NUDT15 is a key genetic factor for prediction of hematotoxicity in pediatric patients who received a standard low dosage regimen of 6-mercaptopurine.

6-Mercaptopurine (6-MP) is commonly used for treatment of acute lymphoblastic leukemia (ALL). The incidence of hematotoxicity caused by this drug is quite high in Asians even using a standard low dosage regimen. The present study was aimed to elucidate the impact of thiopurine S-methyltransferase (TPMT), a nucleoside diphosphate-linked moiety X-type motif 15 (NUDT15), inosine triphosphatase (ITPA) and ATP Binding Cassette Subfamily C Member 4 (ABCC4) polymorphisms on hematotoxicity in pediatric patients who received a standard low starting dose of 6-MP. One hundred and sixty-nine pediatric patients were enrolled and their genotypes were determined. Patients who carried NUDT15∗3 and NUDT15∗2 genotypes were at a 10-15 fold higher risk of severe neutropenia than those of the wild-type during the early months of the maintenance phase. Risk of neutropenia was not significantly increased in patients with other NUDT15 variants as well as in patients with TPMT, ITPA or ABCC4 variants. These results suggest that NUDT15 polymorphisms particularly, NUDT15∗3 and NUDT15∗2, play major roles in 6-MP-induced severe hematotoxicity even when using a standard low dosage of 6-MP and genotyping of these variants is necessary in order to obtain precise tolerance doses and avoid severe hematotoxicity in pediatric patients.

Genetic Polymorphisms of Drug-Metabolizing Enzymes Involved in 6-Mercaptopurine-Induced Myelosuppression in Thai Pediatric Acute Lymphoblastic Leukemia Patients.

Genetic polymorphisms of thiopurine S-methyltransferase (TPMT) and nucleoside diphosphate-linked moiety X-type motif 15 ( NUDT15 ) genes have been proposed as key determinants of 6-mercaptopurine (6-MP)-induced myelosuppression in pediatric acute lymphoblastic leukemia (ALL). In the present study, genotypes of TPMT and NUDT15 were investigated in 178 Thai pediatric patients with ALL by the TaqMan SNP genotyping assay and DNA sequencing. The frequency of TPMT*3C was 0.034. Among NUDT15 variants, NUDT15*3 is the most common variant with the allele frequency of 0.073, whereas those of NUDT15*2 , NUDT15*5 , and NUDT15*6 variants were 0.022, 0.011, and 0.039. These data suggest that a high proportion of Thai pediatric ALL patients may be at risk of thiopurine-induced myelosuppression.

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.

HLA Pharmacogenetic Markers of Drug Hypersensitivity in a Thai Population.

Severe cutaneous adverse drug reactions (SCARs) including Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), and drug reactions with eosinophilia and systemic symptoms (DRESS) are potentially life-threatening cutaneous reactions caused by several drugs. Recently, a number of genes encoding for human antigen presenting proteins, HLA alleles, have been discovered as valid pharmacogenetic markers for prediction of these life-threatening reactions. This study was aimed to determine the distribution of HLA alleles including the HLA class I and class II genes in 183 unrelated individuals of a Thai population using high resolution HLA genotyping in order to obtain 2-field data (4-digit resolution) and compare the frequencies of the HLA alleles that have been proposed as markers of SCARs with other ethnics. Results revealed a high prevalence of pharmacogenetic markers of drug-induced SCARs e.g., B*13:01 for dapsone; B*15:02 for carbamazepine and oxcarbazepine; B*58:01, A*33:03 and C*03:02 for allopurinol; C*08:01, C*14:02 and DRB1*12:02 for co-trimoxazole. Whereas, low prevalence of pharmacogenetic markers of SCARs induced by abacavir, B*57:01 and phenytoin, B*56:02/B*56:04 were noticed. The allele frequencies of B*13:01, B*15:02, and B*58:01 observed in a Thai population were significantly higher than those reported in Japanese and Caucasian populations. Similar to those observed in other Southeast Asian populations, low frequencies of A*31:01 and B*57:01 alleles were noted in the study population. Based on the frequencies of HLA pharmacogenetic markers, Thai and other Southeast Asian populations may at higher risk of drug-induced SCARs compared with Caucasian population.

Comparison between the HLA-B∗58 : 01 Allele and Single-Nucleotide Polymorphisms in Chromosome 6 for Prediction of Allopurinol-Induced Severe Cutaneous Adverse Reactions.

