In vitro tests for drug hypersensitivity reactions: an ENDA/EAACI Drug Allergy Interest Group position paper

Inherent clinical properties of non-immediate hypersensitivity to iodinated contrast media

BACKGROUND

Iodinated contrast media (ICM) is a frequently used compound in radiology. Non-immediate hypersensitivity reactions (HSR) appear when a patient leaves the department and usually are undocumented. True hypersensitivity in this group is rarely proved.

METHODS

Single-centre 2014-2018 data were retrospectively analysed. HSR to ICM were classified and investigated according to the time of occurrence (immediate <1 hour, non-immediate >1 hour). ENDA questionnaire and skin tests (prick or intradermal test) were performed according to ENDA/EAACI recommendations.

RESULTS

69 patients with a clinical history of HSR to ICM were identified, 72.46% were females (n = 50). The average age was 56 (SD ± 13.16) years. Non-immediate HSR occurred in 28.99% (n = 20) patients. The suspected culprit drugs were: iodixanol 20% (n = 4), iopromide 5% (n = 1), diatrizoate 10% (n = 2) and iohexol 10% (n = 2). Among non-immediate HSR 96.00% (n = 19) of patients had skin rashes. A statistically significant correlation was found between the clinical symptoms and the type of reaction (p-value <0.05): isolated skin manifestations mostly occurred in non-immediate HSR 75.00% (n = 15). Only 13.04% (n = 9) of all the patients were proved to be allergic to a certain ICM after the proposed diagnostic workup.

CONCLUSIONS

One-third of the hypersensitivity reactions investigated were classified as non-immediate type. Most of them manifested with isolated skin symptoms. The most frequent culprit drug encountered was iodixanol. The overall non-immediate hypersensitivity confirmation rate after diagnostic evaluation was only 15%.

Evaluation of Hypersensitivity Reactions with Leuprolide Acetate and Triptorelin Acetate in Children

INTRODUCTION

Gonadotropin releasing hormone analogues (GnRHa) are commonly used to treat central precocious puberty (CPP). Generally, they are well-tolerated; however adverse reactions have been reported. Local adverse events occur in 10-15% of the patients who were treated with GnRHa. Anaphylactoid reactions with GnRHa are very rarely seen. The aim of this study is to report our clinical experience with hypersensitivity reactions seen in pediatric patients receiving leuprolide acetate (LA) and triptorelin acetate (TA) in CPP at the single pediatric tertiary medical center and to evaluate the incidence rate of hypersensitivity reactions.

METHODS

This retrospective study included children with CPP who were treated with GnRHa (LA and TA) at our hospital between January 2013 and December 2020. We analyzed clinical characteristics of patients who experienced adverse reactions and analyzed the incidence rate.

RESULTS

Seven side effects (adverse reactions) (0.69%) were observed among total of 1010 CPP patients who were treated with TA and LA. Sterile abscesses were observed in 3 patients (0.29%). None of the patients had an anaphylaxis. Tremors of both hands, a vomiting episode, an urticarial rash, and musculoskeletal stiffness were observed in one patient each.

CONCLUSION

In our study, mild reactions were seen in 7 patients. GnRHa can be safely used and well-tolerated medications; but exceedingly rare, severe reactions can be developed.

An EAACI Task Force report on allergy to beta-lactams in children: Clinical entities and diagnostic procedures

Beta-lactam (BL) allergy suspicion is common in children and constitutes a major public health problem, with an impact on patient's health and on medical costs. However, it has been found that most of these reactions are not confirmed by a complete allergic workup. The diagnostic value of the currently available allergy tests has been investigated intensively recently by different groups throughout the world. This has led to major changes in the management of children with a suspected BL allergy. Particularly, it is now well accepted that skin tests can be skipped before the drug provocation test in children with a benign non-immediate reaction to BL. However, there is still a debate on the optimal allergic workup to perform in children with a benign immediate reaction. In addition, management of children with severe cutaneous adverse drug reactions remains difficult. In this review, based on a selection of the most relevant studies found in the literature, we will review and discuss the diagnosis of different forms of BL allergy in children.

Nanoarchitectures for efficient IgE cross-linking on effector cells to study amoxicillin allergy

BACKGROUND

Amoxicillin (AX) is nowadays the β-lactam that more frequently induces immediate allergic reactions. Nevertheless, diagnosis of AX allergy is occasionally challenging due to risky in vivo tests and non-optimal sensitivity of in vitro tests. AX requires protein haptenation to form multivalent conjugates with increased size to be immunogenic. Knowing adduct structural features for promoting effector cell activation would help to improve in vitro tests. We aimed to identify the optimal structural requirement in specific cellular degranulation to AX using well-precised nanoarchitectures of different lengths.

METHOD

We constructed eight Bidendron Antigens (BiAns) based on polyethylene glycol (PEG) linkers of different lengths (600-12,000 Da), end-coupled with polyamidoamine dendrons that were terminally multi-functionalized with amoxicilloyl (AXO). In vitro IgE recognition was studied by competitive radioallergosorbent test (RAST) and antibody-nanoarchitecture complexes by transmission electron microscopy (TEM). Their allergenic activity was evaluated using bone marrow-derived mast cells (MCs) passively sensitized with mouse monoclonal IgE against AX and humanized RBL-2H3 cells sensitized with polyclonal antibodies from sera of AX-allergic patients.

RESULTS

All BiAns were recognized by AX-sIgE. Dose-dependent activation responses were observed in both cellular assays, only with longer structures, containing spacers in the range of PEG 6000-12,000 Da. Consistently, greater proportion of immunocomplexes and number of antibodies per complex for longer BiAns were visualized by TEM.

CONCLUSIONS

BiAns are valuable platforms to study the mechanism of effector cell activation. These nanomolecular tools have demonstrated the importance of the adduct size to promote effector cell activation in AX allergy, which will impact for improving in vitro diagnostics.

State-of-the-Art on Biomarkers for Anaphylaxis in Obstetrics

Anaphylaxis is an unpredictable systemic hypersensitivity reaction and constitutes a high risk of maternal and fetal morbidity and mortality when occurring during pregnancy. Currently, the acute management of anaphylaxis is based on clinical parameters. A total serum tryptase is only used to support an accurate diagnosis. There is a need to detect other biomarkers to further assess high-risk patients in obstetrics. Our objective is to present biomarkers in this complex interdisciplinary approach beyond obstetrician and anaesthetic management. Candidate biomarkers derive either from mediators involved in immunopathogenesis or upcoming molecules from systems biology and proteomics. Serum tryptase is determined by singleplex immunoassay method and is important in the evaluation of anaphylactic mast cell degranulation but also in the assessment of other risk factors for anaphylaxis such as systemic mastocytosis. Another category of biomarkers investigates the IgE-mediated sensitization to triggers potentially involved in the etiology of anaphylaxis in pregnant women, using singleplex or multiplex immunoassays. These in vitro tests with natural extracts from foods, venoms, latex or drugs, as well as with molecular allergen components, are useful because in vivo allergy tests cannot be performed on pregnant women in such a major medical emergency due to their additional potential risk of anaphylaxis.

