Thiopurines Dosed to a Therapeutic 6-Thioguanine Level in Combination with Adalimumab Are More Effective Than Subtherapeutic Thiopurine-based Combination Therapy or Adalimumab Monotherapy During Induction and Maintenance in Patients with Long-standing Crohn's Disease

Saudi consensus guidance for the diagnosis and management of inflammatory bowel disease in children and adolescents

ABSTRACT

The management of inflammatory bowel disease (IBD) in children and adolescents is challenging. Clear evidence-based guidelines are required for this population. This article provides recommendations for managing IBD in Saudi children and adolescents aged 6-19 years, developed by the Saudi Ministry of Health in collaboration with the Saudi Society of Clinical Pharmacy and the Saudi Gastroenterology Association. All 57 guideline statements are based on the most up-to-date information for the diagnosis and management of pediatric IBD.

Mechanisms and management of loss of response to anti-TNF therapy for patients with Crohn's disease: 3-year data from the prospective, multicentre PANTS cohort study

BACKGROUND

We sought to report the effectiveness of infliximab and adalimumab over the first 3 years of treatment and to define the factors that predict anti-TNF treatment failure and the strategies that prevent or mitigate loss of response.

METHODS

Personalised Anti-TNF therapy in Crohn's disease (PANTS) is a UK-wide, multicentre, prospective observational cohort study reporting the rates of effectiveness of infliximab and adalimumab in anti-TNF-naive patients with active luminal Crohn's disease aged 6 years and older. At the end of the first year, sites were invited to enrol participants still receiving study drug into the 2-year PANTS-extension study. We estimated rates of remission across the whole cohort at the end of years 1, 2, and 3 of the study using a modified survival technique with permutation testing. Multivariable regression and survival analyses were used to identify factors associated with loss of response in patients who had initially responded to anti-TNF therapy and with immunogenicity. Loss of response was defined in patients who initially responded to anti-TNF therapy at the end of induction and who subsequently developed symptomatic activity that warranted an escalation of steroid, immunomodulatory, or anti-TNF therapy, resectional surgery, or exit from study due to treatment failure. This study was registered with ClinicalTrials.gov, NCT03088449, and is now complete.

FINDINGS

Between March 19, 2014, and Sept 21, 2017, 389 (41%) of 955 patients treated with infliximab and 209 (32%) of 655 treated with adalimumab in the PANTS study entered the PANTS-extension study (median age 32·5 years [IQR 22·1-46·8], 307 [51%] of 598 were female, and 291 [49%] were male). The estimated proportion of patients in remission at the end of years 1, 2, and 3 were, for infliximab 40·2% (95% CI 36·7-43·7), 34·4% (29·9-39·0), and 34·7% (29·8-39·5), and for adalimumab 35·9% (95% CI 31·2-40·5), 32·9% (26·8-39·2), and 28·9% (21·9-36·3), respectively. Optimal drug concentrations at week 14 to predict remission at any later timepoints were 6·1-10·0 mg/L for infliximab and 10·1-12·0 mg/L for adalimumab. After excluding patients who had primary non-response, the estimated proportions of patients who had loss of response by years 1, 2, and 3 were, for infliximab 34·4% (95% CI 30·4-38·2), 54·5% (49·4-59·0), and 60·0% (54·1-65·2), and for adalimumab 32·1% (26·7-37·1), 47·2% (40·2-53·4), and 68·4% (50·9-79·7), respectively. In multivariable analysis, loss of response at year 2 and 3 for patients treated with infliximab and adalimumab was predicted by low anti-TNF drug concentrations at week 14 (infliximab: hazard ratio [HR] for each ten-fold increase in drug concentration 0·45 [95% CI 0·30-0·67], adalimumab: 0·39 [0·22-0·70]). For patients treated with infliximab, loss of response was also associated with female sex (vs male sex; HR 1·47 [95% CI 1·11-1·95]), obesity (vs not obese 1·62 [1·08-2·42]), baseline white cell count (1·06 [1·02-1·11) per 1 × 109 increase in cells per L), and thiopurine dose quartile. Among patients treated with adalimumab, carriage of the HLA-DQA1*05 risk variant was associated with loss of response (HR 1·95 [95% CI 1·17-3·25]). By the end of year 3, the estimated proportion of patients who developed anti-drug antibodies associated with undetectable drug concentrations was 44·0% (95% CI 38·1-49·4) among patients treated with infliximab and 20·3% (13·8-26·2) among those treated with adalimumab. The development of anti-drug antibodies associated with undetectable drug concentrations was significantly associated with treatment without concomitant immunomodulator use for both groups (HR for immunomodulator use: infliximab 0·40 [95% CI 0·31-0·52], adalimumab 0·42 [95% CI 0·24-0·75]), and with carriage of HLA-DQA1*05 risk variant for infliximab (HR for carriage of risk variant: infliximab 1·46 [1·13-1·88]) but not for adalimumab (HR 1·60 [0·92-2·77]). Concomitant use of an immunomodulator before or on the day of starting infliximab was associated with increased time without the development of anti-drug antibodies associated with undetectable drug concentrations compared with use of infliximab alone (HR 2·87 [95% CI 2·20-3·74]) or introduction of an immunomodulator after anti-TNF initiation (1·70 [1·11-2·59]). In years 2 and 3, 16 (4%) of 389 patients treated with infliximab and 11 (5%) of 209 treated with adalimumab had adverse events leading to treatment withdrawal. Nine (2%) patients treated with infliximab and two (1%) of those treated with adalimumab had serious infections in years 2 and 3.

