Influence of pharmacogenomic polymorphisms on allopurinol-induced cutaneous adverse drug reactions in Thai patients.

BACKGROUND: Allopurinol has been causing substantial morbidity and mortality particularly in Asian population by producing cutaneous adverse drug reactions (cADRs). Nonetheless, there are no data describing whether other genetics are a valid marker for prediction of allopurinol-induced cADRs patients in addition to HLA-B*58:01 allele. The goal of this study was to identify suitable single nucleotide polymorphisms (SNPs) for allopurinol induced cADRs among Thai patients. METHODS: We conducted a case-control association study after enrolling 57 Thai patients with allopurinol induced cADRs and 101 allopurinol-tolerant controls. The genetic biomarkers and associated SNPs located on chromosome 6p21 were examined by TaqMan® SNP genotyping assays in both the cases and the controls. RESULTS: Out of fifteen SNPs in nine genes, we found four combined SNPs (rs3099844 of HCP5, rs9263726 of PSORS1C1, rs9263733 of POLR2LP, and rs9263745 of CCHCR1) were significantly associated with allopurinol-induced cADRs compared to the tolerant controls (OR 73.2; 95% CI 24.2-266.8; P = 1.9 × 10- 24). The overall sensitivity, specificity, positive predictive value and negative predictive value of these combinations were 84%, 94%, 9%, and 100%, respectively. However, the variant alleles of these SNP combinations were detected in 89.5% (51/57) of the cases. Moreover, the HLA-B*58:01 allele was observed in 86.0% of patients with allopurinol-induced cADRs, but only in 4.0% of tolerant controls (OR: 137.2; 95% CI: 38.3-670.5 and p-value = 1.7 × 10- 27). CONCLUSIONS: Thus, this research confirms the association between the specific HLA-B*58:01 allele and all phenotypes of allopurinol-induced cADRs in Thais. Furthermore, there was found the combined four SNPs (rs3099844, rs9263726, rs9263733, and rs9263745) could be used as alternative novel biomarkers for predicting cADRs in patients taking allopurinol.

Genotypic and Phenotypic Characteristics of Co-Trimoxazole-Induced Cutaneous Adverse Reactions.

BACKGROUND: Co-trimoxazole has been reported as a common culprit drug for various cutaneous adverse drug reactions (CADRs). However, information on genotypic and phenotypic characteristics is still limited. We aimed to study clinical characteristics, genetic suitability, laboratory findings, and treatment outcomes in patients with co-trimoxazole-induced CADR and determine variables associated with severe cutaneous adverse reactions (SCARs). METHODS: The medical records of all patients diagnosed with co-trimoxazole-induced CADR during October 2015 and October 2021 were reviewed. Clinical characteristics and laboratory investigation with an emphasis on human leukocyte antigen (HLA) class I and HLA-DRB1 results linked to subtypes of cutaneous adverse reactions were evaluated. RESULTS: Seventy-two patients diagnosed with co-trimoxazole-induced CADR were included in the study. Mean age at diagnosis was 38.0 ± 14.6 years old, and 72% were female. Subtypes of reactions included maculopapular eruption (MPE; 56.9%), drug reaction with eosinophilia and systemic symptoms (DRESS; 23.6%), Stevens-Johnson syndrome (SJS; 12.5%), fixed drug eruption (4.2%), and urticaria (2.8%). Characteristics that were significantly associated with SCARs included male gender (OR = 3.01, 95% CI: 1.04-8.75), HIV infection (OR = 3.48, 95% CI: 1.13-10.75), prophylactic use of co-trimoxazole (OR = 4.89, 95% CI: 1.54-15.57), and co-trimoxazole administration longer than 10 days (OR = 7.65, 95% CI: 2.57-22.78). HLA-B*38:02 was associated with co-trimoxazole-induced SJS, while HLA-A*11:01, HLA-B*13:01, and HLA-DRB1*12:01 were associated with co-trimoxazole-induced DRESS. HLA-B*52:01 was associated with co-trimoxazole-induced MPE. CONCLUSIONS: Co-trimoxazole could induce various phenotypes of CADRs. Genotypic and phenotypic factors that may potentially predict co-trimoxazole-induced SCARs include male gender, HIV infection, prophylactic and prolonged drug use, as well as the presence of HLA-A*11:01, HLA-B*13:01, HLA-B*38:02, or HLA-DRB1*12:01 alleles.

