Wichittra Tassaneeyakul

Strong association between hla-b * 5801 and allopurinol-induced Stevens–johnson syndrome and toxic epidermal necrolysis in a Thai population

Objectives Allopurinol, a uric acid lowering drug commonly used for hyperuricemia and gouty arthritis, has been reported as a common cause of severe cutaneous adverse drug reactions (SCAR) including Stevens–Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN). A strong association between allopurinol-induced SCAR and HLA-B*5801 was observed in a Han Chinese population with high frequency of this allele, whereas only a moderate association was observed in populations with low frequency (i.e. European and Japanese). This study investigated the relationship between SJS/TEN and HLA-B*5801 in a Thai population that has a high allelic frequency of this allele. Methods Twenty-seven allopurinol-induced SJS/TEN and 54 allopurinol-tolerant patients were enrolled in the study. The presence of HLA-B*5801 and HLA-B genotypes in these patients were analyzed using a PG5801 DNA detection kit and sequence-based typing, respectively. Results All of the 27 (100%) allopurinol-induced SJS/TEN patients who were examined carried HLA-B*5801 whereas only seven (12.96%) of the control patients had this allele. The risk of allopurinol-induced SJS/TEN was significantly greater in patients with HLA-B*5801 when compared with those who did not carry this allele, with an odds ratio of 348.3 (95% confidence interval=19.2–6336.9, Pu2009=u20091.6×10−13). The sensitivity and specificity of the HLA-B*5801 allele for prediction of allopurinol-induced SJS/TEN were 100 and 87%, respectively. By assuming a 0.2% prevalence rate, the positive predictive value and the negative predictive value of the HLA-B*5801 allele was 1.52 and 100%, respectively. Conclusion A strong association of allopurinol-induced SJS/TEN with the HLA-B*5801 allele was observed in a Thai population. The results suggest that HLA-B*5801 is a valid genetic marker for screening Thai individuals who may be at risk for allopurinol-induced life-threatening SJS and TEN.

Association between HLA-B*1502 and carbamazepine-induced severe cutaneous adverse drug reactions in a Thai population

Carbamazepine (CBZ) has been reported as the most common culprit drug for Stevens‐Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) in several Asian countries including Thailand. A strong association between HLA‐B*1502 and CBZ‐induced SJS/TEN has been reported in Han Chinese but not in Caucasian and Japanese populations. A case–control study was conducted to determine whether HLA‐B*1502 is a valid pharmacogenetic test for SJS/TEN caused by CBZ in a Thai population. Among 42 CBZ‐induced patients with SJS/TEN, 37 (88.10%) patients carried the HLA‐B*1502 while only 5 (11.90%) of the CBZ‐tolerant controls had this allele. The risk of CBZ‐induced SJS/TEN was significantly higher in the patients with HLA‐B*1502, with an odds ratio (OR) of 54.76 [95% confidence interval (CI) 14.62–205.13, pu2003=u20032.89u2003×u200310−12]. The sensitivity and specificity of HLA‐B*1502 for prediction of CBZ‐induced SJS/TEN were 88.10%. By assuming a 0.27% as a prevalence rate of CBZ‐induced SJS/TEN in a Thai population, the positive predictive value (PPV) and negative predictive value (NPV) of the HLA‐B*1502 were 1.92% and 99.96%. Results from this study suggest that HLA‐B*1502 may be a useful pharmacogenetic test for screening Thai individuals who may be at risk for CBZ‐induced SJS and TEN.

Caffeine metabolism by human hepatic cytochromes p450: Contributions of 1A2, 2E1 and 3A isoforms