INTERPRETATION

Only around a third of patients with active luminal Crohn's disease treated with an anti-TNF drug were in remission at the end of 3 years of treatment. Low drug concentrations at the end of the induction period predict loss of response by year 3 of treatment, suggesting higher drug concentrations during the first year of treatment, particularly during induction, might lead to better long-term outcomes. Anti-drug antibodies associated with undetectable drug concentrations of infliximab, but not adalimumab, can be predicted by carriage of HLA-DQA1*05 and mitigated by concomitant immunomodulator use for both drugs.

FUNDING

Guts UK, Crohn's and Colitis UK, Cure Crohn's Colitis, AbbVie, Merck Sharp and Dohme, Napp Pharmaceuticals, Pfizer, and Celltrion Healthcare.

Key factors associated with 6-thioguanine and 6-methylmercaptopurine nucleotide concentrations in children treated by thiopurine for acute leukaemia and inflammatory bowel disease

AIMS

Azathioprine (AZA) and 6-mercaptopurine are prescribed in acute lymphoblastic leukaemia (ALL) and inflammatory bowel diseases (IBD). Metabolism to active 6-thioguanine (6TGN) and 6-methylmercaptopurine nucleotides (6MMPN) is variable but therapeutic drug monitoring (TDM) remains debatable. This study reports on factors impacting on red blood cell (RBC) metabolites concentrations in children to facilitate TDM interpretation.

METHODS

The first paediatric TDM samples received during year 2021 were analysed, whatever indication and thiopurine drug. Target concentration ranges were 200-500, <6000 pmol/8 × 108 RBC for 6TGN and 6MMPN.

RESULTS

Children (n = 492) had IBD (64.8%), ALL (22.6%) or another autoimmune disease (12.6%): mean ages at TDM were 7.5 in ALL and 13.7 years in IBD (P < .0001). ALL received 6-mercaptopurine (mean dose 1.7 mg/kg/d with methotrexate), IBD received AZA (1.9 mg/kg/d with anti-inflammatory drugs and/or monoclonal antibodies). Median 6TGN and 6MMPN concentrations were 213.7 [interquartile range: 142.5; 309.6] and 1144.6 [419.4; 3574.3] pmol/8 × 108 RBC, 38.8% of patients were in the recommended therapeutic range for both compounds. Aminotransferases and blood tests were abnormal in 57/260 patients: 8.1% patients had high alanine aminotransaminase, 3.4% of patients had abnormal blood count. Factors associated with increased 6TGN were age at TDM and thiopurine methyltransferase genotype in ALL and AZA dose in IBD. The impact of associated treatment in IBD patients was also significant.

