Adverse Events of Thiopurine Therapy in Pediatric Inflammatory Bowel Disease and Correlations with Metabolites: A Cohort Study.

BACKGROUND: In the recent era of growing availability of biological agents, the role of thiopurines needs to be reassessed with the focus on toxicity. AIMS: We assessed the incidence and predictive factors of thiopurine-induced adverse events (AE) resulting in therapy cessation in pediatric inflammatory bowel disease (IBD), related to thiopurine metabolites and biochemical abnormalities, and determined overall drug survival. METHODS: We performed a retrospective, single-center study of children diagnosed with IBD between 2000 and 2019 and treated with thiopurine therapy. The incidence of AE and overall drug survival of thiopurines were evaluated using the Kaplan-Meier method. Correlations between thiopurine metabolites and biochemical tests were computed using Spearman's correlation coefficient. RESULTS: Of 391 patients with IBD, 233 patients (162 Crohn's disease, 62 ulcerative colitis, and 9 IBD-unclassified) were prescribed thiopurines (230 azathioprine and 3 mercaptopurine), of whom 50 patients (22%) discontinued treatment, at least temporary, due to thiopurine-induced AE (median follow-up 20.7 months). Twenty-six patients (52%) were rechallenged and 18 of them (70%) tolerated this. Sixteen patients (6%) switched to a second thiopurine agent after azathioprine intolerance and 10 of them (63%) tolerated this. No predictive factors for development of AE could be identified. Concentrations of 6-thioguanine nucleotides (6-TGN) were significantly correlated with white blood cell and neutrophil count, 6-methylmercaptopurine (6-MMP) concentrations with alanine aminotransferase and gamma-glutamyltranspeptidase. CONCLUSIONS: Approximately 20% of pediatric patients with IBD discontinued thiopurine treatment due to AE. A rechallenge or switch to mercaptopurine is an effective strategy after development of AE. Concentrations of 6-TGN and 6-MMP are associated with biochemical abnormalities.

Systematic Review and Meta-Analysis of Thiopurine Metabolite Levels and Biochemical Remission in Autoimmune Hepatitis.

BACKGROUND: The utility of measuring thiopurine metabolites (TM) to individualize therapy in autoimmune hepatitis (AIH) has not been defined, and the evidence regarding its use in clinical practice is heterogeneous. This systematic review and meta-analysis aimed to compare the mean concentration of TM between patients in biochemical remission and those not in remission. METHODS: A systematic literature search was conducted using PubMed, Scopus, the Cochrane Library, and Google Scholar for keywords related to TM and AIH. Two reviewers independently searched and selected studies comparing the levels of 6-methyl mercaptopurine (6-MMP) and 6-thioguanine nucleotide (6-TGN) and their ratio in cases of AIH in remission and otherwise. Meta-analysis was performed by calculating the weighted mean difference using the inverse variance heterogeneity model. RESULTS: A total of 1066 records were identified through systematic search; of which, 7 (n = 3 pediatric, n = 4 adults) were considered for inclusion, and 442 TM measurements (n = 128 in children) were analyzed. Mean 6-TGN levels were significantly higher among patients in remission than in those who were not, with a pooled weighted mean difference (WMD) of 15.67 [95% confidence interval (CI), 6.68-24.66] pmol/8 × 108 red blood cells (RBC). The difference was higher in the pediatric age group (WMD, 56.11; 95% CI, 13.60-98.62) than in adults (WMD, 13.77; 95% CI, 4.58-22.97). There was no significant difference in the 6-MMP levels (WMD, -431.7; 95% CI, -1237.4 to 373.9 pmol/8 × 108 RBC; I2 = 82%; n = 3 studies) or 6-MMP/6-TGN ratio among the patients who were in biochemical remission and those who were not (WMD, -0.97; 95% CI, -5.77 to 3.84; I2 = 82%; n = 3 studies). CONCLUSIONS: This meta-analysis suggests a link between 6-TGN levels and biochemical remission in AIH. Further high-quality studies are required to determine the therapeutic cutoff of 6-TGN.