Caffeine (CA) N1-, N3- and N7-demethylase, CA 8-hydroxylase and phenacetin O-deethylase activities were measured in microsomes from 18 separate human livers which had been characterized previously for a range of cytochrome P450 (CYP) isoform-specific activities and immunoreactive CYP protein contents. Correlations between the high affinity components of the three separate CA N-demethylations were highly significant (r = 0.77-0.91, P < 0.001) and each of the three high affinity CA N-demethylations correlated significantly (r = 0.64-0.93, P < 0.05-0.001) with the high affinity phenacetin O-deethylase, 2-acetylaminofluorene N-hydroxylation and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) mutagenicity (all predominantly CYP1A2-mediated reactions). Consistent with these observations, cDNA-expressed human CYP1A2 catalyzed the N1-, N3- and N7-demethylation of CA and apparent Km values were similar (0.24-0.28 mM) for all three reactions and comparable to those observed previously with human liver microsomes. The low affinity components of CA N1- and N7-demethylation correlated significantly (r = 0.55-0.85, P < 0.05-0.001) with immunoreactive CYP2E1 content and the CYP2E1-specific activities 4-nitrophenol and chlorzoxazone hydroxylation. Diethyldithiocarbamate, a selective inhibitor of CYP2E1, inhibited the low affinity CA N1- and N7-demethylation, with IC50 values of 23 microM and 11 microM, respectively. The apparent Km values for CA N1- and N7-demethylation by cDNA-expressed CYP2E1 (namely 28 and 43 mM, respectively) were of a similar order to those calculated for the low affinity microsomal activities. Significant correlations (r = 0.87-0.97, P < 0.001) were observed between CA 8-hydroxylation and immunoreactive CYP3A content and the CYP3A-mediated reactions benzo(a)pyrene hydroxylation, omeprazole sulfoxidation and aflatoxin B1 mutagenesis. Effects of alpha-naphthoflavone, erythromycin, troleandomycin and nifedipine on microsomal CA 8-hydroxylation were generally consistent with CYP3A involvement. Taken together with previous data, the results indicate a major involvement of CYP1A2 in the high affinity component of all three human hepatic CA N-demethylations. In contrast, CYP2E1 appears to be the main enzyme involved in the low affinity components of CA N1- and N7-demethylation while CA 8-hydroxylation is catalysed predominantly by a CYP3A isoform(s).

Caffeine as a probe for human cytochromes P450: validation using cDNA-expression, immunoinhibition and microsomal kinetic and inhibitor techniques.

The molecular basis for the use of caffeine (CA; 1,3,7-trimethylxanthine) as a probe for specific human cytochromes P450 has been investigated. The CA 1-, 3- and 7-demethylations (to form theobromine, paraxanthine and theophylline, respectively) all followed biphasic kinetics in human liver microsomes. Mean apparent Km values for the high- and low-affinity components of the demethylations ranged from 0.13-0.31 nM and 19.2-30.0 mM, respectively. cDNA-expressed CYP1A2 catalysed all three CA demethylations, and the apparent Km for CA 3-demethylation (the major metabolic pathway in humans) by the expressed enzyme was similar to the Km for the high-affinity liver microsomal CA 3-demethylase. IC50 values for inhibition of the CA demethylations by alpha-naphthoflavone were similar for both expressed CYP1A2 and the high-affinity microsomal demethylases. Moreover, CA was a competitive inhibitor of expressed CYP1A2 catalysed phenacetin O-deethylation, with the apparent Ki (0.080 mM) closely matching the apparent Km (0.082 mM) for CA 3-demethylation by the expressed enzyme. Expressed CYP1A1 was additionally shown to catalyse the 3-demethylation of CA, although activity was lower than that observed for CYP1A2. While these data indicate that CYP1A2 is responsible for the high-affinity component of human liver CA 3-demethylation, two limitations associated with the use of CA as an in vitro probe for CYP1A2 activity have been identified: (i) CA 3-demethylation reflects hepatic CYP1A2 activity only at appropriately low substrate concentrations; and (ii) CA is a non-specific CYP1A substrate and CYP1A1 may therefore contribute to CA 3-demethylase activity in tissues in which it is expressed. An anti-CYP3A antibody essentially abolished the 8-hydroxylation of CA to form trimethyluric acid, suggesting formation of this metabolite may potentially serve as a marker of CYP3A isozyme(s) activity.