Effects of polymorphisms in the MTHFR gene on 5-FU hematological toxicity and efficacy in Thai colorectal cancer patients.

Background: The two common methylenetetrahydrofolate reductase (MTHFR) polymorphisms 677G>A and 1298A>C may have been affecting 5-FU toxicity in cancer patients for decades. Drug efficacy has also been shown by previous studies to be affected. In this study, we investigated the effects of these polymorphisms on 5-FU hematological toxicity and treatment efficacy, to provide enhanced pharmacological treatment for cancer patients. Methods: This is a retrospective study involving 52 Thai colorectal cancer patients who were treated with 5-FU based therapy, using TaqMAN real-time PCR to genotype the MTHFR polymorphisms (677G>A and 1298A>C). The toxicity and response rate were assessed using standardized measures. Results: Neutropenia was significantly more likely to be experienced (P=0.049, OR=7.286, 95% CI=0.697-76.181) by patients with the MTHFR 677G>A polymorphism, in the same way as leukopenia (P =0.036, OR=3.333, 95%CI=2.183-5.090) and thrombocytopenia (P<0.001, OR=3.917, 95%CI=2.404-6.382). The MTHFR 1298A>C polymorphism had no statistical association with hematological toxicity in 5-FU treatment. The response rate to 5-FU was not significantly affected by these two polymorphisms. Conclusion: The MTHFR polymorphism 677G>A is a significant risk factor for developing leukopenia, neutropenia and thrombocytopenia as toxic effects of 5-FU therapy in cancer patients. Therefore, patients receiving 5-FU-based therapy should be aware of their polymorphisms as one risk factor for experiencing severe toxicity.

Drug-Induced Severe Cutaneous Adverse Reactions: Insights Into Clinical Presentation, Immunopathogenesis, Diagnostic Methods, Treatment, and Pharmacogenomics.

SCARs are rare and life-threatening hypersensitivity reactions. In general, the increased duration of hospital stays and the associated cost burden are common issues, and in the worst-case scenario, they can result in mortality. SCARs are delayed T cell-mediated hypersensitivity reactions. Recovery can take from 2 weeks to many months after dechallenging the culprit drugs. Genetic polymorphism of the HLA genes may change the selection and presentation of antigens, allowing toxic drug metabolites to initiate immunological reactions. However, each SCARs has a different onset latency period, clinical features, or morphological pattern. This explains that, other than HLA mutations, other immuno-pathogenesis may be involved in drug-induced severe cutaneous reactions. This review will discuss the clinical morphology of various SCARs, various immune pathogenesis models, diagnostic criteria, treatments, the association of various drug-induced reactions and susceptible alleles in different populations, and the successful implementation of pharmacogenomics in Thailand for the prevention of SCARs.

A Comprehensive Review of HLA and Severe Cutaneous Adverse Drug Reactions: Implication for Clinical Pharmacogenomics and Precision Medicine.

Human leukocyte antigen (HLA) encoded by the HLA gene is an important modulator for immune responses and drug hypersensitivity reactions as well. Genetic polymorphisms of HLA vary widely at population level and are responsible for developing severe cutaneous adverse drug reactions (SCARs) such as Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), drug reaction with eosinophilia and systemic symptoms (DRESS), maculopapular exanthema (MPE). The associations of different HLA alleles with the risk of drug induced SJS/TEN, DRESS and MPE are strongly supportive for clinical considerations. Prescribing guidelines generated by different national and international working groups for translation of HLA pharmacogenetics into clinical practice are underway and functional in many countries, including Thailand. Cutting edge genomic technologies may accelerate wider adoption of HLA screening in routine clinical settings. There are great opportunities and several challenges as well for effective implementation of HLA genotyping globally in routine clinical practice for the prevention of drug induced SCARs substantially, enforcing precision medicine initiatives.

