Thiopurine methyltransferase (TPMT) activity and adverse effects of azathioprine in inflammatory bowel disease: long-term follow-up study of 394 patients

Landscape of TPMT and NUDT15 Pharmacogenetic Variation in a Cohort of Canadian Pediatric Inflammatory Bowel Disease Patients

BACKGROUND

Patients with inflammatory bowel disease (IBD) exhibit considerable interindividual variability in medication response, highlighting the need for precision medicine approaches to optimize and tailor treatment. Pharmacogenetics (PGx) offers the ability to individualize dosing by examining genetic factors underlying the metabolism of medications such as thiopurines. Pharmacogenetic testing can identify individuals who may be at risk for thiopurine dose-dependent adverse reactions including myelosuppression. We aimed to evaluate PGx variation in genes supported by clinical guidelines that inform dosing of thiopurines and characterize differences in the distribution of actionable PGx variation among diverse ancestral groups.

METHODS

Pharmacogenetic variation in TPMT and NUDT15 was captured by genome-wide genotyping of 1083 pediatric IBD patients from a diverse Canadian cohort. Genetic ancestry was inferred using principal component analysis. The proportion of PGx variation and associated metabolizer status phenotypes was compared across 5 genetic ancestral groups within the cohort (Admixed American, African, East Asian, European, and South Asian) and to prior global estimates from corresponding populations.

RESULTS

Collectively, 11% of the cohort was categorized as intermediate or poor metabolizers of thiopurines, which would warrant a significant dose reduction or selection of alternate therapy. Clinically actionable variation in TPMT was more prevalent in participants of European and Admixed American/Latino ancestry (8.7% and 7.5%, respectively), whereas variation in NUDT15 was more prevalent in participants of East Asian and Admixed American/Latino ancestry (16% and 15% respectively).

CONCLUSIONS

These findings demonstrate the considerable interpopulation variability in PGx variation underlying thiopurine metabolism, which should be factored into testing diverse patient populations.

Evaluation of tolerance to mercaptopurine in patients with inflammatory bowel disease and gastrointestinal intolerance to azathioprine

BACKGROUND

Thiopurines such as azathioprine (AZA) and mercaptopurine (MP) are commonly utilized to treat inflammatory bowel disease (IBD). Their use is frequently restricted due to gastrointestinal intolerance (GI). Previous retrospective studies have reported that AZA-intolerant patients may benefit from a switch to MP; yet the effectiveness of this strategy has not been prospectively evaluated.

AIMS

To assess GI tolerance to MP in patients who are intolerant to AZA, and to identify clinical predictors of GI intolerance to AZA or MP.

METHODS

A prospective, observational, single-cohort study was performed in 92 thiopurine-naïve IBD patients. They were started on a 50mg dose of AZA and escalated to 2.5mg/kg per day by week 2. Those with GI intolerance were rechallenged with a 50% dose of AZA, after which another dose escalation attempt was made. If symptoms persisted, they were switched to MP.

RESULTS

Thirty (32.6%) of the recruited patients suffered from GI intolerance to AZA. Of these, 15 did not present recurrence of symptoms after rechallenge with lower doses. Of 15 intolerant patients, 14 were switched to MP. Within the MP cohort, 8 patients (57%) were also intolerant to MP, 5 (36%) had no symptoms, and 1 (7%) was lost to follow-up. Female gender was the only independent predictor of GI intolerance to AZA.

CONCLUSIONS

Up to half of the AZA-intolerant patients tolerated a 50% dose rechallenge that was successfully escalated. A switch to MP was tolerated in over a third of cases whom rechallenge failed. Our strategy (challenge-rechallenge-switch) achieved an overall GI tolerance to thiopurines in most of the patients.

Risk-stratified monitoring for thiopurine toxicity in immune-mediated inflammatory diseases: prognostic model development, validation, and, health economic evaluation

Background

Patients established on thiopurines (e.g., azathioprine) are recommended to undergo three-monthly blood tests for the early detection of blood, liver, or kidney toxicity. These side-effects are uncommon during long-term treatment. We developed a prognostic model that could be used to inform risk-stratified decisions on frequency of monitoring blood-tests during long-term thiopurine treatment, and, performed health-economic evaluation of alternate monitoring intervals.

Methods

This was a retrospective cohort study set in the UK primary-care. Data from the Clinical Practice Research Datalink Aurum and Gold formed development and validation cohorts, respectively. People age ≥18 years, diagnosed with an immune mediated inflammatory disease, prescribed thiopurine by their general practitioner for at-least six-months between January 1, 2007 and December 31, 2019 were eligible. The outcome was thiopurine discontinuation with abnormal blood-test results. Patients were followed up from six-months after first primary-care thiopurine prescription to up to five-years. Penalised Cox regression developed the risk equation. Multiple imputation handled missing predictor data. Calibration and discrimination assessed model performance. A mathematical model evaluated costs and quality-adjusted life years associated with lengthening the interval between blood-tests.

Findings

Data from 5982 (405 events over 16,117 person-years) and 3573 (269 events over 9075 person-years) participants were included in the development and validation cohorts, respectively. Fourteen candidate predictors (21 parameters) were included. The optimism adjusted R2 and Royston D statistic in development data were 0.11 and 0.76, respectively. The calibration slope and Royston D statistic (95% Confidence Interval) in the validation data were 1.10 (0.84-1.36) and 0.72 (0.52-0.92), respectively. A 2-year period between monitoring blood-test was most cost-effective in all deciles of predicted risk but the gain between monitoring annually or biennially reduced in higher risk deciles.

Interpretation

This prognostic model requires information that is readily available during routine clinical care and may be used to risk-stratify blood-test monitoring for thiopurine toxicity. These findings should be considered by specialist societies when recommending blood monitoring during thiopurine prescription to bring about sustainable and equitable change in clinical practice.

Funding

National Institute for Health and Care Research.

The Effectiveness and Safety of First-Line Thioguanine in Thiopurine-Naïve Inflammatory Bowel Disease Patients

BACKGROUND

Currently thioguanine is solely used as treatment for inflammatory bowel disease after azathioprine and/or mercaptopurine failure. This study aimed to determine the safety, effectiveness, and 12-month drug survival of thioguanine in thiopurine-naïve patients with inflammatory bowel disease.

METHODS

A retrospective cohort study was performed in thiopurine-naïve patients with inflammatory bowel disease treated with thioguanine as first thiopurine derivate. Clinical effectiveness was defined as the continuation of thioguanine without the (re)initiation of concurrent biological therapy, systemic corticosteroids, or a surgical intervention. All adverse events were categorized by the Common Terminology Criteria for Adverse Events.

RESULTS

A total of 114 patients (male 39%, Crohn's disease 53%) were included with a median treatment duration of 25 months and a median thioguanine dosage of 20 mg/d. Clinical effectiveness at 12 months was observed in 53% of patients, and 78% of these responding patients remained responsive until the end of follow-up. During the entire follow-up period, 26 patients were primary nonresponders, 8 had a secondary loss of response, and 11 patients were unable to cease therapy with systemic corticosteroids within 6 months and were therefore classified as nonresponders. After 12 months, thioguanine was still used by 86% of patients. Fifty (44%) patients developed adverse events (grade 1 or 2) and 9 (8%) patients ceased therapy due to the occurrence of adverse events. An infection was documented in 3 patients, none of them requiring hospitalization and pancytopenia occurred in 2 other patients. No signs of nodular regenerative hyperplasia or portal hypertension were observed.

CONCLUSIONS

At 12 months, first-line thioguanine therapy was clinically effective in 53% of thiopurine-naïve inflammatory bowel disease patients with an acceptable safety profile.

