the smaller molecule – the hapten – can associate with a macromolecule by conversion to an electrophilic and reactive metabolite which can then covalently bond to an endogenous macromolecule, changing its configuration which has the effect of rendering “self” to “non-self” with subsequent immune processing and activation (45, 46). The process of covalent binding via an electrophilic group implies reactive metabolism, with the parent drug – or pro-hapten – being metabolized either spontaneously in vivo, primarily by Phase I isozymes, to a reactive intermediate (15, 46). As an example, the β-lactam antibiotics undergo spontaneous hydrolysis in vivo which produces electrophilic derivatives that covalently bind to lysine residues on proteins such as albumin (47, 48). This raises a question, as while essentially all patients treated with β-lactam antibiotics have β-lactam-haptenated protein in their circulation, only a small minority develop immune-mediated DHRs. Similarly, while the nitroso metabolite of sulfamethoxazole (SMX) has been shown to activate T cells in animal models while the parent SMX does not, it appears that essentially all patients treated with SMX produce a small amount of reactive metabolites but only a small minority of them develop a DHR (49-51). This has been observed with other drugs as well and thus other factors must impact on who does and who does not develop a DHR, suggesting that drug biotransformation and haptenation are the first steps in a complex process (52, 53). The appreciation that biotransformation of drugs does not always involve production of a an inert metabolite but could result in the formation of a reactive metabolite was suggested as early as the 1930s and was crystalized by the pioneering work of Brodie, Mitchell, Gillette and Boyd who demonstrated not only the production of reactive metabolites in vivo but also that these metabolites were key mediators in drug toxicity, for example in the setting of paracetamol overdose (54-58). Subsequent studies have demonstrated the potential role of reactive drug metabolites in drug toxicity (59-63). The role of metabolism appears to be important in immune processing and response. As noted above, β-lactam antibiotics undergoes spontaneous hydrolysis in vivo to produce bβ-lactam-haptenated proteins in essentially all patients treated but only a very small minority develop DHRs (47, 48). This may be due to the need for formation of a reactive or toxic metabolites to fully activate the immune system, which in the case of the β-lactam antibiotics may be related to interaction with lysine metabolites to form compounds known in the case of penicillins as the peniclloyl determinant (or major determinants) and other complexes (minor determinants) (47, 48, 65), Of note, it is now appreciated via in vitro mass-spectrometry that is appears the CYP450 driven metabolism of of amoxicillin can produce a 4-hydroxyphenylacetaldehyde (4HPAA) derivative which had dose-dependent cytotoxity (66). We have demonstrated amoxicillin metabolite-driven differential toxicity in patients who had sustained DRESS during amoxicillin therapy (67). This suggests that, rather than conjugation alone, additional factors such as possibly danger signals may be needed to have a clinically impactful immune response. Drugs associated with a relatively high rate of delayed DHRs such as phenytoin and carbamazepine are known to be extensively metabolized, in some case to known toxic metabolites such as the arene oxide metabolite of carbamazepine (67). Some metabolites can in turn be processed to further toxic moieties. As an example, antibiotic sulphonamides are sulfonyarylamines which unsubstituted amine moiety at the N4 position can be metabolized by Phase I isozyomes to an hydroxylamine which under physiological conditions will auto-oxidize to nitroso, this being very cytotoxic and capable of forming adducts on cysteine, lysine and tyrosine residues (69-71). Metabolism can result in covalent bonds between nucleophilic and electrophilic molecules; these involving sharing of electrons to form electron pairs between atoms in the interacting molecules and are among the most stable bonds observed in biology. We have demonstrated that peripheral blood mononuclear cells – which are predominantly T lymphocytes – isolated from patients who have sustained a delayed DHR to a sulphonamide antibiotic exhibit considerably greater cell death when incubated with the hydroxylamine metabolite of SMX than the cells of drug tolerant controls (39. 72). As well, the cells of the patients post DHR displayed a markedly increased degree of oxidative stress when incubated with reactive sulphonamide metabolites than the cells of tolerant subjects (73). This raises the issue of site of production. While the bulk of human drug metabolism occurs in the liver, many other tissues are metabolically active. Strikingly, most severe delayed DHRs are dominated clinically by cutaneous rather than hepatic expression (34, 74). This may be related to the evanescent nature of reactive drug metabolites and association with cellular macromolecules at or near the site or production. An example illustrating this as a potential mechanism include clozapine, a highly effective second-generation antipsychotic associated with a high rate of agranulocytosis that has been demonstrated to be oxidized by activated neutrophils to a reactive metabolite capable of adducting proteins (75, 76). It is increasingly recognized that the skin is a metabolically active organ and keratinocytes have robust metabolic capacity, which may account for the significant expression of delayed DHRs in the skin (77-81). Thus the Hapten Hypothesis and the Reactive Metabolite are inexorably linked in the that metabolism of the parent drug to a reactive metabolite which can covalently bind to nearby proteins which in turn are recognized and processed by antigen presenting cells as a non-self-antigen an a hapten which in turn leads to processing by the immune system and activation of a dysregulated immune response clinically expressed as delayed drug hypersensitivity, while the reactive/cytotoxic metabolites also can cause directly cell death through a variety of cell death mechanisms including apoptosis, necrosis and necroptosis, which results in release of intracellular ‘danger signals’ that can also prime a dysregulated immune response. This is a compelling but not solitary hypothesis as to the pathophysiology of delayed drug hypersensitivity. The Pharmacological Interference Hypothesis. An alternate hypothesis for the pathophysiology of delayed drug hypersensitivity is the Pharmacological Interference