Spectrum of cutaneous adverse reactions to aromatic antiepileptic drugs and human leukocyte antigen genotypes in Thai patients and meta-analysis.

Aromatic antiepileptic drugs (AEDs)-induced cutaneous adverse drug reactions (cADRs) add up to the limited use of the AEDs in the treatment and prevention of seizures. Human leukocyte antigen-B (HLA-B) alleles have been linked to AEDs-induced cADRs. We investigated the association between cADRs (including Stevens-Johnson syndrome; SJS/toxic epidermal necrolysis; TEN, drug reaction with eosinophilia and systemic symptoms; DRESS, and Maculopapular eruption; MPE) caused by AEDs (phenytoin, carbamazepine, lamotrigine, phenobarbital and oxcarbazepine) and HLA-B alleles in Thai population. Through the case-control study, 166 patients with AEDs-induced cADRs, 426 AEDs-tolerant patients (AEDs-tolerant controls), and 470 healthy subjects (Thai population) were collected. The HLA genotypes were detected using the polymerase chain reaction-sequence specific oligonucleotide probe (PCR-SSOP) method. We also performed a meta-analysis with these data and other populations. The carrier rate of HLA-B*15:02 was significantly different between AEDs-induced cADRs group and AEDs-tolerant group (Odds ratio; OR 4.28, 95% Confidence interval; CI 2.64-6.95, p < 0.001), AEDs-induced cADRs group and Thai population (OR 2.15, 95%CI 1.41-3.29, p < 0.001). In meta-analysis showed the strong association HLA-B*15:02 with AEDs-induced cADRs (OR 4.77, 95%CI 1.79-12.73, p < 0.001). Furthermore, HLA-B*15:02 was associated with SJS/TEN induced by AEDs (OR 10.28, 95%CI 6.50-16.28, p < 0.001) Phenytoin (OR 4.12, 95%CI 1.77-9.59, p = 0.001) and carbamazepine (OR 137.69, 95%CI 50.97-371.98, p < 0.001). This study demonstrated that genetic association for AEDs-induced cADRs was phenotype-specific. A strong association between HLA-B*15:02 and AEDs-induced SJS/TEN was demonstrated with an OR of 10.79 (95%CI 5.50-21.16, p < 0.001) when compared with AEDs-tolerant group. On the other hand, the carrier rates of HLA-B*08:01, HLA-B*13:01, and HLA-B*56:02 were significantly higher in the DRESS group compared with the AEDs-tolerant group (p = 0.029, 0.007, and 0.017, respectively). The HLA-B*15:02 allele may represent a risk factor for AEDs-induced cADRs.

HLA-B*13 :01 Is a Predictive Marker of Dapsone-Induced Severe Cutaneous Adverse Reactions in Thai Patients.