XDH genotypes through gene-gene interactions with NUDT15 affect azathioprine-induced leukopenia in Chinese patients

Aim: To investigate whether genotypes of XDH, GMPS and MOCOS were associated with azathioprine-induced adverse drug reaction (ADR) and had the gene-gene interactions with NUDT15 rs116855232 to induce leukopenia. Methods: Patients who had taken azathioprine were recruited. Genotyping of those gene was performed. Risk factor to ADR was analyzed by logistic regression. The generalized multifactor dimensionality reduction (GMDR) was assessed based on gene-gene interactions with ADR. Results: A total of 111 patients were included in this study, all of whom were Han Chinese. XDH rs2295475 was a risk factor of myelotoxicity (p = 0.022). NUDT15 rs116855232 was a risk factor of myelotoxicity, grade ≥2 leukopenia and drug treatment termination (p-values were <0.05). Rs2295475 and rs116855232 had a gene-gene interaction. The model was associated with grade ≥2 leukopenia (OR: 17.99; 95% CI: 4.11-78.81). Conclusion: Combined testing genotype for rs2295475 and rs116855232 could improve the prediction of azathioprine-induced leukopenia.

Drug monitoring in systemic lupus erythematosus

Therapeutic drug monitoring (TDM) is not yet accepted by systemic lupus erythematosus (SLE) treatment guidelines. Studies in SLE, however, have proven benefit in three areas: identification of non-adherence or poor adherence; targets for clinical benefit; and ranges of toxicity. This review covers the data on three medications commonly used for SLE, drawing on studies from both the SLE and non-SLE literature.

Cytotoxicity of Thiopurine Drugs in Patients with Inflammatory Bowel Disease

The effectiveness of thiopurine drugs in inflammatory bowel disease (IBD) was confirmed more than a half-century ago. It was proven that these can be essential immunomodulatory medications. Since then, they have been used routinely to maintain remission of Crohn’s disease (CD) and ulcerative colitis (UC). The cytotoxic properties of thiopurines and the numerous adverse effects of the treatment are controversial. However, the research subject of their pharmacology, therapy monitoring, and the search for predictive markers are still very relevant. In this article, we provide an overview of the current knowledge and findings in the field of thiopurines in IBD, focusing on the aspect of their cytotoxicity. Due to thiopurines’ benefits in IBD therapy, it is expected that they will still constitute an essential part of the CD and UC treatment algorithm. More studies are still required on the modulation of the action of thiopurines in combination therapy and their interaction with the gut microbiota.

Thiopurine S-methyltransferase genetic polymorphisms in adult patients with inflammatory bowel diseases in the Latvian population

BACKGROUND

Thiopurine methyltransferase (TPMT) plays a significant role in the metabolism of thiopurines, and, for patients with inflammatory bowel disease (IBD), it is useful to perform TPMT genotyping prior to azathioprine (AZA) treatment. In this study, we determined TPMT gene polymorphisms in a cohort of IBD patients in Latvia.

METHODS

DNA samples were obtained from 244 IBD patients, and qPCR was performed for detection of rs1800462, rs1800460, and rs1142345 single-nucleotide polymorphisms (SNPs). Three common, non-functional TPMT alleles (TPMT*2, *3B, and *3C) were identified (women, 51%; men, 49%). TPMT*2, *3A, *3B, and *3C allelic variants detected using qPCR were consistent with restriction fragment length polymorphism (RFLP) data.

RESULTS

Among patients, 78% had ulcerative colitis and 22% had Crohn's disease, with 93.9% of the former carrying a wild-type homozygous TPMT*1/*1 genotype and 6.1% carrying heterozygous genotypes. The most frequent polymorphisms were TPMT*1/*3A (5.3%: two variants: TPMT*3B and TPMT*3C), TPMT*1/*3C (0.4%), and TPMT*1/*2 (0.4%). None of the patients carried a TPMT*3B polymorphism and no patients were homozygous for any mutation.

CONCLUSION

This is the first study to identify TPMT gene polymorphisms in adult IBD patients in Latvia. The results indicate that the frequency of common TPMT alleles is similar to that of other European populations.

Biomarkers Predictive of Response to Thiopurine Therapy in Inflammatory Bowel Disease

The complex nature of inflammatory bowel disease (IBD) often results in treatment failure for many patients. With some patients cycling through multiple therapies before achieving a sustained period of remission, the ability to predict a patient's response to therapeutics could decrease the time from active disease to clinical remission and mucosal healing. The prospect of such individualized treatment of IBD would be aided by accurate biomarkers, both fecal and serological, which have to date shown value as indicators of IBD activity. Here we review the utility of generic biomarkers for inflammation or mucosal healing, such as calprotectin, C-reactive protein (CRP), and fecal hemoglobin (fHb) as predictors of response to treatment of IBD. We further provide a deeper insight into the utility of monitoring the thiopurine treatment by thiopurine metabolites or alternative hematologic parameters. In light of multiple recent publications of biomarkers and biological therapy, our focus in this review is predicting response to thiopurine treatment only, that is, Azathioprine and 6-Mercaptopurine.

Systematic review with meta-analysis: risk factors for thiopurine-induced leukopenia in IBD

BACKGROUND

Thiopurine-induced leukopenia, a frequently observed and potentially life-threatening adverse event, complicates the clinical management of IBD patients.

AIM

To assess risk factors for thiopurine-induced leukopenia in IBD.

METHODS

MEDLINE, EMBASE, BIOSIS and Cochrane library were searched for studies reporting at least one risk factor for thiopurine-induced leukopenia. Pooled odds ratio (OR) was calculated for each potential risk factor using a random effects model. Studies that were not eligible for meta-analysis were described qualitatively.

RESULTS

Seventy articles were included, 34 (11 229 patients) were included in meta-analyses. A significantly higher thiopurine-induced leukopenia risk was found for TPMT (OR 3.9, 95% [CI] 2.5-6.1) and for NUDT15 R139C (OR 6.9, 95% CI 5.2-9.1), G52A (OR 3.2, 95% CI 1.3-7.9) and 36_37ins/delGGAGTC variant carriers (OR 5.6, 95% CI 2.8-11.4). A potential association between high 6-thioguanine nucleotides (6-TGN) or 6-methylmercaptopurine (6-MMP) levels and leukopenia was observed, since most studies reported higher metabolite levels in leukopenic patients (6-TGN: 204-308 (Lennard method) and 397 (Dervieux method), 6-MMP: 4020-10 450 pmol/8 x 10⁸ RBC) compared to controls (6-TGN: 170-212 (Lennard method) and 269 (Dervieux method), 6-MMP: 1025-4550 pmol/8 x 10⁸ RBC).

CONCLUSIONS

TPMT and NUDT15 variants predict thiopurine-induced leukopenia. High 6-TGN and 6-MMP levels might induce leukopenia, although exact cut-off values remain unclear. Potential preventive measures to reduce the risk of thiopurine-induced leukopenia include pre-treatment TPMT and NUDT15 genotyping. Routine thiopurine metabolite measurement might be efficient, yet cut-off levels must be validated in advance.

Do clinical and laboratory parameters predict thiopurine metabolism and clinical outcome in patients with inflammatory bowel diseases?

PURPOSE

The thiopurines azathioprine and 6-mercaptopurine are frequently used for remission maintenance in patients with inflammatory bowel diseases. However, there are therapy failures, and it is unclear whether clinical and laboratory parameters can be used to predict thiopurine metabolite concentrations (as a surrogate for adequate remission maintenance therapy) and clinical outcome in these patients.

METHODS

In this retrospective analysis of clinical routine patient data, multivariate statistical models based on Linear Mixed Models regression and Generalized Estimating Equations logistic regression were developed. The adequacy of the models was assessed using Pearson's correlation and a receiver operating characteristic curve.