CONCLUSION

TDM allowed identification of children who do not reach target levels or remain over treated. Including TDM in follow-up may help physicians to adjust dosage with the aim of reducing adverse effects and improve treatment outcome.

Dose Escalation Patterns of Advanced Therapies in Crohn's Disease and Ulcerative Colitis: A Systematic Literature Review

INTRODUCTION

Dose escalation is one of the treatment approaches studied and suggested in advanced therapies for Crohn's disease (CD) and ulcerative colitis (UC). This study aimed to identify and characterize the dosing escalation patterns of advanced therapies in CD and UC.

METHODS

Two systematic literature reviews (SLRs) were conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. MEDLINE®, Embase®, and Cochrane Library were searched for articles published between January 2011 and October 2021 and limited to non-interventional studies in English language. Congress and bibliographic searches were also conducted. Articles were screened by two independent researchers. Dose escalation patterns were described and summarized considering the regional regulatory label recommendation (in North America [NA] or outside of North America [ONA]).

RESULTS

Among 3190 CD and 2116 UC articles identified in the Ovid searches, 100 CD and 54 UC studies were included in the SLR, with more studies conducted ONA. Most studies reported an initial maintenance dose pattern aligned with the lower starting dose per local regulatory label; however, several ONA studies (n = 13 out of 14) reported ustekinumab every 8 weeks as starting maintenance pattern in CD. In ONA studies, the median within-guideline escalation rates in CD and UC were 43% in ustekinumab (CD only), 33% and 32% for vedolizumab; 29% and 39% for adalimumab; and 14% and 10% for infliximab. Evidence regarding dose escalation patterns for tofacitinib, certolizumab pegol, and golimumab was limited. Some dose escalation patterns outside of label recommendations were observed including ustekinumab every 8 weeks to every 4 weeks and vedolizumab every 8 weeks to every 6 weeks.

CONCLUSION

Dose escalation strategies are widely documented in the literature. The reported dose escalation patterns and escalation rates vary by region and by CD and UC. Most escalation patterns reported were aligned with regulatory recommendations while some reported more diverse or aggressive dose escalation.

PROSPERO REGISTRATION

CRD42021289251.

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.

TNF-Alpha Blockers in Inflammatory Bowel Diseases: Practical Recommendations and a User's Guide: An Update

BACKGROUND

Anti-tumour necrosis factor-alpha (anti-TNF) antagonists have been the mainstay in the treatment of inflammatory bowel diseases (IBDs) for over 20 years.

SUMMARY

This review article aimed to provide an update on recent advances in TNF antagonist therapy for IBDs. Key Messages: Their position in the treatment algorithm has evolved to "rapid step-up therapy" or "top-down therapy" according to disease severity and patients' characteristics. Limitations of anti-TNF antagonists include loss of response in up to 30-50% of patients with or without the development of antibodies. Therapeutic drug monitoring should provide a tailored, personalized approach to this scenario. Recently, biosimilar agents have been approved for IBDs and are considered equivalent in efficacy to the originator.

Combination therapy in inflammatory bowel disease - from traditional immunosuppressors towards the new paradigm of dual targeted therapy

BACKGROUND

Combining immunosuppressors has been proposed as a strategy to enhance treatment efficacy in Inflammatory Bowel Disease (IBD).

AIM

To summarize current evidence on combinations of targeted therapies with traditional immunosuppressors or with other targeted therapies.

METHODS

A literature search on PubMed and Medline databases was performed to identify relevant articles.

