To STRIDE or not to STRIDE: a critique of "treat to target" in ulcerative colitis.

INTRODUCTION: The STRIDE consensus intends to complement the clinical endpoint with an endoscopic endpoint of mucosal healing and others as treatment targets in ulcerative colitis. If these targets are not reached, STRIDE requires dose or timing adjustments or switching the medication. This narrative review provides a critique of this concept. AREAS COVERED: We analyze and discuss the limitations of current endpoints as targets, their currently limited achievability, and the lacking evidence from controlled trials relating to 'treat to target.' The relevant publications in PubMed were identified in a literature review with the key word 'ulcerative colitis.' EXPERT OPINION: In ulcerative colitis, the standard clinical target is measured traditionally by the MAYO-score, but in variable combinations of patient and physician reported outcomes as well as also different definitions of the endoscopic part. Only a score of 0 is more stringent than clinical remission but is only achieved by a minority of patients in first and even less in second line therapy. The concept is not based on clear evidence that patients indeed benefit from appropriate escalation of treatment. Until the STRIDE approach is proven to be superior to standard treatment focusing on clinical well-being, the field should remain reluctant.

To STRIDE or not to STRIDE: a critique of "treat to target" in Crohn´s disease.

INTRODUCTION: The STRIDE consensus suggested to focus on mucosal healing, based on biomarkers and endoscopy, in addition to clinical endpoints as treatment target. This narrative review provides a critique of this concept in Crohn´s disease. AREAS COVERED: We analyze and discuss the limitations of endpoints as targets, their currently limited achievability, and the controversial evidence relating to 'treat to target.' The relevant publications in Pubmed were identified in a literature review with the key word 'Crohn´s disease.' EXPERT OPINION: All targets and endpoints have their limitations, and, even if reached, not all have unequivocally been shown to improve prognosis. The major deficiency of STRIDE is not only the lack of validation and agreement upon endpoints but little evidence of their achievability in a sizable proportion of patients by dose or timing adjustments or switching the medication. Above all, the concept should be based on clear evidence that patients indeed benefit from appropriate escalation of treatment and relevant controlled studies in this regard have been controversial. Until the STRIDE approach is proven to be superior to standard treatment focusing on clinical well-being, the field should remain reluctant and expect more convincing evidence before new targets are approved.

Prioritization in inflammatory bowel disease therapy.

INTRODUCTION: Most guidelines for IBD still recommend step-by-step therapy with initially classic drugs such aminosalicylates (in ulcerative colitis) or steroids but avoid prioritizing certain biological drugs and JAK inhibitors in the complicated course. This review provides an aid to pending therapy decisions. AREAS COVERED: In this review, we analyze the evidence for Crohn's disease as well as ulcerative colitis in order to optimize and 'personalize' the choice of therapy, especially in difficult cases. The relevant publications in Pubmed were identified in a continuous literature review with the key words 'Crohn´s disease' and 'ulcerative colitis.' EXPERT OPINION: Based on this complex data set following standard therapies steroid-refractory Crohn´s disease should preferentially be treated with combined infliximab plus azathioprine or risankizumab, in second line after their failure with ustekinumab or 7adalimumab. In steroid-refractory ulcerative colitis infliximab plus azathioprine or upadacitinib should be preferred in first line, filgotinib, tofacitinib or ustekinumab in second line. A steroid-dependent course in both diseases requires azathioprine or vedolizumab, in second line infliximab or Janus kinase inhibitors. The conclusions drawn from these complex data may be helpful for individual decision making in daily clinical practice.

High In-Hospital Mortality in SARS-CoV-2-Infected Patients with Active Cancer Disease during Omicron Phase of the Pandemic: Insights from the CORONA Germany Study.