hypothesis or the P I hypothesis, so named as a contraction of the P harmacologic interaction of drugs with antigen-specific I mmune receptors concept (82). This concept, first put forward by Werner Pichler, arose based on the observation that SMX, chemically non-reactive, can in vitro stimulate drug-specific T cells at concentrations normally seen in the plasma during sulphonamide therapy in the absence of APC processing but with MHC restriction (83). This binding does not appear to be covalent based as it is unstable and can be dissociated by washing. Of note, this pattern of binding has also been seen with allergy to metals such as nickel (84, 85). Drugs that may cause DHRs though this proposed mechanism would differ from those which most likely work though the ‘hapten’ model in some respects including the type of chemical bond they can make with endogenous molecules (covalent vs non-covalent). Chemical covalent bonds forms between nucleophilic and electrophilic molecules involving sharing of electrons to form electron pairs between atoms in the interacting molecules. These are the most stable type of chemical bonds compared to ionic, metallic, dipole-dipole interactions and hydrogen bonds. Binding of drugs with T-cell receptors is labile and has low affinity (micromolar to millimolar range). Also, as opposed to hapten making reactive drugs, the type of DHRs that can be elicited through the p-i model are restricted to certain types. For example, ß-lactam antibiotics, which can bind covalently to proteins can cause all types of DHRs (Types I to IV), but carbamazepine is only associated with type IV T-cell-mediated skin reactions [89]. The p-i model proposes that drugs can bind non-covalently to MHC molecules or TCR and causing activation of T-cells in a way similar to superantigens in that they do not need processing and can be recognized by T-cells after binding to MHC molecules [90]. Evidence supporting this model exist but the precise mechanism(s) of interaction between drugs and immune receptors is not well elucidated. However, drugs such as lidocaine, SMX, lamotrigine, carbamazepine and p-phenylinediamine have been shown activate T-cells without the need for covalent binding to endogenous proteins and antigen processing [91]. That being said, the evidence supporting the P I Hypothesis is essentially entirely in vitro and given the much weaker association of ionic bonds versus the covalent bonds purported by the Hapten Hypothesis it remains to be determined if this association is sufficient to drive the robust T cell response driving delayed drug hypersensitivity. The Danger Hypothesis. An alternate potential pathophysiologic mechanism has been proposed draws on work demonstrating mechanistic activation of a immune cell by a foreign antigen via a “danger signal” first published in 1970 by Bretscher and Cohn and articulated as a possible mechanism in the pathogenesis of delayed drug hypersensivitiy by Matzinger in 1994 (86-89). The basis of this hypothesis is that the presentation of a potential antigen in the presence of a danger signal – the precise molecular details of which have yet to elucidated – results in immune activation while presentation in the absence of a danger signal results in tolerance (86, 89). This has been suggested as a potential explanation as to why some patients develop delayed drug hypersensitivity while others – in fact, the majority of others – do not (88). Danger signals, while not all have not identified in optimal detail, appear to be primarily intracellular molecules whose release is the product of cellular injury and death. In vitro work has suggested that signals related to cellular injury can impact various models of hypersensitivity (90. 91). The mechanism(s) underlying this remain unclear as the cellular response to danger signals can vary; some molecules can provide positive-feedback signals while others do not (92-94). Of note, given the potential for reactive drug metabolites to generate oxidative stress this suggests that a combination of drug metabolism, hapentation, oxidative stress and misdirected immune processing may be key interacting factors in the development of delayed drug hypersensitivity (95). The Altered Peptide Repertoire Hypothesis. In the case of a small number of drugs an alternate hypothesis may account for drug hypersensitivity. Abacavir, carbamazepine, and allopurinol are associated with a very strong genetic association with very specific HLA haplotypes (96). Abacavir in particular has been associated with a high rate of cutaneous delayed drug hypersensitivity linked to the HLA-B*57:01 haplotype (97, 98). In the case of these drugs, it appears that binding of the drug to the F pocket of the HlA peptide-binding groove of an MHC class I molecule activates T cells by inducing a conformational change which in turn alters the the peptides which are presented to T cells (99, 100). Thus, the T cell tolerance to MHC-restricted peptides which are presented during thymic development is bypassed, resulting in T cell activation clinically expressed as delayed drug hypersensitivity. A murine transgenic mouse model has demonstrated that abacavir can produce mitochondrial stress in macrophages independently of HLA presentation, and that drug-specific and bystander CD8 + T-cells activation and proliferation could be triggered via CD28-mediated pathways with supported by non-regulatory CD4 + T cells (101). Carbamazepine can similarly associate with HLA-B*1502 and alter previously tolerated self-peptides when presented to T cells, again leading to T cell activation and proliferation (100, 102, 103). Both abacavir and carbamazepine produce peptide repertoire shifts, in the case of abacavir from 20-25% and in the care of carbamazepine 15% (100). Specificity is indicted by the fact that antigen presenting cells with related structural alleles such as B*-57:03 do not activate abacavir-specific T cells (100). The Cross Reactivity Hypothesis. Given the complexity of the mechanism(s) leading to delayed drug hypersensitivity, we have proposed a model incorporating many of the concepts in the various hypotheses outlined above, this being the Cross-Reactivity Model. While haptenatation appears to be a key first step in the development of delayed drug hypersensitivity, it also is not likely to be the only step, as while haptenation to some drugs is very common, delayed drug hypersensitivity is not. There are clearly other factors involved, and thus returning to the Danger Hypothesis might provide some insights into contributory factors driving the dysregulated immune response leading to delayed drug hypersensitivity. It has been observed that viral infection appeared to play a role in drug rash as long ago as 1967, with attention primarily focused on Human Herpesvirus 4 (Epstein-Barr Virus) and infectious mononucleosis (104-108). This was spurred by the observation that up to 80% of patients treated with amoxicillin during active viral infection developed a rash, but that after infection the risk of rash in these same patients dropped to that of the general population (107, 108). It has subsequently been demonstrated that a number of other viruses including human herpes virus 6 (HHV-6), HHV-7, cytomegalovirus, herpes simplex virus (HSV), and varicella-zoster virus also have been associated with drug-induced rashes (109. 