RESULTS

Current evidence supports that the combination of infliximab and thiopurines is more effective than monotherapy with both agents in inducing remission in Crohn's Disease and Ulcerative colitis. Data on other combinations of other biologics and traditional immunosuppressors is lacking or show conflicting results. Vedolizumab seems a potentially effective maintenance regimen after calcineurin inhibitors-based rescue therapy in acute severe ulcerative colitis, as an alternative to thiopurines. Dual Targeted Therapy, which is the combination of 2 targeted therapies, might be a reasonable choice in patients with concomitant IBD and extraintestinal manifestations, or in patients with medical-refractory IBD who lack valid alternatives. Combinations with thiopurines are associated with an increased risk of infections and lymphoma. Data on other combinations is scarcer, but no specific safety issue has emerged so far.

CONCLUSIONS

Combination therapies seem to be effective in selected patients, with an overall acceptable safety profile.

Thiopurines and their optimization during infliximab induction and maintenance: A retrospective study in Crohn's disease

BACKGROUND AND AIM

Combining therapy with a thiopurine is favored when commencing infliximab in Crohn's disease; however, the optimal 6-thioguanine nucleotide (TGN) level and how long to continue thiopurines after induction are uncertain. We aimed to compare outcomes after induction and during maintenance in combination therapy versus infliximab monotherapy in Crohn's and to examine whether TGN levels were associated with outcomes.

METHODS

Crohn's patients induced with infliximab with or without concomitant thiopurines were retrospectively identified. Response to induction and clinical outcomes in subsequent 6-month maintenance semesters were analyzed. A TGN level ≥235 pmol/8 × 108 red blood cells was considered therapeutic.

RESULTS

In 89 patients, response to induction was higher in combination therapy than monotherapy (74 vs 47%, P = 0.04). This benefit was only seen in patients with a therapeutic TGN (odds ratio 3.72, confidence interval 1.07-13.0, P = 0.04). Combination therapy during induction yielded a three times longer time to subsequent need for treatment escalation or treatment failure compared with monotherapy (29 vs 9 months, P = 0.01), with both therapeutic and subtherapeutic TGNs independent predictors on multivariate analysis. Among 370 semesters, there was no difference in outcomes between combination therapy and monotherapy (P = 0.42), nor when combination semesters were stratified by therapeutic versus subtherapeutic TGN (P = 0.56). In semester 1 only, a significantly higher remission rate was observed with therapeutic compared with subtherapeutic TGN (76% vs 33%, P = 0.02).

CONCLUSIONS

Combination therapy dosed with an optimized thiopurine was superior to infliximab monotherapy for induction of response, durability of response, and clinical outcomes in the first 6 months following induction. Thereafter, combination therapy yielded no clinical advantage, supporting consideration of thiopurine withdrawal on a case-by-case basis.

Thalidomide Combined With Azathioprine as Induction and Maintenance Therapy for Azathioprine-Refractory Crohn's Disease Patients

The combination therapy of thalidomide and azathioprine (AZA) offers an alternative in clinical practice for Crohn's disease (CD) patients experiencing a loss of response to AZA monotherapy. However, little is known about the efficacy and safety of this combination therapy for patients with CD. This was a retrospective study of 122 consecutive CD patients who lost response to AZA therapy and had switched to a combination therapy of thalidomide and AZA. The primary outcomes were clinical response and clinical remission rates at week 24. Patients who had an initial response to combination therapy were continued on the treatment for remission maintenance. The secondary outcomes were the proportion of clinical relapse throughout maintenance. The Kaplan–Meier method was used to calculate cumulative rates, and Cox regression analysis was used for multivariate analysis. During induction, 80.3% (98/122) patients achieved clinical response within a median duration of 6.5 weeks, (interquartile range, 4.3–8.1 weeks). The rate of clinical remission at 24 weeks was 70.5%. During follow-up, 22.4% (22/98) of the patients that were maintained on combination therapy experienced clinical relapse. The proportions of patients in remission status at 12, 24, and 36 months were 85.1, 78.3, and 70.1%, respectively. Multivariate analysis revealed C-reactive protein >10 mg/L at disease relapse on AZA monotherapy [adjusted hazard ratio (HR), 4.72; 95% CI, 1.19–18.75, P = 0.027] and 6-thioguanine nucleotides level ≥235 pmol/8 × 10⁸ erythrocytes at AZA monotherapy (adjusted HR, 5.32; 95% CI, 1.40–20.14, P = 0.014) were associated with disease relapse on combination therapy. The endoscopic remission rate was 63.6%. Mucosal healing was achieved in 23.6% of the patients. Both Crohn's Disease Endoscopic Index of Severity (13.4 ± 4.92 vs. 6.12 ± 5.24, P < 0.001) and Rutgeerts scores (3.23 ± 0.73 vs. 1.77 ± 1.59, P = 0.003) were significantly decreased with the use of combination therapy. Adverse events occurred in 62 (50.8%) patients, but only 13 (10.7%) necessitated therapy discontinuation. Thalidomide combined with AZA was effective in inducing clinical remission and sustaining long-term steroid-free remission in CD patients who lost response to AZA monotherapy.

