Genotyping of the arylamine N-acetyltransferase polymorphism in the prediction of idiosyncratic reactions to trimethoprim-sulfamethoxazole in infants

N-acetyltransferase Gene Variants Involved in Pediatric Idiosyncratic Drug-Induced Liver Injury

Idiosyncratic drug-induced liver injury (DILI) is a complex multifactorial disease in which the toxic potential of the drug, together with genetic and acquired factors and deficiencies in adaptive processes, which limit the extent of damage, may determine susceptibility and make individuals unique in their development of hepatotoxicity. In our study, we sequenced the exomes of 43 pediatric patients diagnosed with DILI to identify important gene variations associated with this pathology. The result showed the presence of two variations in the NAT2 gene: c.590G>A (p.Arg197Gln) and c.341T>C (p.Ile114Thr). These variations could be found separately or together in 41 of the 43 patients studied. The presence of these variations as a risk factor for DILI could confirm the importance of the acetylation pathway in drug metabolism.

Delayed Drug Hypersensitivity Reactions: Molecular Recognition, Genetic Susceptibility, and Immune Mediators

Drug hypersensitivity reactions are classified into immediate and delayed types, according to the onset time. In contrast to the immediate type, delayed drug hypersensitivity mainly involves T lymphocyte recognition of the drug antigens and cell activation. The clinical presentations of such hypersensitivity are various and range from mild reactions (e.g., maculopapular exanthema (MPE) and fixed drug eruption (FDE)), to drug-induced liver injury (DILI) and severe cutaneous adverse reactions (SCARs) (e.g., Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), drug reaction with eosinophilia and systemic symptoms (DRESS), and acute generalized exanthematous pustulosis (AGEP)). The common culprits of delayed drug hypersensitivity include anti-epileptics, antibiotics, anti-gout agents, anti-viral drugs, etc. Delayed drug hypersensitivity is proposed to be initiated by different models of molecular recognition, composed of drug/metabolite antigen and endogenous peptide, HLA presentation, and T cell receptor (TCR) interaction. Increasing the genetic variants of HLA loci and drug metabolic enzymes has been identified to be responsible for delayed drug hypersensitivity. Furthermore, preferential TCR clonotypes, and the activation of cytotoxic proteins/cytokines/chemokines, are also involved in the pathogenesis of delayed drug hypersensitivity. This review provides a summary of the current understanding of the molecular recognition, genetic susceptibility, and immune mediators of delayed drug hypersensitivity.

The Impact of Pharmacogenetics on Pharmacokinetics and Pharmacodynamics in Neonates and Infants: A Systematic Review

In neonates, pharmacogenetics has an additional layer of complexity. This is because in addition to genetic variability in genes that code for proteins relevant to clinical pharmacology, there are rapidly maturational changes in these proteins. Consequently, pharmacotherapy in neonates has unique challenges. To provide a contemporary overview on pharmacogenetics in neonates, we conducted a systematic review to identify, describe and quantify the impact of pharmacogenetics on pharmacokinetics and -dynamics in neonates and infants (PROSPERO, CRD42022302029). The search was performed in Medline, Embase, Web of Science and Cochrane, and was extended by a PubMed search on the ‘top 100 Medicines’ (medicine + newborn/infant + pharmacogen*) prescribed to neonates. Following study selection (including data in infants, PGx related) and quality assessment (Newcastle–Ottawa scale, Joanna Briggs Institute tool), 55/789 records were retained. Retained records relate to metabolizing enzymes involved in phase I [cytochrome P450 (CYP1A2, CYP2A6, CYP2B6, CYP2C8/C9/C18, CYP2C19, CYP2D6, CYP3A5, CYP2E1)], phase II [glutathione-S-transferases, N-acetyl transferases, UDP-glucuronosyl-transferase], transporters [ATP-binding cassette transporters, organic cation transporters], or receptor/post-receptor mechanisms [opioid related receptor and post-receptor mechanisms, tumor necrosis factor, mitogen-activated protein kinase 8, vitamin binding protein diplotypes, corticotrophin-releasing hormone receptor-1, nuclear receptor subfamily-1, vitamin K epoxide reductase complex-1, and angiotensin converting enzyme variants]. Based on the available overview, we conclude that the majority of reported pharmacogenetic studies explore and extrapolate observations already described in older populations. Researchers commonly try to quantify the impact of these polymorphisms in small datasets of neonates or infants. In a next step, pharmacogenetic studies in neonatal life should go beyond confirmation of these associations and explore the impact of pharmacogenetics as a covariate limited to maturation of neonatal life (ie, fetal malformations, breastfeeding or clinical syndromes). The challenge is to identify the specific factors, genetic and non-genetic, that contribute to the best benefit/risk balance.