110). Further insights have come from the observation that HIV infection appeared to increase the risk of drug-induced skin rash by several fold (111-116). We have demonstrated that this may be associated with drug-induced oxidative stress and alterations in the disulfide proteome; we noted that cultured Jurkat E6.1 cells transfected with HIV-1 transactivator of transcription gene showed imbalanced redox homeostasis and hence reduced ability to deal with oxidative stressors (113). Human primary monocyte-derived macrophages infected with HIV-1 have been shown to have activated NLRP3 inflammasome and IL-1ß secretion, suggesting a mechanistic contribution related to the inflamasome (117). Further to this, viral infection has been shown to induce the mitochondrial antiviral signaling protein MAVS, which in turn mediates type-1 IFN and NF- K B signaling in association with NLRP3 and regulate inflammasome activity (118). An interesting observation is that while viral induced changes may impact on drug handling, drugs may also impact on viruses by reactivation of previously latent viral infections (119-121). This has been most notably described in association with HHV-6 (119, 122). The mechanism(s) by which viral infection contributes to the pathophysiology of delayed drug hypersensitivity remain unclear – as an illustration, while delayed drug hypersensitivity to antimicrobials typically occurs in the context of an infection, for other drugs such as anti-convulsants concurrent infection is distinctly uncommon. In addition to the possible contribution of viral infection, there has been an increasing number of observations linking inflammasome activation with dysregulated immune responses resulting in hypersensitivity (123-125). While the initial observations largely focused primarily on atopic disease, other work has identified a potential role for inflammasomes in the pathophysiology of metal and drug hypersensitivity (126, 127). Inflammasomes are cytosolic multi-protein complexes that play a key part in innate immune responses (128-130). These complexes form in response to stimuli such as pathogen-associated molecular patterns (PAMPs) which are products of infection or danger-associated molecular patterns (DAMPs) which are products of cellular damage including mitochondrial damage and reactive oxidative stress (131). Mechanistically inflammasome activation is mediated by receptor binding, for example by nucleotide-binding domain-like receptors (NLRs), including NLR1, NLR3 and NLR4 (131). There are different types of inflammasomes, classified by the primary sensor proteins that activate the inflammasome; for example, NLRP inflammasomes have NLRs as their primary sensor proteins and are typically activated by bacterial products while AIM2-like receptor inflammasomes recognize double stranded DNA in the cytoplasm (132). Upon activation, inflammasomes trigger inflammation by cleaving pro-inflammatory cytokines such as IL-1β and IL-18 (131). They can also induce cell death, including pyroptosis, programmed cell death differentiated from apoptosis in that pyroptosis involves inflammatory programmed cell death versus the non-inflammatory processes seen in apoptosis (133). Thus the presence of inflammasomes activated by a range of stimuli provides the situation where signals derived from infection (PAMPs) or signals derived from cellular injury (DAMPs) can trigger a profound inflammatory response, suggesting that the inflammasome may be key link in understanding the pathophysiology of delayed drug hypersensitivity, notably given that while hapentation is relatively common delayed drug hypersensitivity is relatively rare. This hypothesis is supported by growing body of evidence demonstrating the involvement of inflammasomes in adverse reactions to drugs and chemicals. Contact sensitivity to the skin sensitizer trinitrochlorobenzene has been shown to be a T-cell mediated response involving inflammasomes activated via an apoptosis-associated speck-like protein containing CARD domain; NLR family pyrin domain containing 3 (NLRP3), which is activated by extracellular ATP and uric acid, is required for the sensitization phase of trinitrochlorobenzene induced contact hypersensitivity, while a murine model has demonstrated the importance of inflammasomes in acetaminophen-induced hepatic injury (134-136). A more direct link is provided by amiodarone. Amiodarone is structurally similar to dronedarone but has a much higher rate of immune-mediated ADRs which include liver injury, interstitial lung disease/fibrosis and thyroid dysfunction (137). Amiodarone reactive metabolites have been shown in vitro to activate inflammasomes while dronedarone does not (138). This may be due to amiodarone metabolites generating DAMPs while dronedarone metabolites do not, which supports the link between production of reactive metabolites with activation of inflammasomes, this in turn resulting in the release of pro-inflammatory cytokines which prime immune cells to generate the inflammatory response expressed clinically as delayed drug hypersensitivity. Additional support for this hypothesis comes from work with the atypical antipsychotic clozapine, which has been known for many years to be associated with agranulocytosis (139). In vitro work has demonstrated that reactive drug metabolites appear to be a key determinant of clozapine-associated agranulocytosis (68,75, 76). When clozapine was studed in vitro using differentiated and nondifferentiated human monocytic THP-1 cells it was found that olanzapine and fluperlapine, which are structurally related but which are not associated with agranulocytosis it was found that clozapine - but not olanzapine or fluperlapine - induced inflammasome-dependent caspase-1 activation and release of IL-1ß (140). Gefitinib has also been shown to activate inflammasomes via DAMP-driven signals, while the 2-hydroxyiminostilbine metabolite of carbamazepine has been shown to drive the