Toxicity of 6-thioguanine: no hepatotoxicity in a series of IBD patients treated with long-term, low dose 6-thioguanine. Some evidence for dose or metabolite level dependent effects?

Implications of Tioguanine Dosing in IBD Patients with a TPMT Deficiency

Tioguanine is metabolised by fewer enzymatic steps compared to azathioprine and mercaptopurine, without generating 6-methylmercaptopurine ribonucleotides. However, thiopurine S-methyl transferase (TPMT) plays a role in early toxicity in all thiopurines. We aimed to describe the hazards and opportunities of tioguanine use in inflammatory bowel disease (IBD) patients with aberrant TPMT metabolism and propose preventative measures to safely prescribe tioguanine in these patients. In this retrospective cohort study, all determined TPMT genotypes (2016-2021) were evaluated for aberrant metabolism (i.e., intermediate and poor TPMT metabolisers). Subsequently, all IBD patients on tioguanine with aberrant TPMT genotypes were evaluated for tioguanine dosages, adverse drug events, lab abnormalities, treatment duration and effectiveness. TPMT genotypes were determined in 485 patients, of whom, 50 (10.3%) and 4 patients (0.8%) were intermediate and poor metabolisers, respectively. Of these patients, 12 intermediate and 4 poor TPMT metabolisers had been prescribed tioguanine in varying doses. In one poor TPMT metaboliser, tioguanine 10 mg/day induced delayed pancytopenia. In general, reduced tioguanine dosages of 5 mg/day for intermediate TPMT metabolisers, and 10 mg two-weekly for poor TPMT metabolisers, resulted in a safe, long-term treatment strategy. Diminished or absent TPMT enzyme activity was related with a pharmacokinetic shift of tioguanine metabolism which is associated with relatively late-occurring myelotoxicity in patients on standard tioguanine dose. However, in strongly reduced dose regimens with strict therapeutic drug and safety monitoring, tioguanine treatment remained a safe and effective option in IBD patients with dysfunctional TPMT.

Development of innovative methodology for determination of 6-thioguanine in whole blood erythrocytes by HPLC-PDA-based technique for medical diagnostics purposes

6-Thioguanine is an immunosuppressive drug, an analogue of guanine, applied to treat acute leukemia and inflammatory bowel disease. Excessive use of 6-thioguanine during clinical treatment may cause side effects. Moreover, providing a dose too low will be ineffective. Therefore, there is a critical need for a rapid, selective and routine approach to quantifying 6-thioguanine in body fluids to support a clinical application. A fully validated HPLC method has been developed to determine 6-thioguanine in whole blood samples using 5-bromouracil as an internal standard. 6-Thioguanine nucleotides were released from erythrocytes by perchloric acid, and then hydrolysed at 100 °C to the parent thiopurine, 6-thioguanine. The following validation parameters of the method were determined: specificity/selectivity, linearity range (479-17,118 ng/mL, R > 0.992), limits of detection (150 ng/mL) and quantification (479 ng/mL), accuracy (- 5.6 < Bias < 14.7), repeatability (CV 1.30-3.24%), intermediate precision (CV 4.19-5.78%), extraction recovery (79.1-103.6%) and carryover. Furthermore, the stability of the drug in whole blood samples under various storage conditions was investigated. The suggested method is suitable for determining 6-thioguanine in whole blood erythrocyte samples for drug level monitoring, thus correct dosing.

Effectiveness and safety of thioguanine as a maintenance therapy of inflammatory bowel disease: Systematic review, meta-analysis and meta-regression

INTRODUCTION

Thiopurines are an important therapy for the maintenance of remission in inflammatory bowel disease (IBD). However, the use of thioguanine has been limited by concerns regarding its toxicity. We performed a systematic review to evaluate its effectiveness and safety in IBD.

METHODS

Electronic databases were searched to identify studies reporting clinical responses and/or adverse events of thioguanine therapy in IBD. We calculated the pooled clinical response and clinical remission rates of thioguanine in IBD. Subgroup analyses were done for the dosage of thioguanine and the type of studies (prospective or retrospective). Meta-Regression was used to analyze the impact of dose on clinical efficacy and occurrence of nodular regenerative hyperplasia.

RESULTS

A total of 32 studies were included. The pooled clinical response rate of thioguanine therapy in IBD was 0.66 (95% C.I. 0.62 - 0.70; I2 = 16%). The pooled clinical response rate with low-dose was similar to high-dose thioguanine therapy [0.65 (95% C.I. 0.59 - 0.70; I2 = 24%) and 0.68 (95% C.I. 0.61 - 0.75; I2 = 18%) respectively]. The pooled remission maintenance rate was 0.71 (95% C.I. 0.58 - 0.81; I2 = 86%). The pooled rates of occurrence of nodular regenerative hyperplasia, liver function tests abnormalities and cytopenia were 0.04 (95% C.I. 0.02 - 0.08; I2 = 75%), 0.11 (95% C.I. 0.08 - 0.16; I2 = 72%) and 0.06 (95% C.I. 0.04 - 0.09; I2 = 62%) respectively. Meta-regression suggested that the risk of nodular regenerative hyperplasia is related to the dose of thioguanine.

CONCLUSION

TG is an efficacious and well-tolerated drug in most patients with IBD. Nodular regenerative hyperplasia, cytopenias, and liver function abnormalities occur in a small subset. Future studies should look into TG as primary therapy in IBD.

The prevalence of nodular regenerative hyperplasia of the liver in long-term thiopurine-treated inflammatory bowel disease patients

INTRODUCTION

Nodular regenerative hyperplasia (NRH) has been associated with thiopurine therapy in patients with inflammatory bowel disease (IBD), but prevalence and prognosis of NRH remain unclear. This study is a cross-sectional search for NRH in IBD patients with long-term azathioprine or 6-mercaptopurine treatment.