Single-dose prolonged drug provocation test, without previous skin testing, is safe for diagnosing children with mild non-immediate reactions to beta-lactams

INTRODUCTION

Mild non-immediate reactions (NIRs) to beta-lactams (BLs) are the most frequent manifestation of drug allergy in children. The diagnostic approach is complex as the utility of skin tests (STs) and lymphocyte transformation tests (LTTs) is controversial. Drug provocation test (DPT) is the gold standard, although no standardized protocols exist. We aimed to investigate the utility of DPT in a unique dose without previous STs, and LTTs in the diagnosis of NIRs to BLs in children.

METHODS

We prospectively evaluated children 0-14 years old referred to the Regional University Hospital of Málaga during 2017-2020 reporting NIRs to BLs. We performed a DPT with a unique dose followed by regular treatment at home. If positive, STs and LTTs were done after the reaction had disappeared.

RESULTS

We included 194 children, having 24 (12.4%) a positive DPT. The main culprit was AX (70.1%) followed by AX-clavulanic acid (CLV) (26.8%) and the main symptoms maculopapular exanthema (MPE) (49.5%) and delayed-urticaria (48.5%). A decrease (p = 0.013) in the interval of days between drug administration and onset of symptoms was observed in positive DPT compared with the original reaction (3.5 vs 6 days), with no differences in the overall percentage of MPE and delayed-appearing urticaria (p = 0.551). No severe reactions occurred during DPT. Moreover, STs were positive in 13.33% and LTTs in 52.9%.

CONCLUSIONS

Single-dose DPT without previous STs is a safe and useful way to assess NIRs to BLs in children. LTT has shown to be useful, confirming a T-cell mechanism involved in these reactions.

Detection of drug-specific immunoglobulin E (IgE) and acute mediator release for the diagnosis of immediate drug hypersensitivity reactions

The diagnosis of a drug hypersensitivity reaction (DHR) is complex. The first step after taking the clinical history is to look for a sensitization to confirm or exclude the diagnosis and to identify the culprit drug. Skin tests are the primary means of detecting sensitization in DHR, but are associated with a risk for a severe reaction and may be contraindicated. In vitro tests offer the potential to support or confirm a diagnosis of DHR and influence medical decision making. For immediate-type DHR, a few validated assays for measurement of specific IgE (sIgE) are commercially available to a limited number of drugs. In addition, several home-made sIgE radioimmunoassays have been used in other studies. The sensitivity of the sIgE assay is drug-dependant and generally low (0-85%) for betalactams and reported heterogeneous for other drugs ranging from 26% for chlorhexidine and 44% for suxamethonium to 92% for chlorhexidine. However, as all these studies included patients, in whom DHR was confirmed only by skin tests and not by provocation, the results have to be interpreted carefully and may be unreliable. Determination of mediators during an acute phase of a reaction may indirectly support the diagnosis of a DHR by demonstrating mast cell and basophil mediator release. Negative in vitro tests do not exclude a DHR or imputability of a drug, but a positive result may support causality and eliminate the necessity for a drug provocation test. Unfortunately, evidence is limited with a lack of well-controlled studies in larger numbers of well-phenotyped patients, which results in susceptibility for bias and a need for future multicenter studies.

Predictive factors of amoxicillin immediate hypersensitivity and validation of PEN-FAST clinical decision rule

BACKGROUND

The challenge of delabeling amoxicillin allergy is an important issue for patients and clinicians, especially when anaphylaxis is reported. A recent study has proposed a clinical decision rule, PEN-FAST, to identify low-risk penicillin allergies.

OBJECTIVE

To validate the PEN-FAST clinical decision rule in a population with high risk of suspected immediate amoxicillin allergy and to identify clinical predictive factors of amoxicillin immediate hypersensitivity.

METHODS

We retrospectively analyzed medical records of patients with a suspected immediate amoxicillin allergy who carried out an allergologic evaluation by a specialist in the Allergy Unit of Strasbourg University Hospital from 2015 to 2020.

RESULTS

A total of 142 adult patients (88 women [62.0%]; median age, 52 [interquartile range, 40.3-62.0] years) were analyzed. Most of them reported anaphylaxis (68.8%). Internal validation of PEN-FAST score revealed a good discrimination with area under the curve of 0.86 (95% confidence interval, 0.79-0.92). A cutoff of less than 3 points for PEN-FAST was used to classify 29 from 142 patients at low risk of allergy, of whom only 2 (6.9%) received positive results of allergy testing. The negative predictive value for successful delabeling was 0.93 (95% confidence interval, 0.77-0.99). Predictive clinical features for immediate amoxicillin hypersensitivity were time since reaction (P < .001), time elapsed between drug intake and first symptom (P < .001), severity grade reaction (P < .001), and treatment or hospitalization required (P < .001).

CONCLUSION

PEN-FAST has been validated to identify low-risk penicillin allergies in our European cohort of patients mainly reporting anaphylaxis. This is the first reported external validation of a penicillin allergy clinical decision rule internationally.

Dendritic cells inclusion and cell-subset assessment improve flow-cytometry-based proliferation test in non-immediate drug hypersensitivity reactions

BACKGROUND

Lymphocyte transformation test (LTT) has been widely used to evaluate non-immediate drug hypersensitivity reactions (NIDHRs). However, the lack of standardization and the low sensitivity have limited its routine diagnostic use. The drug presentation by dendritic cells (DCs) and the assessment of proliferation on effector cells have shown promising results. Flow-cytometry-based methods can help apply these improvements. We aimed to assess the added value of using drug-primed-DCs and the determination of the proliferative response of different lymphocyte subpopulations in NIDHRs.

METHODS

Patients with confirmed NIDHR were evaluated by both conventional (C-LTT) and with drug-primed-DCs LTT (dDC-LTT)analysing the proliferative response in T cells and other effector cell subpopulations by using the fluorescent molecule, carboxyfluorescein diacetate succinimidyl ester (CFSE).