A Systematic Review and Meta-Analysis of Pharmacogenetic Studies in Patients with Chronic Kidney Disease.

Chronic kidney disease (CKD) is an important global public health problem due to its high prevalence and morbidity. Although the treatment of nephrology patients has changed considerably, ineffectiveness and side effects of medications represent a major issue. In an effort to elucidate the contribution of genetic variants located in several genes in the response to treatment of patients with CKD, we performed a systematic review and meta-analysis of all available pharmacogenetics studies. The association between genotype distribution and response to medication was examined using the dominant, recessive, and additive inheritance models. Subgroup analysis based on ethnicity was also performed. In total, 29 studies were included in the meta-analysis, which examined the association of 11 genes (16 polymorphisms) with the response to treatment regarding CKD. Among the 29 studies, 18 studies included patients with renal transplantation, 8 involved patients with nephrotic syndrome, and 3 studies included patients with lupus nephritis. The present meta-analysis provides strong evidence for the contribution of variants harbored in the ABCB1, IL-10, ITPA, MIF, and TNF genes that creates some genetic predisposition that reduces effectiveness or is associated with adverse events of medications used in CKD.

Cost-effectiveness analysis of pretreatment screening for NUDT15 defective alleles.

BACKGROUND: Nucleotide triphosphate diphosphatase (NUDT15) genetic testing in addition to thiopurine methyl transferase (TPMT) is recommended to reduce the incidence of adverse severe myelotoxicity episodes induced by thiopurines. OBJECTIVE: We assessed the cost-effectiveness ratio of combined screening for TMPT and NUDT15 defective alleles by genotyping or next-generation sequencing (NGS) using TPMT genotyping as the reference. Because of the genetic differences in thiopurine toxicity, we tested the screening strategies on individuals of Caucasian and Asian descent. METHODS: A decision tree compared conventional TPMT genotyping with combined TPMT/NUDT15 genotyping or NGS using a Monte-Carlo microsimulation model of patients with inflammatory bowel disease. The main outcome was the incremental cost-effectiveness ratios (ICER) with effectiveness being one averted severe myelotoxicity requiring hospitalization. RESULTS: The mean estimated cost of the TPMT genotyping for one year is twice in Asian compared with Caucasian patients (980 euro/patient versus 488 euro/patient), and the effectiveness of TPMT genotyping in Caucasian avoided 43 severe myelosuppressions per 10 000 patients over a year compared with 3.6 per 10 000 patients in Asian. Combined TPMT/NUDT15 genotyping compared with TPMT genotyping had an ICER of 7 491 281 euro per severe myelotoxicity averted in Caucasian, compared to 619 euro in Asian. The ICER of the NGS-based screening strategy is disproportionally high compared with genotyping, irrespective of ethnic descent. CONCLUSION: With a low cost-effectiveness threshold, combined screening for NUDT15 and TPMT defective alleles is cost-effective compared to TMPT screening alone in patients of Asian descent, but is unrealistic from a cost-effectiveness point of view in Caucasians.

PACSIN2 rs2413739 influence on thiopurine pharmacokinetics: validation studies in pediatric patients.

The aim of the study was to validate the impact of the single-nucleotide polymorphism rs2413739 (T > C) in the PACSIN2 gene on thiopurines pharmacological parameters and clinical response in an Italian cohort of pediatric patients with acute lymphoblastic leukemia (ALL) and inflammatory bowel disease (IBD). In ALL, PACSIN2 rs2413739 T allele was associated with a significant reduction of TPMT activity in erythrocytes (p = 0.0094, linear mixed-effect model, multivariate analysis considering TPMT genotype) and increased severe gastrointestinal toxicity during consolidation therapy (p = 0.049). A similar trend was present also for severe hematological toxicity during maintenance. In IBD, no significant effect of rs2413739 could be found on TPMT activity, however azathioprine effectiveness was reduced in patients carrying the T allele (linear mixed effect, p = 0.0058). In PBMC from healthy donors, a positive correlation between PACSIN2 and TPMT protein concentration could be detected (linear mixed effect, p = 0.045). These results support the role of PACSIN2 polymorphism on TPMT activity and mercaptopurine adverse effects in patients with ALL. Further evidence on PBMC and pediatric patients with IBD supports an association between PACSIN2 variants, TPMT activity, and thiopurines effects, even if more studies are needed since some of these effects may be tissue specific.