MATERIAL AND METHODS

Thirty-three IBD patients with continuous azathioprine/6-mercaptopurine treatment for at least 5 years were included. Laboratory tests, thiopurine metabolite levels, liver histology, MRI were examined for NRH and signs of portal hypertension.

RESULTS

NRH was not observed in this cohort of 33 patients. Nevertheless, some possibly related signs of vascular changes were found by MRI in three patients. Also, splenomegaly, which may be associated with portal hypertension, was found in one patient. No high thiopurine dose neither high metabolite levels were found in these patients.

CONCLUSION

No NRH was found in this group of IBD patients with long-term azathioprine/6-mercaptopurine treatment. Larger multicenter studies are needed to determine the prevalence of NRH in thiopurine-treated IBD patients.

Relationship Between Thiopurine S-Methyltransferase Genotype/Phenotype and 6-Thioguanine Nucleotide Levels in 316 Patients With Inflammatory Bowel Disease on 6-Thioguanine

BACKGROUND

In inflammatory bowel disease (IBD), conventional thiopurine users cease treatment in 60% of cases within 5 years, mostly because of adverse events or nonresponse. In this study, the authors aimed to investigate the role of 6-thioguanine nucleotide (TGN) measurements, geno/phenotyping of thiopurine S-methyltransferase (TPMT), and their mutual relationship with TG therapy in IBD.

METHODS

An international retrospective, multicenter cohort study was performed at 4 centers in the Netherlands (Máxima Medical Centre) and the United Kingdom (Guy's and St. Thomas' Hospital, Queen Elizabeth Hospital, and East Surrey Hospital).

RESULTS

Overall, 526 6-TGN measurements were performed in 316 patients with IBD. The median daily dosage of TG was 20 mg/d (range 10-40 mg/d), and the median duration of TG use was 21.1 months (SD, 28.0). In total, 129 patients (40.8%) had a known TPMT status. In the variant-type and wild-type TPMT genotype metabolism groups, median 6-TGN values were 1126 [interquartile range (IQR) 948-1562] and 467.5 pmol/8 × 10E8 red blood cells (RBCs) (IQR 334-593). A significant difference was observed between the 2 groups (P = 0.0001, t test). For TPMT phenotypes, in the slow, fast, and normal metabolism groups, the median 6-TGN values were 772.0 (IQR 459-1724), 296.0 (IQR 200-705), and 774.5 pmol/8 × 10E8 RBCs (IQR 500.5-981.5), with a significant difference observed between groups (P < 0.001, analysis of variance).

CONCLUSIONS

Our findings indicated that TPMT measurements at TG initiation can be useful but are not necessary for daily practice. TPMT genotypes and phenotypes are both associated with significant differences in 6-TGN levels between metabolic groups. However, the advantage of TG remains that RBC 6-TGN measurements are not crucial to monitor treatments in patients with IBD because these measurements did not correlate with laboratory result abnormalities. This presents as a major advantage in countries where patients cannot access these diagnostic tests.

Thiopurines in Inflammatory Bowel Disease. How to Optimize Thiopurines in the Biologic Era?

Thiopurines have been a cornerstone in the treatment of inflammatory bowel disease (IBD). Although they have been used for more than 50 years, there are still some unsolved issues about their efficacy and, also, some safety concerns, mainly the risk of myelosuppression and life-threatening lymphoproliferative disorders. Furthermore, the development of biological therapy raises the question whether there is still a role for thiopurines in the IBD treatment algorithm. On the other hand, limited cost and wide availability make thiopurines a reasonable option in settings of limited resources and increasing prevalence of IBD. In fact, there is a growing interest in optimizing thiopurine therapy, since pharmacogenomic findings suggest that a personalized approach based on the genotyping of some molecules involved in its metabolism could be useful to prevent side effects. Polymorphisms of thiopurine methyltransferase enzyme (TPMT) that result in low enzymatic activity have been associated with an increased risk of myelotoxicity, especially in Caucasians; however, in Asians it is assumed that the variants of nudix hydrolase 15 (NUDT15) are more relevant in the development of toxicity. Age is also important, since in elderly patients the risk of complications seems to be increased. Moreover, the primo-infection of Epstein Barr virus and cytomegalovirus under thiopurine treatment has been associated with severe lymphoproliferative disorders. In addition to assessing individual characteristics that may influence thiopurines treatment outcomes, this review also discusses other strategies to optimize the therapy. Low-dose thiopurines combined with allopurinol can be used in hypermethylators and in thiopurine-related hepatotoxicity. The measurement of metabolites could be useful to assess compliance, identify patients at risk of adverse events and also facilitating the management of refractory patients. Thioguanine is also a rescue therapy in patients with toxicity related to conventional thiopurine therapy. Finally, the current indications for thiopurines in monotherapy or in combination with biologics, as well as the optimal duration of treatment, are also reviewed.

The continuous rediscovery and the benefit-risk ratio of thioguanine, a comprehensive review

Introduction: In the 1950s, thioguanine (TG), a thiopurine-derivative together with azathioprine (AZA) and mercaptopurine (MP), were developed for the treatment of childhood leukemia. Over the years, the use of TG was also explored for other, mainly immune-mediated and inflammatory, diseases such as in the field of dermatology and rheumatology (e.g. psoriasis, systemic lupus erythematosus (SLE)) and gastroenterology and hepatology (e.g. inflammatory bowel diseases (IBD), autoimmune hepatitis).Areas covered: This review provides a comprehensive overview of all the clinical uses of TG and describes its mechanism of action, pharmacokinetic/pharmacodynamic features, and toxicity.Expert opinion: Thioguanine has shown beneficial clinical effects in hematological (particularly leukemia) and several immune-inflammatory diseases including psoriasis, SLE, polycythemia vera, Churg-Strauss syndrome, IBD, collagenous sprue, refractory celiac disease, and autoimmune hepatitis. Thioguanine is not effective in treating solid-cancers. At relatively low dosages, i.e. 0.2- 0.3mg/kg/day or 20 mg/day, TG has a favorable risk-benefit ratio and is a safe and effective drug in the long-term treatment of amongst other IBD patients. Thioguanine toxicity, especially myelotoxicity, and hepatotoxicity, including nodular regenerative hyperplasia (NRH) of the liver, is limited when dosed adequately. The occurrence of NRH appears dose-dependent and has been especially described during high dose TG above 40 mg/day.