RESULTS

The C-LTT showed a significantly lower sensitivity (29.4%) compared with dDC-LTT (61.8%), which was confirmed analysing each particular clinical entity: SJS-TEN (62.5% vs 87.5%), MPE (15% vs 47.4%) and AGEP (33% vs 80%). When including the effector cell subpopulations involved in each clinical entity, CD3⁺ +CD4⁺ T_h 1 or CD3⁺ +NK cells in SJS-TEN, CD3⁺ +CD4⁺ T_h 1+NK cells in MPE and CD3⁺ +NK cells in AGEP, we could significantly increase the sensitivity of the in vitro test to 100%, 68.4% and 100%, respectively, with an overall sensitivity of 87% and 85% of specificity in NIDHR.

CONCLUSIONS

The use of a flow-cytometry-based test, DCs as drug presenting cells, and focusing on effector cell subpopulations for each clinical entity significantly improved the drug-specific proliferative response in NIDHRs with a unique cellular in vitro test.

Sulfonamide Hypersensitivity

Sulfonamides, particularly antimicrobial sulfonamides, have been implicated as a common cause of a spectrum of hypersensitivity reactions. Immediate IgE-mediated reactions have been reported but are much less common than delayed cutaneous reactions. Delayed cutaneous reactions range from benign exanthems to severe cutaneous reactions such as Stevens Johnson syndrome, toxic epidermal necrolysis, or drug reaction with eosinophilia and systemic symptoms. Sulfonamides can be subclassified as antimicrobial sulfonamides and non-antimicrobial sulfonamides, which are also distinguished by key structural differences, resulting in very low risk of cross-reactivity between these two subclasses. Immediate and delayed skin testing and in vitro testing remain limited as options in evaluating antimicrobial sulfonamide hypersensitivity. Drug challenges continue to play an important role in the evaluation of both immediate and delayed reactions, with a growing body of evidence for the safety of direct challenges regardless of human immunodeficiency virus infection status. While numerous "desensitization" protocols have been described for the management of antimicrobial sulfonamide hypersensitivity, there is limited evidence that such procedures are successful because of an induction of tolerance.

Lymphocyte transformation test and cytokine detection assays: Determination of read out parameters for delayed-type drug hypersensitivity reactions

Drug hypersensitivity reactions (DHRs) occur in certain people and are often not predictable. DHRs can be classified as immediate and delayed reactions regarding to onset of clinical manifestations. Both reactions are considered to be an important public health problem because they can lead to life-threatening conditions; however, this review article will focus on delayed DHRs. The most important points for diagnosis of delayed DHRs are the recognition of drug hypersensitivity characteristics and culprit drug identification. While it is usually difficult to identify a culprit drug; clinical evaluation using the causality assessment method, a non-invasive process, can identify the culprit drug without the need for intensive investigation. Delayed DHRs can cause life-threatening conditions; therefore, in vivo skin tests, as well as drug provocation tests, have to be cautiously performed by a drug allergist and have not been recommended in uncontrolled conditions. ENDA/EAACI has recommended that in vitro tests (if available) be performed prior to any in vivo tests. Therefore, in vitro diagnostic tests can be alternative methods to identify a culprit drug for delayed DHR diagnosis as there is no or very low risk for patients under investigation. There are many testing approaches to identify causative agents for delayed DHRs such as: the lymphocyte transformation test (LTT), cytokine/mediator detection assays (i.e. ELISA and flow cytometry-based bead assays), multiplex bead-based immunoassay and ELISpot. The LTT is the most standardized method whereas it has been available in medical schools affiliated with university hospitals. Other in vitro tests, like cytokine detection assays, have also been used, even though they are still being evaluated. They could supplement LTT results that would provide drug allergist's with documentary evidence and prevent risk to patients by avoiding in vivo or drug provocation testing. Hence, the in vitro tests have been promising tests contributing to the management of the delayed DHR work-up process in clinical practice.

Anaphylaxis associated with the mRNA COVID-19 vaccines: Approach to allergy investigation

Reports about cases of anaphylaxis to mRNA vaccines have created anxiety in the community and could increase vaccine hesitancy in the population. There are no standardized protocols for allergy testing to mRNA vaccines. PEG is currently the only excipient in both vaccines with recognized allergenic potential. Allergy to PEG has been reported with increasing frequency over recent years, often in patients who had repeated systemic allergic reactions/anaphylaxis to several classes of drugs before diagnosis. Proposed protocols are based on current knowledge about potential mechanisms of anaphylaxis associated with the mRNA vaccines, and the assumption that polyethylene glycol (PEG) is the most likely culprit. Allergy testing to PEGs and mRNA vaccines is complex and carries the risk of anaphylaxis and should be conducted in a specialist drug allergy center. Appropriate PEG-free emergency medical treatment and supervision should be readily available.

Allergy to penicillin and betalactam antibiotics

Betalactams are the most frequent cause of hypersensitivity reactions to drugs mediated by a specific immune mechanism. Immediate reactions occur within 1 to 6 hours after betalactam administration, and are generally IgE-mediated. They clinically translate into urticaria, angioedema and anaphylaxis. Non-immediate or delayed reactions occur after 1 hour of administration. These are the most common reactions and are usually mediated by T cells. The most frequent type is the maculopapular or morbilliform exanthematous eruption. Most individuals who report allergies to penicillin and betalactams can tolerate this group of antibiotics. To make diagnosis, a detailed medical history is essential to verify whether it was an immediate or non-immediate reaction. Thereafter, in vivo and/or in vitro tests for investigation may be performed. The challenging test is considered the gold standard method for diagnosis of betalactam hypersensitivity. The first approach when suspecting a reaction to betalactam is to discontinue exposure to the drug, and the only specific treatment is desensitization, which has very precise indications. The misdiagnosis of penicillin allergy affects the health system, since the "penicillin allergy" label is associated with increased bacterial resistance, higher rate of therapeutic failure, prolonged hospitalizations, readmissions, and increased costs. Thus, it is essential to develop strategies to assist the prescription of antibiotics in patients identified with a label of "betalactam allergy" at hospitals, and to enhance education of patients and their caregivers, as well as of non-specialist physicians.

In-Vitro Approaches to Predict and Study T-Cell Mediated Hypersensitivity to Drugs

Mitigating the risk of drug hypersensitivity reactions is an important facet of a given pharmaceutical, with poor performance in this area of safety often leading to warnings, restrictions and withdrawals. In the last 50 years, efforts to diagnose, manage, and circumvent these obscure, iatrogenic diseases have resulted in the development of assays at all stages of a drugs lifespan. Indeed, this begins with intelligent lead compound selection/design to minimize the existence of deleterious chemical reactivity through exclusion of ominous structural moieties. Preclinical studies then investigate how compounds interact with biological systems, with emphasis placed on modeling immunological/toxicological liabilities. During clinical use, competent and accurate diagnoses are sought to effectively manage patients with such ailments, and pharmacovigilance datasets can be used for stratification of patient populations in order to optimise safety profiles. Herein, an overview of some of the in-vitro approaches to predict intrinsic immunogenicity of drugs and diagnose culprit drugs in allergic patients after exposure is detailed, with current perspectives and opportunities provided.