INTRODUCTION: SARS-CoV-2 infected patients with cancer have a worse outcome including a significant higher mortality, compared to non-cancer patients. However, limited data are available regarding in-hospital mortality during the Omicron phase of the pandemic. Therefore, the aim of the study was the comparison of mortality in patients with history of cancer and patients with active cancer disease during the different phases of the COVID-19 pandemic, focusing on the current Omicron variant of concern. METHODS: We conducted a multicenter, observational, epidemiological cohort study at 45 hospitals in Germany. Until July 20, 2022, all adult hospitalized SARS-CoV-2 positive patients were included. The primary endpoint was in-hospital mortality regarding cancer status (history of cancer and active cancer disease) and SARS-CoV-2 virus type. RESULTS: From March 11, 2020, to July 20, 2022, a total of 27,490 adult SARS-CoV-2 positive patients were included in the study. 2,578 patients (9.4%) had diagnosis of cancer, of whom 1,065 (41.3%) had history of cancer, whereas 1,513 (58.7%) had active cancer disease. Overall 3,749 out of the total of 27,490 patients (13.6%) died during the hospital stay. Patients with active cancer disease had a significantly higher mortality compared to patients without cancer diagnosis, in both phases of the pandemic (wild-type to Delta: OR 1.940 [1.646-2.285]); Omicron: 2.864 [2.354-3.486]). After adjustment to co-variables, SARS-CoV-2 infected patients with active cancer disease had the highest risk for in-hospital mortality compared to the other groups, in both phases of the pandemic. CONCLUSION: The CORONA Germany study indicates that hospitalized patients with active cancer disease are at high risk of death during a SARS-CoV-2 infection. Mortality of patients with history of cancer improved to nearly the level of non-cancer patients during Omicron phase.

Retinal Vascular Occlusion after COVID-19 Vaccination: More Coincidence than Causal Relationship? Data from a Retrospective Multicentre Study.

BACKGROUND: To investigate whether vaccination against SARS-CoV-2 is associated with the onset of retinal vascular occlusive disease (RVOD). METHODS: In this multicentre study, data from patients with central and branch retinal vein occlusion (CRVO and BRVO), central and branch retinal artery occlusion (CRAO and BRAO), and anterior ischaemic optic neuropathy (AION) were retrospectively collected during a 2-month index period (1 June-31 July 2021) according to a defined protocol. The relation to any previous vaccination was documented for the consecutive case series. Numbers of RVOD and COVID-19 vaccination were investigated in a case-by-case analysis. A case-control study using age- and sex-matched controls from the general population (study participants from the Gutenberg Health Study) and an adjusted conditional logistic regression analysis was conducted. RESULTS: Four hundred and twenty-one subjects presenting during the index period (61 days) were enrolled: one hundred and twenty-one patients with CRVO, seventy-five with BRVO, fifty-six with CRAO, sixty-five with BRAO, and one hundred and four with AION. Three hundred and thirty-two (78.9%) patients had been vaccinated before the onset of RVOD. The vaccines given were BNT162b2/BioNTech/Pfizer (n = 221), followed by ChadOx1/AstraZeneca (n = 57), mRNA-1273/Moderna (n = 21), and Ad26.COV2.S/Johnson & Johnson (n = 11; unknown n = 22). Our case-control analysis integrating population-based data from the GHS yielded no evidence of an increased risk after COVID-19 vaccination (OR = 0.93; 95% CI: 0.60-1.45, p = 0.75) in connection with a vaccination within a 4-week window. CONCLUSIONS: To date, there has been no evidence of any association between SARS-CoV-2 vaccination and a higher RVOD risk.

Prognostic Impact of Acute Cardiovascular Events in COVID-19 Hospitalized Patients-Results from the CORONA Germany Study.

BACKGROUND: Acute myocardial injury (AMJ), assessed by elevated levels of cardiac troponin, is associated with fatal outcome in coronavirus disease 2019 (COVID-19). However, the role of acute cardiovascular (CV) events defined by clinical manifestation rather than sole elevations of biomarkers is unclear in hospitalized COVID-19 patients. OBJECTIVE: The aim of this study was to investigate acute clinically manifest CV events in hospitalized COVID-19 patients. METHODS: From 1 March 2020 to 5 January 2021, we conducted a multicenter, prospective, epidemiological cohort study at six hospitals from Hamburg, Germany (a portion of the state-wide 45-center CORONA Germany cohort study) enrolling all hospitalized COVID-19 patients. Primary endpoint was occurrence of a clinically manifest CV-event. RESULTS: In total, 132 CV-events occurred in 92 of 414 (22.2%) patients in the Hamburg-cohort: cardiogenic shock in 10 (2.4%), cardiopulmonary resuscitation in 12 (2.9%), acute coronary syndrome in 11 (2.7%), de-novo arrhythmia in 31 (7.5%), acute heart-failure in 43 (10.3%), myocarditis in 2 (0.5%), pulmonary-embolism in 11 (2.7%), thrombosis in 9 (2.2%) and stroke in 3 (0.7%). In the Hamburg-cohort, mortality was 46% (42/92) for patients with a CV-event and 33% (27/83) for patients with only AMJ without CV-event (OR 1.7, CI: (0.94-3.2), p = 0.077). Mortality was higher in patients with CV-events (Odds ratio(OR): 4.8, 95%-confidence-interval(CI): [2.9-8]). Age (OR 1.1, CI: (0.66-1.86)), atrial fibrillation (AF) on baseline-ECG (OR 3.4, CI: (1.74-6.8)), systolic blood-pressure (OR 0.7, CI: (0.53-0.96)), potassium (OR 1.3, CI: (0.99-1.73)) and C-reactive-protein (1.4, CI (1.04-1.76)) were associated with CV-events. CONCLUSION: Hospitalized COVID-19 patients with clinical manifestation of acute cardiovascular events show an almost five-fold increased mortality. In this regard, the emergence of arrhythmias is a major determinant.