Effect of Albumin on Human Liver Microsomal and Recombinant CYP1A2 Activities: Impact on In Vitro-In Vivo Extrapolation of Drug Clearance

Long-chain unsaturated fatty acids inhibit several cytochrome P450 and UDP-glucuronosyltransferase (UGT) enzymes involved in drug metabolism, including CYP2C8, CYP2C9, UGT1A9, UGT2B4, and UGT2B7. Bovine serum albumin (BSA) enhances these cytochrome P450 and UGT activities by sequestering fatty acids that are released from membranes, especially with human liver microsomes (HLM) as the enzyme source. Here, we report the effects of BSA on CYP1A2-catalyzed phenacetin (PHEN) O-deethylation and lidocaine (LID) N-deethylation using HLM and Escherichia coli-expressed recombinant human CYP1A2 (rCYP1A2) as the enzyme sources. BSA (2% w/v) reduced (p < 0.05) the Km values of the high-affinity components of human liver microsomal PHEN and LID deethylation by approximately 70%, without affecting Vmax. The Km (or S50) values for PHEN and LID deethylation by rCYP1A2 were reduced to a similar extent. A fatty acid mixture, comprising 3 μM concentrations each of oleic acid and linoleic acid plus 1.5 μM arachidonic acid, doubled the Km value for PHEN O-deethylation by rCYP1A2. Inhibition was reversed by the addition of BSA. Ki values for the individual fatty acids ranged from 4.7 to 16.7 μM. Single-point in vitro-in vivo extrapolation (IV-IVE) based on the human liver microsomal kinetic parameters obtained in the presence, but not absence, of BSA predicted in vivo hepatic clearances of PHEN O-deethylation and LID N-deethylation that were comparable to values reported in humans, although in vivo intrinsic clearances were underpredicted. Prediction of the in vivo clearances of the CYP1A2 substrates observed here represents an improvement on other experimental systems used for IV-IVE.

Azathioprine-induced fatal myelosuppression in a renal-transplant recipient who carried heterozygous TPMT*1/*3C.

Bone Marrow Transplant 1997; 20: 171. 3. Darrington DL, Vose JM, Anderson JR, et al. Incidence and characterization of secondary myelodysplastic syndrome and acute myelogenous leukemia following high-dose chemotherapy and autologous stem-cell transplantation for lymphoid malignancies. J Clin Oncol 1994; 12: 2527. 4. Pedersen-Bjergaard J, Andersen MK, Christiansen DH. Therapy-related acute myeloid leukemia and myelodysplasia after high-dose chemotherapy and autologous stem cell transplantation. Blood 2000; 95: 3273. 5. Krishnan A, Bhatia S, Slovak ML, et al. Predictors of therapy-related leukemia and myelodysplasia following autologous transplantation for lymphoma: an assessment of risk factors. Blood 2000; 95: 1588.

Risk factors of allopurinol-induced severe cutaneous adverse reactions in a Thai population

Background Allopurinol is one of the most common causes of severe cutaneous adverse drug reactions (SCARs) including drug reactions with eosinophilia and systemic symptoms (DRESS), Stevens–Johnson syndrome (SJS), and toxic epidermal necrolysis (TEN). This study identified the risk factors associated with the development of allopurinol-induced SCARs in a Thai population. Patients and methods Eighty-six allopurinol-induced SCARs (i.e. 19 DRESS and 67 SJS/TEN) and 182 allopurinol-tolerant patients were enrolled in the study. The HLA-B*58:01 allele was determined. Clinical and medicinal data were collected. Results Results from multivariate analysis showed that only the HLA-B*58:01 and female sex were identified as risk factors of allopurinol-induced SCARs in this Thai population. Patients who carried the HLA-B*58:01 allele were at a higher risk of allopurinol-induced DRESS [odds ratio (OR)=149.2, 95% confidence interval (CI)=24.0–∞, P<1.00×10−4]. Similar results were observed in allopurinol-induced SJS/TEN (OR=175.0, 95% CI=44.3–690.9, P=1.69×10−13). The risk of allopurinol-induced SCARs in women was higher than that in men (OR=4.6, 95% CI=1.4–15.6, P=1.44×10−2). The overall mortality rate of allopurinol-induced SCARs was 11.39% and a higher mortality rate was observed in elderly women. Conclusion Among the risk factors identified, the HLA-B*58:01 allele had the greatest impact on the development of both phenotypes of allopurinol-induced SCARs in this studied Thai population. In case HLA-B*58:01 genotyping cannot be accessed, close monitoring of allopurinol usage, especially in elderly women with impaired renal function, is necessary to reduce the mortality rate of these life-threatening SCARs.