The shining DIAMOND for evidence-based treatment strategies for Crohn's disease

Anti-tumor necrosis factor (TNF)-α antibodies are effective therapeutic agents to treat inflammatory bowel disease (IBD). In the biologic era, the development of immunogenicity has been a critical issue for secondary loss of response. The superiority of anti-TNF therapy in combination with immunomodulators (IMs) is well-established for infliximab (IFX) but less evident for adalimumab (ADA). To clarify the contribution of thiopurines to ADA-treated patients with Crohn's disease (CD), the deep remission of immunomodulator and adalimumab combination therapy for Crohn's disease (DIAMOND) studies provided the first randomized comparison of efficacy between ADA monotherapy and ADA with thiopurine. The results of the DIAMOND and DIAMOND2 studies revealed the appropriate ADA therapeutic strategy for immunosuppressant-naïve patients with active CD based on therapeutic drug monitoring, endoscopic findings and clinical issues regarding the use of thiopurines.

Addition of azathioprine to the switch of anti-TNF in patients with IBD in clinical relapse with undetectable anti-TNF trough levels and antidrug antibodies: a prospective randomised trial

OBJECTIVES

In patients with IBD experiencing an immune-mediated loss of response (LOR) to antitumour necrosis factor (anti-TNF), algorithms recommend a switch of anti-TNF without immunosuppressive drug. The aim of our study was to compare in these patients two strategies: either switch to a second anti-TNF alone or with addition of azathioprine (AZA). After randomisation outcomes (time to clinical and pharmacokinetic failure) were compared between the two groups during a 2-year follow-up period.

DESIGN

Consecutive IBD patients in immune-mediated LOR to a first optimised anti-TNF given in monotherapy were randomised to receive either AZA or nothing with induction by a second anti-TNF in both arms. Clinical failure was defined for Crohn's disease (CD) as a Harvey-Bradshaw index ≥5 associated with a faecal calprotectin level >250 µg/g stool and for UC as a Mayo score >5 with endoscopic subscore >1 or as the occurrence of adverse events requiring to stop treatment. Unfavourable pharmacokinetics of the second anti-TNF were defined by the appearance of undetectable trough levels of anti-TNF with high antibodies (drug-sensitive assay) or by that of antibodies (drug-tolerant assay).

RESULTS

Ninety patients (48 CDs) were included, and 45 of them received AZA after randomisation. The second anti-TNF was adalimumab or infliximab in 40 and 50 patients, respectively. Rates of clinical failure and occurrence of unfavourable pharmacokinetics were higher in monotherapy compared with combination therapy (p<0.001; median time of clinical failure since randomisation 18 vs >24 months). At 24 months, survival rates without clinical failure and without appearance of unfavourable pharmacokinetics were respectively 22 versus 77% and 22% versus 78% (p<0.001 for both) in monotherapy versus combination therapy. Only the use of combination therapy was associated with favourable outcomes after anti-TNF switch.

CONCLUSION

In case of immune-mediated LOR to a first anti-TNF, AZA should be associated with the second anti-TNF.