release of DAMPs with subsequent activation of inflammasones in human hepatocarcinoma and macrophage cell lines (141,142). Studies of the supernatant of cells incubated with carbamazepine and other drugs support the role of drug-induced danger signals in inflammasome activation (143, 144). Thus the Cross-Reactivity Hypothesis provides a mechanism that links the hapten hypothesis and the danger hypothesis to provide a unified hypothesis underlying the pathophysiology of drug hypersensitivity, which we have labelled the Cross-Reactivity Hypothesis (Figure 1). This hypothesis proposes that T cell activation driven by epitopes from viral or bacterial infection – PAMPs - or from cellular injury driven by mediators such as oxidative stress and cellular injury from reactive drug metabolites – DAMPs - may cross-react with endogenous peptides that have been haptenated by reactive metabolites of the drug in question. Pro-inflammatory cytokines and chemokines produced though this pathway can prime immune cells to favour reaction over tolerance resulting in the clinical expression of immune dysregulation as delayed drug hypersensitivity. Unresolved Questions While the Cross Reactivity Hypothesis provides a unifying platform to link the Hapten Hypothesis with the Danger Hypothesis, many mechanistic questions remain. In addition to more clarity on the molecular driver(s) of drug hypersensitivity and the genetic determinants, the question of localization remains unclear. As noted above, clozapine is associated with the risk of agranulocytosis. This typically occurs in the absence of cutaneous symptoms. In contrast, carbamazepine hypersensitivity is primarily characterized by rash, with hepatic and renal involvement being less common. The reason(s) for this remain unclear and may represent tissue-specific metabolism and immune processing. Further to this, drug transporters are increasingly recognized as important determinants of tissue-specific drug efficacy and toxicity (145,146). As an example, a panel of drug transporters have been associated with the risk of a serious adverse drug event, anthracycline cardiotoxicity (147). The observations that variants in the drug transporter multidrug resistance-associated protein 2 (MRP2) may result in the accumulation of flucloxacillin and associated protein adducts in the liver, potentially contributing to the risk of flucloxacillin-associated hepatotoxicity and the finding that microarray studies of patients with sulphonamide delayed drug hypersensitivity show a negative correlation between expression of the ABCC5 and SLC25A37 transporters and the risk of drug hypersensitivity lend support to the concept that variations in drug transport may be more important in the pathophysiology of delayed drug hypersensitivity than has been appreciated to date (148, 149). Another set of unresolved questions revolve around presentation. In contrast with immediate hypersensitivity which has some phenotypic variability, delayed drug hypersensitivity has enormous phenotypic variation, from life threatening conditions such as Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis to much less severe presentation such as Serum Sickness Like Reactions and Fixed Drug Eruptions. The mechanism(s) responsible for these variations are unclear but are likely to include genetic variations as well as tissue specific factors. One area in which immediate and delayed drug hypersensitivity are similar is phenotypic consistency, in that while subsequent exposures can lead to a more severe presentation the phenotypic nature tends not to change. The factors that lead to this – whether tissue specific metabolism and immune processing, drug transporter variations, differential disease pathophysiology or a combination thereof – remain areas which merit further thoughtful investigation (10, 150-152). Summary and Final Remarks The pathophysiology of delayed drug hypersensitivity is complex and remains unclear, notably with respect to key mechanistic details. We believe that the Cross Reactivity Hypothesis, while providing a platform unifying key aspects of the Hapten Hypothesis and Danger Hypothesis with emerging knowledge on the role of infection and tissue damage/inflammation, remains an incomplete understanding of the mechanistic details of the pathophysiology of this important class of adverse drug effects. The increasing appreciation of genetic variations in informing the potential risk for delayed drug hypersensitivity – and the paired appreciation that in many case the positive predictive value is painfully low – point to the need for a clearer understanding of the pathophysiology of these reactions to inform more targeted – and ideally more clinically impactful – genetic prediction and diagnostic strategies. As well, a better knowledge of the pathophysiology of these reactions is essential in rational pharmacology approaches to design and discover targeted therapeutic interventions to reduce the burden of and improve the outcome of delayed drug hypersensitivity. References 1. Formica D, Sultana J, Cutroneo PM, Lucchesi S, Angelica R, Crisafulli S, Ingrasciotta Y, Salvo F, Spina E, Trifirò G. The economic burden of preventable adverse drug reactions: a systematic review of observational studies. Expert Opin Drug Saf 2018;17(7):681-695. 2. Patton K, Borshoff DC. Adverse drug reactions. Anaesthesia 2018;73 Suppl 1:76-84. 3. Laroche ML, Tarbouriech N, Jai T, Valnet-Rabier MB, Nerich V. Economic burden of hospital admissions for adverse drug reactions in France: The IATROSTAT-ECO study. Br J Clin Pharmacol 2025;91(2):439-450. 4. Coleman JJ, Pontefract SK. Adverse drug reactions. Clin Med (Lond) 2016 ;16(5):481-485. 5. Johansson SG, Hourihane JO, Bousquet J , et al. A revised nomenclature for allergy. An EAACI position statement from the EAACI nomenclature task force . Allergy 200156: p. 813-24. 6. Johansson SG, Bieber T, Dahl R , et al. Revised nomenclature for allergy for global use: Report of the Nomenclature Review Committee of the World Allergy Organization, October 2003 . J Allergy Clin Immunol 2004;113: 832-6. 7. Uetrecht JP. New concepts in immunology relevant to idiosyncratic drug reactions: the ”danger hypothesis” and innate immune system . Chem Res Toxicol 1999; 12:387-95. 8. Elzagallaai AA, Rieder MJ Genetic markers of drug hypersensitivity in pediatrics: current state and promise . Expert Rev Clin Pharmacol 2022;15:715-728 9. Kuruvilla R, Scott K, Pirmohamed SM.Pharmacogenomics of Drug Hypersensitivity: Technology and Translation . Immunol Allergy Clin North Am 2022; 42:335-355. 