Combination Therapy With Infliximab and Azathioprine Improves Infliximab Pharmacokinetic Features and Efficacy: A Post Hoc Analysis.

BACKGROUND & AIMS: Among immunosuppressive- and biologic-naïve patients with moderately-to-severely active Crohn's disease (CD), a higher proportion of those treated with the combination of infliximab and azathioprine achieved corticosteroid-free remission at week 26 (CSFR26) than those given infliximab monotherapy; patients given the combination therapy also had higher serum concentrations of infliximab. Enhanced benefit of combination therapy may occur through synergistic modes of action or the influence of azathioprine on infliximab pharmacokinetics. METHODS: We analyzed data from 206 patients from whom week 30 serum samples were available: 97 received infliximab monotherapy (5 mg/kg, n = 97) and 109 received combination therapy (2.5 mg/kg/day; n = 109). Proportions of patients achieving CSFR26 and mucosal healing (absence of ulcers) at week 26 were calculated for each quartile of serum concentrations of infliximab, and exposure-response relationships were compared. RESULTS: Within quartiles of serum concentrations of infliximab, CSFR26 did not differ significantly between patients who received combination therapy vs monotherapy. However, among patients in the lowest quartile of serum concentration of infliximab, twice as many patients who received infliximab monotherapy achieved CSFR26 vs combination therapy. Anti-drug antibodies were detected only in the lowest quartile of serum concentrations of infliximab-in 35.9% of patients given monotherapy and 8.3% of patients given combination therapy. CONCLUSION: Among patients with CD and similar serum concentrations of infliximab, combination therapy with azathioprine was not significantly more effective than infliximab monotherapy. Combination therapy with azathioprine appears to improve efficacy by increasing pharmacokinetic features of infliximab. ClinicalTrials.gov, NCT00094458.

American Gastroenterological Association Institute Technical Review on the Role of Therapeutic Drug Monitoring in the Management of Inflammatory Bowel Diseases.

Therapeutic drug monitoring (TDM), which involves measurement of drug or active metabolite levels and anti-drug antibodies, is a promising strategy that can be used to optimize inflammatory bowel disease therapeutics. It is based on the premise that there is a relationship between drug exposure and outcomes, and that considerable inter-individual variability exists in how patients metabolize the drug (pharmacokinetics) and the magnitude and duration of response to therapy (pharmacodynamics). Therefore, the American Gastroenterological Association has prioritized clinical guidelines on the role of TDM in the management of inflammatory bowel disease. To inform these clinical guidelines, this technical review was developed in accordance with the GRADE (Grading of Recommendations Assessment, Development, and Evaluation) framework for interventional and prognostic studies, and focused on the application of TDM for biologic therapy, specifically anti-tumor necrosis factor-α agents, and for thiopurines. Focused questions address the benefits and risks of a strategy of reactive TDM (in patients with active inflammatory bowel disease) to guide treatment changes compared with empiric treatment changes, and the benefits and risks of a strategy of routine proactive TDM (during routine clinical care in patients with quiescent disease) compared with no routine TDM. Additionally, the review addresses the benefits and risks of routine measurement of thiopurine methyltransferase enzyme activity or genotype before starting thiopurine therapy compared with empiric weight-based dosing and explores the performance of different trough drug concentrations for anti-tumor necrosis factor agents and thiopurines to inform clinical decision making when applying TDM in a reactive setting. Due to a paucity of data, this review does not address the role of TDM for more recently approved biologic agents, such as vedolizumab or ustekinumab.

