6-Thioguanine Nucleotide Levels Are Associated With Mucosal Healing in Patients With Crohn's Disease

A Review of Therapeutic Drug Monitoring in Patients with Inflammatory Bowel Disease Receiving Combination Therapy

Background: Inflammatory Bowel Disease (IBD) impacts millions worldwide, presenting a major challenge to healthcare providers and patients. The advent of biologic therapies has enhanced the prognosis, but many patients exhibit primary or secondary non-response, underscoring the need for rigorous monitoring and therapy optimization to improve outcomes. Objective: This narrative review seeks to understand the role of therapeutic drug monitoring (TDM) in optimizing treatment for IBD patients, especially for those on combination therapies of biologics and immunomodulators. Methods: A comprehensive synthesis of the current literature was undertaken, focusing on the application, benefits, limitations, and future directions of TDM in patients receiving a combination of biologic therapies and immunomodulators. Results: While biological therapies have improved outcomes, rigorous monitoring and therapy optimization are needed. TDM has emerged as a pivotal strategy, enhancing outcomes cost-effectively while reducing adverse events. While most data pertain to monotherapies, TDM's applicability also extends to combination therapy. Conclusion: TDM plays a crucial role in the treatment optimization of IBD patients on combination therapies. Further research is needed to fully understand its potential and limitations in the broader context of IBD management.

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.

Optimizing Therapies Using Therapeutic Drug Monitoring: Current Strategies and Future Perspectives

Therapeutic drug monitoring (TDM) has emerged as a strategy for treatment optimization in inflammatory bowel diseases to maximize benefit and to reach more stringent, objective end points. Optimal drug concentrations in inflammatory bowel disease vary according to treatment target, disease phenotype, inflammatory burden, and timing of sampling during the treatment cycle. This review provides an update on TDM with biologic and oral small molecules, evaluates the role of reactive vs proactive TDM, and identifies the gaps in current evidence. In the future, adaptations to how we use TDM may contribute further to the goal of personalized treatment in patients with IBD.

Low-Dose Azathioprine in Combination with Allopurinol: The Past, Present and Future of This Useful Duo

The inflammatory bowel diseases (IBD) are complex immune-mediated inflammatory diseases that are associated with significant morbidity around the world. As our understanding of IBD, and other immune-mediated inflammatory diseases, advances the number of therapeutic targets has increased which has rapidly driven the development and introduction of new therapies. While these new therapies have shown promise they come with the significant drawback of high costs. For many IBD patients around the world the cost of newer therapies is prohibitive which means treating clinicians often need to turn to optimising simpler, older, and inexpensive medications. The concept of optimising well established cheaper medications is not unique to the management of IBD as health systems all over the world look to reduce costs while simultaneously improving patient outcomes. Despite thiopurines being used in the management IBD for over 60 years, many clinicians are still hesitant to use them due to perceptions around limited efficacy and poor tolerance. One method identified to potentially increase utilisation of thiopurines involves the coadministration of allopurinol. In this review we will explore the history, pharmacology, recent studies and give recommendations for the utilisation of the usual duo of azathioprine combined with allopurinol.

Evolving Role of Thiopurines in Inflammatory Bowel Disease in the Era of Biologics and New Small Molecules