HLA-B*13:01 allele has been identified as the genetic determinant of dapsone hypersensitivity syndrome (DHS) among leprosy and non-leprosy patients in several studies. Dapsone hydroxylamine (DDS-NHOH), an active metabolite of dapsone, has been believed to be responsible for DHS. However, studies have not highlighted the importance of other genetic polymorphisms in dapsone-induced severe cutaneous adverse reactions (SCAR). We investigated the association of HLA alleles and cytochrome P450 (CYP) alleles with dapsone-induced SCAR in Thai non-leprosy patients. A prospective cohort study, 16 Thai patients of dapsone-induced SCARs (5 SJS-TEN and 11 DRESS) and 9 Taiwanese patients of dapsone-induced SCARs (2 SJS-TEN and 7 DRESS), 40 dapsone-tolerant controls, and 470 general Thai population were enrolled. HLA class I and II alleles were genotyped using polymerase chain reaction-sequence specific oligonucleotides (PCR-SSOs). CYP2C9, CYP2C19, and CYP3A4 genotypes were determined by the TaqMan real-time PCR assay. We performed computational analyses of dapsone and DDS-NHOH interacting with HLA-B*13:01 and HLA-B*13:02 alleles by the molecular docking approach. Among all the HLA alleles, only HLA-B*13:01 allele was found to be significantly associated with dapsone-induced SCARs (OR = 39.00, 95% CI = 7.67-198.21, p = 5.3447 × 10-7), SJS-TEN (OR = 36.00, 95% CI = 3.19-405.89, p = 2.1657 × 10-3), and DRESS (OR = 40.50, 95% CI = 6.38-257.03, p = 1.0784 × 10-5) as compared to dapsone-tolerant controls. Also, HLA-B*13:01 allele was strongly associated with dapsone-induced SCARs in Asians (OR = 36.00, 95% CI = 8.67-149.52, p = 2.8068 × 10-7) and Taiwanese (OR = 31.50, 95% CI = 4.80-206.56, p = 2.5519 × 10-3). Furthermore, dapsone and DDS-NHOH fit within the extra-deep sub pocket of the antigen-binding site of the HLA-B*13:01 allele and change the antigen-recognition site. However, there was no significant association between genetic polymorphism of cytochrome P450 (CYP2C9, CYP2C19, and CYP3A4) and dapsone-induced SCARs (SJS-TEN and DRESS). The results of this study support the specific genotyping of the HLA-B*13:01 allele to avoid dapsone-induced SCARs including SJS-TEN and DRESS before initiating dapsone therapy in the Asian population.

Genetic Association of Co-Trimoxazole-Induced Severe Cutaneous Adverse Reactions Is Phenotype-Specific: HLA Class I Genotypes and Haplotypes.

Co-trimoxazole (CTX) causes various forms of severe cutaneous adverse reactions (SCARs). This case-control study was conducted to investigate the involvement between genetic variants of human leukocyte antigen (HLA) and CYP2C9 in CTX-induced SCARs, including Stevens-Johnson syndrome (SJS)/toxic epidermal necrolysis (TEN) and drug reaction with eosinophilia and systemic symptoms (DRESS) in Thai patients. Thirty cases of CTX-induced SCARs were enrolled and compared with 91 CTX-tolerant controls and 150 people from the general Thai population. Cases comprised 18 SJS/TEN and 12 DRESS patients. This study demonstrated that genetic association of CTX-induced SCARs was phenotype-specific. HLA-B*15:02 and HLA-C*08:01 alleles were significantly associated with CTX-induced SJS/TEN, whereas the HLA-B*13:01 allele was significantly associated with CTX-induced DRESS. In addition, a significant higher frequency of HLA-A*11:01-B*15:02 and HLA-B*13:01-C*03:04 haplotypes were detected in the group of CTX-induced Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN) and DRESS cases, respectively. Genetic association of CTX-induced SCARs is phenotype-specific. Interestingly, these association was observed only in HIV-infected patients but not in non-HIV-infected patients.

Genetic Diversity of HLA Class I and Class II Alleles in Thai Populations: Contribution to Genotype-Guided Therapeutics.