TRIAL REGISTRATION NUMBER

03580876.

Safety of drugs used for the treatment of Crohn's disease

INTRODUCTION

Medications in treating Crohn's disease (CD) have evolved over the last two decades, particularly with the use of biologic agents. There are, however, concerns about the safety and adverse events associated with these medications. The authors review the safety profile of immunosuppressive medications used in Crohn's disease in adult patients.

AREAS COVERED

The authors performed a literature search until October 2018 to examine safety data on thiopurines, methotrexate, anti-TNFα agents, vedolizumab and ustekinumab. The authors focused on 'trial' and 'real-world' data for the biologic agents. Safety in pregnancy and the elderly are also presented.

EXPERT OPINION

Available data in CD suggest that immunosuppressive medications are relatively safe, although there are concerns about an elevated risk of serious infections, skin cancer and lymphoma particularly with thiopurines and anti-TNFα agents. Data on vedolizumab and ustekinumab suggest these newer biologic agents are well tolerated; however, longer term data in CD are required to identify risks with extended use. Apart from methotrexate, there appear to be no adverse congenital outcomes with exposure of drugs during pregnancy.

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.

Prospective Observational Evaluation of Time-Dependency of Adalimumab Immunogenicity and Drug Concentrations: The POETIC Study

OBJECTIVES

Adalimumab is usually self-injected at home, making prospective serial-sampling studies challenging and scarce. This has led to a gap in knowledge about evolution of anti-adalimumab antibodies (AAAs) over time and its correlation with clinical and inflammatory outcomes.

METHODS

A program for home visits by physicians at induction, every 3 months and at event of relapse, was established prospectively for Crohn's disease (CD) patients. At each visit, patients' clinical scores were determined and sera were obtained for C-reactive protein, drug, and AAA levels. This cohort was compared to a parallel prospective cohort of infliximab-treated CD patients. In a subgroup of 29 patients, trough and in-between-trough levels were compared, to elucidate the importance of timing of sampling during the injection cycle.

RESULTS

Ninety-eight CD patients starting adalimumab were prospectively followed (median follow-up 44 weeks) and 621 serum samples were analyzed. Thirty-three patients (32%) developed AAA; 18/33 (55%) of them as early as week 2, and 26/33 (79%) by week 14. Induction period AAAs were strongly associated with primary non-response (odds ratio (OR) = 5.4, 95% confidence interval (CI): 1.6-17.8, p = 0.005). As compared to antibodies-to-infliximab (ATI), AAA formation rate over time was significantly lower (p = 0.01) and AAA were much more specific-85% of AAA events were associated with loss-of-response compared with 58% rate for ATI (p = 0.01). In 29 patients sampled serially during an injection cycle, levels of drug and AAA seemed comparable between four time-points during a single cycle both in patients with or without AAA (n = 8, n = 21, respectively).

CONCLUSIONS

When followed prospectively and serially, AAAs are found to arise earlier than previously appreciated and their impact may be more pronounced for primary rather than secondary, non-response. Drug and AAA levels were similar both at trough and in-between injections, enabling to simplify therapeutic drug monitoring of adalimumab.

Therapeutic Drug Monitoring in Pediatric Inflammatory Bowel Disease

PURPOSE OF REVIEW

Therapeutic drug monitoring (TDM) has emerged as a useful tool to optimize the use of drug therapies in adults with inflammatory bowel disease (IBD), including both Crohn's disease (CD) and ulcerative colitis (UC), especially during the use of biological therapies, for which the pharmacokinetics and pharmacodynamics are highly variable among patients. Fewer data exist in children. This review examines the current literature on TDM in pediatric IBD.