Analytical and Sample Preparation Protocol for Therapeutic Drug Monitoring of 12 Thiopurine Metabolites Related to Clinical Treatment of Inflammatory Bowel Disease.

Thiopurines (TP) represent an important therapeutic tool for the treatment of inflammatory bowel diseases (IBD) in the current situation of rising incidence and health care costs. The results of multiple clinical studies aimed at finding correlations between levels of TP metabolites and response of IBD patients to the treatment are, however, often controversial due to variability in analytical and sample preparation procedures among these studies. In this work, therefore, an updated analytical and sample preparation procedure for therapeutic drug monitoring (TDM) of TP metabolites in blood samples obtained from patients with IBD was proposed to establish a unified protocol. An advanced analytical method based on ion-exchange liquid chromatography hyphenated with tandem mass spectrometry (IEC-ESI-MS/MS) was used for the determination of the profiles of 12 individual TP metabolites in the particular steps of sample preparation procedure including blood collection, red blood cells (RBC) isolation, lysis, and storage. Favorable performance parameters of the IEC-ESI-MS/MS method (LLOQs 1⁻10 nmol/L, accuracy 95⁻105%, intra-day and inter-day precision < 10%, selectivity demonstrated via no sample matrix interferences) and acceptable stability (peak area fluctuations < 15%) of clinical samples under the proposed sample preparation conditions {(i) EDTA anticoagulant tube for the blood collection; (ii) 4 °C and 4 h between the sample collection and RBC isolation; (iii) phosphate-buffered saline for RBC washing and re-suspendation; (iv) -20 °C for RBC lysis and short-term storage; (v) 50 mmol/L phosphate buffer, pH 7.4, 10 mmol/L DTT as a stabilizing medium for TPN in RBC lysates} demonstrated the suitability of such protocol for a well-defined and reliable routine use in studies on thiopurines TDM.

Clinical experience of optimising thiopurine use through metabolite measurement in inflammatory bowel disease. / Experiencia en práctica clínica de optimización de tiopurinas mediante determinación de sus metabolitos en la enfermedad inflamatoria intestinal.

INTRODUCTION: Thiopurine therapy can be optimised by determining the concentration of the drug's metabolites. PATIENTS AND METHODS: Retrospective analysis on a prospective database of 31 patients with inflammatory bowel disease who failed therapy with thiopurines. Thiopurine metabolites (6-thioguanine, 6-TGN and 6-methylmercaptopurine, 6-MMP) were measured by high-performance liquid chromatography (Laboratorios Cerba, Barcelona) and treatment was duly adjusted in accordance with the results. Clinical response was reassessed after six months. RESULT: Despite the appropriate theoretical dose of thiopurines being administered, the dose was insufficient in 45.6% of patients (nonadherence to treatment suspected in 6.45%) and 16.2% received an excessive dose or the drug was metabolised by other metabolic pathways. After treatment was optimised based on metabolite levels, only 25.8% (8/31) were prescribed a biological agent, while 74.2% of cases (23/31) were managed through dose optimisation alone. DISCUSSION: Monitoring thiopurine metabolite levels may help clinicians to assess non-responsive patients before adding or switching to another drug (generally a biological agent), thereby avoiding any additional costs or potential toxicity. This strategy may also help to identify patients receiving an insufficient dose and those with an alternative metabolic pathway, who could be candidates for low-dose AZA with allopurinol, as well as patients who are suspected of being non-adherent. In three out of four patients, switching to a biological agent can be avoided.

A novel ABCC6 haplotype is associated with azathioprine drug response in myasthenia gravis.