Sulfamethoxazole-trimethoprim-induced liver injury and genetic polymorphisms of NAT2 and CYP2C9 in Taiwan

OBJECTIVES

Sulfamethoxazole-trimethoprim (SMX-TMP) is one of the most frequently used antibiotics. SMX is metabolized by N-acetyltransferase (NAT) and cytochrome P450 2C9 (CYP2C9) to nontoxic or toxic intermediates. Little is known about the association between genetic variations of these enzymes and SMX-TMP-induced liver injury (SILI). The aim of this study was to explore the genetic polymorphisms of NAT2 and CYP2C9 and the susceptibility to SILI in a Han Chinese population.

METHODS

A total of 158 patients with SILI and 145 controls were recruited in this study. PCR-based genotyping with matrix-assisted laser desorption ionization-time of flight was used to assay the major NAT2 and CYP2C9 genotypes including NAT2 rs1495741, rs1041983, rs1801280, CYP2C9 rs1799853, rs1057910 and rs4918758.

RESULTS

The SILI group had a higher frequency of the NAT2 rs1495741 variant AA genotype and rs1041983 variant TT genotype than the controls (42.4 vs. 25.5%; P = 0.008, and 40.5 vs. 25.5%; P = 0.022, respectively). The SILI group had more slow acetylators than the controls (43.7 vs. 25.5%; P = 0.001). There were no significant differences in the genetic variations of CYP2C9 between the SILI and control groups. After adjusting for confounding factors, the NAT2 slow acetylators still had an increased risk of SILI (adjusted OR: 2.49; 95% confidence interval: 1.46-4.24; P = 0.001), especially in those with hepatocellular and mixed type SILI.

CONCLUSIONS

NAT2 slow acetylators are associated with a higher risk of SILI in the Han Chinese population. However, CYP2C9 genetic polymorphisms are not associated with the susceptibility to SILI.

Model Based Evaluation of Hypersensitivity Adverse Drug Reactions to Antimicrobial Agents in Children

Drug use in children is-in most cases-supported by extrapolation of data generated from clinical trials in adult populations. This puts children at higher risk of developing adverse drug reactions (ADRs) due to "off-label" use of drugs and dosing issues. Major types of ADRs are drug hypersensitivity reactions, an idiosyncratic type of ADRs that are largely unpredictable and can cause high morbidity and mortality in a hard-to-identify specific population of patients. Lack of a complete understanding of the pathophysiology of DHRs and their unpredictive nature make them problematic in clinical practice and in drug development. In addition, ethical and legal obstacles hinder conducting large clinical trials in children, which in turn make children a "therapeutic orphan" where clear clinical guidelines are lacking, and practice is based largely on the personal experience of the clinician, hence making modeling desirable. This brief review summarizes the current knowledge of model-based evaluation of diagnosis and management of drug hypersensitivity reactions (DHRs) to antimicrobial drugs in the pediatric population. Ethical and legal aspects of drug research in children and the effect of different stages of child development and other factors on the risk of DHRs are discussed. The role of animal models, in vitro models and oral provocation test in management of DHRs are examined in the context of the current understanding of the pathophysiology of DHRs. Finally, recent changes in drug development legislations have been put forward to encourage drug developers to conduct trials in children clearly indicate the urgent need for evidence to support drug safety in children and for modeling to guide these clinical trials.

