Therapeutic drug monitoring of thiopurines: Effect of reduced 6-thioguanine nucleotide target levels in IBD patients

Aim: The effect of the Dutch nationwide adjustment of reduced 6-TGN target values (from 600-1200 pmol/8x108 RBC to 320-630 pmol/8x108 RBC) on toxicity and clinical outcome of thiopurine treatment in patients with inflammatory bowel disease (IBD) has not yet been established. Therefore the authors determined the incidence of toxicity-induced discontinuations and efficacy at both target concentrations. Methods: This retrospective study was performed in IBD patients treated with azathioprine or mercaptopurine. Two groups were defined: the former target (FT) group with target concentrations of 600-1200 pmol/8x10^8 RBC and the adjusted target (AT) group with target concentrations of 320-630 pmol/8x10^8 RBC. Patients were followed for maximum 52 weeks or until discontinuation of thiopurine therapy. Data were collected from the local hospital electronic health software of Rijnstate Hospital. Results: 151 patients were included, 76 in the FT group and 75 in the AT group. At week 52, 100 out of 150 patients (66%) of the total population discontinued thiopurine therapy. Forty-eight of this discontinuations were due toxicity (48%). The estimated cumulative incidence of toxicity was higher in the FT group compared to the AT group (47% and 35% respectively, p=0.25). No loss of efficacy was seen in the AT group. Conclusion: Reduction of the target range may lead to less toxicity induced discontinuations. In addition, this study did not find any indication that the reduction of the target range diminished efficacy.

Meta-Analysis of NUDT15 Genetic Polymorphism on Thiopurine-Induced Myelosuppression in Asian Populations

Backgound: The high incidence of thiopurine-induced myelosuppression in Asians is known to be attributable to genetic variation in thiopurine metabolism. A quantitative synthesis to summarize the genetic association with thiopurine-induced myelosuppression in Asians was therefore conducted.Methods: A Literature search was performed from January 2016 to May 2021 in the following databases: PubMed, Web of Science, and Embase and addition search included the studies from Zhang et al. Two reviewers independently extracted the following data: the author’s name, year of publication, ethnicity, drugs, diseases, genetic polymorphisms, onset, type of myelosuppression and results of Hardy-Weinberg equilibrium. The Newcastle-Ottawa Scale was used to assess the quality of the studies. The pooled odds ratios (OR) and 95% confidence intervals (CI) were calculated to evaluate the associations of NUDT15 and the risk of thiopurine-induced myelosuppression stratified by onset and type of myelosuppressive. Subgroup analysis by NUDT15 genetic polymorphisms was performed.Results: A total of 30 studies was included in this meta-analysis. The overall OR for the relationship between NUDT15 genetic polymorphisms and thiopurine-induced early onset of leukopenia and neutropenia in Asian populations were 11.43 (95% CI 7.11–18.35) and 16.35 (95% CI 10.20–26.22). Among NUDT15 polymorphisms, NUDT15*3 showed a significantly increased risk of early leukopenia (OR 15.31; 95% CI 9.65–24.27) and early neutropenia (OR 15.85; 95% CI 8.80–28.53). A significantly higher thiopurine-induced early neutropenic risk was also found for NUDT15*2 (OR 37.51; 95% CI 1.99–708.69). Whereas, NUDT15*5 and NUDT15*6 variants showed a lower risk of leukopenia.Conclusion: This study suggests that NUDT15*3 and NUDT15*2 are important genetic markers of thiopurine-induced early onset of myelotoxicity in Asians, therefore, early detection of these variants before initiating thiopurine therapy is necessary.

Optimizing Thiopurine Therapy with a Xanthine Oxidase Inhibitor in Patients with Systemic Autoimmune Diseases: A Single-Centre Experience