OBJECTIVE: We investigated the association of single nucleotide polymorphisms (SNPs) in drug-metabolizing enzymes and transporters (DMETs) with the response to azathioprine (AZA) in patients affected by myasthenia gravis (MG) to determine possible genotype-phenotype correlations. PATIENTS AND METHODS: Genomic DNA from 180 AZA-treated MG patients was screened through the Affymetrix DMET platform, which characterizes 1931 SNPs in 225 genes. The significant SNPs, identified to be involved in AZA response, were subsequently validated by allelic discrimination and direct sequencing. SNP analysis was carried out using the SNPassoc R package and the haploblocks were determined using haploview software. RESULTS: We studied 127 patients in the discovery phase and 53 patients in the validation phase. We showed that two SNPs (rs8058694 and rs8058696) found in ATP-binding cassette subfamily C member 6, a subfamily member of ATP-binding cassette genes, constituted a new haplotype associated with AZA response in MG patients in the discovery cohort (P=0.011; odds ratio: 0.40; 95% confidence interval: 0.20-0.83) and in the combined cohort (P=0.04; odds ratio: 1.58). CONCLUSION: These findings highlight the role that the ATP-binding cassette subfamily C member 6 haplotype may play in AZA drug response. In view of the significant effects and AZA intolerance, these novel SNPs should be taken into consideration in pharmacogenetic profiling for AZA.

Analytical Pitfalls of Therapeutic Drug Monitoring of Thiopurines in Patients With Inflammatory Bowel Disease.

The use of thiopurines in the treatment of inflammatory bowel disease (IBD) can be optimized by the application of therapeutic drug monitoring. In this procedure, 6-thioguanine nucleotides (6-TGN) and 6-methylmercaptopurine (6-MMP) metabolites are monitored and related to therapeutic response and adverse events, respectively. Therapeutic drug monitoring of thiopurines, however, is hampered by several analytical limitations resulting in an impaired translation of metabolite levels to clinical outcome in IBD. Thiopurine metabolism is cell specific and requires nucleated cells and particular enzymes for 6-TGN formation. In the current therapeutic drug monitoring, metabolite levels are assessed in erythrocytes, whereas leukocytes are considered the main target cells of these drugs. Furthermore, currently used methods do not distinguish between active nucleotides and their unwanted residual products. Last, there is a lack of a standardized laboratorial procedure for metabolite assessment regarding the substantial instability of erythrocyte 6-TGN. To improve thiopurine therapy in patients with IBD, it is necessary to understand these limitations and recognize the general misconceptions in this procedure.

LC-MS/MS Analysis of Erythrocyte Thiopurine Nucleotides and Their Association With Genetic Variants in Patients With Neuromyelitis Optica Spectrum Disorders Taking Azathioprine.

BACKGROUND: Azathioprine is a first-line drug in treating neuromyelitis optica spectrum disorders (NMOSD). To exhibit its bioactivity, azathioprine needs to be converted to thiopurine nucleotides (TPNs) including 6-thioguanine nucleotides (6-TGNs) and 6-methylmercaptopurine nucleotides (6-MMPNs) that are affected by genetic polymorphisms. This study aims to develop an LC-MS/MS method for the analysis of erythrocyte concentrations of TPNs and to evaluate their associations with variants of various genes (MTHFR, TPMT, HLA, SLC29A1, SLC28A2, SLC28A3, ABCB1, and ABCC4) in patients with NMOSD. METHODS: Erythrocyte 6-TGNs and 6-MMPNs were converted to their free bases 6-thioguanine and 6-methylmercaptopurine derivative by 1-hour acid hydrolysis at 95°C. An LC-MS/MS method was developed, validated, and used to study 32 patients with NMOSD to determine these free bases. Genetic variants were identified by MassARRAY (Sequenom) and multiple SNaPshot techniques. The associations between genetic variants and the concentrations of TPNs or the 6-MMPNs:6-TGNs ratio were evaluated by PLINK software using linear regression. RESULTS: Methanol and water were used for separation with a total run time of 6.5 minutes. The lowest limit of quantification was 0.1 µmol/L with an injection volume of 10 µL. rs10868138 (SLC28A3) was associated with a higher erythrocyte concentration of 6-TGNs (P = 0.031), whereas rs12378361 (SLC28A3) was associated with a lower erythrocyte concentration of 6-TGNs (P = 0.0067). rs507964 (SLC29A1) was significantly associated with a lower erythrocyte concentration of 6-MMPNs (P = 0.024) and a lower 6-MMPNs:6-TGNs ratio (P = 0.029). CONCLUSIONS: An LC-MS/MS method for the analysis of erythrocyte TPNs was developed, validated, and used to study 32 patients with NMOSD. SLC29A1 and SLC28A3 were associated with the erythrocyte concentrations of TPNs and 6-MMPNs:6-TGNs ratio. Further studies are needed to confirm these results.