Human leukocyte antigen (HLA) class I and II are known to have association with severe cutaneous adverse reactions (SCARs) when exposing to certain drug treatment. Due to genetic differences at population level, drug hypersensitivity reactions are varied, and thus common pharmacogenetics markers for one country might be different from another country, for instance, HLA-A*31:01 is associated with carbamazepine (CBZ)-induced SCARs in European and Japanese while HLA-B*15:02 is associated with CBZ-induced Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN) among Taiwanese and Southeast Asian. Such differences pose a major challenge to prevent drug hypersensitivity when pharmacogenetics cannot be ubiquitously and efficiently translated into clinic. Therefore, a population-wide study of the distribution of HLA-pharmacogenetics markers is needed. This work presents a study of Thai HLA alleles on both HLA class I and II genes from 470 unrelated Thai individuals by means of polymerase chain reaction sequence-specific oligonucleotide (PCR-SSO) in which oligonucleotide probes along the stretches of HLA-A, -B, -C, -DRB1, -DQA1, and -DQB1 genes were genotyped. These 470 individuals were selected according to their regional locations, which were from North, Northeast, South, Central, and a capital city, Bangkok. Top ranked HLA alleles in Thai population include HLA-A*11:01 (26.06%), -B*46:01 (14.04%), -C* 01:02 (17.13%), -DRB1*12:02 (15.32%), -DQA1*01:01 (24.89%), and -DQB1*05:02 (21.28%). The results revealed that the distribution of HLA-pharmacogenetics alleles from the South had more HLA-B75 family that a typical HLA-B*15:02 pharmacogenetics test for SJS/TEN screening would not cover. Besides the view across the nation, when compared HLA alleles from Thai population with HLA alleles from both European and Asian countries, the distribution landscape of HLA-associated drug hypersensitivity across many countries could be observed. Consequently, this pharmacogenetics database offers a comprehensive view of pharmacogenetics marker distribution in Thailand that could be used as a reference for other Southeast Asian countries to validate the feasibility of their future pharmacogenetics deployment.

Association between HLA-B Alleles and Carbamazepine-Induced Maculopapular Exanthema and Severe Cutaneous Reactions in Thai Patients.

The HLA-B∗15:02 allele has been reported to have a strong association with carbamazepine-induced Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN) in Thai patients. The HLA-B alleles associated with carbamazepine-induced maculopapular exanthema (MPE) and the drug reaction with eosinophilia and systemic symptoms (DRESS) among the Thai population have never been reported. The aim of the present study was to carry out an analysis of the involvement of HLA-B alleles in carbamazepine-induced cutaneous adverse drug reactions (cADRs) in the Thai population. A case-control study was performed by genotyping the HLA-B alleles of Thai carbamazepine-induced hypersensitivity reaction patients (17 MPE, 16 SJS/TEN, and 5 DRESS) and 271 carbamazepine-tolerant controls. We also recruited 470 healthy Thai candidate subjects who had not taken carbamazepine. HLA-B∗15:02 showed a significant association with carbamazepine-induced MPE (P = 0.0022, odds ratio (OR) (95% confidence interval [CI]) = 7.27 (2.04-25.97)) and carbamazepine-induced SJS/TEN (P = 4.46 × 10-13; OR (95% CI) = 70.91(19.67-255.65)) when compared with carbamazepine-tolerant controls. Carbamazepine-induced SJS/TEN also showed an association with HLA-B∗15:21 allele (P = 0.013; OR (95% CI) = 9.54 (1.61-56.57)) when compared with carbamazepine-tolerant controls. HLA-B∗58:01 allele was significantly related to carbamazepine-induced MPE (P = 0.007; OR (95% CI) = 4.73 (1.53-14.66)) and DRESS (P = 0.0315; OR (95% CI) = 7.55 (1.20-47.58)) when compared with carbamazepine-tolerant controls. These alleles may serve as markers to predict carbamazepine-induced cADRs in the Thai population.

Association of HLA-A and HLA-B Alleles with Lamotrigine-Induced Cutaneous Adverse Drug Reactions in the Thai Population.