RESULTS

This study included 273 patients and 1158 thiopurine metabolite measurements as well as routine laboratory and clinical data. In the statistical models, thiopurine metabolite concentrations and the odds of non-remission based on different clinical and laboratory parameters were computed. Correlation (r²) between predicted and measured thiopurine metabolites were 0.40 (p < 0.001) for 6-thioguanine nucleotides and 0.53 (p < 0.001) for 6-methyl-mercaptopurine nucleotides, respectively. The model for remission classified data sets in remission and non-remission with a sensitivity of 63% and a specificity of 73%. The area under the receiver operating characteristic curve of the model was 0.72.

CONCLUSIONS

Although the models are not yet accurate enough to be used in clinical routine, model-based prediction of thiopurine metabolite concentrations and of outcome is feasible. Until more accurate models are developed and validated, traditional therapeutic drug monitoring of thiopurine metabolites in patients with inflammatory bowel diseases under thiopurine therapy stays the best tool to individualize therapy.

Early Arthritis Is Associated With Failure of Immunosuppressive Drugs and Severe Pediatric Crohn's Disease Evolution

BACKGROUND

Crohn's disease (CD) is a chronic relapsing inflammatory disease. To optimize therapeutic decision making, it is essential to identify parameters that allow early prediction of a severe disease course. The aim of this study was to assess the link between arthritis and medium-term therapeutic failure in pediatric CD.

METHODS

We conducted a population-based cohort study with prospectively collected electronic data. To be included, patients must be younger than 17 years and have a confirmed CD diagnosed between 2005 and 2014. The primary outcome was the percentage of patients with at least 1 therapeutic failure of immunosuppressive drugs during the 2 years after the CD diagnosis, with a propensity score analysis.

RESULTS

We included 272 patients with CD. The median age was 12.1 years (interquartile [10.1-14.2]). Sixty-five patients (23.9%) developed arthritis, which predominantly occurred during the first year after CD diagnosis. We found a highly significant association between arthritis and therapeutic failure of immunosuppressive drugs after 2 years (OR = 6.9; 95% confidence interval [CI], 2.7-18.0; P < 0.0001; propensity score matching analysis). Arthritis was also significantly associated with introduction of biotherapy due to luminal disease 2 years after diagnosis (OR = 3.2, 95% CI, 1.8-6.0; P = 0.0001). Similar results were obtained after 4 years, and arthritis was significantly associated with a higher number of hospitalizations for luminal flare-up or complications after 4 years (OR = 2.2; 95% CI, 1.2-3.9; P = 0.007).

CONCLUSIONS

Arthritis was strongly associated with medium-term therapeutic failure of pediatric CD. Occurrence of arthritis early in the disease may justify closer follow-up visits or specific therapeutic management.

Purine Synthesis Inhibitors, 6-thioguanine and Azathioprine: Forgotten Treatment Options in Psoriasis and Psoriatic Arthritis

Background

The thiopurine drugs azathioprine and 6-thioguanine have been shown to induce significant clinical improvement in patients with moderate to severe psoriasis and/or psoriatic arthritis.

Objective

The aim of this paper is to present a comprehensive review of the available literature concerning the off-label role of thiopurine drugs in the treatment of psoriasis and psoriatic arthritis.

Methods

Studies published with English abstracts between 1960 and 2008 identified in MEDLINE and PubMed with the keywords purine synthesis inhibitors, thiopurine, 6-thioguanine, azathioprine, psoriasis and psoriatic arthritis were reviewed.

Results

Although 6-thioguanine and azathioprine have shown significant efficacy, their side effect profiles have discouraged their use for moderate to severe psoriasis.

Conclusion

For treatment of psoriasis and psoriatic arthritis, purine synthesis inhibitors should not be forgotten. They represent an entirely different option and provide an alternative therapy, especially for difficult cases.

Anti-Tumour Necrosis Factor Therapy for Paediatric Crohn's Disease: Improved Benefits Through Treatment Optimisation, Deeper Understanding of Its Risks, and Reduced Costs due to Biosimilar Availability

Antibodies directed to tumour necrosis factor-α (TNF-α) are very effective in treating paediatric Crohn's disease (CD). Over the last few years, research has provided important new insights into how to optimise this treatment's effectiveness. Research on predictors for anti-TNF treatment responsiveness has revealed potential markers, but data on their accuracy in paediatric CD patients are lagging behind. Also, new evidence has become available on the safety profile of anti-TNF antibodies that suggests the assumed increased malignancy risk seen in patients on anti-TNF and thiopurine combination treatment may be linked more to thiopurine use and not to anti-TNF treatment. In addition, the early results of CT-P13, an infliximab biosimilar, in CD patients confirm the expected similarity with its originator. Thus, the effectiveness of anti-TNF antibody treatment is slowly improving, its malignancy risk is lower than assumed, and its costs are reduced by the introduction of equally effective biosimilars. Together, these trends allow for a more prominent role for anti-TNF antibodies in future treatment of paediatric CD.

Measurements of 6-thioguanine nucleotide levels with TPMT and NUDT15 genotyping in patients with Crohn's disease

The association between the 6-thioguanine nucleotide (6-TGN) level and clinical remission in Crohn’s disease (CD) remains controversial. Thiopurine-induced leukopenia is a life-threatening complication of CD in Asians that was recently shown to strongly correlate with NUDT15 genetic variants. This study aimed to determine the relationship between thiopurine metabolite levels and therapeutic response, and to investigate the association of NUDT15, TPMT, and thiopurine metabolites with leukopenia in patients with CD. We enrolled 165 adult patients with CD undergoing thiopurine treatment. Clinical evaluation and laboratory examinations were carried out every 2–3 months. We measured thiopurine metabolites levels and genotyped NUDT15 and TPMT. During the median 12-month observational period, 95 (67.9%) patients exhibited clinical response and 45 (32.1%) did not respond to the treatment. The median 6-TGN level was significantly higher in responders than in non-responders (P < 0.001). The odds ratio of patients with a 6-TGN level ≥230 pmol/8 × 10⁸ red blood cells for showing a clinical response was 4.63 (95% CI 1.62–11.9). NUDT15 variant types were strongly associated with developing leukopenia. Patients with NUDT15 homozygous variant genotype developed severe early leukopenia with an average reduction of 88.2% (range, 84–94%) from the baseline white blood cell count at 4 weeks. Our findings support the role of therapeutic drug monitoring in thiopurine maintenance treatment to optimize thiopurine therapy, especially, for non-responding CD patients. Thiopurine treatment should not be recommended to patients with NUDT15 homozygous variant genotype due to severe early leukopenia.

Safety of treatments for inflammatory bowel disease: Clinical practice guidelines of the Italian Group for the Study of Inflammatory Bowel Disease (IG-IBD)

Inflammatory bowel diseases are chronic conditions of unknown etiology, showing a growing incidence and prevalence in several countries, including Italy. Although the etiology of Crohn's disease and ulcerative colitis is unknown, due to the current knowledge regarding their pathogenesis, effective treatment strategies have been developed. Several guidelines are available regarding the efficacy and safety of available drug treatments for inflammatory bowel diseases. Nevertheless, national guidelines provide additional information adapted to local feasibility, costs and legal issues related to the use of the same drugs. These observations prompted the Italian Group for the Study of Inflammatory Bowel Disease (IG-IBD) to establish Italian guidelines on the safety of currently available treatments for Crohn's disease and ulcerative colitis. These guidelines discuss the use of aminosalicylates, systemic and low bioavailability corticosteroids, antibiotics (metronidazole, ciprofloxacin, rifaximin), thiopurines, methotrexate, cyclosporine A, TNFα antagonists, vedolizumab, and combination therapies. These guidelines are based on current knowledge derived from evidence-based medicine coupled with clinical experience of a national working group.