10. Elzagallaai A, Rieder MJ. A comprehensive update on the human leukocyte antigen and idiosyncratic adverse drug reactions. Expert Review Drug Metabol Toxicol 2025;23:1-12. 11. Coombs R. Gell P, Classifications of allergic reactions responsible for clinical hypersensitivity and disease , in Clinical aspects of immunology , P. Gell, R. Coombs, and P. Lachman, Editors. 1975, Blackwell Scientific Publications: London. p. 761-81. 12. Ackroyd JF, Rook A. Allergy Drug Reactions in Clinical aspects of immunology , P. Gell, R. Coombs, Editors. 1963, Blackwell Scientific Publications: London. p. 693-755. 13. Feng Y, Xu L, Zhang J, Bin J, Pang X, He S, Fang L. Allergenic protein-induced type I hypersensitivity models: a review. Front Allergy 2024;5:1481011. 14. Pallardy M, Bechara R, Whritenour J, et al. on behalf of the HESI Immuno-Safety Technical Committee, Drug Hypersensitivity Reactions Project Team, Drug hypersensitivity reactions: review of the state of the science for prediction and diagnosis, Toxicological Sci 2024; 200:11–30. 15. Elzagallaai AA, Rieder MJ. Pathophysiology of drug hypersensitivity. Br J Clin Pharmacol 2024;90:1856-1868. 16. Demoly P, Viola M, Rebelo Gomes E , et al. , Epidemiology and Causes of Drug Hypersensitivity , in Drug Hypersensitivity , W. Pichler, Editor. 2007, Karger: Basel. p. 2-17. 17. Mockenhaupt M Epidemiology of cutaneous adverse drug reactions . Chem Immunol Allergy 2012; 97:1-17. 18. Warrington R, Silviu-Dan F. Drug allergy. Allergy Asthma Clin Immunol. 2011;7 Suppl 1(Suppl 1):S10. 19. Khan DA, Solensky R. Drug allergy. J Allergy Clin Immunol 2010;125:S126–37. 20. Schnyder B, Brockow K. Pathogenesis of drug allergy–current concepts and recent insights. Clin Exp Allergy 2015 ;45(9):1376-83. 21. Goh SJR, Tuomisto JEE, Purcell AW, Mifsud NA, Illing PT. The complexity of T cell-mediated penicillin hypersensitivity reactions . Allergy 2021;76(1):150-167. 22. Green EA, Fogarty K, Ishmael FT. Penicillin Allergy: Mechanisms, Diagnosis, and Management. Prim Care 2023;50(2):221-235. 23. Jeimy S, Wong T, Ben-Shoshan M, Copaescu AM, Isabwe GAC, Ellis AK. Drug allergy. Allergy Asthma Clin Immunol 2025;20(Suppl 3):78. 24. Torres MJ, Blanca M. The complex clinical picture of beta-lactam hypersensitivity: penicillins, cephalosporins, monobactams, carbapenems, and clavams. Med Clin North Am 2010;94:805-20. 25. Bhattacharya S. The facts about penicillin allergy: a review. J Adv Pharm Technol Res 2010;1(1):11-7. 26. Khan DA. Banerji A, Blumenthal KG . et al . Drug allergy: A 2022 practice parameter update J Allergy Clin Immunol 2022;150:1333 – 1393. 27. Wong T, Atkinson A, t’Jong G, Rieder MJ, Chan ES, Abrams EM. Beta-lactam allergy in the paediatric population. Paediatr Child Health 2020;25(1):62-63. 28. Mirakian R, Leech SC, Krishna MT, et al. Management of allergy to penicillins and other beta-lactams. Clin Exp Allergy 2015 Feb;45:300-327. 29. Minaldi E, Phillips EJ, Norton A. Immediate and Delayed Hypersensitivity Reactions to Beta-Lactam Antibiotics. Clin Rev Allergy Immunol 2022;62(3):449-462. 30. Ali SB, Le TA, Ahmadie A, Yuson C, Kette F, Hissaria P, Smith WB. The role of major and minor determinants in penicillin allergy testing: Time to revisit an old friend? J Allergy Clin Immunol Glob 2023;2(4):100132. 31. Zhang X, Hu F, Hana M et al. An updated review of the diagnostic methods in drug hypersensitivity reactions. Allergy Med 2025;4:100045. 32. Pichler WJ, Adam J, Daubner B , et al. Drug hypersensitivity reactions: pathomechanism and clinical symptoms . Med Clin North Am 2010;94:645-64. 33. Yacoub MR, Berti A, Campochiaro C, Tombetti E, Ramirez GA, Nico A, Di Leo E, Fantini P, Sabbadini MG, Nettis E, Colombo G. Drug induced exfoliative dermatitis: state of the art. Clin Mol Allergy 2016;14(1):9 34. Guvenir H, Arikoglu T, Vezir E , et al. Clinical Phenotypes of Severe Cutaneous Drug Hypersensitivity Reactions . Curr Pharm Des 2019;25:3840-3854. 35. Hama N, Abe R, Gibson A, Phillips EJ. Drug-Induced Hypersensitivity Syndrome (DIHS)/Drug Reaction With Eosinophilia and Systemic Symptoms (DRESS): Clinical Features and Pathogenesis. J Allergy Clin Immunol Pract 2022;10(5):1155-1167. 36. Frantz R, Huang S, Are A, Motaparthi K. Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis: A Review of Diagnosis and Management. Medicina (Kaunas) 2021;57(9):895 37. Wasuwanich P, So JM, Chakrala TS, Chen J, Motaparthi K. Epidemiology of Stevens-Johnson syndrome and toxic epidermal necrolysis in the United States and factors predictive of outcome. JAAD Int 2023;13:17-25. 38. Rieder MJ. Immune mediation of hypersensitivity adverse drug reactions: implications for therapy . Expert Opin Drug Saf 2009;8:331-43. 39. Elzagallaai AA and Rieder M. In vitro testing for diagnosis of idiosyncratic adverse drug reactions: Implications for pathophysiology . Br J Clin Pharmacol 2015;80:889-900. 40. Balakirski G, Merk HF. Cutaneous allergic drug reactions: update on pathophysiology, diagnostic procedures and differential diagnosic . Cutan Ocul Toxicol 2017;36:307-316. 41. Likic R and Bevanda Glibo D. Pathophysiology of allergic drug reactions . Psychiatr Danub 2019;31:66-69. 42. Wang CW, Divito SJ, Chung WH , et al. Advances in the Pathomechanisms of Delayed Drug Hypersensitivity . Immunol Allergy Clin North Am 2022;42:357-373. 43. Harry W. Schroeder, Robert R. Rich, 6 - Antigens and Antigen Presentation, Editor(s): Robert R. Rich, Thomas A. Fleisher, Harry W. Schroeder, Cornelia M. Weyand, David B. Corry, Jennifer M. Puck, Clinical Immunology (Sixth Edition), Elsevier, 2023 Pages 93-106, 44. Landsteiner K, Jacobs L. Studies on the Sensitization of Animals with Simple Chemical Compounds . J Exp Med 1935;61:643-56. 45. Pichler WJ. Drug induced autoimmunity. Curr OpinionAllergy Clin Immunol 2003;3: 249– 253. 46. Naisbitt DJ, Pirmohamed M, Park BK. Immunopharmacology of hypersensitivity reactions to drugs. Curr Allergy Asthma Rep 2003;3(1):22-9. 47. Levine BB and Ovary Z. Studies on the mechanism of the formation of the penicillin antigen. III. The N-(D-alpha-benzylpenicilloyl) group as an antigenic determinant responsible for hypersensitivity to penicillin G . J Exp Med 1961;114:875-904. 48. Meng X, Al-Attar Z, Yaseen FS , et al. Definition of the Nature and Hapten Threshold of the beta-Lactam Antigen Required for T Cell Activation In Vitro and in Patients . J Immunol 2017;198:4217-4227. 49. Naisbitt DJ, Gordon SF, Pirmohamed M , et al. Antigenicity and immunogenicity of sulphamethoxazole: demonstration of metabolism-dependent haptenation and T-cell proliferation in vivo . Br J Pharmacol 2001 133:295-305. 50. Rieder MJ, Uetrecht J, Shear NH, Spielberg SP: Synthesis and in vitro toxicity of hydroxylamine metabolites of sulphonamides. J Pharmacol Exp Ther 1988;244:724-728. 