Background: Thiopurines are a mainstay of therapy for autoimmune diseases. However, up to 20% to 30% of patients experience overproduction of the methylated metabolites, known as 6-MMP, to the detriment of the active metabolite, 6-thioguanine nucleotide (6-TGN). These patients, commonly referred to as “shunters”, are predisposed to thiopurine resistance and hepatotoxicity. In patients with inflammatory bowel diseases, the combination of thiopurine with a xanthine oxidase inhibitor (XOI) is used to reverse this skewed metabolism and to prevent treatment failure or hepatotoxicity. Data on the use of this strategy for patients with other diseases are limited. Objectives: To investigate and describe the use of thiopurine–XOI combination therapy in shunters with systemic autoimmune diseases. Methods: Shunters treated in the study hospital between January 1, 2005, and December 31, 2015, were identified using the hospital’s laboratory database, and clinical data were collected retrospectively. For each patient with optimization of thiopurine therapy, clinical and laboratory data were assessed over a 6-month period. Results: Thirty-four patients were identified as shunters; for 14 of these patients, thiopurine therapy was optimized with an XOI. In these 14 patients, the median dose of azathioprine was reduced from 1.95 to 0.78 mg/kg with combination therapy. In addition, median 6-TGN level increased from 135 to 385 pmol/8 × 108 erythrocytes (p = 0.001); furthermore, 6-TGN levels rose to above 235 pmol/8 ×108 erythrocytes for 11 of the 14 patients. Conversely, the median 6-MMP level decreased from 6267 to 271 pmol/8 × 108 erythrocytes (p = 0.001). Except for a 12% increase in mean corpuscular volume, no clinically significant changes in blood count were recorded. Notable infections were reported in 3 patients, and 1 patient had to discontinue treatment because of cytopenia. After 6 months, median prednisone daily dose was reduced by 74%, from 16.7 mg to 4.4 mg (p = 0.005), and 4 patients had been weaned off corticosteroids. Of the 14 patients, 11 (79%) were in full remission, and 2 (14%) were in partial remission. Conclusion: Optimizing thiopurine therapy with an XOI may be a safe and effective strategy for patients with systemic autoimmune diseases. RÉSUMÉ Contexte : Les thiopurines sont des piliers de l’intervention thérapeutique contre les maladies auto-immunes. Cependant, 20 % à 30 % des patients surproduisent des métabolites méthylés (connus sous le nom 6-MMP), au détriment du métabolite actif, le nucléotide 6-thioguanine (6-TGN). Ces patients, communément appelés « courts-circuiteurs » sont prédisposés à résister à la thiopurine et à l’hépatotoxicité. Pour les patients ayant des maladies inflammatoires intestinales, on utilise la combinaison de thiopurine avec une xanthine oxydase inhibitrice (XOI) afin d’inverser ce métabolisme anormal et prévenir l’échec du traitement ou l’hépatotoxicité. Les données concernant l’adoption de cette stratégie pour les patients atteints d’autres maladies sont limitées. Objectifs : Étudier et décrire l’utilisation de la thérapie combinée de thiopurine et de XOI pour les « courts-circuiteurs » ayant des maladies auto-immunes systémiques. Méthodes : Les « courts-circuiteurs » traités dans l’hôpital où s’est déroulée l’étude entre le 1er janvier 2005 et le 31 décembre 2015 ont été identifiés à l’aide de la base de données du laboratoire de l’hôpital et les données cliniques ont été recueillies de manière rétrospective. L’évaluation des données cliniques et de laboratoire de chaque patient bénéficiant d’une optimisation de la thérapie par la thiopurine a porté sur six mois de traitement. Résultats : Trente-quatre patients ont été identifiés comme « courts-circuiteurs » et 14 d’entre eux ont bénéficié d’une optimisation de la thérapie par la thiopurine à l’aide d’une XOI. Ces derniers ont subi une thérapie de combinaison qui a fait passer la dose moyenne d’azathioprine de 1,95 à 0,78 mg/kg. De plus, le niveau moyen de 6-TGN est passé de 135 à 385 pmol/8 × 108 érythrocytes (p = 0,001). En outre, 11 des 14 patients ont vu le niveau de 6-TGN passer à plus de 235 pmol/8 ×108 érythrocytes. Inversement, le niveau moyen de 6-MMP est passé de 6267 à 271 pmol/8 × 108 érythrocytes (p = 0,001). À l’exception d’une augmentation de 12 % du volume corpusculaire moyen, aucun changement clinique important dans la numération globulaire n’a été noté. Trois patients ont développé des infections notables et l’un d’eux a dû arrêter le traitement à cause d’une cytopénie. Après six mois, la dose moyenne quotidienne de prednisone a été réduite de 74 %, pour passer de 16,7 mg à 4,4 mg (p = 0,005), et quatre patients ont été sevrés des corticostéroïdes. Sur les 14 patients, 11 (79 %) ont été déclarés en rémission totale et 2 (14 %) en rémission partielle. Conclusion : L’optimisation de la thérapie par la thiopurine associée à une XOI pourrait être sécuritaire et constituer une stratégie efficace pour les patients ayant une maladie auto-immune systémique.

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.