Hepatotoxicity during 6-thioguanine treatment in inflammatory bowel disease and childhood acute lymphoblastic leukaemia: A systematic review

Background

The recently established association between higher levels of DNA-incorporated thioguanine nucleotides and lower relapse risk in childhood acute lymphoblastic leukaemia (ALL) calls for reassessment of prolonged 6-thioguanine (6TG) treatment, while avoiding the risk of hepatotoxicity.

Objectives

To assess the incidence of hepatotoxicity in patients treated with 6TG, and to explore if a safe dose of continuous 6TG can be established.

Data sources

Databases, conference proceedings, and reference lists of included studies were systematically searched for 6TG and synonyms from 1998–2018.

Methods

We included studies of patients with ALL or inflammatory bowel disorder (IBD) treated with 6TG, excluding studies with 6TG as part of an intensive chemotherapy regimen. We uploaded a protocol to PROSPERO (registration number CRD42018089424). Database and manual searches yielded 1823 unique records. Of these, 395 full-texts were screened for eligibility. Finally, 134 reports representing 42 studies were included.

Results and conclusions

We included data from 42 studies of ALL and IBD patients; four randomised controlled trials (RCTs) including 3,993 patients, 20 observational studies including 796 patients, and 18 case reports including 60 patients. Hepatotoxicity in the form of sinusoidal obstruction syndrome (SOS) occurred in 9–25% of the ALL patients in two of the four included RCTs using 6TG doses of 40–60 mg/m²/day, and long-term hepatotoxicity in the form of nodular regenerative hyperplasia (NRH) was reported in 2.5%. In IBD patients treated with 6TG doses of approximately 23 mg/m²/day, NRH occurred in 14% of patients. At a 6TG dose of approximately 12 mg/m²/day, NRH was reported in 6% of IBD patients, which is similar to the background incidence. According to this review, doses at or below 12 mg/m²/day are rarely associated with notable hepatotoxicity and can probably be considered safe.

Evolving Considerations for Thiopurine Therapy for Inflammatory Bowel Diseases-A Clinical Practice Update: Commentary

Thiopurines (azathioprine, mercaptopurine, thioguanine) and methotrexate are widely used in a variety of clinical management scenarios for ulcerative colitis and Crohn's disease. With the introduction of biologic therapies over the last 2 decades, controversies have emerged as to how these immunomodulators should be used in clinical practice, either alone as monotherapies or in combination with biologic therapies. Here, we provide a summary of evidence and our interpretations regarding how physicians can or should incorporate these agents into clinical practice. We have organized the review into sections regarding their utility as monotherapy or as combination therapy with biologics and safety considerations. Clinical pharmacologic considerations are important regarding both efficacy and safety.

Idiopathic portal hypertension with regard to thiopurine treatment

Idiopathic portal hypertension (IPH) is an infrequent adverse reaction to the use of thiopurines that tends to be overlooked. Herein, we present a patient with ileocolic Crohn's disease treated with azathioprine who presented ascites, esophageal varices and splenomegaly without any signs of liver cirrhosis. A portal hemodynamics study revealed a normal portosystemic gradient compatible with presinusoidal portal hypertension. Finally, IPH was diagnosed after a liver biopsy. IPH secondary to thiopurines is due to a 6-thioguanine nucleotide (6-TGN)-dependent reaction and occurs predominantly between three months and three years after the start of treatment. The onset is usually insidious and thrombocytopenia is the first manifestation. The definitive diagnosis is obtained by liver biopsy.

Is there a role for thioguanine therapy in IBD in 2017 and beyond?

Conventional thiopurines are effective for the maintenance of remission of Crohn's disease and ulcerative colitis, however, up to half of patients are intolerant or unresponsive to these medications. Thioguanine is an alternative thiopurine that has shown efficacy in inflammatory bowel disease, and is particularly useful to circumvent certain side effects associated with conventional thiopurines, for example, pancreatitis. Its association with nodular regenerative hyperplasia of the liver has hindered its widespread use. Areas covered: We aim to outline the rational use of thioguanine, including safety monitoring, with particular regard to hepatotoxicity. A literature search was performed: PubMed was searched for full papers and abstracts published in English since January 2000 using the following terms, alone and in combination: 'azathioprine', 'thiopurine', 'Crohn's disease', 'inflammatory bowel disease', 'nodular regenerative hyperplasia', 'mercaptopurine', 'thioguanine', 'ulcerative colitis'. Further relevant papers were identified from the reference lists of selected papers. Expert commentary: Despite optimisation strategies such as metabolite measurements and the use of allopurinol, a significant proportion of patients will remain intolerant to thiopurines, especially those with allergic reactions, including pancreatitis. For this subgroup of patients we suggest that low dose thioguanine is an alternative to other therapies that are either parenteral or expensive.

How I treat my inflammatory bowel disease-patients with thiopurines?