Metabolite monitoring to guide thiopurine therapy in systemic autoimmune diseases

6-Thioguanine nucleotide (6-TGN) is the active metabolite of thiopurine drugs azathioprine and 6-mercaptopurine. 6-Methylmercaptopurine (6-MMP) is an inactive and potentially hepatotoxic metabolite. A subgroup of patients (shunters) preferentially produce 6-MMP instead of 6-TGN, therefore displaying thiopurine resistance and risk for hepatotoxicity. Outside inflammatory bowel disease literature, few data exist regarding individualized thiopurine therapy based on metabolite monitoring. This study sought to describe metabolite monitoring in patients receiving weight-based thiopurine for systemic autoimmune diseases. Patients were enrolled using a laboratory database, and data were retrospectively collected. The correlation between the highest thiopurine dose (mg/kg) and the 6-TGN concentration (pmol/8 × 10⁸ erythrocytes) was estimated with Pearson's correlation coefficient. Seventy-one patients with various systemic autoimmune conditions were enrolled. The correlation between the thiopurine dose and the 6-TGN level was weak for the overall patient sample (r = 0.201, p = 0.092) and for the subgroup of non-shunters (r = 0.278, p = 0.053). Subjects with 6-MMP levels >5700 pmol/8 × 10⁸ erythrocytes had more hepatic cytolysis compared to subjects with 6-MMP <5700, OR = 4.36 (CI 95% 1.18-16.13, p = 0.027). Twenty-two patients (31%) were identified as shunters. Six shunters developed hepatotoxicity, five of which had 6-MMP concentration >5700. Eleven non-shunters had hepatotoxicity, one of which had 6-MMP >5700. Thiopurine metabolite monitoring shows wide variability in 6-TGN levels among patients treated with weight-based thiopurine for systemic autoimmune diseases. Thirty-one percent of the patients in our series fulfilled the shunter definition. Thiopurine metabolite monitoring and dose adjustment to improve maintenance of remission and avoid hepatotoxicity should be studied prospectively.

Review article: recent advances in pharmacogenetics and pharmacokinetics for safe and effective thiopurine therapy in inflammatory bowel disease

BACKGROUND

Azathioprine and mercaptopurine have a pivotal role in the treatment of inflammatory bowel disease (IBD). However, because of their complex metabolism and potential toxicities, optimal use of biomarkers to predict adverse effects and therapeutic response is paramount.

AIM

To provide a comprehensive review focused on pharmacogenetics and pharmacokinetics for safe and effective thiopurine therapy in IBD.

METHODS

A literature search up to July 2015 was performed in PubMed using a combination of relevant MeSH terms.

RESULTS

Pre-treatment thiopurine S-methyltransferase typing plus measurement of 6-tioguanine nucleotides and 6-methylmercaptopurine ribonucleotides levels during treatment have emerged with key roles in facilitating safe and effective thiopurine therapy. Optimal use of these tools has been shown to reduce the risk of adverse effects by 3-7%, and to improve efficacy by 15-30%. For the introduction of aldehyde oxidase (AOX) into clinical practice, the association between AOX activity and AZA dose requirements should be positively confirmed. Inosine triphosphatase assessment associated with adverse effects also shows promise. Nucleoside diphosphate-linked moiety X-type motif 15 variants have been shown to predict myelotoxicity on thiopurines in East Asian patients. However, the impact of assessments of xanthine oxidase, glutathione S-transferase, hypoxanthine guanine phosphoribosyltransferase and inosine monophosphate dehydrogenase appears too low to favour incorporation into clinical practice.

CONCLUSIONS

Measurement of thiopurine-related enzymes and metabolites reduces the risk of adverse effects and improves efficacy, and should be considered part of standard management. However, this approach will not predict or avoid all adverse effects, and careful clinical and laboratory monitoring of patients receiving thiopurines remains essential.

Physician Perspectives on Unresolved Issues in the Management of Ulcerative Colitis: The UC Horizons Project

BACKGROUND

There is still uncertainty about what constitutes the best therapeutic practice in ulcerative colitis (UC).

OBJECTIVE

The purpose of the "UC Horizons Project" was to raise a series of questions regarding the management of UC to provide responses based on the best scientific evidence available.

METHODS

The 11 members of the scientific committee prepared draft answers to the 10 questions from available evidence after a literature search. A total of 48 Spanish gastroenterology specialists nationwide participated in the project. The national meeting discussed the 10 issues in working groups and reached consensus regarding the recommendations by anonymous, interactive vote following the Delphi methodology. Final answers were developed, based on evidence and clinical experience of the participants.

RESULTS

All the recommendations achieved a high level of agreement in the plenary vote, although the quality of the evidence was markedly heterogeneous. The lowest percentage of agreement corresponded to the questions with the weakest level of evidence, highlighting the necessity of conducting further studies in these areas. The recommendations focused on (1) aminosalicylates therapy (regarding dose and appropriateness of coadministration with thiopurines), (2) corticosteroid therapy (regarding dose and route of administration), (3) thiopurine treatment (regarding indications and possibility of withdrawal), (4) anti-tumor necrosis factor therapy (regarding appropriateness of combination with thiopurines, intensification, or discontinuation of treatment), and (5) colorectal cancer (regarding risk and time trends).

CONCLUSIONS

The UC Horizons Project raised a series of eminently practical questions about the management of UC and provided responses based on the best scientific evidence available.

Thiopurines in the Management of Crohn's Disease: Safety and Efficacy Profile in Patients with Normal TPMT Activity-A Retrospective Study

Background and Aims. Thiopurines are used in the treatment of Crohn's disease (CD) and thiopurine S-methyltransferase (TPMT) activity can guide thiopurine dosing to avoid adverse events. This retrospective study evaluated the safety and efficacy of starting thiopurines at low dose versus full dose in patients with CD and normal TPMT. Methods. This was a single center retrospective study including adult CD patients with normal TPMT levels (≥25 nmol/hr/g Hgb) who were followed for 1 year. Patients started at full dose of azathioprine (2-2.5 mg/kg) or 6-mercaptopurine (1-1.5 mg/kg) were compared to patients started at low dose. Harvey-Bradshaw index, treatment failure, and drug-related adverse events were recorded. Results. Our study included 134 patients. Both groups had similar incidences of drug-related adverse events and discontinuation of therapy due to side effects. Fifty-six percent of all adverse events occurred within 31 days and 92% occurred within 3 months of therapy. Clinical response favored the full-dose group at 6 months (69% versus 27%, p = 0.0542). Conclusions. Our study indicates that it is safe to start patients on full-dose thiopurine when they have a normal TPMT given its very similar toxicity profile to patients started on low dose. This may also positively impact efficacy.

Impact of Genetic Polymorphisms on 6-Thioguanine Nucleotide Levels and Toxicity in Pediatric Patients with IBD Treated with Azathioprine

BACKGROUND

Thiopurine-related toxicity results in discontinuation of therapy in up to 30% of patients with inflammatory bowel disease. Although thiopurine S-methyltransferase (TPMT) is implicated in toxicity, not all toxicity can be attributed to TPMT polymorphisms. We investigated the effects of polymorphisms of genes involved in thiopurine and folate metabolism pathways on 6-thioguanine nucleotide levels and toxicity.

METHODS

Retrospective clinical data and blood samples were collected from 132 pediatric patients with inflammatory bowel disease treated with azathioprine. Eighty-seven genetic polymorphisms of 30 genes were screened using the MassARRAY system, and 70 polymorphisms of 28 genes were selected for further analysis.

RESULTS

TPMT genotype (P < 0.001), concurrent use of mesalazine (P = 0.006), ABCC5 (rs2293001) (P < 0.001), ITPA (rs2236206 and rs8362) (P = 0.010 and P = 0.003), and ABCB1 (rs2032582) (P = 0.028) were all associated with the ratio of 6-thioguanine nucleotides to azathioprine dose. ADK (rs10824095) (P = 0.004, odds ratio [OR] = 6.220), SLC29A1 (rs747199) (P = 0.016, OR = 5.681), and TYMS (rs34743033) (P = 0.045, OR = 3.846) were associated with neutropenia. ABCC1 (rs2074087) (P = 0.022, OR = 3.406), IMPDH1 (rs2278294) (P = 0.027, OR = 0.276), and IMPDH2 (rs11706052) (P = 0.034, OR = 3.639) had a significant impact on lymphopenia.