Drug-specific history, skin and in vitro tests can reduce the need for drug provocation tests in betalactam-hypersensitivity

BACKGROUND

Many patients report questionable drug hypersensitivity reactions (DHR) to betalactam antibiotics. A workup is required for objectivation. Direct drug provocation tests (DPTs) omitting a prior allergy workup are increasingly recommended as the primary diagnostic approach. However, apart from the risk of severe side effects, DPTs often are a scarce resource in overloaded healthcare-systems. We investigated how many cases can be solved by drug-specific history, drug-specific IgE, and skin tests obviating the need for DPT.

METHODS

We conducted a chart review in a retrospective cohort of 932 patients in an allergy outpatient centre from 2016 to 2017. Patients had been submitted to drug-specific history and specific IgE-, skin prick-, intradermal- and patch-tests with early and late readings with a series of penicillins and cephalosporins but DPTs were no option.

RESULTS

Overall, positive in vitro and/or skin tests were found in 96/932 (10.3%) patients. Drug-specific IgE was detected in 40/932 (4.3%) patients, 61/787 (7.8%) patients had positive skin tests. In vitro tests to Pencillin V showed the highest rate of positivity 24/479 (5.0%) and early readings of ampicillin the highest amongst the skin tests (3/49, 6.1%). Immediate skin tests were more often positive than delayed ones (75:45). The combination of all parameters including drug-specific history solved 346/932 (37.1%) cases while 586/932 (62.9%) remained unresolved. Self-reported DHR could be less often confirmed in females and young children (p < 0.05).

CONCLUSIONS

Testing with betalactams applying simple, cheap, and safe skin and blood tests can solve a third of DHR-cases on a high throughput scale.

Lymphocyte transformation test: History and current approaches

Drug-induced hypersensitivity reactions encompass a variety of different clinical phenotypes ranging from harmless rashes to fatal reactions. They can be classified into allergic (i.e. drug allergy) and non-allergic reactions (i.e. non-allergic hypersensitivity). Drug allergies in turn can either be antibody (e.g. IgE) or T cell-mediated. One of the diagnostic tools for the in vitro detection of drug allergy is the lymphocyte transformation test (LTT) which is based on the activation and expansion of the drug-specific memory T cells following co-incubation of the patient's peripheral mononuclear cells (PMBC) with the suspected drug in vitro. The read-out parameter in the classical LTT is T cell proliferation which can be measured as counts per minute following the addition of radiolabeled thymidine to the cell culture. However, in the course of time different modifications of the classical LTT with regard to the read-out parameters and methods have been proposed. Likewise, variations of the LTT platform itself have been described in the literature. This review article describes the development of the classical LTT and its use in the context of drug allergy detection and summarizes the modifications which have been published over time.

Diagnostic workup including CD203c-based basophil activation test in immediate hypersensitivity due to metronidazole and ornidazole and evaluation of cross-reactivity in between

BACKGROUND

Little is known about the diagnostic approaches for immediate hypersensitivity reactions (IHRs) due to 5-nitroimidazole antibiotics. The aim was to evaluate the usefulness of in vivo tests and basophil activation test (BAT) for the diagnosis of IHRs due to metronidazole and ornidazole and to determine possible cross-reactivity in between.

METHODS

Forty-nine patients with a clear history of IHRs due to these drugs and 20 healthy subjects who were known to tolerate these drugs were included. Skin tests (STs) and single-blind placebo-controlled drug provocation tests (SBPCDPTs) were performed with both drugs whereas BAT was applied only with the culprit drug.

RESULTS

The most and least common reaction types were urticaria/angioedema (34.7%) and anaphylaxis (14.3%), respectively. SBPCDPTs were positive in 15 out of 47 patients, and only 7 had positive STs. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of STs for metronidazole/ornidazole were 33.3%/16.6%, 94.2%/97.3%, 60%/50%, and 84.6%/88.1%, respectively. BAT was positive in 12 out of 15 patients and negative in 10 control subjects, giving a sensitivity rate of 71.4% (CI, 29.0%-96.3%) for metronidazole and 83.3% (CI, 35.8%-99.5%) for ornidazole. The optimal concentration of both drugs for BAT was determined as 5 mg/mL. No cross-reactivity among two drugs was observed according to in vivo tests.

CONCLUSIONS

Our study showed that SBPCDPT and BAT are both useful diagnostic tools for IHRs due to 5-nitroimidazole antibiotics and can be used as supplementary to each other. No cross-reactivity between metronidazole and ornidazole in IHRs exists.

The Role of Benzylpenicilloyl Epimers in Specific IgE Recognition

The high prevalence of allergy to β-lactam antibiotics is a worldwide issue. Accuracy of diagnostic methods is important to prove tolerance or allergy, with skin test considered the best validated in vivo method for diagnosing immediate reactions to β-lactams. Although drug provocation test is the reference standard, it cannot be performed in highly risk reactions or in those with positive skin tests. For skin tests, the inclusion of major and minor determinants of benzylpenicillin (BP) is recommended. Commercial skin test reagents have changed along time, including as minor determinants benzylpenicillin, benzylpenicilloate (BPO), and benzylpenilloate (PO). Major determinants consists of multivalent conjugates of benzylpenicilloyl coupled through amide bond to a carrier polymer, such as penicilloyl-polylysine (PPL) or benzylpenicilloyl-octalysine (BP-OL). The chemical stability of such reagents has influenced the evolution of the composition of the commercial kits, as this requirement is necessary for improving the quality and standardization of the product. In this work, we provide a detailed study of the chemical stability of BP determinants. We observed that those structures suffer from an epimerization process in C-5 at different rates. Butylamine-Benzylpenicilloyl conjugates (5R,6R)-Bu-BPO and (5S,6R)-Bu-BPO were selected as a simple model for mayor determinant to evaluate the role of the different epimers in the immunoreactivity with sera from penicillin-allergic patients. In vitro immunoassays indicate that any change in the chemical structure of the antigenic determinant of BP significantly affects IgE recognition. The inclusion of stereochemically pure compounds or mixtures may have important implications for both the reproducibility and sensitivity of in vivo and in vitro diagnostic tests.