Thiopurines are essential drugs to maintain remission in patients with inflammatory bowel disease (IBD). Thiopurines used in IBD are azathioprine (2.0-2.5 mg/kg), mercaptopurine (1.0-1.5 mg/kg) and thioguanine (0.2-0.3 mg/kg). However, mainly due to numerous adverse events associated with thiopurine use, almost 50% of the patients have to discontinue conventional thiopurine treatment. Extensive monitoring and the application of several treatment strategies, such as split-dose administration, co-administration with allopurinol or dose reduction/increase, may increase the chance of successful therapy. With this review, we provide practical information on how thiopurines are initiated and maintained in two thiopurine research centers in The Netherlands. We provide clinical information concerning safety issues, indications and management of therapy that may serve as a guide for the administration of thiopurines in IBD patients in daily practice.

Efficacy of thioguanine treatment in inflammatory bowel disease: A systematic review

AIM

To critically assess the available literature regarding the efficacy of thioguanine treatment in inflammatory bowel disease (IBD) patients, irrespective of the (hepato-) toxicity profile.

METHODS

A systematic literature search of the MEDLINE database using PubMed was performed using the keywords “thioguanine”, “6-TG”, “thioguanine”, “inflammatory bowel disease”, “IBD”, “Crohn’s disease”, “Ulcerative colitis” and “effectiveness” in order to identify relevant articles published in English starting from 2000. Reference lists of the included articles were cross-checked for missing articles. Reviewed manuscripts concerning the effectiveness of thioguanine treatment in IBD were reviewed by the authors and the data were extracted. Data were subsequently analyzed with descriptive statistics. Due to the lack of standardized outcomes, a formal meta-analysis was not performed.

RESULTS

A total of 11 applicable studies were found that involved the effectiveness of thioguanine therapy in IBD. Eight studies were conducted in a prospective manner, in the remaining three studies, data was collected retrospectively. In total, 353 IBD-patients (225 patients with Crohn’s disease, 119 with ulcerative colitis and nine with unclassified IBD) with prior azathioprine/mercaptopurine resistance and/or intolerance (n = 321) or de novo thioguanine administration (n = 32) were included for analysis, of which 228 (65%) had clinical improvement on thioguanine therapy, based on standard IBD questionnaires, biochemical parameters or global physician assessments. Short-term results were based on 268 treatment years (median follow-up 9 mo, range 3-22 mo) with a median daily dose of 20 mg (range 10-80 mg). Discontinuation, mostly due to adverse events, was reported in 72 patients (20%).

CONCLUSION

The efficacy of thioguanine therapy in IBD patients intolerant to conventional thiopurine therapy is observed in 65%, with short term adverse events in 20% of patients.

Review article: the association between nodular regenerative hyperplasia, inflammatory bowel disease and thiopurine therapy

BACKGROUND

Nodular regenerative hyperplasia (NRH) is increasingly being recognised in patients with inflammatory bowel disease (IBD). However, the pathogenesis and incidence of NRH in IBD, and the putative roles played by azathioprine (AZA), mercaptopurine (MP), or tioguanine (TG) remain unclear.

AIMS

To summarise the data on the association between NRH and thiopurine therapy in patients with IBD.

METHODS

A literature search was performed in PubMed and MEDLINE databases using the keywords 'nodular regenerative hyperplasia AND (inflammatory bowel disease OR Crohn's disease OR ulcerative colitis) AND (azathioprine OR mercaptopurine OR tioguanine OR thioguanine).' No time limit was placed on studies included.

RESULTS

Inflammatory bowel disease patients treated with AZA have a cumulative incidence of NRH of approximately 0.6% and 1.28% at 5 and 10 years, respectively, whereas those treated with high-dose TG (>40 mg/day) have a frequency of NRH of up to 62%, which is higher in patients with elevated liver enzymes and/or thrombocytopaenia than those without these abnormalities (frequency 76% vs. 33%). Conversely, low-dose TG therapy (<20 mg/day) is relatively safe, with no cases of NRH observed. NRH has also been found in 6% of operated thiopurine-naïve IBD patients. Male gender, older age, and stricturing disease/small bowel resection have been consistently identified as high-risk factors for NRH.

CONCLUSIONS

The pathogenesis of nodular regenerative hyperplasia in patients with IBD is complex and multifactorial involving disease-specific, genetic and iatrogenic risk factors. Clinicians should maintain a high index of suspicion for diagnosing nodular regenerative hyperplasia, especially in IBD patients with high-risk factors on thiopurine therapy, regardless of the presence of laboratory abnormalities.

A skewed thiopurine metabolism is a common clinical phenomenon that can be successfully managed with a combination of low-dose azathioprine and allopurinol

BACKGROUND AND AIMS

A skewed thiopurine metabolism is a phenomenon associated with both poor treatment response and toxicity. Our aim was to evaluate the frequency of this phenomenon and the relationship to thiopurine methyltransferase (TPMT) function.

METHODS

All thiopurine metabolite measurements in adult patients (n=4033) between January 2006 and April 2012 were assessed to evaluate the occurrence of a skewed metabolism and the relationship to TPMT genotype and activity.

RESULTS

A skewed metabolism was observed in 14% of all patients. It only developed in patients with a normal TPMT genotype, but was observed at all TPMT activity levels within the normal range (9.1-24.2 U/ml RBC). Two cases that illustrate typical clinical scenarios of a skewed metabolism and the effect of combination treatment with low-dose azathioprine and allopurinol are presented.

CONCLUSIONS

A skewed metabolism is a common clinical phenomenon in patients with a normal TPMT function, which can develop at all TPMT activity levels within the normal range. We suggest that metabolite measurements should be considered in patients not responding to treatment and in those with hepatotoxicity or myelotoxicity in order to detect a skewed metabolism, since this phenomenon can be successfully managed by a combination of low-dose azathioprine and allopurinol.