CONCLUSIONS

This study describes genetic polymorphisms in genes whose products may affect pharmacokinetics and which may predict the relative likelihood of benefit or risk from thiopurine treatment. These findings may serve as a basis for personalized thiopurine therapy in pediatric patients with inflammatory bowel disease, although our data need to be validated in further studies.

Update on pathogenesis and predictors of response of therapeutic strategies used in inflammatory bowel disease

The search for biomarkers that characterize specific aspects of inflammatory bowel disease (IBD), has received substantial interest in the past years and is moving forward rapidly with the help of modern technologies. Nevertheless, there is a direct demand to identify adequate biomarkers for predicting and evaluating therapeutic response to different therapies. In this subset, pharmacogenetics deserves more attention as part of the endeavor to provide personalized medicine. The ultimate goal in this area is the adjustment of medication for a patient’s specific genetic background and thereby to improve drug efficacy and safety rates. The aim of the following review is to utilize the latest knowledge on immunopathogenesis of IBD and update the findings on the field of Immunology and Genetics, to evaluate the response to the different therapies. In the present article, more than 400 publications were reviewed but finally 287 included based on design, reproducibility (or expectancy to be reproducible and translationable into humans) or already measured in humans. A few tests have shown clinical applicability. Other, i.e., genetic associations for the different therapies in IBD have not yet shown consistent or robust results. In the close future it is anticipated that this, cellular and genetic material, as well as the determination of biomarkers will be implemented in an integrated molecular diagnostic and prognostic approach to manage IBD patients.

Clinical predictors of thiopurine-related adverse events in Crohn's disease

AIM: To determine the incidence and predictors of thiopurine-related adverse events.

METHODS: Subjects with Crohn’s disease who were followed in the Alberta Inflammatory Bowel Disease Consortium patient database registry were identified. Retrospective chart review was conducted between August 5^th, 2010 and June 1^st, 2012. We collected data on: age at diagnosis; sex; disease location and behaviour at time of prescribing thiopurine; perianal fistulising disease at or prior to thiopurine prescription; smoking status at time of thiopurine prescription, use of corticosteroid within 6 mo of diagnosis; dosage, age at onset, and cessation of 5-aminosalicyclic acid (5-ASA); anti-tumour necrosis factor medication exposure and intestinal resection before thiopurine prescription. The primary outcome of interest was the first adverse event that led to discontinuation of the first thiopurine medication used. Logistic regression models were used to associate clinical characteristics with outcomes after adjusting for potential confounders. Risk estimates were presented as odds ratios (OR) with 95% CI. Effect modification by age and sex were explored.

RESULTS: Our cohort had a median follow-up duration of 5.8 years [interquartile range (IQR 25^th-75^th) 2.7-9.1]. Thiopurine therapy was discontinued in 31.3% of patients because of: hypersensitivity reactions (7.1%), acute pancreatitis (6.2%), gastrointestinal intolerance (5.4%), leucopenia (3.7%), hepatotoxicity (3.4%), infection (1.1%) and other reasons (4.3%). A higher incidence of thiopurine withdrawal was observed in patients over the age of 40 (39.4%, P = 0.007). A sex-by-age interaction (P = 0.04) was observed. Females older than 40 years of age had an increased risk of thiopurine discontinuation due to an adverse event (age above 40 vs age below 40, adjusted OR = 2.8; 95%CI: 1.4-5.6). In contrast, age did not influence thiopurine withdrawal in males (age above 40 vs below 40, adjusted OR = 0.9; 95%CI: 0.4-2.1). Other clinical variables (disease location and phenotype, perianal disease, smoking history, history of intestinal resection and prior 5-ASA or corticosteroid use) were not associated with an increased risk an adverse event leading to therapy cessation.

CONCLUSION: Thiopurine withdrawal due to adverse events is commoner in women over the age of 40 at prescription. These findings need to be replicated in other cohorts.

Use of Thiopurines in Inflammatory Bowel Disease: A Consensus Statement by the Korean Association for the Study of Intestinal Diseases (KASID)

BACKGROUND/AIMS

For decades, thiopurines have been the mainstay of inflammatory bowel disease (IBD) treatment and will play an important role in the future. However, complex metabolism and various side effects limit the use of these potent drugs in clinical practice. The Korean Association for the Study of Intestinal Diseases developed a set of consensus statements with the aim of guiding clinicians on the appropriate use of thiopurines in the management of IBD.

METHODS

Sixteen statements were initially drafted by five committee members. The quality of evidence and classification of recommendation were assessed according to the Grading of Recommendations Assessment, Development and Evaluation system. The statements were then circulated to IBD experts in Korea for review, feedback, and then finalized and accepted by voting at the consensus meeting.

RESULTS

The consensus statements comprised four parts: (1) pre-treatment evaluation and management strategy, including value of thiopurine S-methyltransferase screening, dosing schedule, and novel biomarkers for predicting thiopurine-induced leukopenia; (2) treatment with thiopurines with regards to optimal duration of thiopurine treatment and long-term outcomes of combination therapy with anti-tumor necrosis factors; (3) safety of thiopurines, especially during pregnancy and lactation; and (4) monitoring side effects or efficacy of therapy using biomarkers.

CONCLUSIONS

Thiopurines are an effective treatment option for patients with IBD. Management decisions should be individualized according to the risk of relapse and adverse events.

Managing refractory Crohn's disease: challenges and solutions

The goals of treatment for active Crohn’s disease (CD) are to achieve clinical remission and improve quality of life. Conventional therapeutics for moderate-to-severe CD include 5-aminosalicylic acid, corticosteroids, purine analogs, azathioprine, and 6-mercaptopurine. Patients who fail to respond to conventional therapy are treated with tumor necrosis factor (TNF)-α inhibitors such as infliximab and adalimumab, but their efficacy is limited due to primary nonresponse or loss of response. It is suggested that this requires switch to another TNF-α inhibitor, a combination therapy with TNF-α blockade plus azathioprine, or granulocyte and monocyte adsorptive apheresis, and that other therapeutic options having different mechanisms of action, such as blockade of inflammatory cytokines or adhesion molecules, are needed. Natalizumab and vedolizumab are neutralizing antibodies directed against integrin α4 and α4β7, respectively. Ustekinumab is a neutralizing antibody directed against the receptors for interleukin-12 and interleukin-23. Here, we provide an overview of therapeutic treatments that are effective and currently available for CD patients, as well as some that likely will be available in the near future. We also discuss the advantages of managing patients with refractory CD using a combination of TNF-α inhibitors plus azathioprine or intensive monocyte adsorptive apheresis.

Leukopenia predicts remission in patients with inflammatory bowel disease and Behcet's disease on thiopurine maintenance

BACKGROUNDS

The thiopurine drugs, azathioprine (AZA), and 6-mercaptopurine (6-MP) are well-established drugs for the treatment of inflammatory bowel disease (IBD). Although leukopenia is a well-recognized side effect of AZA/6-MP treatment, its association with therapeutic effects has yet to be determined. We therefore evaluated the influences of thiopurine-induced leukopenia on the long-term prognosis of IBD.