Novel method to analyze cell kinetics for the rapid diagnosis and determination of the causative agent in allergy

Drug-induced allergy (DIA), an unexpectedly triggered side effect of drugs used for therapeutic purposes, is a serious clinical issue that needs to be resolved because it interrupts the treatment of the primary disease. Since conventional allergy testing is insufficient to accurately predict the occurrence of DIA or to determine the drugs causing it, the development of diagnostic and predictive tools for allergic reactions is important. We demonstrated a novel method, termed high-sensitive allergy test (HiSAT), for the rapid diagnosis of allergy (within 1 hr; with true-positive diagnosis rates of 89% and 9% for patients with and without allergy-like symptoms, respectively). HiSAT analyzes the cell kinetics as an index against chemotactic factors in a patient’s serum, as different from the diagnosis using conventional methods. Once allergy has occurred, HiSAT can be used to determine the causative medicine using culture supernatants incubated with the subject’s lymphocytes and the test allergen. This test is more efficient (60%) than the lymphocyte transformation test (20%). Furthermore, in HiSAT, cell mobility significantly increases in a dose-dependent manner against supernatant incubated with lymphocytes from a subject with pollinosis collected at a time when the subject is without allergic symptoms and the antigen. The result demonstraed that HiSAT might be a promising method to rapidly diagnose DIA or to determine with high accuracy the antigen causing allergy.

Biotin-Labelled Clavulanic Acid to Identify Proteins Target for Haptenation in Serum: Implications in Allergy Studies

Clavulanic acid (CLV) and amoxicillin, frequently administered in combination, can be independently involved in allergic reactions. Protein haptenation with β-lactams is considered necessary to activate the immune system. The aim of this study was to assess the suitability of biotinylated analogues of CLV as probes to study protein haptenation by this β-lactam. Two synthetic approaches afforded the labeling of CLV through esterification of its carboxylic group with a biotin moiety, via either direct binding (CLV-B) or tetraethylenglycol linker (CLV-TEG-B). The second analogue offered advantages as solubility in aqueous solution and potential lower steric hindrance for both intended interactions, with the protein and with avidin. NMR reactivity studies showed that both CLV and CLV-TEG-B reacts through β-lactam ring opening by aliphatic amino nitrogen, however with different stability of resulting conjugates. Unlike CLV conjugates, that promoted the decomposition of clavulanate fragment, the conjugates obtained with the CLV-TEG-B remained linked, as a whole structure including biotin, to nucleophile and showed a better stability. This was a desired key feature to allow CLV-TEG-B conjugated protein detection at great sensitivity. We have used biotin detection and mass spectrometry (MS) to detect the haptenation of human serum albumin (HSA) and human serum proteins. MS of conjugates showed that HSA could be modified by CLV-TEG-B. Remarkably, HSA preincubation with CLV excess only reduced moderately the incorporation of CLV-TEG-B, which could be attributed to different protein interferences. The CLV-TEG-B fragment with opened β-lactam was detected bound to the ^404-430HSA peptide of the treated protein. Incubation of human serum with CLV-TEG-B resulted in the haptenation of several proteins that were identified by 2D-electrophoresis and peptide mass fingerprinting as HSA, haptoglobin, and heavy and light chains of immunoglobulins. Taken together, our results show that tagged-CLV keeps some of the CLV features. Moreover, although we observe a different behavior in the conjugate stability and in the site of protein modification, the similar reactivity indicates that it could constitute a valuable tool to identify protein targets for haptenation by CLV with high sensitivity to get insights into the activation of the immune system by CLV and mechanisms involved in β-lactams allergy.

Risk of True Allergy to Local Anesthetics: 10-Year Experience from an Anesthesia Allergy Clinic in China

Background

Local anesthetics (LAs) have been widely used throughout the healthcare settings, especially in local anesthesia and pain management. The incidence of allergic reactions to LAs remains uncertain. The danger of allergic reactions to the use of LAs in every day of clinical practice is a matter of great concern. Therefore, it is necessary to investigate the risk of true allergy to LAs.

Methods

This study retrospectively evaluated the medical records of patients who were referred to an anesthesia allergy clinic in China and underwent allergy tests with LAs over a 10-year period from 2009 to 2019. The following information was collected from medical records: demographics of the patients, reasons for referral, clinical features of drug hypersensitivity reaction (DHR), and test results with LAs. Skin tests combined with an in vitro method, basophil activation test (BAT), were used to investigate allergic reactions to LAs.

Results

A group of 109 patients were included in the analysis. The main reason for referral was the presence of a suspected DHR after procedures with LAs (n=68, 62%), the second most common reason for referral was a history of DHR to other drugs and the need to use LAs for upcoming procedures (n=41, 38%). Of the 68 patients with a suspected DHR to LAs, only six cases presented true allergy and showed positive results in skin tests and/or BAT. And all 41 patients who had a history of DHR to other drugs presented negative in all tests.

Conclusion

Risk of true allergy to LAs may be very low. However, patients with a suspected history of DHR to LAs should be considered for allergy tests. Skin tests and BAT may be useful in the investigation and diagnosis of true allergy to LAs in clinical practice.

The complexity of T cell-mediated penicillin hypersensitivity reactions

Penicillin refers to a group of beta-lactam antibiotics that are the first-line treatment for a range of infections. However, they also possess the ability to form novel antigens, or neoantigens, through haptenation of proteins and can stimulate a range of immune-mediated adverse reactions-collectively known as drug hypersensitivity reactions (DHRs). IgE-mediated reactions towards these neoantigens are well studied; however, IgE-independent reactions are less well understood. These reactions usually manifest in a delayed manner as different forms of cutaneous eruptions or liver injury consistent with priming of an immune response. Ex vivo studies have confirmed the infiltration of T cells into the site of inflammation, and the subsets of T cells involved appear dependent on the nature of the reaction. Here, we review the evidence that has led to our current understanding of these immune-mediated reactions, discussing the nature of the lesional T cells, the characterization of drug-responsive T cells isolated from patient blood, and the potential mechanisms by which penicillins enter the antigen processing and presentation pathway to stimulate these deleterious responses. Thus, we highlight the need for a more comprehensive understanding of the underlying genetic and molecular basis of penicillin-induced DHRs.

Piperacillin-Tazobactam Allergies: An Exception to Usual Penicillin Allergy

Purpose

The majority of penicillin allergy labels are false, and skin tests (ST) have high negative predictive value (NPV) of up to 90%. Piperacillin-tazobactam (PT) allergy has been suspected to be an exception to this, but existing literature is scarce. We investigate the epidemiology, clinical characteristics, testing outcomes and predictive value of ST in patients referred for suspected PT allergies.

Methods

The records of all patients referred for suspected PT allergy testing and prescription rates of PT in all Hong Kong public hospitals (2015–2019) were analyzed.

Results

There was an increase in both PT prescriptions and number of newly reported PT allergies between 2015 and 2019. The majority (91.1%) of patients with suspected PT allergy had at least 1 underlying medical co-morbidity or immunosuppressant use leading to increased risk of infections. Thirty-six patients with suspected PT allergy completed ST. Two patients had positive ST, and 32/34 patients with negative ST underwent drug provocation testing (DPT). Nine of these patients were diagnosed with PT allergy based on positive DPT. Overall, 11/34 (32.4%) were diagnosed with PT allergy and the NPV of ST was 71.9%.