Severe cutaneous adverse drug reactions (SCARs) are life-threatening reactions. The strong association between the HLA-B∗58 : 01 allele and allopurinol-induced SCARs is well recognized. Screening for HLA-B∗58 : 01 allele before prescribing allopurinol in some populations has been recommended. Several single-nucleotide polymorphisms (SNPs) in chromosome 6 have been found to be tightly linked with the HLA allele, and these SNPs have been proposed as surrogate markers of the HLA-B∗58 : 01 allele. This study aimed to evaluate the association between three SNPs in chromosome 6 and allopurinol-induced SCARs in a Thai population. The linkage disequilibrium between the HLA-B∗58 : 01 allele and these SNPs was also evaluated. Results showed that three SNPs including rs9263726, rs2734583, and rs3099844 were significantly associated with allopurinol-induced SCARs but with a lower degree of association when compared with the HLA-B∗58 : 01 allele. The sensitivity, specificity, PPV, and NPV of these SNPs were comparable to those of the HLA-B∗58 : 01 allele. Although detection of the SNP is simpler and less expensive compared with that of the HLA-B∗58 : 01 allele, these SNPs were not perfectly linked with the HLA-B∗58 : 01 allele. Screening using these SNPs as surrogate markers of the HLA-B∗58 : 01 allele to avoid SCARs prior to allopurinol administration needs caution because of their imperfect linkage with the HLA-B∗58 : 01 allele.

Comparative pharmacodynamic effects of two clopidogrel formulations under steady-state conditions in healthy Thai volunteers
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OBJECTIVE: Clopidogrel is a commonly used antiplatelet aggregation agent. Compared with the reference clopidogrel product, most commercially available generic clopidogrel products contain different crystalline forms of clopidogrel. This study was aimed to compare the pharmacodynamics of a commonly used generic clopidogrel product in Thailand with the reference clopidogrel product under steady state conditions. METHODS: A multiple-dose, randomized 2-way crossover study was conducted in 32 healthy male Thai volunteers. The subjects were assigned to receive 75 mg once daily of the test or the reference product for 7 days with a 2-week wash out period. Blood samples were collected on days 1, 5, 6, and 7 prior to drug administration and at 1, 2, 3, 4, 8, 12, and 24 hours after the last dose administered. The antiplatelet aggregation effects of clopidogrel were determined by using two different ex-vivo platelet aggregation tests including the whole blood impedance assay (WBA) and the VerifyNow® P2Y12 assay. Both pharmacodynamic parameters, the maximal antiplatelet effect (Emax) and the areas under the antiplatelet effect-time curve (AUEC0-24h), were calculated. RESULTS: Neither the mean values of Emax (90.70 ± 15.15 vs. 89.50 ± 10.71% inhibition) nor of AUEC0-24h (1,892.84 ± 657.22 vs. 1,853.58 ± 673.95% inhibition × h) under steady-state conditions obtained using the WBA method of these two clopidogrel products were significantly different. The results obtained using the VerifyNow® P2Y12 assay were consistent with those of the WBA assay. CONCLUSION: This study clearly demonstrated that ex-vivo antiplatelet aggregation effect under steady-state conditions of the test product was not significantly different from the reference product.
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The impact of genetic polymorphisms of drug metabolizing enzymes on the pharmacodynamics of clopidogrel under steady state conditions.

Clopidogrel is an antiplatelet drug that requires biotransformation steps to its active metabolite via cytochromes P450 (CYP), particularly CYP2C19 and CYP3A5 as well as paraoxonase-1 (PON1). The impact of CYP3A5 and PON1 genetic polymorphisms on the response of this drug is unclear. This study aimed to elucidate the degree of genetic polymorphisms of key drug metabolizing enzymes on the antiplatelet effect of clopidogrel. Thirty-five healthy subjects were treated with 75 mg/day clopidogrel for 7 days and serial blood samples were collected for measurement of antiplatelet effect using whole blood impedance aggregometry and VerifyNow(®) P2Y12 methods. The areas under the antiplatelet effect-time curves, maximal and minimal antiplatelet effects of clopidogrel obtained from both methods were significantly different among subjects with different CYP2C19 genotypes. In contrast, these pharmacodymamic parameters measured by both methods of subjects with different PON1 or CYP3A5 genotypes were not significantly different. Among the heterozygous CYP2C19*2 subjects, all pharmacodynamic parameters measured by whole blood impedance aggregometry were significantly different between subjects with different CYP3A5*3 genotypes. Our data suggests that CYP2C19 genetic polymorphism play a major role in the clopidogrel response, however, the impact of CYP3A5 genetic polymorphism, may be pronounced in the subjects who carried the loss-functional allele of CYP2C19.