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

Cost-effectiveness analysis of HLA-B*58: 01 genetic testing before initiation of allopurinol therapy to prevent allopurinol-induced Stevens–Johnson syndrome/toxic epidermal necrolysis in a Malaysian population

Objective Studies found a strong association between allopurinol-induced Stevens–Johnson syndrome (SJS)/toxic epidermal necrolysis (TEN) and the HLA-B*58:01 allele. HLA-B*58:01 screening-guided therapy may mitigate the risk of allopurinol-induced SJS/TEN. This study aimed to evaluate the cost-effectiveness of HLA-B*58:01 screening before allopurinol therapy initiation compared with the current practice of no screening for Malaysian patients with chronic gout in whom a hypouricemic agent is indicated. Methods This cost-effectiveness analysis adopted a societal perspective with a lifetime horizon. A decision tree model coupled with Markov models were developed to estimate the costs and outcomes, represented by quality-adjusted life years (QALYs) gained, of three treatment strategies: (a) current practice (allopurinol initiation without HLA-B*58:01 screening); (b) HLA-B*58:01 screening before allopurinol initiation; and (c) alternative treatment (probenecid) without HLA-B*58:01 screening. The model was populated with data from literature review, meta-analysis, and published government documents. Cost values were adjusted for the year 2016, with costs and health outcomes discounted at 3% per annum. A series of sensitivity analysis including probabilistic sensitivity analysis were carried out to determine the robustness of the findings. Results Both HLA-B*58:01 screening and probenecid prescribing were dominated by current practice. Compared with current practice, HLA-B*58:01 screening resulted in 0.252 QALYs loss per patient at an additional cost of USD 322, whereas probenecid prescribing resulted in 1.928 QALYs loss per patient at an additional cost of USD 2203. One SJS/TEN case would be avoided for every 556 patients screened. At the cost-effectiveness threshold of USD 8695 per QALY, the probability of current practice being the best choice is 99.9%, in contrast with 0.1 and 0% in HLA-B*58:01 screening and probenecid prescribing, respectively. This is because of the low incidence of allopurinol-induced SJS/TEN in Malaysia and the lower efficacy of probenecid compared with allopurinol in gout control. Conclusion This analysis showed that HLA-B*58:01 genetic testing before allopurinol initiation is unlikely to be a cost-effective intervention in Malaysia.

Outcomes of a Randomized Controlled Trial Comparing Modified High Dose Omeprazole and Amoxicillin Triple Therapy with Standard Triple Therapy for Helicobacter Pylori Eradication

Background: Helicobacter pylori (H. pylori) infection is related to peptic ulcer diseases and gastric cancer and eradication of H. pylori should be expected to decrease the risk of their development. Factors affecting H. pylori eradication are antibiotic resistance, CYP2C19 genotypes, drug regimen and patient compliance. Increment of omeprazole and amoxicillin dosage in clarithromycin-containing triple therapy regimen may overcome these problems and may be a better choice than the conventional clarithromycin-containing triple therapy regimen. Objective: To compare the eradication rates with modified triple therapy (MTT) and standard triple therapy (STT) as first-line treatment. Materials and Methods: The study was an open label, multicenter, randomized controlled trial. A total of 170 patients infected with H. pylori diagnosed by rapid urease test were randomly assigned into 2 groups. The first was treated with a 14-day MTT (20 mg omeprazole t.i.d., 500 mg amoxicillin t.i.d., and 500 mg clarithromycin b.i.d.) and the second with a 14-day STT (20 mg omeprazole b.i.d., 1000 mg amoxicillin b.i.d., and 500 mg clarithromycin b.i.d.). H. pylori eradication was evaluated by 14C-urea breath test. CYP2C19 genotypes, clarithromycin resistance, side effects and patient compliance were also recorded. Results: There were 85 patients in each group. The H. pylori eradication rate in the MTT group was 84.7% by ITT analysis and 91.1% by PP analysis, compared to the STT group values of 76.5% and 87.8% (p = 0.18 and 0.51), respectively. CYP2C19 genotypes and patient compliance were similar in both groups. Prevalence of clarithromycin resistance was 7.0%. Side effects were all mild with no significant differences between the twogroups. Conclusions: MTT is not superior to STT. From this study, MTT may not be recommended as the first-line treatment for H. pylori infection in Thailand because eradication rates proved to be less than 90% by ITT analysis.