METHODS

We included 196 IBD patients [45 with ulcerative colitis (UC), 68 with Crohn's disease (CD), and 83 with intestinal Behçet's disease (BD)] who were treated with AZA/6-MP and achieved remission between January 2006 and December 2012. We retrospectively analyzed patient characteristics, AZA/6-MP maintenance dose (mg/kg), the lowest white blood cell (WBC) count during AZA/6-MP treatment, duration of remission, and the occurrence of relapse. We compared the clinical variables between leukopenic (n = 120, WBC count <4,000/μL) and nonleukopenic (n = 76, WBC count ≥ 4,000/μL) patients.

RESULTS

The two groups were well matched for baseline clinical characteristics. The cumulative relapse-free survival rate was higher in the leukopenic group than the nonleukopenic group by Kaplan-Meier survival analysis (log-rank test, P < 0.001). On multivariate analysis, age, duration of AZA/6-MP treatment, presence of macrocytosis, and the presence of leukopenia were negatively associated with relapse (odds ratios 0.975, 0.988, 0.563, and 0.390, respectively). On subgroup analysis, the cumulative relapse-free survival rate was significantly higher in the leukopenic group than in the nonleukopenic group for all types of IBDs, including UC, CD, and intestinal BD (log-rank test, P = 0.032, 0.047, and 0.002, respectively).

CONCLUSION

Leukopenia during thiopurine maintenance therapy was associated with prolonged remission in patients with IBD and Behcet's disease.

A practical guide to the use of thiopurines in oral medicine

Thiopurines are widely used as first-line immunosuppressive therapies in the management of chronic inflammatory oral disease. However, despite over half a century of clinical experience, the evidence base for their use is limited. The aims of this paper were to review the evidence for the use of thiopurines in oral medicine and provide a contemporary model of thiopurine metabolism and mechanism of action and a rationale for clinical use and safe practice.

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.

Monitoring thiopurine metabolites in korean pediatric patients with inflammatory bowel disease

PURPOSE

This study aimed to assess the role of thiopurine S-methyltransferase (TPMT) and 6-thioguanine nucleotide (6-TGN) as predictors of clinical response and side effects to azathioprine (AZA), and estimate the optimal AZA dose in Korean pediatric inflammatory bowel disease (IBD) patients.

MATERIALS AND METHODS

One hundred and nine pediatric IBD patients in whom AZA treatment was required were enrolled. Thiopurine metabolites were monitored since September 2010. Among them, 83 patients who had prescribed AZA for at least 3 months prior to September 2010 were enrolled and followed until October 2011 to evaluate optimal AZA dose, adverse effects and disease activity before and after thiopurine metabolite monitoring.

RESULTS

The result of the TPMT genotype was that 102 patients were *1/*1 (wild type), four were *1/*3C, one was *1/*6, one was *1/*16 (heterozygote) and one was *3C/*3C (homozygote). Adverse effects happened in 31 patients pre-metabolite monitoring and in only nine patients post-metabolite monitoring. AZA dose was 1.4±0.31 mg/kg/day before monitoring and 1.1±0.46 mg/kg/day after monitoring (p<0.001). However, there were no statistical differences in disease activity during metabolite monitoring period (p=0.34). Adverse effects noticeably decreased although reduction of the AZA dose since monitoring.

CONCLUSION

TPMT genotype and thiopurine metabolite monitoring could be helpful to examine TPMT genotypes before administering AZA and to measure 6-TGN concentrations during prescribing AZA in IBD patients.

The utility of thiopurine methyltransferase enzyme testing in inflammatory bowel disease

OBJECTIVE

To assess the levels of red blood cell thiopurine methyltransferase (TPMT) in subjects with inflammatory bowel disease (IBD) and to determine how these levels impacted thiopurine dosing and leukopenia over the first six months of therapy.

METHODS

A retrospective chart review was performed on all adult IBD patients (n=423, 88.2% Caucasian) who had TPMT levels measured by 11 participating gastroenterologists in Manitoba between 2008 and 2010. In addition to descriptive data, white blood cell count, dose and reason for discontinuation were analyzed for the first six months of therapy. Patients receiving ≥2.0 mg/kg of azathioprine (AZA) or ≥1.0 mg/kg of 6-mercapatopurine were considered to be 'substantially' dosed.

RESULTS

Of the 423 patients, 8.3% had intermediate levels and 93.4% had normal levels of TPMT. Only one subject had a low level. A total of 216 patients had sufficient data to be included for full analysis. Patients with intermediate TPMT levels were generally started at lower doses of thiopurine than patients with normal TPMT levels (mean [± SD] 1.0±0.6 mg/kg versus 1.8±0.5 mg/kg). Of the subjects with normal TPMT levels, only 37.8% were dosed with ≥2.0 mg/kg of AZA. Each month, approximately 5% of subjects were leukopenic. These subjects received a mean overall AZA dose of 1.9±0.3 mg/kg and had a mean white blood cell count of 3.8±0.4×10(9)/L.

CONCLUSIONS

Normal TPMT levels did not prevent the development of leukopenia, although life-threatening leukopenia was rare. Physicians are not using TPMT levels to substantially dose thiopurines at the outset, which may limit the speed at which adequate doses are reached to facilitate remission.

Successful azathioprine treatment with metabolite monitoring in a pediatric inflammatory bowel disease patient homozygous for TPMT*3C

Thiopurine S-methyltransferase (TPMT) methylates purine analogues, showing TPMT activity in inverse relation to concentrations of active metabolites such as 6-thioguanine nucleotide (6-TGN). With conventional dosing of thiopurines, patients with homozygous variant TPMT alleles consistently suffer from severe myelosuppression. Here, we report a patient with TPMT*3C/*3C who managed successfully with monitoring of thiopurine metabolites. The patient was an 18-year-old male diagnosed with Crohn's disease. The standard dose of azathioprine (AZA) (1.8 mg/kg/day) with mesalazine (55.6 mg/kg/day) was prescribed. Two weeks after starting AZA treatment, the patient developed leukopenia. The DNA sequence analysis of TPMT identified a homozygous missense variation (NM_000367.2: c.719A>G; p.Tyr240Cys), TPMT*3C/*3C. He was treated with adjusted doses of azathioprine (0.1-0.2 mg/kg/day) and his metabolites were closely monitored. Leukopenia did not reoccur during the follow-up period of 24 months. To our knowledge, this is the first case of a patient homozygous for TPMT*3C successfully treated with azathioprine in Korea. While a TPMT genotyping test may be helpful to determine a safe starting dose, it may not completely prevent myelosuppression. Monitoring metabolites as well as routine laboratory tests can contribute to assessing drug metabolism and optimizing drug dosing with minimized drug-induced toxicity.

Adverse events associated with azathioprine treatment in korean pediatric inflammatory bowel disease patients

PURPOSE

This study was aimed to evaluate the frequency and course of adverse events associated with azathioprine treatment in Korean pediatric patients with inflammatory bowel disease.

METHODS

Total of 174 pediatric patients (age range, 1 to 19 years) with inflammatory bowel disease who received azathioprine in order to maintain remission at Samsung Medical Center (Seoul, Korea) from January 2002 through December 2012 were included in this study. Medical records of these subjects were retrospectively reviewed regarding the development of adverse events associated with azathioprine treatment.

RESULTS

Ninety-eight patients (56.3%) of 174 patients experienced 136 episodes of adverse events, requiring dose reduction in 31 patients (17.8%), and discontinuation in 18 patients (10.3%). The mean dose of azathioprine that had been initially administered was 1.32±0.42 mg/kg/day. Among the adverse reactions, bone marrow suppression developed in 47 patients (27.0%), requiring dose reduction in 22 patients (12.6%) and discontinuation in 8 patients (4.6%). Other adverse events that occurred were gastrointestinal disturbance (15.5%), hair loss (12.1%), pancreatitis (7.5%), arthralgia (6.9%), hepatotoxicity (2.9%), skin rash/allergic reactions (2.9%), headache/dizziness (2.3%), sepsis (0.6%), and oral mucositis (0.6%).