Candidate HLA genes for prediction of co-trimoxazole-induced severe cutaneous reactions.

BACKGROUND: Co-trimoxazole is a sulfonamide-containing antibiotic that is effective in the treatment of several infections and for prophylaxis of Pneumocystis jiroveci pneumonia. This drug has been reported as a common culprit drug for the Stevens-Johnson syndrome (SJS) and for toxic epidermal necrolysis (TEN). Human leukocyte antigens (HLAs) play a key role in the immunopathogenesis of severe cutaneous reactions induced by several drugs. This study investigated the association between the HLA class I and HLA-DRB1 polymorphisms and co-trimoxazole-induced SJS/TEN in a Thai population. METHODS: Forty-three patients with co-trimoxazole-induced SJS/TEN and 91 co-trimoxazole-tolerant patients were enrolled in the study. HLA class I and HLA-DRB1 were genotyped using the reverse sequence-specific oligonucleotide probe method. RESULTS: The frequencies of three alleles of HLA, namely HLA-B*15:02, HLA-C*06:02, and HLA-C*08:01, were significantly higher in the co-trimoxazole-induced SJS/TEN group compared with controls. The risks for co-trimoxazole-induced SJS/TEN in patients with the HLA-B*15:02, HLA-C*06:02, or HLA-C*08:01 allele were about 3-11-fold higher when compared with those who did not carry one of these alleles. Individuals who carried the HLA-B*15:02-C*08:01 haplotype had a 14-fold higher risk for co-trimoxazole-induced SJS/TEN. CONCLUSION: Evidence of associations between co-trimoxazole-induced SJS/TEN and HLA alleles including HLA-B*15:02, HLA-C*06:02, and HLA-C*08:01 were found in the study population. These findings may suggest that apart from the HLA molecules, other molecules involved in the molecular pathogenesis of these severe cutaneous adverse drug reactions may play an important role in the susceptibility of individuals to SJS/TEN caused by co-trimoxazole.

Comparative bioavailability of two moxifloxacin tablet products after single dose administration under fasting conditions in a balanced, randomized and cross-over study in healthy volunteers.

Moxifloxacin, a 4th generation of fluoroquinolones, is a broad spectrum antibacterial agent against respiratory tract pathogens, including Gram-positive and Gram-negative bacteria, anaerobic bacteria and atypical respiratory tract pathogens. In order to evaluate the efficacy and safety of generic moxifloxacin products, the bioequivalence of these generic products with an approved reference formulation should be demonstrated. Thus, the aim of this study was to compare the rate and extent of absorption of a new generic film coated moxifloxacin tablet product (Rapiflox®, Atlantic Laboratories Corporation Ltd., Bangkok, Thailand) with that of a reference product (Avelox®, Bayer Health Care AG, Leverkusen, Germany) when given as a single dose. A crossover study was performed in 20 healthy Thai volunteers. The subjects received either a 400 mg tablet of the reference or test product after overnight fasting. Blood samples were collected at pre-dose (0 hour) and at 0.25, 0.5, 1, 1.5, 2, 3, 4, 6, 8, 12, 24 and 34 hours post-dose. Moxifloxacin plasma level was measured by a validated HPLC method with fluorescence detector. Pharmacokinetic parameters were calculated using a non-compartmental model. The geometric mean of maximum concentration (Cmax) of the test product was 4,069.64 ng/ml, with median time to achieve maximum concentration (tmax) at 2 hours (range 0.25 - 6.00 hours), while the geometric mean Cmax and median tmax of the reference product was 4,211.98 ng/ml and 2.00 hours (range 0.25 - 8.00 hours). Furthermore, the geometric means of AUC0-tlast and AUC0-∞ for the test product were 49,731.66 and 51,865.89 ng×h/ml while those of the reference product were 51,927.97 and 54,455.93 ng×h/ml. The geometric mean of the ratios of Test/Reference for the logtransformed Cmax, AUC0-tlast and AUC0-∞ of moxifloxacin and their 90% CIs were 96.62% (83.21 - 112.19%), 95.77% (87.07 - 105.34%) and 95.24 (86.52 - 104.85%), respectively. Therefore, it can be concluded that these two moxifloxacin tablet products were bioequivalent in healthy Thai volunteers under fasting condition.