Conclusions

There is growing utilization of PT and corresponding cases of suspected allergies. The majority of suspected PT allergies had increased risk for recurrent infections. Unlike other penicillin allergy, there is a high rate of genuine PT allergy (up to 30%) and a poor NPV of ST (up to 70%). DPT remains the gold standard for accurate diagnosis, and all patients with a suspected allergy should undergo thorough allergy workup.

Penicillin and cephalosporin cross-reactivity: role of side chain and synthetic cefadroxil epitopes

BACKGROUND

Analysis of cross-reactivity is necessary for prescribing safe cephalosporins for penicillin allergic patients. Amoxicillin (AX) is the betalactam most often involved in immediate hypersensitivity reactions (IHRs), and cefadroxil (CX) the most likely cephalosporin to cross-react with AX, since they share the same R1 side chain, unlike cefuroxime (CO), with a structurally different R1. We aimed to analyse cross-reactivity with CX and CO in patients with confirmed IHRs to AX, including sIgE recognition to AX, CX, CO, and novel synthetic determinants of CX.

METHODS

Fifty-four patients with confirmed IHRs to AX based on skin test (ST) and/or drug provocation test (DPT) were included. Serum sIgE to AX and benzylpenicillin was determined by Radioallergosorbent test (RAST). Two potential determinants of CX, involving intact or modified R1 structure, with open betalactam ring, were synthesised and sIgE evaluated by RAST inhibition assay.

RESULTS

Tolerance to CX (Group A) was observed in 64.8% cases and cross-reactivity in 35.2% cases (Group B). Cross-reactivity with CO was only found in 1.8% cases from Group B. ST to CX showed a negative predictive value of 94.6%. RAST inhibition assays showed higher recognition to CX as well as to both synthetic determinants (66% of positive cases) in Group B.

CONCLUSIONS

Cross-reactivity with CX in AX allergic patients is 35%, being ST not enough for prediction. R1, although critical for recognition, is not the unique factor. The synthetic determinants of CX, 1-(HOPhG-Ser-Bu) and 2-(pyrazinone) are promising tools for determining in vitro cross-reactivity to CX in AX allergic patients.

Biomarkers for diagnosis and prediction of therapy responses in allergic diseases and asthma

Modern health care requires a proactive and individualized response to diseases, combining precision diagnosis and personalized treatment. Accordingly, the approach to patients with allergic diseases encompasses novel developments in the area of personalized medicine, disease phenotyping and endotyping, and the development and application of reliable biomarkers. A detailed clinical history and physical examination followed by the detection of IgE immunoreactivity against specific allergens still represents the state of the art. However, nowadays, further emphasis focuses on the optimization of diagnostic and therapeutic standards and a large number of studies have been investigating the biomarkers of allergic diseases, including asthma, atopic dermatitis, allergic rhinitis, food allergy, urticaria and anaphylaxis. Various biomarkers have been developed by omics technologies, some of which lead to a better classification of distinct phenotypes or endotypes. The introduction of biologicals to clinical practice increases the need for biomarkers for patient selection, prediction of outcomes and monitoring, to allow for an adequate choice of the duration of these costly and long‐lasting therapies. Escalating healthcare costs together with questions about the efficacy of the current management of allergic diseases require further development of a biomarker‐driven approach. Here, we review biomarkers in diagnosis and treatment of asthma, atopic dermatitis, allergic rhinitis, viral infections, chronic rhinosinusitis, food allergy, drug hypersensitivity and allergen immunotherapy with a special emphasis on specific IgE, the microbiome and the epithelial barrier. In addition, EAACI guidelines on biologicals are discussed within the perspective of biomarkers.

Advances and novel developments in drug hypersensitivity diagnosis

A correct diagnosis of drug hypersensitivity reactions (DHRs) is very important for both the patient and health system. However, DHRs diagnosis is complex, time consuming, requires trained personnel, is not standardized for many drugs, involves procedures not exempt of risk, and in most cases lacks standardized in vivo and in vitro tests. Thus, there is an urgent need for improving the different approaches to diagnose patients with suspected DHRs. In this review, we have analyzed the advances performed in immediate and nonimmediate DHRs diagnosis during the last two years and obtained several conclusions: the significant heterogeneity in current practice among centers illustrates the need to re-evaluate, update, and standardize in vivo tests and protocols for the diagnosis and management of patients with suspected drug allergy. Regarding in vitro tests, the latest studies have focused on increasing their sensitivity or on establishing the sensitivity and specificity for the tests performed with new drugs. There seems to be a consensus about combining in vivo and in vitro tests as the best way to increase the diagnostic accuracy.

Predominant patterns of β-lactam hypersensitivity in a single German Allergy Center: exanthem induced by aminopenicillins, anaphylaxis by cephalosporins

Background

Penicillins and other β-lactam antibiotics are the most common elicitors of allergic drug reaction. However, data on the pattern of clinical reaction types elicited by specific β-lactams are scarce and inconsistent. We aimed to determine patterns of β-latam allergy, i.e. the association of a clinical reaction type with a specific β-lactam antibiotic.

Methods

We retrospectively evaluated data from 800 consecutive patients with suspected β-lactam hypersensitivity over a period of 11 years in a single German Allergy Center.

Results

β-lactam hypersensitivity was definitely excluded in 595 patients, immediate-type (presumably IgE-mediated) hypersensitivity was diagnosed in 70 and delayed-type hypersensitivity in 135 cases. Most (59 out of 70, 84.3%) immediate-type anaphylactic reactions were induced by a limited number of cephalosporins. Delayed reactions were regularly caused by an aminopenicillin (127 out of 135, 94.1%) and usually manifested as a measles-like exanthem (117 out of 135, 86.7%). Intradermal testing proved to be the most useful method for diagnosing β-lactam allergy, but prick testing was already positive in 24 out of 70 patients with immediate-type hypersensitivity (34.3%). Patch testing in addition to intradermal testing did not provide additional information for the diagnosis of delayed-type hypersensitivity. Almost all β-lactam allergic patients tolerated at least one, usually several alternative substances out of the β-lactam group.

Conclusions

We identified two patterns of β-lactam hypersensitivity: aminopenicillin-induced exanthem and anaphylaxis triggered by certain cephalosporins. Intradermal skin testing was the most useful method to detect both IgE-mediated and delayed-type β-lactam hypersensitivity.

Does delayed urticaria induced by drug allergy exist?