CONCLUSION

Bone marrow suppression, especially leukopenia was most commonly associated with azathioprine treatment in Korean pediatric inflammatory bowel disease patients. Close observation for possible adverse events is required in this population with inflammatory bowel diseases who are under treatment with azathioprine.

Safety of thiopurine therapy in inflammatory bowel disease: long-term follow-up study of 3931 patients

BACKGROUND

To evaluate the safety of thiopurines in patients with inflammatory bowel disease. To identify predictive factors associated with the development of thiopurine-induced adverse events.

METHODS

Long-term incidence of adverse events was estimated in patients from a prospectively maintained Spanish nationwide database using Kaplan-Meier analysis. Cox regression analysis was performed to identify potential predictive factors of adverse events.

RESULTS

Three thousand nine hundred and thirty-one patients were included. Ninety-five percent of patients were on azathioprine. The median follow-up with thiopurines was 44 months (range, 0-420). Adverse events occurred at a median of 1 month after starting treatment. The cumulative incidence of adverse events was 26%, with an annual risk of 7% per patient-year of treatment. Most frequent adverse events were nausea (8%), hepatotoxicity (4%), myelotoxicity (4%), and pancreatitis (4%). Four patients had lymphoma. Female and Crohn's disease increased the risk of having nausea. The risk of hepatotoxicity was lower in females and higher in Crohn's disease. The risk of myelotoxicity was significantly higher in patients treated with mercaptopurine and in females. The risk of pancreatitis was higher in Crohn's disease. Overall, 17% of patients discontinued thiopurine treatment due to adverse events. Thirty-seven percent of these patients started thiopurines again and 40% of them had adverse events again.

CONCLUSIONS

As many as 1 of 4 patients on thiopurine therapy had adverse events during follow-up. A relatively high proportion of patients (17%) had to discontinue the treatment with thiopurines due to adverse events. However, more than half of patients that restarted thiopurine treatment after its discontinuation due to adverse events tolerated it. Several predictive factors for some adverse events have been identified.

Should thiopurine methyltransferase genotypes and phenotypes be measured before thiopurine therapy in patients with inflammatory bowel disease?

BACKGROUND AND AIMS

Not all of the adverse effects to thiopurine therapy can be explained by thiopurine methyltransferase (TPMT) polymorphisms. This study was intended to evaluate the value of TPMT genotype and phenotype measurement during the first year of thiopurine therapy.

METHODS

Consecutive patients with inflammatory bowel disease (IBD) who were receiving azathioprine or 6-mercaptopurine were followed up for 12 months. TPMT genotypes and phenotypes were examined in patients with IBD before thiopurine therapy and in unrelated healthy volunteers by polymerase chain reaction and high-performance liquid chromatography.

RESULTS

A total of 199 patients and 300 healthy volunteers were included at 2 centers. Forty-seven of the 199 patients (23.62%) exhibited adverse effects during the entire course of thiopurine therapy. Two (1%) patients carrying TPMT*3C developed leucopenia at week 4 of azathioprine treatment. The TPMT*3C had a specificity of 100% (163/163) but a sensitivity of 5.56% (2/36) for predicting leucopenia. The calculated optimal cutoff activity for high TPMT activity and decreased TPMT activity was 4.75 U/mL red blood cells. The risk of leucopenia increased in the decreased TPMT group (odds ratio: 20.25; 95% confidence interval: 2.19-187.17; P = 0.004) and increased more during the initial 3 months of thiopurine therapy (odds ratio: 34.80; 95% confidence interval: 3.71-326.77; P = 0.001). Leucopenia occurred more frequently in the patients cotreated with 5-aminosalicylates than in those not cotreated (32.81% versus 11.11%, respectively, P < 0.001).

CONCLUSIONS

The results of this study suggest that the value of TPMT genotyping before thiopurine therapy is limited in Chinese patients with IBD, considering the low sensitivity of predicting leucopenia, and that phenotyping is a more cost-effective tool that can be successfully used in patients. The coadministration of 5-aminosalicylates results in a high frequency of leucopenia in patients receiving azathioprine or 6-mercaptopurine.

[Guidelines for the management of Crohn's disease]

Crohn's disease (CD) is a chronic inflammatory bowel disease (IBD) with uncertain etiopathogenesis. CD can involve any site of gastrointestinal tract from the mouth to anus and is associated with serious complications such as bowel strictures, perforations, and fistula formation. The incidence and prevalence rates of CD in Korea are still lower than those of Western countries, but have been rapidly increasing during the past decades. Although there are no definitive curative modalities for CD, various medical and surgical therapies are currently applied for diverse clinical situations of CD. However, a lot of decisions on the management of CD are made depending on the personal experiences and choices of physicians. To suggest preferable approaches to diverse problems of CD and to minimize the variations according to physicians, guidelines for the management of CD are needed. Therefore, IBD Study Group of the Korean Association for the Study of the Intestinal Diseases has set out to develop the guidelines for the management of CD in Korea. These guidelines were developed using the adaptation methods and encompass the treatment of inflammatory disease, stricturing disease, and penetrating disease. The guidelines also cover the indication of surgery, prevention of recurrence after surgery, and CD in pregnancy and lactation. These are the first Korean guidelines for the management of CD and the update with further scientific data and evidences is needed.

Clinical outcomes and prognostic factors for thiopurine maintenance therapy in patients with intestinal Behcet's disease

BACKGROUND

To date, there have been no studies focusing on the efficacy of thiopurine therapy in intestinal Behcet's disease (BD). We conducted this study to investigate clinical outcomes and predictors of clinical relapse in intestinal BD patients receiving thiopurine maintenance therapy.

METHODS

We reviewed the medical records of all patients with intestinal BD who received thiopurine therapy in a single tertiary academic medical center between March 1986 and October 2010. The cumulative probabilities of clinical relapse after remission were calculated using the Kaplan-Meier method. Predictors of clinical relapse were identified by univariate analysis using the log-rank test and by multivariate analysis using Cox proportional hazards regression models.

RESULTS

Of a total of 272 patients with intestinal BD, 67 (24.6%) received their first course of thiopurine therapy at our center. Thirty-nine (58.2%) of the 67 patients constantly received thiopurines for maintaining medically or surgically induced remission. The cumulative relapse rates at 1 year, 2 years, 3 years, and 5 years after remission were 5.8%, 28.7%, 43.7%, and 51.7%, respectively. On multivariate analysis, a younger age (<25 years) at diagnosis and a lower hemoglobin level (<11 g/dL) were independent predictive factors for relapse in intestinal BD patients receiving thiopurine maintenance therapy.

CONCLUSIONS

Thiopurine therapy showed a relatively good effect for maintenance of remission in intestinal BD patients. However, a younger age at diagnosis and a lower hemoglobin level were associated with a poor response to thiopurines, necessitating early adoption of effective alternative therapeutic options in these risk groups.

Validation of a genotyping method for analysis of TPMT polymorphisms

BACKGROUND

Thiopurine methyltransferase (TPMT) catalyzes the methylation of thiopurine drugs such as azathioprine and 6-mercaptopurine. Several mutations in the TPMT gene correlate with low enzyme activity and adverse effects such as myelotoxicity. Hence, genotyping TPMT makes it possible to identify patients at high risk for drug toxicity.

OBJECTIVE

The aim of this study was to validate a TPMT genotyping method by comparing it with a conventional polymerase chain reaction (PCR) approach.

METHODS

LightSNiP is a real-time PCR method for the detection of TPMT*2, *3B, and *3C without a sequencing step. We evaluated the frequencies of 3 TPMT alleles in 111 white adult patients by comparing genotyping by LightSNiP with conventional PCR (sequencing).

RESULTS

No differences were observed between conventional genotyping with sequencing and LightSNiP for *2, *3B, and *3C, suggesting the validity of this method.