Use of thiopurines in inflammatory bowel disease

The use of thiopurines as immunosuppression for the treatment of refractory or chronic active inflammatory bowel disease is established for both Crohn's disease and ulcerative colitis. Nevertheless, many questions remain concerning the optimal treatment regimens of azathioprine, 6-mercaptopurine and thioguanine. We will briefly summarize dose recommendations, indications for thiopurine therapy and side effects which are relevant in clinical practice. We discuss some currently debated topics, including the combination of azathioprine and allopurinol, switching of thiopurine therapy in case of side effects, the use of azathioprine in pregnancy, the infection risk using thiopurines and the evidence when to stop thiopurines. Excellent reviews have been published on the thiopurine metabolic pathway which will not be discussed here in detail.

Recent advances using immunomodulators for inflammatory bowel disease

Use of the immunomodulators thiopurines and methotrexate (MTX) in the treatment of inflammatory bowel disease (IBD), i.e., Crohn's disease and ulcerative colitis (UC), is considered to be good clinical practice. However, despite being administered to a considerable number of IBD patients over the years, questions remain about the most rational treatment regimens of azathioprine (AZA), 6-mercaptopurine (6-MP), and MTX, and results from a range of recent studies necessitate increased attention to how to optimize the use of these immunomodulators. First and foremost, it is of utmost importance to define the subgroup of IBD patients in need of immunomodulators, including those in need of combination therapy with biologic agents, especially because some side effects may be rather severe. Second, colorectal cancer is observed more often in IBD patients than in the background population. However, a recent nationwide Dutch study pointed to a preventive effect of thiopurines. Finally, the need for an appropriate approach to the discontinuation of immunomodulators is emphasized. Since controversy continues regarding the most appropriate use of immunomodulators, this paper is focusing on pharmacokinetics, pharmacogenetics, and therapeutic blood testing, as well as the occurrence of adverse events, when using AZA, 6-MP, and MTX in an attempt to determine a more up-to-date and rational treatment regimen in IBD.

Hepatotoxicity associated with 6-methyl mercaptopurine formation during azathioprine and 6-mercaptopurine therapy does not occur on the short-term during 6-thioguanine therapy in IBD treatment

BACKGROUND AND AIMS

High concentrations of methylated thiopurine metabolites, such as 6-methyl mercaptopurine, are associated with hepatotoxicity during administration of the conventional thiopurines azathioprine or 6-mercaptopurine in IBD patients. Metabolization of the non-conventional thiopurine 6-thioguanine does not generate 6-methyl mercaptopurine. Hence, the aim of our study was to evaluate hepatotoxicity during 6-thioguanine in IBD patients who previously failed conventional thiopurines due to 6-methyl mercaptopurine associated hepatotoxicity.

METHODS

A retrospective single center intercept cohort study was performed of IBD patients using 6-thioguanine between January 2006 and July 2010 after failing conventional thiopurine therapy due to 6-methyl mercaptopurine associated hepatotoxicity. The primary outcome was the occurrence of 6-thioguanine induced hepatotoxicity, scaled according to the Common Terminology Criteria for Adverse Events.

RESULTS

Nineteen patients were included. Median duration of 6-thioguanine therapy (median daily dosage 21 mg (9-24)) was 23 weeks (6-96). Hepatotoxicity did not reoccur in 15 out of 19, whereas grade 1 toxicity persisted in 4 patients (p<0.001). Median aspartate aminotransferase and alanine aminotransferase concentrations decreased from 34 U/l (20-59) and 64 U/l (15-175) to 23 U/l (18-40; p=0.003) and 20 U/l (14-48; p=0.019), respectively.

CONCLUSION

Hepatotoxicity does not reoccur during 6-thioguanine treatment in most IBD patients who failed conventional thiopurines due to 6-methyl mercaptopurine associated hepatotoxicity. Hence, at least at short-term, 6-thioguanine appears a justifiable alternative thiopurine for these IBD patients.

Safety and efficacy of the immunosuppressive agent 6-tioguanine in murine model of acute and chronic colitis

BACKGROUND

Oral thiopurines are effective and widely used in treatment of inflammatory bowel disease (IBD) in humans, although their use is limited due the development of adverse events. Here, we examine the efficacy and toxicity of oral treatment with 6-tioguanine (6-TG) and azathioprine (AZA) in a murine model of IBD.

METHODS

We induced acute or chronic colitis in BALB/c mice by one or four cycles of 3% dextran sulphate sodium (DSS), respectively. Mice were treated by daily gavages of various dosages of 6-tioguanine, azathioprine, or by phosphate buffered saline (PBS) starting the first day of DSS or after two cycles of DSS, respectively. We monitored the efficacy and toxicity by measuring the weight change and serum alanine aminotransferase (ALT) activity and by disease severity and histology, at the end of the experiment. Moreover, we measured cytokine production after colon fragment cultivation by enzyme-linked immunoabsorbent assay and numbers of apoptotic cells in the spleen by flow cytometry.

RESULTS

6-TG is effective in the treatment of acute DSS-induced colitis in a dose-dependent manner and 40 μg of 6-TG is significantly more effective in the treatment of acute colitis than both AZA and PBS. This effect is accompanied by decrease of IL-6 and IFN-γ production in colon. We did not observe histological abnormalities in liver samples from control (PBS) or 6-TG treated mice. However, liver samples from most mice treated with AZA showed mild, yet distinct signs of hepatotoxicity. In chronic colitis, all thiopurine derivatives improved colitis, 20 μg of 6-TG per dose was superior. High doses of 6-TG led to significant weight loss at the end of the therapy, but none of the thiopurine derivatives increased levels of serum ALT. Both thiopurine derivatives reduced the proportion of apoptotic T helper cells, but a high production of both IL-6 and TGF-β was observed only in colon of AZA-treated mice.