With the help of a routine clinical case about delayed urticaria induced by drug, we have analyzed the scientific societies reports published during the last 5 years on this topic. We highlighted the differences between the EAACI consensus and documents on drug allergy, commenting their positions and some of their definitions on delayed urticaria. However, the question of disagreement between definitions of delayed urticaria can generate confusion. It would be beneficial to have more and "official" clearness about this topic because of its important clinical application to our patients.

Diagnosis and management of the drug hypersensitivity reactions in Coronavirus disease 19: An EAACI Position Paper

Coronavirus disease 2019 (COVID-19), a respiratory tract infection caused by a novel human coronavirus, the severe acute respiratory syndrome coronavirus 2, leads to a wide spectrum of clinical manifestations ranging from asymptomatic cases to patients with mild and severe symptoms, with or without pneumonia. Given the huge influence caused by the overwhelming COVID-19 pandemic affecting over three million people worldwide, a wide spectrum of drugs is considered for the treatment in the concept of repurposing and off-label use. There is no knowledge about the diagnosis and clinical management of the drug hypersensitivity reactions that can potentially occur during the disease. This review brings together all the published information about the diagnosis and management of drug hypersensitivity reactions due to current and candidate off-label drugs and highlights relevant recommendations. Furthermore, it gathers all the dermatologic manifestations reported during the disease for guiding the clinicians to establish a better differential diagnosis of drug hypersensitivity reactions in the course of the disease.

Minimal agreement between basophil activation test and immunoassay in diagnosis of penicillin allergy

INTRODUCTION

Basophil activation test (BAT) and immunoassays are the most widely used in vitro tests to diagnose IgE-mediated allergic reactions to penicillin. However, studies to determine if one test is interdependent from another are limited.

OBJECTIVE

The present study aimed to measure the agreement between BAT and immunoassay in diagnosis of penicillin allergy.

METHOD

BAT was performed using penicillin G (Pen G), penicillin V (Pen V), penicilloyl-polylysine (PPL), minor determinant mix (MDM), amoxicillin (Amx) and ampicillin (Amp) in 25 patients. Immunoassay of total IgE (tIgE) and specific IgE (sIgE) antibodies to Pen G, Pen V, Amx and Amp were quantified. Skin prick test (SPT) using PPL-MDM, Amx, Amp and Clavulanic acid were also performed.

RESULTS

Minimal agreement was observed between BAT and immunoassay (k=0.25). Of two BAT-positive patients, one patient is positive to Amx (59.27%, SI=59) and Amp (82.32%, SI=82) but sIgE-negative to all drug tested. This patient is also SPT-positive to both drugs. Another patient is BAT-positive to Pen G (10.18%, SI=40), Pen V (25.07%, SI=100) and Amp (19.52%, SI=79). In sIgE immunoassay, four patients were sIgE-positive to at least one of the drugs tested. The sIgE level of three patients was between low and moderate and they were BAT-negative. One BAT-positive patient had a high level of sIgE antibodies (3.50-17.5kU/L) along with relatively high specific to total IgE ratio ≥0.002 (0.004-0.007).

CONCLUSIONS

The agreement between BAT and immunoassay is minimal. Performing both tests provides little increase in the sensitivity of allergy diagnosis work-up for immediate reactions to penicillin.

Synchronous Telemedicine in Allergy: Lessons Learned and Transformation of Care During the COVID-19 Pandemic

Background

The outbreak of the COVID-19 pandemic facilitated a rapid transition to non–face-to-face models of care across the allergy services.

Objective

To describe the outcomes of the use of synchronous telemedicine for outpatient consultations in a tertiary adult allergy center.

Methods

We retrospectively reviewed all non–face-to-face appointments during the second month of the pandemic in the United Kingdom.

Results

A total of 637 non–face-to-face appointments for unique patients were booked between April 1 and 30, 2020; 91% were new consultations. Most referrals (81.5%) were related to nondrug reactions. The overall “Did Not Attend” rate was 15.7%. A total of 439 patients were assessed for nondrug reactions; 87% were new appointments. Food-related reactions (50.4%), urticaria/angioedema (23.2%), and rhinitis (18.1%) were the most common reasons for new referrals. Two hundred twenty-one (57.7%) of these patients required further allergy testing, primarily for suspected food allergy. More than 42% of the new patients, mainly referred for urticaria/angioedema, were discharged after their remote assessment. Less than 10% of the follow-up patients required additional testing. Ninety-seven new patients were assessed for a suspected drug reaction, predominantly to beta-lactam antibiotics (57.7%). Sixty-nine patients (71%) required further investigations, but a notable 29% did not require further allergy input. The overall experience was very good/good for most patients (85%).

Conclusion

Telemedicine can transform the current models of allergy care. Screening criteria for selecting suitable new patients are required. A telemedicine-based drug allergy service model can be more time- and cost-effective, and improve patient access to specialist care.

Clinical value of in vitro tests for the management of severe drug hypersensitivity reactions

Drug hypersensitivity reactions (DHRs) occasionally present with severe cutaneous adverse reactions (SCARs) which result in a high risk of morbidity and mortality. Although SCARs are rare, the occurrence could lead to a significant increase in healthcare and economic burden, especially when more than one possible culprit drug is implicated. Therefore, the accurate identification of the culprit drug(s) is important for correct labeling and subsequent patient education and avoidance. To date, clinical evaluation using causality assessment has limitations because the assessment may be inaccurate due to the overlapping timelines when multiple drugs are initiated/continued. Moreover, drug provocation tests (DPTs) which is the gold standard in diagnosis, are contraindicated, and in vivo skin tests may also be associated with risks of triggering SCAR. The European Network for Drug Allergy recommended that in vitro tests, if available, should be performed before any in vivo tests. Basophil activation tests and lymphocyte transformation tests, could serve as reliable in vitro tests for both immediate and delayed-type DHR. Many academic medical centers with affiliated laboratory services offer these tests in the diagnostic evaluation of SCARs in clinical practice. This not only complements identification of the culprit drug(s), but may also be used to test for potentially non cross-reactive alternatives, hence avoiding DPTs. In this review, we summarize the roles of in vitro tests in identifying the culprit drug(s) in SCARs, issues with utilization and interpretation of test results, and our experience in clinical practice.

Diagnostic procedures & practices in drug allergy/hypersensitivity: a survey of 13 Asian countries

BACKGROUND

The issues and challenges in the diagnosis of drug allergy/hypersensitivity among children and adults in Asia are likely to be different from non-Asian countries.

OBJECTIVE

To study the diagnostic modalities used in the evaluation and management of drug allergy/drug hypersensitivity reactions (DHRs) among member societies of the Asia Pacific Association of Allergy, Asthma and Clinical Immunology (APAAACI).