Twenty-five years of biologicals in IBD: What´s all the hype about?

Twenty-five years ago the field was revolutionized by the introduction of infliximab as the first hybrid anti-TNF-antibody. Subsequently, other humanized anti-TNFs were developed and marketed, followed by antibodies to new targets including integrins (vedolizumab) and interleukin 12/23 (ustekinumab). All these so-called biologicals were shown in registrational trials to induce remission superior to placebo but consistently were effective in only a minority of patients. Even though in most trials only the responders were selected to continue on the respective medication for maintenance, many experienced a secondary loss of response and only a minority of usually <25% of the initial cohort achieved long-term (1 year) remission. In 'real life studies', the outcome was somewhat better, probably due to proper selection of patients and open, mostly retrospective study designs. A clear benefit of biologicals is apparent in otherwise treatment refractory patients, in extraintestinal manifestations and in Crohn´s disease (CD) with fistulizing complications. Biologicals achieve mucosal healing (MH) more often than corticosteroids or thiopurines, and MH is associated with improved prognosis. However, this does not justify escalating treatment until MH is reached since controlled trials proving this point of 'treat to target' are lacking both in ulcerative colitis and CD. Surgical rates have decreased with increasing use of biologicals, but disease progression has not been proven to improve. With the exception of opportunistic infections, serious adverse events are rare. In conclusion, biologicals have changed the scene considerably and expanded our armamentarium, but there is also a marketing hype fostering expectations without evidence.

Tula Virus as Causative Agent of Hantavirus Disease in Immunocompetent Person, Germany.

We report molecular evidence of Tula virus infection in an immunocompetent patient from Germany who had typical signs of hantavirus disease. Accumulating evidence indicates that Tula virus infection, although often considered nonpathogenic, represents a threat to human health.

Therapeutic peptides in inflammatory bowel disease.

INTRODUCTION: Therapeutic peptides in inflammatory bowel diseases essentially comprise cytokines affecting immune response, growth factors and monoclonal antibodies directed against key targets of mucosal inflammation, in particular, tumor necrosis factor-a (TNF-a). The latter have revolutionized standard medical treatment which previously was restricted to mesalamine, corticosteroids or classical immunosuppressants. AREAS COVERED: We review current evidence of the use of the so-called biologicals, including the well-established TNF-a antagonists and novel peptides and monoclonal antibodies developed for these diseases. The focus is on controlled clinical trials and meta-analyses, if available. Limitations and biases of these studies are important but tend to be ignored. Safety is also an important issue with opportunistic infections and lymphoma as relevant risks. There is significant heterogeneity between different countries, guidelines and opinions within the scientific community regarding clinical indications, even apart from pharmacoeconomics and reimbursement. EXPERT OPINION: TNF blockers have greatly extended medical options in inflammatory bowel diseases. Their more or less extensive use in nearly all patients or only a few selected indications is a matter of debate. It proved difficult to reproduce this success with other antibody targets as well as with immunomodulatory cytokines and growth factors. The most promising novel peptide is vedolizumab, an antibody against α4ß7 integrin.

The debated role for thiopurines in Crohn's disease.

There is a new debate on the role of thiopurines in Crohn's disease. This viewpoint discusses the current evidence and balances thiopurines against other treatment options in the therapeutic algorithm of Crohn's disease.

Differences between treatment guidelines--Germany.

When looking at different treatment guidelines the topics most debated for Crohn's disease are the following: (a) the use of mesalamine for remission induction and maintenance in mild to moderate Crohn's disease; (b) the early use of anti-TNF antibodies in Crohn's disease with or without classical immunomodulators for remission induction, and (c) remission induction in steroid-refractory disease with anti-TNF antibodies or calcineurin inhibitors. The topics mentioned above will be discussed with regard to the statements of the German Gastroenterology Association (DGVS) on the basis of the underlying evidence.