51. Brackett CC. Sulfonamide allergy and cross-reactivity. Curr Allergy Asthma Rep 2007;7(1):41-8. 52. Adair K, Meng X, Naisbitt DJ. Drug hapten-specific T-cell activation: Current status and unanswered questions . Proteomics 2021;21:2000267. 53. Yaseen FS, Saide K, Kim SH , et al. Promiscuous T-cell responses to drugs and drug-haptens . J Allergy Clin Immunol 2015;136:474-6 e8. 54. Fieser LF. Carcinogenic activity, structure, and chemical reactivity of polynuclear aromatic hydrocarbons . Am J Cancer 1983;34:37-124. 55. Miller EC, Miller JA. In vivo combinations between carcinogens and tissue constituents and their possible role in carcinogenesis . Cancer Res 1952;12:547-56. 56. Mitchell JR, Jollow DJ, Potter WZ , et al. Acetaminophen-induced hepatic necrosis. I. Role of drug metabolism . J Pharmacol Exp Ther 1973;187:185-94. 57. Boyd MR, Burka LT, Wilson BJ. Distribution, excretion, and binding of radioactivity in the rat after intraperitoneal administration of the lung-toxic furan, [14C]4-Ipomeanol . Toxicol Appl Pharmacol 1975;32:147-57. 58. Gillette JR, Michell JR, and Brodie BB. Biochemical mechanisms of drug toxicity. Annu Rev Pharmacol 1974;14:271-288. 59. Rieder MJ, Uetrecht J, Shear NH, Spielberg SP: Synthesis and in vitro toxicity of hydroxylamine metabolites of sulphonamides. J Pharmacol Exp Ther 1988;244:724-728. 60. Hess, D, Bird IA, Almawi WY, Rieder MJ: The hydroxylamine of sulfamethoxazole synergizes with FK506 and cyclosporin A, inhibiting T-cell proliferation. J Pharmacol & Exp Ther 1997;281:540-548. 61. Njoku D, Laster MJ, Gong DH , et al. Biotransformation of halothane, enflurane, isoflurane, and desflurane to trifluoroacetylated liver proteins: association between protein acylation and hepatic injury . Anesth Analg 1997 84:173-8. 62. Pirmohamed M, Kitteringham NR, Park BK. The role of active metabolites in drug toxicity . Drug Saf 1994;11:114-44. 63. Cho T, Uetrecht J. How Reactive Metabolites Induce an Immune Response That Sometimes Leads to an Idiosyncratic Drug Reaction . Chem Res Toxicol 2017;30: 295-314. 64. Batchelor FR, Dewdney JM, Gazzard D. Penicillin allergy: the formation of the penicilloyl determinant . Nature 1965;206:362-4. 65. Zhao Z, Batley M, D’Ambrosio C , et al. In vitro reactivity of penicilloyl and penicillanyl albumin and polylysine conjugates with IgE-antibody . J Immunol Methods 2000:242:43-51. 66. Szultka M, Krzeminski R, Jackowski M , et al. Identification of In Vitro Metabolites of Amoxicillin in Human Liver Microsomes by LC-ESI/MS . Chromatographia 2014;77:1027-1035. 67. Dhir A, Kular H, Elzagallaai AA, Carleton B, Rieder MJ, Mak R, Wong T. DRESS induced by amoxicillin-clavulanate in two pediatric patients confirmed by lymphocyte toxicity assay. Allergy Asthma Clin Immunol 2021;17(1):37. 68. Maggs JL, Williams D, Pirmohamed M et al. The metabolic formation of reactive intermediates from clozapine, a drug associated with agranulocytosis in man . J Pharmacol Exp Ther 1995;275:1463-75. 69. Hess, DA, Sisson ME, Suria H, Wijsman J, Puvanesasingham R, Madrenas J, Rieder MJ: Cytoxicity of sulfonamide reactive metabolies: Apoptosis and selective toxicity of CD8+ cells by t he hydroxylamine of sulfamethoxazole. The FASEB J 1999;13:1688-1698. 70. Tailor A, Waddington JC, Hamlett J et al. Definition of Haptens Derived from Sulfamethoxazole: In Vitro and in Vivo . Chem Res Toxicol 2019;32:2095-2106. 71. Lavergne SN, Wang H, Callan HE et al. ”Danger” conditions increase sulfamethoxazole-protein adduct formation in human antigen-presenting cells . J Pharmacol Exp Ther 2009;331:372-81. 72. Elzagallaai AA, Jahedmotlagh Z, Del Pozzo-Magana BR , et al. Predictive value of the lymphocyte toxicity assay in the diagnosis of drug hypersensitivity syndrome . Mol Diagn Ther 2010 14: p. 317-22. 73. Elzagallaai A, Sultan EA, Loubani E, Bend JR, Rieder MJ. Role of Oxidative Stress in Hypersensitivity Reactions to Sulfonamides. J Clin Pharmacol 2020;60:409-421. 74. Marks ME, Botta RK, Abe R et al . Updates in SJS/TEN: collaboration, innovation, and community. Front Med (Lausanne) 2023;10:1213889. 75. Tschen A, Rieder MJ, Oyewumi K, Freeman D: The cytotoxicity of clozapine metabolites: Implications for predicting clozapine-induced agranulocytosis. Clin Pharmacol Ther 1999:65:526-532 . 76. Maggs JL, Williams D, Pirmohamed M , et al. The metabolic formation of reactive intermediates from clozapine, a drug associated with agranulocytosis in man . J Pharmacol Exp Ther 1995; 275:1463-75. 77. Sharma A, Saito Y, Hung SI , et al. The skin as a metabolic and immune-competent organ: Implications for drug-induced skin rash . J Immunotoxicol 2019;16:1-12. 78. Sharma AM, Klarskov K, and Uetrecht J. Nevirapine bioactivation and covalent binding in the skin . Chem Res Toxicol 2013;26:410-21. 79. 7Sharma AM, Novalen M, Tanino T , et al. 12-OH-nevirapine sulfate, formed in the skin, is responsible for nevirapine-induced skin rash . Chem Res Toxicol 2013;26 817-27. 80. Sharma AM and Uetrecht J. Bioactivation of drugs in the skin: relationship to cutaneous adverse drug reactions . Drug Metab Rev 2014;46:1-18. 81. Pirmohamed M, Madden S, and Park BK. Idiosyncratic drug reactions. Metabolic bioactivation as a pathogenic mechanism . Clin Pharmacokinet 1996;31: 215-30. 82. Pichler WJ. The p-i Concept: Pharmacological Interaction of Drugs With Immune Receptors. World Allergy Organ J 2008;1:96-102. 83. Schnyder B, Mauri-Hellweg D, Zanni M , et al. Direct, MHC-dependent presentation of the drug sulfamethoxazole to human alphabeta T cell clones . J Clin Invest 1997;100:136-41. 84. Moulon C, Vollmer J, Weltzien HU/ Characterization of processing requirements and metal cross-reactivities in T cell clones from patients with allergic contact dermatitis to nickel . Eur J Immunol 1995;25:3308-15. 85. Romagnoli P, Spinas GA, Sinigaglia F. Gold-specific T cells in rheumatoid arthritis patients treated with gold . J Clin Invest 1992;89:254-8. 86. Bretscher P, Cohn M. A theory of self-nonself discrimination . Science 1970; 169:1042-9. 87. Matzinger P. Tolerance, danger, and the extended family . Annu Rev Immunol 1994;12:991-1045. 88. Matzinger P. An innate sense of danger . Semin Immunol 1998;10:399-415. 89. Pirmohamed M, Naisbitt DJ, Gordon F , et al. The danger hypothesis–potential role in idiosyncratic drug reactions . Toxicol 2002;181:55-63. 90. Soussi FEA, Brusilovsky M, Buck E, et al . Autologous Organoid-T Cell Co-Culture Platform for Modeling of Immune-Mediated Drug-Induced Liver Injury. Adv Sci (Weinh) 2025 Sep 26:e08584. 91. Won S, Jeong NH, Choi YA, et al . Amygdalin alleviates atopic dermatitis-like skin inflammation via inhibition of Th2 immune responses. Immunopharmacol Immunotoxicol 2025 Oct;47(5):656-665. 