Background: Lamotrigine (LTG) is commonly used for treatment of epilepsy and bipolar disorder. It is one of the common cause of cutaneous adverse drug reactions (CADR). Clinical symptoms of LTG-induced CADR range from maculopapular exanthema (MPE) to severe cutaneous adverse reactions (SCAR). This study aimed to determine the association of the LTG-induced CADR with human leukocyte antigen (HLA) alleles in Thai patients. Methods: Fifteen patients with LTG-induced CADR [10 MPE; 4 Stevens-Johnson syndrome; and 1 drug reaction with eosinophilia and systemic symptoms] and 50 LTG-tolerant controls were included in the study. HLA-A and HLA-B genotyping was performed using polymerase chain reaction-sequence-specific oligonucleotides probes. Results: The proportion of HLA-A∗02:07 and HLA-B∗15:02 allele carriers were significantly higher in the LTG-induced CADR group than in the tolerant controls [odds ratio (OR): 7.83; 95% confidence interval (CI): 1.60-38.25; P = 0.013, and OR: 4.89; 95% CI: 1.28-18.67; P = 0.014]. In addition, subjects with HLA-A∗33:03, HLA-B∗15:02, and HLA-B∗44:03 were significantly higher in the LTG-induced MPE group than in the tolerant controls (OR: 8.27; 95% CI: 1.83-37.41; P = 0.005, OR: 7.33; 95% CI: 1.63-33.02; P = 0.005; and OR: 10.29; 95% CI: 1.45-72.81; P = 0.029). In contrast to the LTG-induced MPE group, there were no significant differences between HLA alleles and LTG-induced SCAR group. Conclusion:HLA-A∗02:07 and HLA-B∗15:02 were associated with LTG-induced CADR in Thai patients. We also identified an association between HLA-A∗33:03, HLA-B∗15:02, and HLA-B∗44:03 and LTG-induced MPE in this population. These results suggest that these alleles could be useful screening markers for preventing CADR before LTG treatment in Thai patients, but further replication studies with larger sample sizes are needed.

Dapsone-induced severe cutaneous adverse drug reactions are strongly linked with HLA-B*13: 01 allele in the Thai population.

OBJECTIVES: A previous publication in Chinese leprosy patients showed that the HLA-B*13:01 allele is a strong genetic marker for dapsone-induced drug hypersensitivity reactions, however there are no data describing whether HLA-B*13:01 is a valid marker for prediction of dapsone-induced drug hypersensitivity reactions in other ethnicities or nonleprosy patients. The aim of this study is to investigate whether there is an association between HLA genotypes and dapsone-induced severe cutaneous adverse reactions (SCARs) in Thai nonleprosy patients. PATIENTS AND METHODS: HLA-B genotypes of 15 patients with dapsone-induced SCARs (11 drug reaction with eosinophilia and systemic symptoms, 4 Stevens-Johnson syndrome/toxic epidermal necrolysis), 29 control patients, and 986 subjects from the general Thai population were determined by the reverse PCR sequence-specific oligonucleotides probe. RESULTS: The HLA-B*13:01 allele was significantly associated with dapsone-induced SCARs compared with dapsone-tolerant controls (odds ratio: 54.00, 95% confidence interval: 7.96-366.16, P=0.0001) and the general population (odds ratio: 26.11, 95% confidence interval: 7.27-93.75, P=0.0001). In addition, HLA-B*13:01 associated with dapsone-induced SJS-TEN (OR: 40.50, 95% confidence interval: 2.78-591.01, P=0.0070) and DRESS (OR: 60.75, 95% confidence interval: 7.44-496.18, P=0.0001). CONCLUSION: This study demonstrated an association between HLA-B*13:01 and dapsone-induced SCARs including Stevens-Johnson syndrome/toxic epidermal necrolysis and drug reaction with eosinophilia and systemic symptoms in nonleprosy patients. Moreover, these results suggest that the HLA-B*13:01 allele may be a useful genetic marker for prediction of dapsone-induced SCARs in Thai and Han-Chinese populations.

HLA-B (*) 58:01 for Allopurinol-Induced Cutaneous Adverse Drug Reactions: Implication for Clinical Interpretation in Thailand.