Genetic variants associated with T cell-mediated cutaneous adverse drug reactions: A PRISMA-compliant systematic review-An EAACI position paper

Drug hypersensitivity reactions (DHRs) are associated with high global morbidity and mortality. Cutaneous T cell-mediated reactions classically occur more than 6 hours after drug administration and include life-threatening conditions such as toxic epidermal necrolysis, Stevens-Johnson syndrome, and hypersensitivity syndrome. Over the last 20 years, significant advances have been made in our understanding of the pathogenesis of DHRs with the identification of human leukocyte antigens as predisposing factors. This has led to the development of pharmacogenetic screening tests, such as HLA-B*57:01 in abacavir therapy, which has successfully reduced the incidence of abacavir hypersensitivity reactions. We have completed a PRISMA-compliant systematic review to identify genetic associations that have been reported in DHRs. In total, 105 studies (5554 cases and 123 548 controls) have been included in the review reporting genetic associations with carbamazepine (n = 31), other aromatic antiepileptic drugs (n = 24), abacavir (n = 11), nevirapine (n = 14), trimethoprim-sulfamethoxazole (n = 11), dapsone (n = 4), allopurinol (n = 10), and other drugs (n = 5). The most commonly reported genetic variants associated with DHRs are located in human leukocyte antigen genes and genes involved in drug metabolism pathways. Increasing our understanding of genetic variants that contribute to DHRs will allow us to improve diagnosis, develop new treatments, and predict and prevent DHRs in the future.

Evaluation of polymorphisms in the sulfonamide detoxification genes NAT2, CYB5A, and CYB5R3 in patients with sulfonamide hypersensitivity

OBJECTIVE

To determine whether polymorphisms in the sulfonamide detoxification genes, CYB5A (encoding cytochrome b(5)), CYB5R3 (encoding cytochrome b(5) reductase), or NAT2 (encoding N-acetyltransferase 2) were over-represented in patients with delayed sulfonamide drug hypersensitivity, compared with control patients who tolerated a therapeutic course of trimethoprim-sulfamethoxazole without adverse event.

METHODS

DNA from 99 nonimmunocompromised patients with sulfonamide hypersensitivity who were identified from the Personalized Medicine Research Project at the Marshfield Clinic, and from 99 age-matched, race-matched, and sex-matched drug-tolerant controls, were genotyped for four CYB5A and five CYB5R3 polymorphisms, and for all coding NAT2 SNPs.

RESULTS

CYB5A and CYB5R3 SNPs were found at low allele frequencies (<3-4%), which did not differ between hypersensitive and tolerant patients. NAT2 allele and haplotype frequencies, as well as inferred NAT2 phenotypes, also did not differ between groups (60 vs. 59% slow acetylators). Finally, no difference in NAT2 status was found in a subset of patients with more severe hypersensitivity signs (drug reaction with eosinophilia and systemic symptoms) compared with tolerant patients.

CONCLUSION

We found no evidence of a substantial involvement of these nine CYB5A or CYB5R3 polymorphisms in sulfonamide hypersensitivity risk, although minor effects cannot be completely ruled out. Despite careful medical record review and full resequencing of the NAT2 coding region, we found no association of NAT2 coding alleles with sulfonamide hypersensitivity (predominantly cutaneous eruptions) in this adult Caucasian population.

Polymorphism in glutamate cysteine ligase catalytic subunit (GCLC) is associated with sulfamethoxazole-induced hypersensitivity in HIV/AIDS patients

Background

Sulfamethoxazole (SMX) is a commonly used antibiotic for prevention of infectious diseases associated with HIV/AIDS and immune-compromised states. SMX-induced hypersensitivity is an idiosyncratic cutaneous drug reaction with genetic components. Here, we tested association of candidate genes involved in SMX bioactivation and antioxidant defense with SMX-induced hypersensitivity.

Results

Seventy seven single nucleotide polymorphisms (SNPs) from 14 candidate genes were genotyped and assessed for association with SMX-induced hypersensitivity, in a cohort of 171 HIV/AIDS patients. SNP rs761142 T > G, in glutamate cysteine ligase catalytic subunit (GCLC), was significantly associated with SMX-induced hypersensitivity, with an adjusted p value of 0.045. This result was replicated in a second cohort of 249 patients (p = 0.025). In the combined cohort, heterozygous and homozygous carriers of the minor G allele were at increased risk of developing hypersensitivity (GT vs TT, odds ratio = 2.2, 95% CL 1.4-3.7, p = 0.0014; GG vs TT, odds ratio = 3.3, 95% CL 1.6 – 6.8, p = 0.0010). Each minor allele copy increased risk of developing hypersensitivity 1.9 fold (95% CL 1.4 – 2.6, p = 0.00012). Moreover, in 91 human livers and 84 B-lymphocytes samples, SNP rs761142 homozygous G allele carriers expressed significantly less GCLC mRNA than homozygous TT carriers (p < 0.05).