CONCLUSIONS

Use of 6-TG in the treatment of experimental colitis in mice appears superior to AZA administration and placebo. In contrast to 6-TG, the use of AZA resulted in histological liver abnormalities.

Difficulties and possibilities with thiopurine therapy in inflammatory bowel disease--proceedings of the first Thiopurine Task Force meeting

BACKGROUND

Thiopurines, such as azathioprine and mercaptopurine, are of pivotal importance in the treatment of inflammatory bowel disease. Although these drugs have been used for several decades, still many questions remain unanswered.

AIM

To provide an overview of clinically and scientifically challenging topics concerning thiopurine therapy in inflammatory bowel disease treatment.

METHODS

The first meeting of the Thiopurine Task Force Interest Group was held during the 2009 United European Gastroenterology Week in London (GASTRO2009). The topics of this meeting were of particular clinical and scientific interest. Additional literature was identified by performing a Pubmed search using the search terms 'inflammatory bowel disease', 'azathioprine', '6-mercaptopurine' and 'thioguanine'.

RESULTS

The following topics were discussed: therapeutic drug monitoring; the synergy of thiopurines with aminosalicylates and allopurinol; serious adverse events such as opportunistic infections, hepatotoxicity, carcinogenicity and pancreatitis; prolongation of thiopurines during clinical remission; indications for thiopurines in the postoperative setting; and the potential use of thioguanine. Specific interesting and clinically relevant topics for potential future research are provided.

CONCLUSIONS

Thiopurines remain central to inflammatory bowel disease treatment, although future studies are required to substantiate a more personalised medicine approach to their use.

Prolonged thioguanine therapy is well tolerated and safe in the treatment of ulcerative colitis

BACKGROUND

Thioguanine has been used for the treatment of inflammatory bowel disease, in particular for patients who failed conventional thiopurine therapy. To date, thioguanine has been infrequently studied in ulcerative colitis.

AIM

To evaluate the tolerability, safety and efficacy of thioguanine in the treatment of ulcerative colitis.

METHODS

A database analysis was performed on inflammatory bowel disease patients who had failed conventional thiopurine therapy and were treated with thioguanine. Rates and reasons for treatment failure were assessed. Laboratory values, abdominal ultrasonography, liver biopsy and endoscopic remission rates were evaluated.

RESULTS

Forty-six patients were included and median treatment duration was 22 months (range 0.3-72.0). Nine patients failed thioguanine therapy: six due to adverse events, three due to therapy resistance. Concomitant treatment with aminosalicylates protected against thioguanine failure (hazard ratio (HR) 0.11, 95% CI 0.03-0.48). When performed, ultrasonography (n = 21) revealed no suspected therapy-related pathology in all but one patient, in whom hepatomegaly was observed. Liver histology (n = 12) predominantly revealed no abnormalities (n = 4) or non-specific regeneration (n = 4); none showed nodular regenerative hyperplasia. At follow-up, 40% of colonoscopies revealed endoscopic remission as compared with 10% at baseline (P = 0.180).

CONCLUSIONS

Long-term use of thioguanine appears to be well tolerated and relatively safe in ulcerative colitis patients who failed conventional thiopurine therapy.

Assessment of non-cirrhotic portal hypertension associated with thiopurine therapy in inflammatory bowel disease

Thiopurines represent an effective and widely used immunosuppressant in the therapeutic armamentarium of inflammatory bowel disease. However up to 25% of patients may be unable to continue the drug due to side effects. The incidence of hepatotoxicity associated with thiopurine use is reported between 0% and 32%. Veno-occlusive disease, peliosis hepatis, perisinusoidal fibrosis and nodular regenerative hyperplasia have all been described with thiopurines. Recent trials of 6-tioguanine, although successful in patients with allergies to azathioprine or mercaptopurine, have been compromised by increased hepatotoxicity, either veno-occlusive disease or nodular regenerative hyperplasia. We describe a report of nodular regenerative hyperplasia in a Crohn's disease patient associated with 6-mercaptopurine therapy and have reviewed the management and the literature regarding this complication. Our report strengthens the importance of further safety studies to evaluate the etiology, prevalence, risk factors and screening modalities for hepatotoxicity, in particular of nodular regenerative hyperplasia, in patients treated with thiopurines for inflammatory bowel disease.

Thiopurine therapy in inflammatory bowel disease

The thiopurines azathioprine and 6-mercaptopurine have been used in the treatment of Crohn's disease and ulcerative colitis for over 40 years. Randomized controlled trials have supported their use in the treatment of active disease, as well as for the maintenance of disease remission. Presently, the most debated issues surrounding the thiopurines include: the role of thiopurine methyltransferase and metabolite-adjusted dosing in enhancing efficacy and minimizing toxicity; the timing of thiopurine use, that is, earlier versus later use during the course of the disease; the selection of thiopurine monotherapy versus combination therapy with an anti-TNF-α; agent; and the safety profile of thiopurines. Accumulated evidence has supported the safety of 6-mercaptopurine/azathioprine use in pregnancy and lactation. Thiopurine therapy in inflammatory bowel diseases is associated with an increased risk of lymphoproliferative disorders. Factoring their proven efficacy over a broad range of clinical scenarios within Crohn's disease and ulcerative colitis together with their overall safety profile and convenient and inexpensive once-daily oral administration, azathioprine and 6-mercaptopurine remain among the mainstays of Crohn's disease and ulcerative colitis therapy.