92. Gallucci S, Matzinger P. Danger signals: SOS to the immune system . Curr Opin Immunol 2001;13:114-9. 93. Gallucci S, Lolkema M, Matzinger P. Natural adjuvants: endogenous activators of dendritic cells . Nat Med 1999;5:1249-55. 94. Shi Y, Zheng W, Rock KL. Cell injury releases endogenous adjuvants that stimulate cytotoxic T cell responses . Proc Natl Acad Sci USA 2000;97:14590-5. 95. Elzagallaai AA, Sultan EA, Bend JR, et al . Role of Oxidative Stress in Hypersensitivity Reactions to Sulfonamides . J Clin Pharmacol 2020;60(3):409-421, 96. Elzagallaai A, Rieder MJ. A comprehensive update on the human leukocyte antigen and idiosyncratic adverse drug reactions. Expert Review Drug Metabol Toxicol 2025; 23:1-12. 97. Rauch A, Nolan D, Martin A , et al. Prospective genetic screening decreases the incidence of abacavir hypersensitivity reactions in the Western Australian HIV cohort study . Clin Infect Dis 2006;43:99-102. 98. Kuruvilla R, Scott K, Pirmohamed SM. Pharmacogenomics of Drug Hypersensitivity: Technology and Translation. Immunol Allergy Clin North Am 2022;42(2):335-355. 99. Ostrov DA, Grant BJ, Pompeu YA , et al. Drug hypersensitivity caused by alteration of the MHC-presented self-peptide repertoire . Proc Natl Acad Sci U S A 2012; 109:9959-64. 100. Illing PT, Vivian JP, Dudek NL , et al. Immune self-reactivity triggered by drug-modified HLA-peptide repertoire . Nature 2012;486:554-8. 101. Cardone M, Baghdassarian HM, Khalaj M, et al . Insights into regulatory T-cell and type-I interferon roles in determining abacavir-induced hypersensitivity or immune tolerance. Front Immunol 2025;16:1612451. 102. Zhou P, Zhang S, Wang Y, Yang C, Huang J. Structural modeling of HLA-B*1502/peptide/carbamazepine/T-cell receptor complex architecture: implication for the molecular mechanism of carbamazepine-induced Stevens-Johnson syndrome/toxic epidermal necrolysis. J Biomol Struct Dyn 2016;34(8):1806-17. 103. Tham KM, Yek JJL, Liu CWY. Unraveling the genetic link: an umbrella review on HLA-B*15:02 and antiepileptic drug-induced Stevens-Johnson syndrome/toxic epidermal necrolysis. Pharmacogenet Genomics 2024;34(5):154-165. 104. Pullen H, Wright N, and Murdoch JM. Hypersensitivity reactions to antibacterial drugs in infectious mononucleosis . Lancet 1967;2:1176-8. 105. Levy M. The combined effect of viruses and drugs in drug-induced diseases . Med Hypotheses 1984;14: 293-6. 106. Onodi-Nagy K, Kinyo A, Meszes A , et al. Amoxicillin rash in patients with infectious mononucleosis: evidence of true drug sensitization . Allergy Asthma Clin Immunol 2015:1:1. 107. Renn CN, Straff W, Dorfmuller A , et al. Amoxicillin-induced exanthema in young adults with infectious mononucleosis: demonstration of drug-specific lymphocyte reactivity . Br J Dermatol 2002;147:1166-70. 108. Thompson DF, Ramos CL. Antibiotic-Induced Rash in Patients With Infectious Mononucleosis . Ann Pharmacother 2017;51:154-162. 109. Shiohara T, Kano Y. A complex interaction between drug allergy and viral infection . Clin Rev Allergy Immunol 2007;33:124-33. 110. Shiohara T, Ushigome Y, Kano Y , et al. Crucial Role of Viral Reactivation in the Development of Severe Drug Eruptions: a Comprehensive Review . Clin Rev Allergy Immunol 2015; 49:192-202. 111. Coopman SA, Johnson RA, Platt R , et al. Cutaneous disease and drug reactions in HIV infection . N Engl J Med 1993;328:1670-4. 112. Rzany B, Mockenhaupt M, Stocker U , et al. Incidence of Stevens-Johnson syndrome and toxic epidermal necrolysis in patients with the acquired immunodeficiency syndrome in Germany . Arch Dermatol 1993 129:1059. 113. Adeyanju K, Bend JR, Rieder MJ , et al. HIV-1 tat expression and sulphamethoxazole hydroxylamine mediated oxidative stress alter the disulfide proteome in Jurkat T cells . Virol J 2018;15:p. 82. 114. Bigby M, Jick S, Jick H , et al. (1986) Drug-induced cutaneous reactions. A report from the Boston Collaborative Drug Surveillance Program on 15,438 consecutive inpatients, 1975 to 1982 . JAMA 1986;256:3358-63. 115. Gordin FM, Simon GL, Wofsy CB , et al. Adverse reactions to trimethoprim-sulfamethoxazole in patients with the acquired immunodeficiency syndrome . Ann Intern Med 1984;100:495-9. 116. Hennessy S, Strom BL, Berlin JA , et al. Predicting cutaneous hypersensitivity reactions to cotrimoxazole in HIV-infected individuals receiving primary Pneumocystis carinii pneumonia prophylaxis . J Gen Intern Med 1995;10:380-6. 117. Hernandez JC, Latz E, Urcuqui-Inchima S. HIV-1 induces the first signal to activate the NLRP3 inflammasome in monocyte-derived macrophages . Intervirology 2014;57:36-42. 118. McAuley JL, Tate MD, MacKenzie-Kludas CJ , et al. Activation of the NLRP3 inflammasome by IAV virulence protein PB1-F2 contributes to severe pathophysiology and disease . PLoS Pathog 2013:9:e1003392. 119. Zhu H, Komaroff AL, Ren V. Relevance of Human Herpesvirus 6 Reactivation in Drug Rash With Eosinophilia and Systemic Symptoms. JAMA Dermatol 2024;160(6):687. 120. Chan LCE, Sultana R, Choo KJL, et al . Viral reactivation and clinical outcomes in Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS). Sci Rep 2024;14(1):28492. 121. Mizukawa Y, Shiohara T. Recent advances in the diagnosis and treatment of DIHS/DRESS in 2025. Allergol Int 2025;74(3):372-379. 122. Akai N, Hashimoto T, Okuno S, Takai S, Satoh T. Apalutamide-Induced Drug-Induced Hypersensitivity Syndrome/Drug Reaction With Eosinophilia and Systemic Symptoms Involving Reactivation of Human Herpesvirus-6 and Cytomegalovirus: A Case Report. J Dermatol 2025;52(7):e658-e660. 123. Guo H, Liu H, Jian Z, Cui H, Fang J, Zuo Z, Deng J, Li Y, Wang X, Zhao L, Geng Y, Ouyang P, Lai W, Chen Z, Huang C. Nickel induces inflammatory activation via NF-κB, MAPKs, IRF3 and NLRP3 inflammasome signaling pathways in macrophages. Aging (Albany NY) 2019;11(23):11659-11672. 124. Xu J, Tang Y, Shen C, Li K, Zhao M, Zhou F, Tian S, Yu J, Ding Z, Chen Y. Melastoma dodecandrum polysaccharide alleviates allergic rhinitis in mice through modulating NLRP3 and IL-17 axis. Int Immunopharmacol 2025;161:115054. 125. Sun Y, Zhou Y, Peng T, Huang Y, Lu H, Ying X, Kang M, Jiang H, Wang J, Zheng J, Zeng C, Liu W, Zhang X, Ai L, Peng Q. Preventing NLRP3 inflammasome activation: Therapeutic atrategy and challenges in atopic dermatitis. Int Immunopharmacol 2025;144:113696. 126. Zhou H, Wang L, Lv W, Yu H. The NLRP3 inflammasome in allergic diseases: mechanisms and therapeutic implications . Clin Exp Med 2024;24(1):231. 127. Zhang C, Qiao P, Zhang J, Luo Y, Xiao C, Shen S, Hasegawa A, Qiao H, Wang G, Abe R, Fu M. A carbamazepine metabolite activates NLRP3 and controls skin homing of CD8 + T-cells in SJS/TEN. J Dermatol Sci 2024;116(3):80-89. 