Conclusions

rs761142 in GCLC was found to be associated with reduced GCLC mRNA expression and with SMX-induced hypersensitivity in HIV/AIDS patients. Catalyzing a critical step in glutathione biosynthesis, GCLC may play a broad role in idiosyncratic drug reactions.

Human N-acetyltransferase 1 *10 and *11 alleles increase protein expression through distinct mechanisms and associate with sulfamethoxazole-induced hypersensitivity

OBJECTIVES

N-acetyltransferase 1 (NAT1) metabolizes drugs and environmental carcinogens. NAT1 alleles *10 and *11 have been proposed to alter protein level or enzyme activity compared with wild-type NAT1 *4 and to confer cancer risk, through uncertain pathways. This study characterizes regulatory polymorphisms and underlying mechanisms of NAT1 expression.

METHODS

We measured allelic NAT1 mRNA expression and translation, as a function of multiple transcription start sites, alternative splicing, and three 3'-polyadenylation sites in human livers (one of which was discovered in this study), B lymphocytes, and transfected cells. In a clinical study of 469 patients with HIV/AIDS treated with the NAT1/NAT2 substrate sulfamethoxazole (SMX), associations were tested between SMX-induced hypersensitivity and NAT1 *10 and *11 genotypes, together with known NAT2 polymorphisms.

RESULTS

NAT1 *10 and *11 were determined to act as common regulatory alleles accounting for most NAT1 expression variability, both leading to increased translation into active protein. NAT1 *11 (2.4% minor allele frequency) affected 3'-polyadenylation site usage, thereby increasing formation of NAT1 mRNA with intermediate length 3'-untranslated region (major isoform) at the expense of the short isoform, resulting in more efficient protein translation. NAT1 *10 (19% minor allele frequency) increased translation efficiency without affecting 3'-untranslated region polyadenylation site usage. Livers and B-lymphocytes with *11/*4 and *10/*10 genotypes displayed higher NAT1 immunoreactivity and NAT1 enzyme activity than the reference genotype *4/*4. Patients who carry *10/*10 and *11/*4 (fast NAT1 acetylators) were less likely to develop hypersensitivity to SMX, but this was observed only in individuals who are also carrying a slow NAT2 acetylator genotype.

CONCLUSION

NAT1 *10 and *11 significantly increase NAT1 protein level/enzyme activity, enabling the classification of carriers into reference and rapid acetylators. Rapid NAT1 acetylator status seems to protect against SMX toxicity by compensating for slow NAT2 acetylator status.

Influence of NAT2 polymorphisms on sulfamethoxazole pharmacokinetics in renal transplant recipients

The sulfamethoxazole (SMX)-trimethoprim drug combination is routinely used as prophylaxis against Pneumocystis pneumonia during the first 3 to 6 months after renal transplantation. The objective of this study was to examine the impact of N-acetyltransferase 2 (NAT2) and CYP2C9 polymorphisms on the pharmacokinetics of SMX in 118 renal transplant recipients. Starting on day 14 after renal transplantation, patients were administered 400 mg/day-80 mg/day of SMX-trimethoprim orally once daily. On day 14 after the beginning of SMX therapy, plasma SMX concentrations were determined by a high-performance liquid chromatography method. The SMX area under the concentration-time curve from 0 to 24 h (AUC(0-24)) for 15 recipients with the NAT2 slow acetylator genotype (NAT2 5/ 6, - 6/ 6, - 6/ 7, and - 7/ 7) was significantly greater than that for 56 recipients with the NAT2 rapid acetylator genotype (homozygous for NAT2 4) (766.4 ± 432.3 versus 537.2 ± 257.5 μg-h/ml, respectively; P = 0.0430), whereas there were no significant differences in the SMX AUC(0-24) between the CYP2C9 1/ 1 and - 1/ 3 groups. In a multiple regression analysis, the SMX AUC(0-24) was associated with NAT2 slow acetylator polymorphisms (P = 0.0095) and with creatinine clearance (P = 0.0499). Hepatic dysfunction in NAT2 slow acetylator recipient patients during the 6-month period after SMX administration was not observed. SMX plasma concentrations were affected by NAT2 polymorphisms and renal dysfunction. Although standard SMX administration to patients with NAT2 slow acetylator polymorphisms should be accompanied by monitoring for side effects and drug interaction effects from the inhibition of CYP2C9, SMX administration at a low dose (400 mg) as prophylaxis may not provide drug concentrations that reach the level necessary for the expression of side effects. Further studies with a larger sample size should be able to clarify the relationship between SMX plasma concentration and side effects.