Gastrointestinal and liver adverse effects of drugs used for treating IBD

Drugs used for treating inflammatory bowel disease are known to have a number of gastrointestinal and liver adverse effects. 5-ASA products are relatively safe and have few adverse events. In contrast sulfasalazine has side effects in 11-40% of treated patients including fatigue, nausea, abdominal pain and diarrhoea. Glucocorticoids can induce or propagate peptic ulcers and upper GI bleeding especially in combination with NSAIDs. Thioguanins may have severe gastrointestinal side effects including gastrointestinal complaints (in up to 12%), hepatotoxicity (up to 4%) and pancreatitis (1%). Nodular regenerative hyperplasia (NRH) is an important potential side effect of thiopurine therapy especially in men with Crohn's disease after ileocecal resection. NRH may ultimately lead to portal hypertension. A major concern of methotrexate therapy in IBD besides myelosuppression and pulmonary fibrosis is hepatotoxicity. 5mg of folic acid substitution per week potentially decreases gastrointestinal side effects by 80% without interfering with the efficacy of methotrexate. Besides renal dysfunction, tremor, hirsutism, hypertension and gum hyperplasia cyclosporine is known to have a number of gastrointestinal side effects that occur with less frequency such as diarrhoea (up to 8%) nausea and vomiting (up to 10%) and hepatotoxicity in 1-4%. Rare gastrointestinal adverse events are gastritis and peptic ulcers. Paying attention to these potential deleterious side effects is mandatory for physicians treating IBD patients.

Safe 6-thioguanine therapy of a TPMT deficient Crohn's disease patient by using therapeutic drug monitoring

The immunosuppressive thiopurines, azathioprine (AZA) and 6-mercaptopurine (6-MP), have proven efficacy in steroid-dependant or refractory inflammatory bowel disease (IBD). In case of TPMT deficiency serious myelosuppression may occur. 6-thioguanine (6-TG), has been suggested in case of AZA and 6-MP resistant or intolerant patients. Our case demonstrates that very low dose 6-TG under close clinical surveillance and frequent therapeutic drug monitoring, may be a rescue drug for IBD-patients with low or without functional TPMT activity.

Therapeutic strategies for the management of ulcerative colitis

Induction and maintenance of remission, mucosal healing, the avoidance of surgical intervention, and decreasing the likelihood of cancer developing are the primary therapeutic goals in ulcerative colitis (UC). For the traditional therapies, 5-aminosalicylic acid (including mesalamine), corticosteroids, and thiopurines (azathioprine and mercaptopurine), there are major changes evolving in terms of formulation, patterns of use, and appreciation of long-term benefits and toxicities. The calcineurin inhibitors cyclosporin and tacrolimus, and infliximab, have recently defined, well-established roles. Preliminary supportive evidence is emerging in relation to novel antiinflammatory molecules such as curcumin, manipulation of the bacterial flora, enhancement of the mucosal barrier, and direct epithelial restoration. For patients in whom the disease is resistant to standard simple therapies, strategies are required to integrate these developing and new therapies into clinical practice. This review aims to highlight the evidence supporting new patterns of use of existing therapies and new therapies, and to devise therapeutic pathways that incorporate these new treatments. We propose how treatment might be optimized to improve the outcome in patients with mild-to-moderately active UC, chronic active UC, resistant proctitis, and fulminant UC.

6-Thioguanine therapy in Crohn's disease--observational data in Swedish patients

BACKGROUND AND AIMS

Adverse events (AE) leading to discontinuation or dose-reduction of thiopurine therapy (TP) occur in 9-28% of patients with inflammatory bowel disease. 6-Thioguanine (6-TG) has been proposed as an alternative treatment in patients intolerant for azathioprine (AZA), but some concerns have been raised about drug safety.

METHODS

We evaluated in a prospective manner the tolerance and efficacy of 6-TG in 23 Crohn's disease (CD) patients (13 men, median age 41 (19-65) years) with prior intolerance (n=18) or resistance (n=5) to AZA and/or 6-mercaptopurine (6-MP). In addition, eight patients had tried mycophenolate mofetil. Seventeen patients (74%) had undergone intestinal resection, often several times.

RESULTS

Patients were treated with a median daily dose of 40 mg 6-TG (range 20-60) for 259 (15-2272) days. Seven of 13 patients (54%) with active disease went into remission after 8 (4-26) weeks. Sixteen patients (70%) experienced AE that lead to discontinuation (n=10) after 85 (15-451) days or dose reduction (n=6) after 78 (10-853) days. Ten of 18 patients (56%) with prior TP-intolerance discontinued 6-TG treatment due to AE compared to none of five patients with TP-resistance (p=0.046). Of 13 patients that tolerated 6-TG, eight discontinued the drug due to therapeutic failure (n=5) or safety concerns (n=3). Eight patients (35%) continued treatment beyond 12 months. There was no significant difference in maximum thioguanine nucleotide levels between patients with AE leading to discontinuation/dose reduction and patients without AE, 652 (99-2488) vs. 551 (392-1574) pmol/8 x 10(8) RBC; p=0.80.

CONCLUSIONS

In this cohort of CD patients with severe disease failing traditional thiopurine treatment, a small fraction (22%) had long-term benefit of 6-TG-treatment. 6-TG therapy seems to offer a limited therapeutic gain for patients intolerant to both AZA and 6-MP and other treatment options should be considered.

Further experience with the use of 6-thioguanine in patients with Crohn's disease

BACKGROUND

6-Thioguanine (6-TG) is efficacious in patients with Crohn's Disease (CD) failing conventional immunosuppression but there are reports of hepatotoxicity. We report our experience of the safety and efficacy of 6-TG in a series of patients with CD.

METHODS

A retrospective study of patients with CD who failed thiopurines +/- methotrexate between 2001 and 2006 was performed. Indications for 6-TG were; active disease, to allow infliximab withdrawal, steroid sparing, or fistula closure. Patients underwent regular review and those treated longer than 1 year were advised to have liver magnetic resonance imaging (MRI) and liver biopsy.