Mucosal improvement in patients with moderate to severe postoperative endoscopic recurrence of Crohn's disease and azathioprine metabolite levels.

BACKGROUND: The value of azathioprine metabolites (6-thioguanine nucleotides [6-TGN]) in monitoring clinical treatment response is still controversially discussed. Data regarding thiopurine metabolite levels and endoscopic improvement are lacking. METHODS: Data were analyzed post hoc from a 1-year, multicenter, double-blind, double-dummy, randomized trial comparing azathioprine 2.0 to 2.5 mg/kg per day versus mesalamine 4 g/d in a subset of 23 postoperative patients with Crohn's disease (CD) treated with azathioprine and having moderate-to-severe endoscopic recurrence according to a modified 6-grade score. Red blood cell (RBC) concentrations of 6-TGN, 6-methyl-mercaptopurine ribonucleotides (6-MMPR), and 6-methyl-thioguanine nucleotides (6-MTGN) were indicated as follows: area under the concentration-time curve, average concentration (C av), and concentration at the final study visit. RESULTS: Overall, 74% of patients showed an improvement in the modified endoscopic score (P = 0.022). Median endoscopic score reduced from 4 at the baseline to 2 at the final visit. Patients with a high C av for 6-TGN (≥ 193 pmol/8 × 10(8) RBC; P = 0.017) or 6-MTGN (≥ 79.2 pmol/8 × 10(8) RBC; P = 0.035) significantly improved in endoscopic score, and the improvement in endoscopic score correlated with C av for 6-TGN (r = -0.51; P = 0.013). For concentration at the final visit, higher values for 6-TGN (≥ 142 pmol/8 × 10(8) RBC; P = 0.017) were associated with a better postoperative score. Sensitivity analysis revealed a significant correlation between 6-TGN (area under the concentration-time curve) and postoperative endoscopic improvement. CONCLUSIONS: Our post hoc analysis from a double-blind, randomized trial suggests that higher RBC 6-TGN levels are associated with endoscopic improvement in patients with severe postoperative endoscopic recurrence of CD. Thus, our study provides first evidence on the utility of monitoring of thiopurine metabolites to achieve mucosal response in CD.

Azathioprine versus mesalazine for prevention of postoperative clinical recurrence in patients with Crohn's disease with endoscopic recurrence: efficacy and safety results of a randomised, double-blind, double-dummy, multicentre trial.

OBJECTIVE: The aim of the study was to compare azathioprine versus mesalazine tablets for the prevention of clinical recurrence in patients with postoperative Crohn's disease (CD) with moderate or severe endoscopic recurrence. METHODS: This was a 1 year, double-blind, double-dummy, randomised study which took place in 21 gastroenterology centres in Austria, the Czech Republic, Germany and Israel. The study participants were 78 adults with CD who had undergone resection with ileocolonic anastomosis in the preceding 6-24 months without subsequent clinical recurrence and with a Crohn's disease activity index (CDAI) score <200, but with moderate or severe endoscopic recurrence. The study drugs were azathioprine 2.0-2.5 mg/kg/day or mesalazine 4 g/day over 1 year. The primary end point was therapeutic failure during 1 year, defined as a CDAI score > or = 200 and an increase of > or = 60 points from baseline, or study drug discontinuation due to lack of efficacy or intolerable adverse drug reaction. RESULTS: Treatment failure occurred in 22.0% (9/41) of azathioprine-treated patients and 10.8% (4/37) of mesalazine-treated patients, a difference of 11.1% (95% CI -5.0% to 27.3%, p=0.19). Clinical recurrence was significantly less frequent with azathioprine versus mesalazine (0/41 (0%) vs 4/37 (10.8%), p=0.031), whereas study drug discontinuation due to adverse drug reactions only occurred in azathioprine-treated patients (9/41 (22.0%) vs 0%, p=0.002). The proportion of patients showing > or = 1 point reduction in Rutgeerts score between baseline and month 12 was 63.3% (19/30) and 34.4% (11/32) in the azathioprine and mesalazine groups, respectively (p=0.023). CONCLUSIONS: In this population of patients with postoperative CD at high risk of clinical recurrence, superiority for azathioprine versus mesalazine could not be demonstrated for therapeutic failure.

Determination of 6-thioguanosine diphosphate and triphosphate and nucleoside diphosphate kinase activity in erythrocytes: novel targets for thiopurine therapy?