TNF, LTA, HSPA1L and HLA-DR gene polymorphisms in HIV-positive patients with hypersensitivity to cotrimoxazole

AIMS

Sulfamethoxazole in combination with trimethoprim (cotrimoxazole) is used for prophylaxis and treatment of several opportunistic infections in HIV-infected patients. It is associated with a high incidence of hypersensitivity reactions, which is thought to have an immune basis. Genetic polymorphisms in MHC are known to predispose to hypersensitivity reactions to a structurally diverse group of drugs in HIV-positive patients. The aim of the study was to determine whether functional polymorphisms in TNF, LTA, HSPA1L and HLA-DRB1 genes influence the risk of cotrimoxazole hypersensitivity in HIV-infected patients.

METHODS

We genotyped 136 HIV-positive patients with (n = 53) and without (n = 83) cotrimoxazole hypersensitivity using a combination of PCR-based techniques, including PCR-restriction fragment length polymorphisms, PCR-sequence specific oligonucleotides and real-time PCR. Genotypes and the haplotype frequencies were analyzed using the chi(2) test in the Haploview and CLUMP programs.

RESULTS

No statistically significant difference in SNP or haplotype frequencies were found in HIV-infected sulfamethoxazole hypersensitive patients compared with controls.

CONCLUSION

Our data show that MHC polymorphisms are not major predisposing factors for cotrimoxazole hypersensitivity, although we cannot exclude a minor contribution. An environmental factor (i.e., HIV infection) seems to predominate over any of the genetic factors so far investigated in increasing the risk of cotrimoxazole hypersensitivity.

Association of the diplotype configuration at the N-acetyltransferase 2 gene with adverse events with co-trimoxazole in Japanese patients with systemic lupus erythematosus

Although co-trimoxazole (trimethoprim-sulphamethoxazole) is an effective drug for prophylaxis against and treatment of Pneumocystis pneumonia, patients often experience adverse events with this combination, even at prophylactic doses. With the aim being to achieve individual optimization of co-trimoxazole therapy in patients with systemic lupus erythematosus (SLE), we investigated genetic polymorphisms in the NAT2 gene (which encodes the metabolizing enzyme of sulphamethoxazole). Of 166 patients with SLE, 54 patients who were hospitalized and who received prophylactic doses of co-trimoxazole were included in the cohort study. Adverse events occurred in 18 patients; only two experienced severe adverse events that lead to discontinuation of the drug. These two patients and three additional ones with severe adverse events (from other institutions) were added to form a cohort sample and were analyzed in a case-control study. Genotype was determined using TaqMan methods, and haplotype was inferred using the maximum-likelihood method. In the cohort study, adverse events occurred more frequently in those without the NAT2*4 haplotype (5/7 [71.4%]) than in those with at least one NAT2*4 haplotype (13/47 [27.7%]; P = 0.034; relative risk = 2.58, 95% confidence interval = 1.34-4.99). In the case-control study the proportion of patients without NAT2*4 was significantly higher among those with severe adverse events (3/5 [60%]) than those without severe adverse events (6/52 [11.5%]; P = 0.024; odds ratio = 11.5, 95% confidence interval = 1.59-73.39). We conclude that lack of NAT2*4 haplotype is associated with adverse events with co-trimoxazole in Japanese patients with SLE.

N-acetyltransferase 2 slow acetylator genotype associated with adverse effects of sulphasalazine in the treatment of inflammatory bowel disease

AIM

N-acetyltransferase 2 (NAT2) is an important enzyme catalyzing N-acetylation of sulfasalazine (SASP). The aim of the present study was to investigate associations of the genotypes of NAT2 with inflammatory bowel disease (IBD), and with adverse effects of SASP, which is used as the first-line treatment of IBD.