RESULTS

All 30 patients treated with 6-TG during the period were included. The median dose and duration of 6-TG was 40 mg daily and 21.5 months, respectively. Initial clinical response was achieved in 18/30 (60%). Eleven of 29 (38%) (1 unrelated death) remained in remission at a median 44 months follow-up. Seven of 30 (23%) discontinued 6-TG due to adverse effects; 7/30 (23%) patients developed abnormal liver function tests (LFTs) during treatment, mostly transient and mild. One patient developed a portal hypertensive syndrome resolving on cessation of 6-TG. Of 11 liver biopsies, none showed nodular regenerative hyperplasia (NRH). The median red blood cell 6-thioguanine nucleotide (6-TGN) level was 807 pmol/10(8).

CONCLUSIONS

6-TG has good clinical efficacy for third-line immunosuppression in CD but hepatotoxicity remains a concern. However, previous reports of NRH in 6-TG-treated inflammatory bowel disease patients have not been substantiated by this cohort.

Recent advances in the management of Crohn's disease

In the last 10 years many advances have been achieved in the treatment of patients with Crohn's disease, particularly in the field of biological agents. Infliximab, a tumour necrosis factor alpha antagonist, has been recently added to the therapeutic armamentarium for Crohn's disease and has greatly improved our treatment options. Infliximab has demonstrated efficacy in the induction and maintenance of remission in luminal and fistulizing Crohn's disease both in adults and children. However, the potential development of autoantibodies and the risk of serious adverse events limit the possibility of a wider use of infliximab. Searching for less immunogenicity and higher effectiveness in the last years a number of biological agents have been developed. Adalimumab, a fully human monoclonal antibody anti tumour necrosis factor alpha, has resulted effective and safe in patients with Crohn's disease, both naive and refractory to infliximab, presenting also the advantage of subcutaneous way of administration. Natalizumab also showed promising results in terms of efficacy but its safety is still under investigation. To date no particular advances have been recently appeared in the literature concerning conventional immunosuppressive drugs. Surgery remains a valid resort for refractory patients. Autologous stem cell transplantation represents a new hope as rescue treatment for patients with severe refractory Crohn's disease.

Absence of nodular regenerative hyperplasia after low-dose 6-thioguanine maintenance therapy in inflammatory bowel disease patients

BACKGROUND

The use of 6-thioguanine has been proposed as a rescue drug for inflammatory bowel disease patients. Initial data on short-term efficacy and toxicity of 6-thioguanine were promising; however, these have been challenged by reports concerning its potential hepatotoxic effect (nodular regenerative hyperplasia). We proposed that these histological liver abnormalities may well be dose- or level-dependent.

AIMS

We performed a prospective multi-centre study on the hepatotoxic potential of long-term and (as compared with prior studies) low-dose 6-thioguanine use.

PATIENTS

Inflammatory bowel disease patients using 6-thioguanine for at least 30 consecutive months and consenting to undergo a liver biopsy were enrolled.

METHODS

Liver biopsy specimens were scored by two pathologists, unaware of clinical data. Laboratory parameters, determined prior to initiation of 6-thioguanine therapy and prior to biopsy, were reviewed.

RESULTS

Twenty-eight biopsies were analysed. The majority of patients (89%) were azathioprine and/or 6-mercaptopurine intolerant inflammatory bowel disease patients. In 26 patients (93%) no signs of nodular regenerative hyperplasia were detected; in two additional patients nodular regenerative hyperplasia could not be excluded due to inconclusive pathological findings. The mean 6-thioguanine dosage, 6-thioguaninenucleotides level, duration of use and cumulative dosage were 19.5mg, 564 pmol/8 x 10(8) RBC, 38 months and 22491 mg, respectively.

CONCLUSIONS

We have demonstrated that low-dose 6-thioguanine maintenance therapy in inflammatory bowel disease patients is not likely to be associated with induction of nodular regenerative hyperplasia. The induction of nodular regenerative hyperplasia appears to be 6-thioguanine dose or 6-thioguaninenucleotides level dependent.

6-thioguanine associated nodular regenerative hyperplasia in patients with inflammatory bowel disease may induce portal hypertension

BACKGROUND

Recent studies suggest an association between 6-thioguanine (6-TG) therapy and hepatic nodular regenerative hyperplasia (NRH) in patients with inflammatory bowel disease (IBD). An influence of 6-TG on portal pressure remains to be determined. The aim of the study was to examine the functional relevance of long-term 6-TG treatment on hepatic hemodynamics in IBD patients and its association with NRH.

METHODS

Patients treated with 6-TG for IBD underwent measurement of the hepatic venous pressure gradient (HVPG) and liver biopsy. 6-TG therapy was stopped when NRH was diagnosed. If elevated, HVPG measurement was repeated after 1 yr.

RESULTS

Twenty-six patients (15 women, 11 men; median age 41 yr, range 23-76) treated with 6-TG for 38 months (median; range 12-45) were included. Among 24 patients with sufficient liver biopsy, 6 patients (25%) were diagnosed with NRH. In these 6 patients, the HVPG was higher (median HVPG 7 mmHg, range 3-14) than in the 18 patients without NRH (median 3 mmHg, range 2-5; P < 0.001). In the patients with NRH, two had clinically significant portal hypertension (CSPH) (13 and 14 mmHg, respectively); in one patient the HVPG was slightly elevated (7 mmHg). No overt clinical signs of portal hypertension were observed. One year after stopping 6-TG therapy, HVPG decreased in all 3 patients with initially elevated HVPG levels.

CONCLUSIONS

We demonstrate that IBD patients under long-term 6-TG therapy are at a substantial risk for developing NRH. NRH results in elevation of HVPG and may cause CSPH. Discontinuation of 6-TG therapy extenuates portal hypertension and may thus reduce the risk of complications.