128. Lamkanfi M, Dixit VM. Mechanisms and functions of inflammasomes. Cell 2014;157(5):1013-22. 129. Guo, H., Callaway, J., Ting, JY. Inflammasomes: mechanism of action, role in disease, and therapeutics. Nat Med 2015;211:677–687. 130. Fu J, Wu H. Structural Mechanisms of NLRP3 Inflammasome Assembly and Activation. Annu Rev Immunol 2023;41:301-316. 131. Zheng, D., Liwinski, T., Elinav, E. Inflammasome activation and regulation: toward a better understanding of complex mechanisms. Cell Discov 2020;6:36 132. Man SM, Kanneganti TD. Regulation of inflammasome activation . Immunol Rev 2015;265 6-21. 133. Vasudevan SO, Behl B, Rathinam VA. Pyroptosis-induced inflammation and tissue damage. Se min Immunol 2023;69:101781. 134. Watanabe H, Gaide O, Petrilli V , et al. Activation of the IL-1 beta-processing inflammasome is involved in contact hypersensitivity . J Invest Dermatol. 2007;127:1956-63. 135. Sutterwala FS, Ogura Y, Szczepanik M , et al. Critical role for NALP3/CIAS1/Cryopyrin in innate and adaptive immunity through its regulation of caspase-1 . Immunity 2006;24:317-27. 136. Imaeda AB, Watanabe A, Sohail MA , et al. Acetaminophen-induced hepatotoxicity in mice is dependent on Tlr9 and the Nalp3 inflammasome . J Clin Invest 2009;119:305-14. 137. Park HS and Kim YN (2014) Adverse effects of long-term amiodarone therapy . Korean J Intern Med 2014;29:571-3. 138. Kato R, Ijiri Y, Hayashi T. Amiodarone, Unlike Dronedarone, Activates Inflammasomes via Its Reactive Metabolites: Implications for Amiodarone Adverse Reactions . Chem Res Toxicol 2021;34:1860-1865. 139. Mijovic A, MacCabe JH. Clozapine-induced agranulocytosis . Ann Hematol 2020;99:2477-2482. 140. Sernoskie SC, Lobach AR, Kato R , et al. Clozapine Induces an Acute Proinflammatory Response That Is Attenuated by Inhibition of Inflammasome Signaling: Implications for Idiosyncratic Drug-Induced Agranulocytosis . Toxicol Sci 2022;186:70-82 141. Kato R, Ijiri Y, Hayashi T , et al. (2020) Reactive metabolite of gefitinib activates inflammasomes: implications for gefitinib-induced idiosyncratic reaction . J Toxicol Sci 2020;45:673-680. 142. Kato R, Ijiri Y, Hayashi T , et al. The 2-Hydroxyiminostilbene Metabolite of Carbamazepine or the Supernatant from Incubation of Hepatocytes with Carbamazepine Activates Inflammasomes: Implications for Carbamazepine-Induced Hypersensitivity Reactions .Drug Metab Dispos 2019;47:1093-1096. 143. Kato R,Uetrecht J. Supernatant from Hepatocyte Cultures with Drugs That Cause Idiosyncratic Liver Injury Activates Macrophage Inflammasomes . Chem Res Toxicol 2017;30:1327-1332. 144. Weston JK, Uetrecht J. Activation of inflammasomes by agents causing idiosyncratic skin reactions: a possible biomarker . Chem Res Toxicol 2014;27:949-51. 145. Liu X. Overview: Role of Drug Transporters in Drug Disposition and Its Clinical Significance. Adv Exp Med Biol 2019;1141:1-12. 146. Chothe PP, Argikar UA, Mitra P et al . Drug transporters in drug disposition - highlights from the year 2023. Drug Metab Rev 2024;56(4):318-348. 147. Aminkeng F, Ross CJD, Rassekh SR, Rieder MJ, Bhavsar AP, Sanatani S, Bernstein D, Hayden MR, Amstutz U, Carleton BC. Pharmacogenomic screening for anthracycline-induced cardiotoxicity in childhood cancer. Br J Clin Pharmacol 2017;83(5):1143-1145. 148. Waddington JC, Ali SE, Penman SL , et al. Cell Membrane Transporters Facilitate the Accumulation of Hepatocellular Flucloxacillin Protein Adducts: Implication in Flucloxacillin-Induced Liver Injury . Chem Res Toxicol 2020; 3:2939-2943. 149. Reinhart JM, Rose W, Panyard DJ , et al. RNA expression profiling in sulfamethoxazole-treated patients with a range of in vitro lymphocyte cytotoxicity phenotypes . Pharmacol Res Perspect 2018; 6:e00388. 150. Weston JK,Uetrecht J. Activation of inflammasomes by agents causing idiosyncratic skin reactions: a possible biomarker . Chem Res Toxicol 2-14;27:949-51. 151. Manson LEN, van den Hout WB, Guchelaar HJ. Genotyping for HLA Risk Alleles to Prevent Drug Hypersensitivity Reactions: Impact Analysis. Pharmaceuticals (Basel) 2021;15(1):4. Table 1 Potential Hypotheses for Drug Hypersensitivity The Hapten Hypothesis The drug is metabolized to a reactive metabolite(s) which covalently binds to an endogenous macromolecule to form a neo-antigen that is recognized by the immune system as non-self antigen. The reactive metabolite may also produce tissue and cell damage. The p-i Concept This Hypothesis postulates that drugs/metabolite can reversibly and non-covalently interact with immune cells receptors to initiate the reaction regardless of antigen processing and presentation. The Danger Hypothesis The immune system mounts a full response to an invading antigen when other molecules in the form of Danger Signals are present. Danger Signals can be released during the process of necrosis/necroptosis or secondary to to viral or bacterial infection. The Altered Peptide Repertoire Hypothesis This hypothesis proposes that a change in the peptide repertoire presented by MHC molecules on APCs drives T-cells activation in the context of drug molecules targeting specific regions in the MHC complex. The Cross Reactivity Hypothesis We propose this hypothesis as a unifying platform to consider the role of both viral activation and other concomitant infections as well as cellular/tissue injury in the pathophysiology of DHRs. This hypothesis proposes that activated T-cells directed against viral or bacterial epitope or other antigens associated with tissue injury may cross react with endogenous peptides ‘haptenated’ by the culprit drug as well as potentially activating inflammasome, leading to the clinical expression of a dysregulated immune response as a delayed DHR. Figure 1. Proposed hypotheses for Delayed Drug Hypersensitivity Supplementary Material File (figure 1.pdf) Download 153.10 KB Information & Authors Information Version history V1 Version 1 16 October 2025 Copyright This work is licensed under a Non Exclusive No Reuse License. Authors Affiliations Michael Rieder 0000-0003-3079-2873 [email protected] University of Western Ontario View all articles by this author Abdelbaset Elzagallaai 0000-0002-4036-9123 Western University View all articles by this author Metrics & Citations Metrics Article Usage 257 views 186 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Michael Rieder, Abdelbaset Elzagallaai. The pathophysiology of drug hypersensitivity. Authorea . 16 October 2025. DOI: https://doi.org/10.22541/au.176060171.10861959/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu . 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