PATIENTS AND METHODS

The wildtype allele (NAT2*4) and three variant alleles (NAT2*5B, NAT2*6A and NAT*7B) of the NAT2 gene were determined in 101 patients with IBD (84 patients with ulcerative colitis and 17 patients with Crohn's disease) and 109 healthy controls by the polymerase chain reaction-restriction fragment length polymorphism method. Sixty-eight patients with IBD treated with SASP were followed, and their adverse reactions were recorded.

RESULTS

Eleven patients (16%) experienced adverse effects from SASP, including nine cases of sulfapyridine (SP) dose-related adverse effects and two cases of hypersensitivity (skin rash). Patients with the slow acetylator genotypes without the NAT2*4 allele experienced adverse effects more frequently (36%) than those with the fast acetylator genotypes with at least one NAT2*4 allele (11%), but the results were not significantly different (OR of 0.26, 95% CI 0.065 to 1.004; P=0.051). However, those with the slow acetylator genotypes experienced more SP dose-related adverse effects than those with the fast acetylator genotypes (36% versus 8%, OR of 0.17, 95% CI 0.039 to 0.749; P=0.019).

CONCLUSIONS

The NAT2 gene polymorphism was not associated with susceptibility to IBD in Chinese populations, but the NAT2 slow acetylator genotypes were significantly associated with SP dose-related adverse effects of SASP in the treatment of IBD.

Simultaneous determination of 7 N-acetyltransferase-2 single-nucleotide variations by allele-specific primer extension assay

BACKGROUND

Genotyping of N-acetyltransferase-2 (NAT2) is useful in predicting the risk for toxicity of NAT2 substrates. Current methods cannot detect the 7 most important single-nucleotide variations in NAT2 simultaneously in 1 tube.

METHODS

We developed an assay that uses allele-specific primer extension (ASPE) and microsphere hybridization for the simultaneous detection of 7 single-nucleotide variations in NAT2. Using 12 samples previously genotyped by a TaqMan-based assay for method development and as positive controls, we amplified the genetic locus of NAT2 comprising the single-nucleotide variations of interest by PCR and then performed ASPE with allele-specific primers and biotinylated dCTP followed by bead hybridization and streptavidin-R-phycoerythrin binding. Genotypes were determined according to the allele-specific fluorescent signal ratios.

RESULTS

The mean (SD) allelic ratios for homozygous common, heterozygous variant, and homozygous variant NAT2 genotypes were 0.0394 (0.0113) (n = 80), 0.4372 (0.0270) (n = 148), and 0.9331 (0.0127) (n = 325). The assay had 100% (95% confidence interval, 99%-100%) within-run reproducibility for 12 samples repeated 6 times and 100% (98%-100%) between-run reproducibility for a 5-sample subset run on 6 different days. NAT2 genotypes of 30 blinded samples determined by this assay were 100% (98%-100%) concordant with results obtained using the TaqMan method.

CONCLUSIONS

The developed assay can simultaneously determine single-nucleotide variations in NAT2. The assay demonstrates no overlap in allele-specific signal ratios between homozygous common, heterozygous, and homozygous variant and shows agreement with a reference method and reproducibility of genotype identification.

Pharmacogenetics of the arylamine N-acetyltransferases

The arylamine N-acetyltransferases (NATs) are involved in the metabolism of a variety of different compounds that we are exposed to on a daily basis. Many drugs and chemicals found in the environment, such as those in cigarette smoke, car exhaust fumes and in foodstuffs, can be either detoxified by NATs and eliminated from the body or bioactivated to metabolites that have the potential to cause toxicity and/or cancer. NATs have been implicated in some adverse drug reactions and as risk factors for several different types of cancers. As a result, the levels of NATs in the body have important consequences with regard to an individual's susceptibility to certain drug-induced toxicities and cancers. This review focuses on recent advances in the molecular genetics of the human NATs.