BACKGROUND: The aim of this study was to investigate the predisposition to different types of allopurinol-induced cutaneous adverse drug reactions (CADR), including Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN; SJS-TEN, n = 13), drug reaction with eosinophilia and systemic symptoms (DRESS, n = 10) and Maculopapular eruption (MPE; n = 7), conferred by HLA-B (*) 58:01 in a Thai population. METHODS: This case-control association study compares 30 patients with allopurinol-induced CADR, allopurinol-tolerant control patients (n = 100), and a Thai general population (n = 1095). Patients' human leukocyte antigen type B (HLA-B) alleles were genotyped by using a two-stage sequence-specific oligonucleotide probe system. RESULTS: Of a total 30 patients with CADR due to allopurinol, 29 (96.7%) patients were found to be at least heterozygous for HLA-B (*) 58:01, compared to only 4.0% in allopurinol-tolerant patients (p < 0.001). Odds ratio (OR) for the association of HLA-B (*) 58:01 with allopurinol-induced CADR in this population was 696.0 (95% CI: 74.8-6475.0). The HLA-B (*) 58:01 allele was present in all patients with allopurinol-induced SJS-TEN (OR = 579.0, 95%CI: 29.5-11362.7, p < 0.001) and DRESS (OR 430.3, 95%CI: 22.6-8958.9, p < 0.001). Additionally, OR of HLA-B (*) 58:01 was highly significant in the allopurinol-induced MPE patients (OR 144.0, 95%CI: 13.9-1497.0, p < 0.001). CONCLUSION: In this study we confirmed the association between HLAB (*) 58:01 and allopurinol-induced SJS-TEN in a Thai population. In addition, we identified an association between HLA-B (*) 58:01 and allopurinol-induced DRESS and MPE in this population. Therefore, HLA-B (*) 58:01 can be used as a pharmacogenetic marker for allopurinol-induced CADR including SJS-TEN, DRESS and MPE. These results suggest that screening for HLA-B (*) 58:01 alleles in patients who will be treated with allopurinol would be clinically helpful in preventing the risk of developing CARD in a Thai patients. Summary Regardless of phenotype, this is the first pharmacogenetic study of allopurinol-induced CADR in patients of Thai ancestry.In this study we confirmed the association between HLA-B (*) 58:01 and allopurinol-induced SJS-TEN, DRESS, and MPE in Thai population.Regarding to our findings, the pharmacogenetic interpretation could be generalized to drug hypersensitivity including DRESS, SJS-TEN, and MPE.

Associations between HLA class I and cytochrome P450 2C9 genetic polymorphisms and phenytoin-related severe cutaneous adverse reactions in a Thai population.

BACKGROUND: Phenytoin is one of the most common causative drugs of several types of severe cutaneous adverse reactions (SCAR) such as Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), and drug reactions with eosinophilia and systemic symptoms (DRESS). Genetic polymorphisms of the human leukocyte antigens (HLA) and cytochromes P450 (CYP) have been proposed as key elements for the susceptibility to phenytoin-related SCAR in certain ethnicities. This study investigated the associations between the genetic polymorphisms of HLA class I and CYP2C9 and phenytoin-related SCAR in a Thai population. MATERIALS AND METHODS: Sixty phenytoin-related SCAR (i.e. 39 SJS/TEN and 21 DRESS) and 92 phenytoin-tolerant patients were enrolled in the study. The genotypes of HLA class I and CYP2C9 were determined. RESULTS: Six HLA alleles including HLA-A*33:03, HLA-B*38:02, HLA-B*51:01, HLA-B*56:02, HLA-B*58:01, and HLA-C*14:02 were significantly associated with phenytoin-related SJS/TEN, whereas only the HLA-B*51:01 was significantly associated with phenytoin-related DRESS. The odds ratios of phenytoin-related SJS/TEN in the patients who carried one of these alleles ranged from 4- to 10-fold. The frequencies of patients who carried the HLA-B*15:02 in the SJS/TEN (12.82%) or the DRESS (9.52%) groups were not significantly different from that of the controls (14.13%). The higher risk of phenytoin-related SJS/TEN was observed in the patients with CYP2C9*3 (odds ratio=4.30, 95% confidence interval=1.41-13.09, P<0.05). CONCLUSION: Neither SJS/TEN nor DRESS caused by phenytoin was significantly associated with the HLA-B*15:02. The CYP2C9*3 variant was significantly associated with phenytoin-related SJS/TEN, but not DRESS. Certain alleles of HLA, particularly HLA-B*56:02, were significantly associated with phenytoin-related SCAR in the study population.