P512 Safety of reduced clinical monitoring in patients with stable Inflammatory Bowel Disease on maintenance thiopurine therapy

Background Thiopurine-treated inflammatory bowel disease (IBD) patients are monitored every 3 to 4 months with outpatient visits and laboratory assessments to evaluate disease activity and safety of therapy. However, the risk of thiopurine-related adverse events decreases after the initiation phase. The aim of this study was to assess the safety of reduced clinical monitoring in steroid-free quiescent IBD patients on stable maintenance thiopurine monotherapy. Methods This single-centre prospective cohort study evaluated a reduced monitoring strategy that involved 6-monthly laboratory assessment combined with alternating outpatient and phone appointments, during 104 weeks. We enrolled IBD patients who were in steroid-free remission > 6 months on thiopurine monotherapy including azathioprine, 6-mercaptopurine or tioguanine. The primary outcome was thiopurine-related adverse events (AE) requiring change or discontinuation of thiopurine therapy after 104 weeks of follow-up. Secondary outcomes were assessed at week 52 and included other thiopurine-related AEs and laboratory abnormalities. Results We included 85 patients (42 years median age, 61.2% Crohn’s disease, 62% female) with a median disease duration of 12.5 years. At baseline, 47 patients were treated with azathioprine (55.3%), 25 with 6-mercaptopurine (29.4%) and 13 with tioguanine (15.3%) for a median duration of 6.7 years. During 104 weeks of follow-up, thiopurine therapy was ceased in two patients because of multiple infections (n=1) and gastrointestinal complaints (n=1). Other reasons for thiopurine cessation (n=37) were stable remission (n=26), patient preferences (n=9) and high 6-TGN levels (n=2). In total, 20 patients underwent thiopurine dose adjustments due to high metabolite levels (n=9), remission (n=3), disease flare (n=3), patient preferences (n=3), and low metabolite levels (n=2). At 52 weeks, 27 laboratory abnormalities were observed, yet none required therapy adjustments. In 13 patients (15.3%) myelotoxicity was detected, including mild leukopenia (n=11), mild and moderate thrombopenia (n=2). In 16.5%, hepatoxicity was observed (n=14) including mild (n=9) and moderate (n=1) elevated aspartate aminotransferase and mild elevated alkaline phosphatase (n=4). Conclusion A reduced monitoring strategy appeared relatively safe in a strictly selected cohort of stable thiopurine-treated IBD patients. Overall, two patients had to cease thiopurine therapy due to thiopurine-related AEs independent of monitoring frequency. No laboratory abnormalities required therapy adjustments and 57.1% of patients continued therapy throughout 104 weeks of follow-up. This strategy may contribute to safe reduction of time and health care costs for both IBD patients and physicians in daily IBD practice.

Real-World Long-Term Remission Maintenance for 10 Years With Thiopurines in Ulcerative Colitis

Background To evaluate the therapeutic outcomes and long-term prognosis of patients receiving remission maintenance therapy using thiopurines for ulcerative colitis (UC). Methods Of 193 biologic-naive patients with UC who began thiopurine therapy at our hospital between 2000 and 2019, 161 patients were included after the exclusion of 32 patients who were intolerant to thiopurines and discontinued the drugs within 3 months. Short- and long-term clinical outcomes were retrospectively analyzed. Subsequently, the patients were divided into 2 groups (exacerbation and nonexacerbation groups) and clinical outcomes were analyzed and compared. Multivariate analysis was performed to identify risk factors for UC exacerbation. Finally, adverse events observed in 193 patients were examined. Results Clinical remission rates at 2 months, 6 months, and 1 year after the start of thiopurine therapy were 50.0%, 58.0%, and 63.9%, respectively. At 1, 2, 5, and 10 years, the cumulative event-free rates were 77.6%, 60.8%, 48.5%, and 42.2%, respectively; the cumulative UC exacerbation rates were 17.0%, 32.5%, 42.2%, and 43.7%, respectively; and the cumulative colectomy rates were 0.6%, 1.3%, 8.5%, and 10.7%, respectively. Prior use of steroids (dose ≥40 mg/d) was a significant risk factor for UC exacerbation during remission maintenance therapy with thiopurines (hazard ratio, 2.26; 95% confidence interval, 1.18–4.34; P = 0.014). Adverse reactions occurred in 42 patients (21.8%; 46 events). Concurrent diseases were observed in 18 patients (9.3%). Conclusions Thiopurines were effective for long-term maintenance of remission in steroid-dependent/refractory UC. Their effect weakened in only a few patients continuously treated with them for 4 years or longer.