Outcomes in Pediatric Autoimmune Hepatitis and Significance of Azathioprine Metabolites.

OBJECTIVES: Autoimmune hepatitis (AIH) is a common pediatric liver disease and long-term remission is usually maintained with azathioprine (AZA). There is no consensus on the target range for AZA active metabolite 6-thioguanine (6-TGN) levels in pediatric AIH. The aim of the present study was to characterize the outcomes of pediatric patients with AIH and determine correlations between AZA dosing or 6-TGN metabolite levels and biochemical remission. METHODS: A retrospective chart review was performed and data on presentation, laboratories including AZA metabolite levels, medication use, and outcomes were collected. RESULTS: Between 2002 and 2013, 66 children with AIH were identified (mean age at diagnosis 9.6 ±â€Š5.1 years) with a mean follow-up period of 2.9 ±â€Š3.2 years. Common presenting symptoms included jaundice, fatigue, and abdominal pain. The majority of subjects received steroids for induction and AZA for maintenance of remission. Seventy-nine percent achieved biochemical remission (mean time to remission 6.2 ±â€Š9.2 months), 14% were in the induction phase of therapy, 6% required liver transplantation, and 18% were weaned off immunosuppression and remained in remission. 6-TGN levels ranging from 50 to 250 pmol/8 × 10 red blood cell count were associated with biochemical remission (alanine aminotransferase levels of ≤50 U/L). CONCLUSIONS: The vast majority of children with AIH maintain a sustained remission with AZA monotherapy. Biochemical remission was maintained with 6-TGN levels much lower than that recommended for inflammatory bowel disease. These findings suggest that patients should be maintained at the lowest AZA dose possible that is associated with biochemical remission.

Small airway dysfunction in chronic hypersensitivity pneumonitis.

BACKGROUND AND OBJECTIVE: Lung biopsies from patients with hypersensitivity pneumonitis (HP) have demonstrated small airway (SA) involvement, but there is no information concerning SA function in HP, and it is unknown whether pharmacological treatment could modify its function. SA function in patients with chronic HP using ultrasonic pneumography (UPG) and impulse oscillometry (IOS) was explored. We also compared initial results with those obtained after 4 weeks of standardized treatment with azathioprine and prednisone. METHODS: The study group consisted of adults with recent diagnoses of HP. All patients completed UPG, IOS, spirometry, body plethysmography, single-breath carbon monoxide diffusing capacity (DLCO ) and the 6-min walk test (6MWT). The fraction of exhaled nitric oxide (FENO ) was obtained to assess eosinophilic airway inflammation. Measurements were taken at diagnosis and after 4 weeks of treatment. RESULTS: A total of 20 consecutive patients (16 women) with chronic HP participated in the study. Median age was 50 years (interquartile range (IQR): 42-54). At diagnosis, the UPG phase 3 slope was abnormally high, consistent with maldistribution of ventilation. For IOS, all patients had low reactance at 5 Hz (X5) and elevated reactance area (AX) reflecting low compliance, and only eight (40%) patients had elevated R5 (resistance at 5 Hz (total)) and R5-20 (resistance at 5 Hz-resistance at 20 Hz (peripheral)) attributed to SA resistance. In contrast, FENO parameters were within normal limits. After treatment, forced vital capacity (FVC), the 6-min walk distance and the distribution of ventilation showed significant improvement, although DLCO did not. CONCLUSION: Patients with chronic HP have SA abnormalities that are partially revealed by the UPG and IOS tests. Lung volumes, but not gas exchange, improved after treatment with azathioprine and prednisone.