In recent years, with the increasing availability of biologic therapies and due to safety concerns, the role of thiopurines in the management of inflammatory bowel disease has been questioned. While acknowledging that the benefit/risk ratio of biologic therapies is very high, they are expensive and are not required by a majority of patients. Therefore, thiopurines do retain an important role as steroid-sparing and maintenance agents when used as monotherapy, and in combination therapy with biologics due to their clinical and pharmacokinetic optimization of anti-tumor necrosis factor agents in particular. Safety concerns with thiopurines are real but also relatively rare, and with careful pre-treatment screening and ongoing monitoring thiopurine benefits outweigh risks in the majority of appropriately selected patients. Measurement of newer pharmacogenomic markers such as nudix hydrolase 15 (NUDT15), when combined with knowledge of existing known mutations (e.g., thiopurine S-methyltransferase-TPMT), will hopefully minimize the risk of potentially life-threatening leukopenia by allowing for pre-treatment dosing stratification. Further optimization of thiopurine dosing via measurement of thiopurine metabolites should be performed routinely and is superior to weight-based dosing. The association of thiopurines with malignancies including lymphoproliferative disorders needs to be recognized in all patients and individualized in each patient. The decrease in lymphoma risk after thiopurine cessation provides an incentive for thiopurine de-escalation in appropriate patients after a period of prolonged deep remission. This review will summarize the current role of thiopurines in inflammatory bowel disease management and provide recommendations for commencing and monitoring therapy, and when to consider de-escalation.

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.

Normal Ranges of Thiopurine Methyltransferase Activity Do Not Affect Thioguanine Nucleotide Concentrations With Azathioprine Therapy in Inflammatory Bowel Disease

Background

Thiopurine methyltransferase (TPMT) activity influences azathioprine conversion into active metabolite 6-thioguanine nucleotide (6-TGN). Low TPMT activity correlates with high 6-TGN and risk for myelosuppression. Conversely, normal-to-high TPMT activity may be associated with low 6-TGN and drug resistance, the so-called hypermetabolizers. Our aim was to identify the effect of normal-to-high TPMT activity on 6-TGN concentrations in an inflammatory bowel disease population.

Methods

A retrospective chart review of patients aged ≥18 with inflammatory bowel disease, on azathioprine, with documented TPMT activity and 6-TGN concentration was performed. Correlations were evaluated via the Spearman rho correlation coefficient. Linear regression was used to determine the effect of TPMT activity on 6-TGN accounting for confounders. Relationships between TPMT activity, drug dose, and 6-TGN levels were defined via average causal mediation effects.

Results

One hundred patients were included. No correlation was observed between TPMT activity, azathioprine dosing, and metabolite concentrations. Overall, 39% of the cohort had a therapeutic 6-TGN level of >230 pmol/8 × 10⁸ red blood cells (RBCs). No patient under 1 mg/kg achieved a therapeutic 6-TGN level, whereas 42% of patients taking 2.5 mg/kg did. The median 6-TGN concentration was higher for those in remission (254 pmol/8 × 10⁸ RBCs, interquartile range: 174, 309) versus those not in remission (177 pmol/8 × 10⁸ RBCs, interquartile range: 94.3, 287.8), though not significantly (P = 0.08). Smoking was the only clinical factor associated with 6-TGN level. On multivariate linear regression, only age, azathioprine dose, and obese body mass index were predictive of metabolite concentration.

Conclusions

Variations within the normal range of TPMT activity do not affect 6-TGN concentration.

Inflammatory Bowel Disease - Non-biological treatment

Nowadays, non-biological treatments remain valuable approaches among the therapeutic armamentarium of inflammatory bowel disease (IBD). Mesalamine is the core treatment of mild‑to‑moderate ulcerative colitis (UC) and corticosteroids are crucial for the induction of remission of moderate‑to‑severe flares in both UC and Crohn's disease (CD). Even approaches as cyclosporine, tacrolimus, azathioprine, methotrexate, and surgery still have a nuclear position as strategies to induce and/or maintain remission in IBD. Due to their particularities and to the accumulated evidence, each of these strategies conquered peculiar roles in the overall IBD strategy, all of them contributing to better outcomes. This review emphasizes the particular roles that non-biological treatments gained over time: recent mesalamine formulations to increase adhesion rates, higher doses of 5-ASA for high-risk patients, MMX technology to improve drug release and attain higher bowel concentrations, cyclosporine as a bridge to vedolizumab, tacrolimus as a potential alternative to thiopurines or infliximab, azathioprine in combination therapy with infliximab and dubious in monotherapy, and surgery as a mean to a "better end".