Mechanistic perspectives on sulfonamide-induced cutaneous drug reactions

PURPOSE OF REVIEW

Idiosyncratic drug reactions continue to limit the therapeutic utility of sulfonamide drugs because of their associated morbidity and mortality. Cutaneous reactions are the predominant reasons for withdrawal of such drugs from use in patients. As a consequence of the recognized metabolic and immunologic capability of the skin, an understanding of the pathogenic role of this tissue in the development of sulfonamide-induced cutaneous drug reactions may provide insight into the mechanisms and risk factors for these and other adverse drug events.

RECENT FINDINGS

In the present review we discuss currently available mechanistic information, including issues related to drug bioactivation and adduct formation, immunoresponsiveness, and immune dysregulation, for the development of sulfonamide-induced (delayed-type) cutaneous drug reactions. The potential application of findings from several related areas of research are also discussed within the context of the pathogenesis of these cutaneous reactions.

SUMMARY

Despite progress, numerous unresolved issues support the testing of novel hypotheses, the search for additional risk factors, and the need for a global approach, including links between laboratory and clinical paradigms. These issues must be addressed if we are to gain an understanding of the mechanistic bases for these cutaneous drug reactions.

Polymorphism of the N-acetyltransferase 2 gene as a susceptibility risk factor for antituberculosis drug-induced hepatitis

Antituberculosis drug-induced hepatitis is one of the most prevalent drug-induced liver injuries. Isoniazid is the major drug incriminated in this hepatotoxicity. Isoniazid is mainly metabolized to hepatotoxic intermediates by N-acetyltransferase (NAT). However, the association of polymorphic NAT acetylator status and antituberculosis drug-induced hepatitis is debatable. To determine whether acetylator status is a risk factor for antituberculosis drug-induced hepatitis, we genotyped NAT2 in 224 incident tuberculosis patients who received antituberculosis treatment. Antituberculosis drug-induced hepatitis was diagnosed based on a positive isoniazid rechallenge test and exclusion of viral hepatitis. Acetylator status was determined by genotyping NAT2 in patients using a polymerase chain reaction with restriction fragment length polymorphism. Univariate analysis and logistic regression analysis were used to evaluate the risk factors of isoniazid-induced hepatitis. Thirty-three patients (14.7%) were diagnosed with antituberculosis drug-induced hepatitis. Slow acetylators had a higher risk of hepatotoxicity than rapid acetylators (26.4% vs. 11.1%, P =.013). Among patients with hepatotoxicity, slow acetylators had significantly higher serum aminotransferase levels than rapid acetylators. Logistic regression showed that slow-acetylator status (odds ratio [OR], 3.66; 95% CI, 1.58-8.49; P =.003) and age (OR, 1.09; 95% CI, 1.04-1.14; P <.001) were the only 2 independent risk factors for antituberculosis drug-induced hepatitis. In conclusion, slow-acetylator status of NAT2 is a significant susceptibility risk factor for antituberculosis drug-induced hepatitis. Additionally, slow acetylators are prone to develop more severe hepatotoxicity than rapid acetylators. Regular monitoring of serum aminotransferase levels is mandatory in patients receiving antituberculosis treatment, especially in slow acetylators.

Recognising antibacterial hypersensitivity in children

Adverse reactions to antibacterial agents are not uncommon in children. They are classified as 'immediate' or 'nonimmediate' according to the time interval between drug administration and onset. Immediate reactions occur within 1 hour and are manifested by urticaria and/or angioedema, bronchospasm and anaphylactic shock; immunological reactions are mediated by IgE antibodies. The main nonimmediate reactions (occuring after more than 1 hour) are maculopapular rash, urticaria and serum sickness; T lymphocytes may participate in maculopapular rash. Clinical assessment of such reactions is complex. The patient's history is fundamental; the allergological examination includes in vivo and in vitro tests selected on the basis of the clinical features and the phase of reaction. In the late phase, prick and intradermal tests are sensitive in evaluating beta-lactam allergy. Together with delayed-reading intradermal testing, patch testing seems to be useful in diagnosing maculopapular reactions to systemically administered aminopenicillins. Determination of specific IgE levels is the most common in vitro method for diagnosing immediate reactions. In the acute phase, serum tryptase and urinary N-methylhistamine assays are reliable in diagnosing type I pathogenic mechanisms in immediate reactions. Unfortunately, there are few in vitro tests for evaluating other reactions, and most are not fully validated. In selected cases, provocation tests should be performed.