CONCLUSIONS

Compared with the conventional PCR sequencing method, the data suggest that LightSNiP correctly detected the TPMT *2, *3B, and *3C in this select population.

Thiopurine methyltransferase genotype and thiopurine S-methyltransferase activity in Greek children with inflammatory bowel disease

BACKGROUND

Azathioprine (AZA) and 6-mercaptopurine (6MP) are used in the treatment of pediatric inflammatory bowel disease (IBD). Genetic variations in thiopurine S-methyltranfarase (TPMT) gene have been correlated with enzyme activity and with the occurrence of adverse events to AZA and 6MP. The aim of the present study was to examine the sensitivity and specificity of TPMT genotyping for TPMT enzymatic activity, reducing harm from thiopurine by pretesting, and the association of thiopurine toxicity with TPMT status in children with IBD.

METHODS

TPMT red blood cell (RBC) activity was measured by using a radiochemical method and genotype was determined for the TPMT alleles *2, *3A, *3B and *3C in 108 thiopurinetreated pediatric IBD patients with a mean age of 11.3 years (range 3-16).

RESULTS

Significant TPMT activity differences between wild-type and heterozygous and homozygous mutated subjects were observed. We divided TPMT activity into three categories according to frequency distribution: low (16.67%), intermediate (25.92%) and high (57.41%). The whole population included a total of 77.78% of homozygous wild-type subjects, 15.74% heterozygous variants, 1.85% homozygous variants and five (4.63%) compound heterozygous variant TPMT*3B/*3C. The overall concordance rate between TPMT genotypes and phenotypes was 88.2%. Seven carriers of at least one variant allele and low or intermediate TPMT activity developed adverse effects.

CONCLUSIONS

Our findings suggest that carriers of at least one variant allele and both intermediate and absent TPMT activity have an increased risk of developing thiopurine-induced myelotoxicity compared with individuals with normal genotype and TPMT activity.

Outcome predictors for thiopurine maintenance therapy in patients with Crohn's disease

BACKGROUND

Little is known about the factors that predict clinical relapse in Crohn's disease patients receiving thiopurine therapy to maintain remission. The objective of this study was, therefore, to investigate these factors.

METHODS

A total of 82 Crohn's disease patients who received their first course of azathioprine or 6-mercaptopurine treatment at Severance Hospital between June 1996 and July 2007 were recruited to the study. During the follow-up period (25.5 ± 16.6 months) 19 patients (23.2%) discontinued the medication because of significant adverse effects. Forty-five patients who continued to receive thiopurines to maintain medically or surgically induced remission were enrolled in the study. After adjusting the maintenance dose, patients in remission were followed at 2-3 month intervals. Relapse was defined as a Crohn's disease activity index ≥ 150.

RESULTS

The male-to-female ratio was 1.5:1 and the mean age was 26.3 ± 7.1 years. Cumulative relapse was 18.0% after one year and 49.2% after three years. According to multivariate Cox regression analysis, younger age (<30 years) at thiopurine therapy and increased C-reactive protein level (≥ 0.5 mg/dL) at remission were independent predictors of relapse (hazard ratio 19.751, 95%-confidence interval (CI) 1.996-195.402, P = 0.011 and hazard ratio 9.001, 95% CI 1.583-51.181, P = 0.013, respectively).

CONCLUSIONS

Younger age (<30 years) and increased C-reactive protein level at remission were independent predictors of relapse in Crohn's disease patients receiving thiopurines to maintain remission. These high-risk groups warrant closer observation and possibly early introduction of biological agents.

Use of thiopurine testing in the management of inflammatory bowel diseases in clinical practice: a worldwide survey of experts

BACKGROUND

We performed a worldwide survey to evaluate the extent to which gastroenterologists who are experts in the field of inflammatory bowel diseases (IBDs) are utilizing thiopurine metabolism in practice.

METHODS

This was a Web-based cross-sectional survey consisting of 12 multiple-choice and open-ended questions.

RESULTS

Between December 2009 and April 2010, 175 questionnaires were received. The proportion of practitioners with access and reimbursement for thiopurine S-methyltransferase (TPMT) genotype, TPMT phenotype, 6-thioguanine nucleotides (6-TGN) levels, and 6-methylmercaptopurine ribonucleotides (6-MMP) levels was 48%, 54%, 44%, and 35%, respectively. Before azathioprine initiation, TPMT genotype and phenotype were performed by only 30% and 43% of responders, respectively. In patients on thiopurine therapy, 6-TGN and 6-MMP levels were determined by 54% and 44% of responders, respectively. Only 27% of physicians always wait for TMPT activity/genotype results before initiating azathioprine and 81% do not routinely recheck metabolite levels after dose escalation or reduction. In cases of very high or low TPMT activity, 75% and 74% of practitioners take into account TMPT activity result, respectively. If access to all azathioprine metabolite measurements was available and if all these tests were reimbursed by public health insurance, 47% of responders would use these tests more often in their practice. The availability and reimbursement of TPMT status and azathioprine metabolites strongly influenced experts' attitudes.

CONCLUSIONS

Thiopurine testing is relatively underutilized by IBD gastroenterologists. The availability and reimbursement of TPMT status and azathioprine metabolites strongly influence the management of IBD patients treated with thiopurines.

Thiopurine methyl-transferase activity and azathioprine metabolite concentrations do not predict clinical outcome in thiopurine-treated inflammatory bowel disease patients

BACKGROUND

Low thiopurine-methyl-transferase (TPMT) activity and high 6-thioguanine-nucleotide (6TGN) concentrations have been linked to therapeutic success in inflammatory bowel disease patients treated with thiopurines; however, this has not been implemented in clinical practice.

AIM

To identify a therapeutic threshold value for TPMT or 6TGN concentrations, and their capability to predict treatment safety and efficacy.

METHODS

Prospective multicentre study including steroid-resistant/dependent patients starting thiopurines. The TPMT activity was determined at inclusion (>5 U/mL required). Azathioprine metabolites [6TGN, 6-methyl-mercaptopurine ribonucleotides (6MMP), and 6TGN/6MMP and 6TGN/TPMT ratios] were periodically monitored during steroid tapering and after withdrawal for 6 months or until a new flare occurred.

RESULTS

A total of 113 patients were analysed (62% clinical response). Areas under the receiver operating characteristic (ROC) curve (AUC) relating clinical response and metabolite levels at 2, 4 and 6 months after steroid withdrawal were less than 0.7. The AUCs relating final response and initial TPMT activity or metabolite concentrations at 2, 4, 8 and 16 weeks after starting thiopurines were less than 0.7. No cut-off point with worthwhile sensitivity/specificity was found. Eight (7%) patients developed thiopurine-related toxicity that could not be linked to TPMT activity or 6TGN levels.

CONCLUSIONS

Our results do not support determination of TPMT activity or 6TGN concentrations to predict treatment outcome, and no useful serum metabolites threshold value to adjust the drug's dose was identified.

A case of Crohn's disease with improvement after azathioprine-induced pancytopenia

The immunosuppressant azathioprine (AZA) is widely used in the treatment of inflammatory bowel disease (IBD) for both inducing and maintaining remission. However, the adverse effects of AZA can often necessitate a dose reduction or discontinuation. Bone marrow suppression is one of the most serious complications with AZA treatment. On the other hand, some reports have suggested that neutropenia during AZA therapy reduced the relapse rates of IBD patients, and there have been some cases where eradication of the sensitized leukocytes by leukapheresis or bone marrow transplantation improved the IBD, which may explain the relevant role of neutropenia in controlling disease activity. This report describes the case of a 22-year-old male patient who had Crohn's colitis and complicated perianal fistulas that required immunosuppression; he achieved endoscopically determined remission and showed accelerated mucosal healing as well as clinical remission following the AZA-induced pancytopenia.