Role of Thiopurines in Pediatric Inflammatory Bowel Diseases: A Real-Life Prospective Cohort Study

OBJECTIVES

Use of thiopurines for inflammatory bowel diseases (IBDs) is declining in some parts of the world. We aimed to explore outcomes of thiopurines and predictors of response in a real-world prospective cohort of children with dose optimization.

METHODS

Children with IBD treated with thiopurines without biologics were enrolled. Dosing was guided by thiopurine S-methyltransferase-activity at baseline and by clinical response and toxicity at 4 months; 1 year into the study, therapeutic drug monitoring at 4 months was also considered in the decision making. The primary outcome was steroid-free remission without treatment escalation by 12 months (SFR), using the intention-to-treat approach.

RESULTS

A total of 129 children were included (74% Crohn disease [CD] and 26% ulcerative colitis [UC]). SFR was achieved in 37 (39%) CD and 13 (39%) UC patients, and SFR with normal erythrocyte sedimentation rate/C-reactive protein in 20 (21%) and 9 (27%), respectively. At 4 months, mean corpuscular volume/white blood cell ratio and Δ absolute neutrophil count weakly correlated with 6-thioguanine (r = 0.33, P = 0.02 and r = 0.32, P = 0.02, respectively). In CD, SFR was associated with 4-month median weighted Pediatric Crohn Disease Activity Index (2.5 [IQR 0-7.5] in responders vs 5 in nonresponders [0-12.5], P = 0.048) and Δabsolute neutrophil count (1.7 [IQR 0.7-4.1] vs 0.05 [-2.3-0.9]; P = 0.03). Mild drug-related adverse events were recorded in 30 children (22%), 3 required stopping the drug.

CONCLUSIONS

In this real-life prospective cohort using dose optimization, thiopurines were safe and effective in 21% of CD and 27% of UC patients, including normalization of C-reactive protein and erythrocyte sedimentation rate. Thiopurines remain a viable option in the treatment algorithm of mild-moderate pediatric IBD, especially in girls whose risk for lymphoma is lower.

Can We Predict the Toxicity and Response to Thiopurines in Inflammatory Bowel Diseases?

Thiopurines are a cheap, effective treatment option in the management of inflammatory bowel disease (IBD). However, with the growing choice of targeted therapies available, as well as the well-documented toxicities of thiopurines, the role of thiopurines has been questioned. Nevertheless, given their inexpense in an era of spiraling healthcare costs, thiopurines remain an attractive option in the right patients. In the age of personalized medicine, being able to predict patients who will respond as well as those that will develop toxicity to a treatment is vital to tailoring therapy. This review will summarize the available literature with respect to predictors of response and toxicity to thiopurines in order to guide management in IBD. Specifically, toxicities addressed will include myelotoxicity, hepatotoxicity, pancreatitis, alopecia, gastrointestinal and flu-like symptoms, and complications associated with Epstein-Barr virus. While more work needs to be done to further our ability to predict both response to and side effects from therapies, pharmacogenomic research shows significant promise in its ability to personalize our use of thiopurines.

Key insights from therapeutic drug monitoring in Crohn's disease patients

INTRODUCTION

The incidence and prevalence of Crohn's disease are increasing causing a significant disease burden. Therapeutic drug monitoring (TDM) is advocated as a promising tool for personalized or individual-tailored therapy strategies and has been welcomed as a new means to improve current therapy strategies. Nevertheless, pharmacokinetic-based TDM has limitations, and straightforward target concentrations for most therapies are lacking. Areas covered: In the following concise review of literature, key insights of TDM in thiopurine, methotrexate, anti-TNF, vedolizumab and ustekinumab therapy for Crohn's disease are being described. Expert opinion: Therapeutic drug monitoring may, up till now, be helpful to adjust thiopurine and infliximab therapy, primarily in a reactive setting, in case of inefficacy and of occurrence of adverse event. With this restricted application, the goal of individualized therapy based on TDM has not yet been achieved.