6-Thioguanine nucleotides are the sum of 6-thioguanosine 5'-monophosphate (TGMP), -diphosphate (TGDP), and -triphosphate (TGTP) representing essential metabolites involved in drug action of thiopurines. Elevated levels of TGDP have been associated with poor response to azathioprine therapy in patients with inflammatory bowel disease. The conversion of TGDP to TGTP is supposed to be catalyzed by nucleoside diphosphate kinase (NDPK). The aim of this work was to investigate simultaneously individual 6-thioguanosine phosphate levels and NDPK activity in red blood cells (RBCs) of patients on azathioprine therapy. Ion-pair high-performance liquid chromatography methods with fluorescence and ultraviolet detection were applied to quantify individual levels of 6-thioguanosine 5'-phosphates and NDPK activity, respectively, in RBCs. Recombinantly expressed NDPK isoforms A and B were unequivocally identified to catalyze the formation of TGTP (30.6 +/- 3.88 nmol x min x mg for NDPK A versus 41.2 +/- 1.05 nmol x min x mg for NDPK B). Comprehensive analyses on the stability of TGMP, TGDP, and TGTP and the reproducibility of NDPK activity in RBCs were performed to provide a reliable sampling protocol for clinical practice. Of note, isolation of RBCs within 6 hours followed by immediate storage at -80 degrees C is crucial for prevention of degradation of 5'-phosphates. In a clinical study of 37 patients on azathioprine, TGTP was the predominant 6-thioguanosine phosphate in RBCs. In contrast, three patients showed TGTP/(TGDP + TGTP) ratios of 57.2%, 64.3%, and 66% corresponding to elevated TGDP levels. NDPK activity ranged from 4.1 to 11.3 nmol x min x mg hemoglobin. No correlation between NDPK activity and the 6-thioguanosine phosphate levels was found. The question whether interindividual variability of NDPK activity may explain differences in 6-thioguanosine 5'-phosphates levels has to be investigated in a prospective large-scale study.

Genetic variants of Wnt transcription factor TCF-4 (TCF7L2) putative promoter region are associated with small intestinal Crohn's disease.

Reduced expression of Paneth cell antimicrobial alpha-defensins, human defensin (HD)-5 and -6, characterizes Crohn's disease (CD) of the ileum. TCF-4 (also named TCF7L2), a Wnt signalling pathway transcription factor, orchestrates Paneth cell differentiation, directly regulates the expression of HD-5 and -6, and was previously associated with the decrease of these antimicrobial peptides in a subset of ileal CD. To investigate a potential genetic association of TCF-4 with ileal CD, we sequenced 2.1 kb of the 5' flanking region of TCF-4 in a small group of ileal CD patients and controls (n = 10 each). We identified eight single nucleotide polymorphisms (SNPs), of which three (rs3814570, rs10885394, rs10885395) were in linkage disequilibrium and found more frequently in patients; one (rs3814570) was thereby located in a predicted regulatory region. We carried out high-throughput analysis of this SNP in three cohorts of inflammatory bowel disease (IBD) patients and controls. Overall 1399 healthy individuals, 785 ulcerative colitis (UC) patients, 225 CD patients with colonic disease only and 784 CD patients with ileal involvement were used to determine frequency distributions. We found an association of rs3814570 with ileal CD but neither with colonic CD or UC, in a combined analysis (allele positivity: OR 1.27, 95% CI 1.07 to 1.52, p = 0.00737), which was the strongest in ileal CD patients with stricturing behaviour (allele frequency: OR 1.32, 95% CI 1.08 to1.62, p = 0.00686) or an additional involvement of the upper GIT (allele frequency: OR 1.38, 95% CI 1.03 to1.84, p = 0.02882). The newly identified genetic association of TCF-4 with ileal CD provides evidence that the decrease in Paneth cell alpha-defensins is a primary factor in disease pathogenesis.

Azathioprine-induced suicidal erythrocyte death.