Therapeutic drug monitoring in inflammatory bowel disease.

PURPOSE OF REVIEW: There are an expanding number of therapies available to treat pediatric inflammatory bowel disease (IBD). As pediatric gastroenterologists attempt to achieve complete intestinal mucosal healing for their patients, it has become more important to gain an understanding of how to maximize the efficacy of our medications while minimizing their toxicities. We aim to provide an overview of therapeutic drug monitoring in IBD with an emphasis on the biologic therapies (antitumor necrosis factor and anti-integrin monoclonal antibodies). RECENT FINDINGS: Recent findings do support optimized drug dosing for infliximab based on early trough levels, but question the utility of checking these values in patients doing well in maintenance therapy. Patients with severe colonic inflammation may be at increased risk for needing optimization with dose escalation because of medication loss in the stool. Dose escalation can recapture response in some patients with a secondary loss of response, including those with low level antibody formation. The monitoring of nontrough drug levels to allow timelier dose adjustment as well as the role of drug monitoring with anti-integrin therapy are areas of active research. SUMMARY: Therapeutic drug monitoring is an effective strategy in the management of pediatric IBD that can help patients achieve mucosal healing and aid the clinical decision-making of the pediatric gastroenterologist.

Rac1 as a Potential Pharmacodynamic Biomarker for Thiopurine Therapy in Inflammatory Bowel Disease.

BACKGROUND: Azathioprine and mercaptopurine (MP) are effective in treating patients with inflammatory bowel disease (IBD). Immunosuppressive effects of thiopurines involve T-cell apoptosis after inhibition of GTPase Ras-related C3 botulinum toxin substrate 1 (Rac1). This study aimed to assess whether expression and activity of Rac1 or phosphorylated ezrin-radixin-moesin (pERM) in patients with IBD could provide a useful biomarker for the pharmacodynamic thiopurine effect and might be related to clinical effectiveness. METHODS: This was a 2-stage study: stage 1 concerned a cross-sectional cohort of patients with IBD clinically in remission and treated with (n = 10) or without stable weight-based thiopurine therapy (n = 11) and healthy controls (n = 6); stage 2 concerned a prospective study regarding IBD patients with clinically active disease who initiated MP therapy (n = 11) compared with healthy controls (n = 11). Expression and activity of Rac1 and ERM and pERM were determined. RESULTS: The median Rac1 expression was statistically significantly reduced by thiopurine maintenance therapy {0.54 [interquartile range (IQR) 0.47-0.88] versus 0.80 arbitrary units [IQR 0.64-1.46]} compared with patients without immunosuppressive therapy (P = 0.042), but not Rac1 activity and pERM. In responders to MP therapy (n = 6), both median active Rac1 [93 (IQR 81-151) to 76 ng Rac1/mg protein (IQR 62-98)] and Rac1 expression [16.2 (8.8-29.4) to 1.5 arbitrary units (0.9-5.3)] decreased (P = 0.028). In nonresponders (n = 3), Rac1 expression and activity increased. CONCLUSIONS: IBD patients treated with thiopurines had a lower expression of Rac1 compared with those not treated with thiopurine. Effective MP therapy led to decreasing concentrations of Rac1-GTP and Rac1 expression. Therefore, Rac1-GTP and expression of Rac1, but not phosphorylation of ERM, form potentially pharmacodynamic markers of therapeutic thiopurine effectiveness in patients with IBD.

Pharmacogenomics and personalized medicine: a review focused on their application in the Chinese population.