METHODS

A questionnaire comprising 41 questions was circulated electronically to member societies and individual members of APAAACI between January 23, 2020 and March 6, 2020.

RESULTS

Twenty-six respondents from 15 member societies and 1 individual member responded. European DHR guidelines were most commonly used. Skin prick and intradermal testing was used by 100%, with only 60% having access to commercial penicillin skin test reagents. In vitro-specific IgE tests were used by 75%, and basophil activation test by 56.3% for immediate DHR. Patch tests were used by 75% in contrast to lymphocyte transformation tests by 25% for nonimmediate DHR. Drug provocation tests were used by 68.8%, the most common indication being to exclude hypersensitivity where history/symptoms were not suggestive of drug hypersensitivity/allergy (93.3%). Human leukocyte antigen (HLA) genotype testing was mandatory among 25% respondents before new carbamazepine prescriptions, and 8.3% for allopurinol prescriptions.

CONCLUSIONS

There was increased use of skin testing for iodinated contrast media hypersensitivity and patch testing for nonimmediate DHR. HLA genotype testing prior to new carbamazepine, allopurinol and abacavir prescriptions remain variable despite strong associations for severe cutaneous adverse reactions with Asian ethnicity. Results of this survey form a useful framework for developing educational and training needs and for improving access to drug allergy diagnostic and treatment modalities across APAAACI member societies.

Characterization of amoxicillin and clavulanic acid specific T-cell clones from patients with immediate drug hypersensitivity

BACKGROUND

Betalactam (BL) antibiotics are the most common cause of drug hypersensitivity. Amoxicillin (AX), which is often prescribed alongside clavulanic acid (Clav), is the most common elicitor. The aim of this study was to determine whether AX and Clav-responsive T-cells are detectable in patients with immediate hypersensitivity to AX-Clav, to assess whether these T-cells display the same specificity as that detected in skin and provocation testing, and to explore T-cell activation pathways.

METHODS

Drug-specific T-cell clones were generated from immediate hypersensitive patients´ blood by serial dilution and repetitive mitogen stimulation. Antigen specificity was assessed by measurement of proliferation and cytokine release. CD4+ /CD8+ phenotype and chemokine receptor expression were analyzed by flow cytometry.

RESULTS

110 AX-specific and 96 Clav-specific T-cell clones were generated from seven patients with positive skin test to either AX or Clav. Proliferation of AX- and Clav-specific clones was dose-dependent, and no cross-reactivity was observed. AX- and Clav-specific clones required antigen-presenting cells to proliferate, and drugs were presented to CD4+ and CD8+ T-cells by MHC class-II and I, respectively. A higher secretion of IL-13 and IL-5 was detected in presence of the culprit drug compared with the alternative drug. Clones expressed CD69, CCR4, CXCR3, and CCR10.

CONCLUSIONS

Our study details the antigen specificity and phenotype of T-cell clones generated from patients with AX-Clav-induced immediate hypersensitivity diagnosed by positive skin test. AX- and Clav-specific clones were generated from patients irrespective of whether AX or Clav was the culprit, although differences in cytokine secretion were observed.

In vitro identification of drugs inducing systemic hypersensitivity reactions known in vivo to be associated with specific HLA genotypes

Hypersensitivity drug reactions (HDRs) are common among drugs, despite this, there are no validated in vitro or in vivo methods for screening the sensitizing potential of drugs in the preclinical phase. We previously developed the THP-1 activation assay, based on CD86 upregulation and IL-8 production, for the in vitro identification of drugs able to induce selective dendritic cell activation. In this paper, we investigated the predictive capacity of the method toward drugs associated with HDRs for which a correlation with specific human leukocyte antigens (HLA) have been demonstrated. For that purpose, abacavir, carbamazepine and clozapine were used. Metformin was used as negative control. Dose- and time-course experiments were conducted. The surface markers CD86, CD54 and HLA-DR were evaluated by flow cytometry analysis, whereas IL-8 release by ELISA. Abacavir, carbamazepine and clozapine gave positive results with CD86 upregulation and/or IL-8 release, with abacavir also inducing HLA-DR. The test reveals the ability of drugs to induce dendritic cell activation (signals 1/2), that preceded the adaptive immune response, which will be manifested only in a minority of patients carrying the specific HLA genotypes. The idea is to integrate this simple method during drug development to identify the potential of drugs to induce hypersensitivity reactions in the pre-clinical phase.

Role of in vivo and in vitro Tests in the Diagnosis of Severe Cutaneous Adverse Reactions (SCAR) to Drug

Severe cutaneous adverse reactions (SCAR) are life-threatening conditions including acute generalized exanthematous pustulosis (AGEP), Stevens-Johnson Syndrome (SJS), toxic epidermal necrolysis (TEN) and drug reaction with eosinophilia and systemic symptoms (DRESS). Diagnosis of causative underlying drug hypersensitivity (DH) is mandatory due to the high morbidity and mortality upon re-exposure with the incriminated drug. If an underlying DH is suspected, in vivo test, including patch tests (PTs), delayed-reading intradermal tests (IDTs) and in vitro tests can be performed in selected patients for which the suspected culprit drug is mandatory, or in order to find a safe alternative treatment. Positivity of in vivo and in vitro tests in SCAR to drug varies depending on the type of reaction and the incriminated drugs. Due to the severe nature of these reactions, drug provocation test (DPT) is highly contraindicated in patients who experienced SCAR. Thus, sensitivity is based on positive test results in patients with a suggestive clinical history. Patch tests still remain the first-line diagnostic tests in the majority of patients with SCAR, followed, in case of negative results, by delayed-reading IDTs, with the exception of patients with bullous diseases where IDTs are still contra-indicated. In vitro tests have shown promising results in the diagnosis of SCAR to drug. Positivity is particularly high when the lymphocyte transformation test (LTT) is combined with cytokines and cytotoxic markers measurement (cyto-LTT), but this still has to be confirmed with larger studies. Due to the rarity of SCAR, large multi-center collaborative studies are needed to better study the sensitivity and specificity of in vivo and in vitro tests.

Drug Allergy in Children: What Should We Know?

The drug allergy "label" may have a lifetime of consequences for a child. Many children with alleged drug allergies are proven to be tolerant to the culprit medication when challenged. The field of drug hypersensitivity is a recently evolving field of research, but studies on its epidemiology and diagnostic tools are lacking in children. Clinical history is significant in the diagnosis and classification of drug hypersensitivity in children. Diagnostic tools have been evaluated in a limited number of children; therefore, the guidelines are mainly in line with those for adults. Here, we review the clinical characteristics, main drugs, risk factors, and diagnosis of drug hypersensitivity to aid in its accurate diagnosis in children.