RECENT FINDINGS

Drug clearance is affected by a number of patient and disease factors. For thiopurines, adjusting dosing by monitoring 6-thioguanine (6TGN) and 6-methylmercaptopurine ((6MMP) levels is demonstrated to maximize response and minimize toxicity, while monitoring metabolite levels when treating with anti-tumor necrosis factor (anti-TNF) remain controversial. While in adults the use of TDM in the setting of loss of response to anti-TNF therapy is established, in children, only a small number of studies exist, but these too have encouraging results. There are however, conflicting data regarding the optimal timing of TDM, comparing "reactive" monitoring and "proactive" monitoring. No such data exist in pediatrics. TDM is cost-effective, and dose reduction may represent a safety benefit. There are limited adult data for use of TDM for the newer biologics, vedolizumab and ustekinumab, but early results suggest similarly promising utility. The use of TDM in pediatric IBD is increasing in clinical practice, with similar efficacy to adults demonstrated in children with loss of response to anti-TNF therapy. More prospective studies are needed in children to examine proactive monitoring and utility of TDM with newer biologics.

Combination Immunosuppression in IBD

Whether to use biologic treatment for inflammatory bowel disease as monotherapy or in combination with immunosuppressives has been a matter of debate in the last 2 decades. Combination therapy was not superior in any of the registration trials for Crohn's disease and ulcerative colitis for TNF antagonists, vedolizumab, or ustekinumab. It needs to be mentioned, though, that none of these trials were powered to detect such differences, and that many patients entered the trial after having failed conventional immunosuppressives.Postmarketing studies revealed that patients on background immunosuppression have a lower risk of immunogenicity (often resulting in infusion/injection reactions) than patients on monotherapy. In the SONIC and UC-SUCCESS trials, superiority of the combination azathioprine-infliximab was demonstrated in Crohn's disease and ulcerative colitis, respectively. This trial design has not been used with any other biologic for IBD, so far. Meanwhile, it has also become clear that combination treatment with TNF antagonists is associated with increased toxicity, mainly infections, but also malignancy such as lymphoproliferative disease. This toxicity could perhaps be reduced by using lower doses of immunosuppressives, a strategy that has been shown to be equally potent in reducing immunogenicity. Additionally, combination treatment could be used for a limited period of time (12 months or even shorter) since most immunogenicity develops in the beginning of the biologic treatment. Patients who develop anti-drug-antibodies later on can often be rescued by reintroduction of thiopurines or methotrexate.In summary, combination treatment is certainly beneficial with infliximab, at least in the first 12 months of treatment. With other TNF antagonists, vedolizumab, and ustekinumab, the available data do not offer clear guidance. In patients without increased risk of toxicity, and certainly in those with limited treatment options, it may be wise to offer combination treatment with all biologics for the time being and at least during the initiation phase.

Recommendations of the Spanish Working Group on Crohn's Disease and Ulcerative Colitis (GETECCU) on the use of thiopurines in inflammatory bowel disease

Thiopurines (azathioprine and mercaptopurine) are widely used in patients with inflammatory bowel disease. In this paper, we review the main indications for their use, as well as practical aspects on efficacy, safety and method of administration. They are mainly used to maintain remission in steroid-dependent disease or with ciclosporin to control a severe ulcerative colitis flare-up, as well as to prevent postoperative Crohn's disease recurrence, and also in combination therapy with biologics. About 30-40% of patients will not respond to treatment and 10-20% will not tolerate it due to adverse effects. Before they are prescribed, immunisation status against certain infections should be checked. Determination of thiopurine methyltransferase activity (TPMT) is not mandatory but it increases initial safety. The appropriate dose is 2.5mg/kg/day for azathioprine and 1.5mg/kg/day for mercaptopurine. Some adverse effects are idiosyncratic (digestive intolerance, pancreatitis, fever, arthromyalgia, rash and some forms of hepatotoxicity). Others are dose-dependent (myelotoxicity and other types of hepatotoxicity), and their surveillance should never be interrupted during treatment. If therapy fails or adverse effects develop, management can include switching from one thiopurine to the other, reducing the dose, combining low doses of azathioprine with allopurinol and assessing metabolites, before their use is ruled out. Non-melanoma skin cancer, lymphomas and urinary tract tumours have been linked to thiopurine therapy. Thiopurine use is safe during conception, pregnancy and breastfeeding.