The field of pharmacogenomics was initiated in the 1950s and began to thrive after the completion of the human genome project 10 years ago. Thus far, more than 100 drug labels and clinical guidelines referring to pharmacogenomic biomarkers have been published, and several key pharmacogenomic markers for either drug safety or efficacy have been identified and subsequently adopted in clinical practice as pre-treatment genetic tests. However, a tremendous variation of genetic backgrounds exists between different ethnic groups. The application of pharmacogenomics in the Chinese population is still a long way off, since the published guidelines issued by the organizations such as US Food and Drug Administration require further confirmation in the Chinese population. This review highlights important pharmacogenomic discoveries in the Chinese population and compares the Chinese population with other nations regarding the pharmacogenomics of five most commonly used drugs, ie, tacrolimus, cyclosporine A, warfarin, cyclophosphamide and azathioprine.

Intrauterine exposure and pharmacology of conventional thiopurine therapy in pregnant patients with inflammatory bowel disease.

OBJECTIVE: Several studies have demonstrated a favourable safety profile for thiopurine use for inflammatory bowel disease (IBD) during pregnancy. We performed a study in pregnant patients with IBD who were using thiopurines, in order to determine the influence of pregnancy on thiopurine metabolism and to assess intrauterine exposure of the fetus to thiopurines. DESIGN: Female patients with IBD receiving steady-state thiopurines and planning a pregnancy were prospectively enrolled. 6-Thioguanine nucleotide (6-TGN) and 6-methylmercaptopurine (6-MMP) concentrations were determined, combined with routine laboratory tests, before, during and after pregnancy. Thiopurine metabolites were measured in umbilical cord blood immediately after delivery. RESULTS: Thirty patients who were using azathioprine (28 patients, median dose 1.93 mg/kg) or mercaptopurine (two patients, doses 1.32 and 0.94 mg/kg) were included. During pregnancy, median 6-TGN decreased over time (p=0.001). while 6-MMP increased, without causing myelotoxicity or hepatotoxicity. After delivery, both 6-TGN and 6-MMP levels returned to preconception baseline levels. Fetal 6-TGN concentrations correlated positively with maternal 6-TGN levels (p<0.0001). No 6-MMP was detected in the newborns, except one born with pancytopenia and high alkaline phosphatase activity; the mother of this infant had severe pre-eclampsia. All infants had normal Apgar scores, but 60% had anaemia at birth. No major congenital abnormalities were observed. CONCLUSIONS: Pregnancy has a major effect on maternal thiopurine metabolism. In utero the unborn child is exposed to 6-TGN, but not to 6-MMP. Sixty per cent of the infants were born with anaemia, which raises the question whether infants should be tested for possible anaemia immediately after birth.

Implementation of TPMT testing.

The activity of the enzyme thiopurine methyltransferase (TPMT) is regulated by a common genetic polymorphism. One in 300 individuals lack enzyme activity and 11% are heterozygous for a variant low activity allele and have an intermediate activity. The thiopurine drugs azathioprine, mercaptopurine and thioguanine are substrates for TPMT; these drugs exhibit well documented myelosuppressive effects on haematopoietic cells and have a track record of idiosyncratic drug reactions. The development of severe bone marrow toxicity, in patients taking standard doses of thiopurine drugs, is associated with TPMT deficiency whilst the TPMT heterozygote is at an increased risk of developing myelosuppression. Factors influencing TPMT enzyme activity, as measured in the surrogate red blood cell, are discussed in this review to enable an appreciation of why concordance between TPMT genotype and phenotype is not 100%. This is particularly important for lower/intermediate TPMT activities to avoid misclassification of TPMT status. TPMT testing is now widely available in routine service laboratories. The British National Formulary suggests TPMT testing before starting thiopurine drugs. Dermatologists were quick to adopt routine TPMT testing whilst gastroenterologists do not specifically recommend TPMT screening. TPMT testing is mandatory prior to the use of mercaptopurine in childhood leukaemia. Thiopurine drug dose and other treatment related influences on cell counts explain some of the differing recommendations between clinical specialities. TPMT testing is cost-effective and the major role is in the identification of the TPMT deficient individual prior to the start of thiopurine drugs.