BACKGROUND: Azathioprine is widely used as an immunosuppressive drug. The side effects of azathioprine include anemia, which has been attributed to bone marrow suppression. Alternatively, anemia could result from accelerated suicidal erythrocyte death or eryptosis, which is characterized by exposure of phosphatidylserine (PS) at the erythrocyte surface and by cell shrinkage. METHODS: The present experiments explored whether azathioprine influences eryptosis. According to annexin V binding, erythrocytes from patients indeed showed a significant increase of PS exposure within 1 week of treatment with azathioprine. In a second series, cytosolic Ca2+ activity (Fluo3 fluorescence), cell volume (forward scatter), and PS-exposure (annexin V binding) were determined by FACS analysis in erythrocytes from healthy volunteers. RESULTS: Exposure to azathioprine (> or =2 microg/mL) for 48 hours increased cytosolic Ca2+ activity and annexin V binding and decreased forward scatter. The effect of azathioprine on both annexin V binding and forward scatter was significantly blunted in the nominal absence of extracellular Ca2+. CONCLUSIONS: Azathioprine triggers suicidal erythrocyte death, an effect presumably contributing to azathioprine-induced anemia.

A systematic survey evaluating 6-thioguanine-related hepatotoxicity in patients with inflammatory bowel disease.

OBJECTIVE: Drug-induced liver injury was recently reported as a major complication leading to hepatic nodular regenerative hyperplasia (NRH) in patients with inflammatory bowel disease (IBD) and 6-thioguanine (6-TG) therapy. The aim of the study was to evaluate the prevalence of 6-TG-related hepatotoxicity in a large multi-centered IBD population by means of a systematic online survey. METHODS: Clinical and laboratory data, imaging techniques (sonography, CT, MRI) and histology of liver biopsies were surveyed in IBD patients treated with 6-TG. The decision on whether liver imaging and/or liver biopsy were performed was exclusively at the discretion of the investigator. RESULTS: 6-TG use was fully documented in 296 patients (median treatment duration 56 weeks, range < 1-207). Laboratory signs of drug-induced liver injury were found in 43 patients (14.5%). Liver imaging revealed pathologic results in 68/176 patients (38.6%). Liver biopsy was performed in a subset of 60 patients; using silver-reticulin staining (n = 59), NRH was considered in 16 patients (27.1%). Age was the only independent, albeit weak, risk factor for development of NRH. CONCLUSION: This large online survey confirms the strong association between 6-TG treatment and the significant risk of development of NRH in patients with IBD. The definitive diagnosis of NRH depends solely upon liver biopsy.

Thiopurine treatment in inflammatory bowel disease: clinical pharmacology and implication of pharmacogenetically guided dosing.

This review summarises clinical pharmacological aspects of thiopurines in the treatment of chronic inflammatory bowel disease (IBD). Current knowledge of pharmacogenetically guided dosing is discussed for individualisation of thiopurine therapy, particularly to avoid severe adverse effects. Both azathioprine and mercaptopurine are pro-drugs that undergo extensive metabolism. The catabolic enzyme thiopurine S-methyltransferase (TPMT) is polymorphically expressed, and currently 23 genetic variants have been described. On the basis of an excellent phenotype-genotype correlation for TPMT, genotyping has become a safe and reliable tool for determination of a patient's individual phenotype. Thiopurine-related adverse drug reactions are frequent, ranging from 5% up to 40%, in both a dose-dependent and -independent manner. IBD patients with low TPMT activity are at high risk of developing severe haematotoxicity if pharmacogenetically guided dosing is not performed. Based on several cost-benefit analyses, assessment of TPMT activity is recommended prior to thiopurine therapy in patients with IBD. The underlying mechanisms of azathioprine/mercaptopurine-related hepatotoxicity, pancreatitis and azathioprine intolerance are still unknown. Although the therapeutic response appears to be related to 6-thioguanine nucleotide (6-TGN) concentrations above a threshold of 230-260 pmol per 8 x 10(8) red blood cells, at present therapeutic drug monitoring of 6-TGN can be recommended only to estimate patients' compliance.Drug-drug interactions between azathioprine/mercaptopurine and aminosalicylates, diuretics, NSAIDs, warfarin and infliximab are discussed. The concomitant use of allopurinol without dosage adjustment of azathioprine/mercaptopurine leads to clinically relevant severe haematotoxicity due to elevated thiopurine levels. Several studies indicate that thiopurine therapy in IBD during pregnancy is safe. Thus, azathioprine/mercaptopurine should not be withdrawn in strictly indicated cases of pregnant IBD patients. However, breastfeeding is contraindicated during azathioprine/mercaptopurine therapy. Use of azathioprine/mercaptopurine for induction and maintenance of remission in corticosteroid-dependent or corticosteroid-refractory IBD, particularly Crohn's disease, is evidence based. To improve response rates in thiopurine therapy of IBD, comprehensive analyses including metabolic patterns and genome-wide profiling in patients with azathioprine/mercaptopurine treatment are required to identify novel candidate genes.