Mercaptopurine metabolite results in clinical gastroenterology practice

Low adherence to treatment is a weak link in the problems of ulcerative colitis

Aim. To determine factors of adherence to treatment in patients with ulcerative colitis (UC). Materials and methods. The study was performed in the department of treatment of inflammatory bowel diseases in Loginov Moscow Clinical Scientific Center from 2019 till 2021 years by surveying 1089 patients with UC. This analysis revealed patients with high adherence (HAP) and low adherence to treatment (LAP). Results. In the survey analysis was determined, that there were more low-adherence patients, than high-adherence patients [596 (59.6%) and 404 (40.4%), respectively, (р0.001)]. In the group of HAP (100%) were 297 women (73.5%) and 107 (26.5%) men (р0.001). Also in this group prevailed patients with duration of disease more 5 years 305 (75.5%) and extraintestinal manifestations 261 (64.6%); р0.001. In the group of LAP (100%) were more patients younger 44 years, with bad habits and who did not follow diet (р0.001). The rate of UC reccurence more than 1 time per year was higher in LAP group 430 (72.1%), versus 137 (33.9%) patients in HAP (р0.001). The frequency of surgical procedures in UC patients was significantly higher in LAP 12 (2.0%) in comparison with 2 (0.5%) in HAP group (р0.001). Conclusion. In our study was determined, that among UC patients, examined in the department of inflammatory bowel diseases, 60% patients had low adherence to treatment. High adherence to the treatment is statistically significantly associated with female gender, family accommodation, non-working patients, extraintestinal manifestations, additional medical maintenance. Low adherence to the treatment is associated with steroids, male gender, age less than 44 year, bad habits (smoking, alcohol consumption), higher education, complicated UC and frequency of reccurences.

Usefulness of Measuring Thiopurine Metabolites in Children with Inflammatory Bowel Disease and Autoimmunological Hepatitis, Treated with Azathioprine

Introduction

Thiopurines, such as azathioprine (AZA) and 6-mercaptopurine (6-MP), are immunomodulatory agents, used for the maintenance of remission in children with inflammatory bowel disease (IBD)—Crohn's disease (CD) and ulcerative colitis (UC), as well as with autoimmunological hepatitis (AIH). Measurements of thiopurine metabolites may allow identifying patients at risk for toxicity and nonadherence. It can also provide an explanation for the ineffectiveness of the treatment, observed in some patients. Patients and Methods. A retrospective analysis was carried out of sixty-eight patients (thirty-six patients with CD, eighteen with UC, and fourteen with AIH), treated with AZA. Thiopurine metabolites, 6-thioguanine nucleotide (6-TGN) and 6-methylmercaptopurine (6-MMP), were assayed by high-performance liquid chromatography (HPLC), and the AZA dose was adjusted when 6-TGN concentration was known.

Result

Only twenty-five (41%) children had therapeutic 6-TGN concentrations, ten (16%) subjects had suboptimal 6-TGN concentrations, and twenty-six subjects (43%) had 6-TGN concentrations above the recommended therapeutic range. 6-MMP was not above the therapeutic range in any case. Seven subjects revealed undetectable 6-TGN and 6-MMP levels, indicating nonadherence. The mean AZA dose after the 6-TGN concentration-related adjustment did not differ, in comparison to the initial dose, either in IBD or AIH groups. The mean AZA dose was lower in AIH than in IBD. The subjects with an optimal 6-TGN level presented with a higher ratio of remission (88%) than the under- or overdosed patients (60% and 69%), respectively (Chi − square test = 3.87, p < 0.05).

Conclusion

Timely measurements of thiopurine metabolites can be a useful tool to identify nonadherent patients before a decision is taken to switch to another drug. We may also spot the patients who receive either too low or too high doses, compensating dose deviations in an appropriate way. The patients with optimal 6-TGN levels presented a higher percentage of remission than the under- or overdosed patients. In most patients, both initial and adjusted AZA doses, lower than suggested in guidelines, appeared to be sufficient to maintain remission.

Evidence to Support Inclusion of Pharmacogenetic Biomarkers in Randomised Controlled Trials

Pharmacogenetics and biomarkers are becoming normalised as important technologies to improve drug efficacy rates, reduce the incidence of adverse drug reactions, and make informed choices for targeted therapies. However, their wider clinical implementation has been limited by a lack of robust evidence. Suitable evidence is required before a biomarker's clinical use, and also before its use in a clinical trial. We have undertaken a review of five pharmacogenetic biomarker-guided randomised controlled trials (RCTs) and evaluated the evidence used by these trials to justify biomarker inclusion. We assessed and quantified the evidence cited in published rationale papers, or where these were not available, obtained protocols from trial authors. Very different levels of evidence were provided by the trials. We used these observations to write recommendations for future justifications of biomarker use in RCTs and encourage regulatory authorities to write clear guidelines.

Revisiting the Role of Thiopurines in Inflammatory Bowel Disease Through Pharmacogenomics and Use of Novel Methods for Therapeutic Drug Monitoring

Azathioprine and 6-mercaptopurine, often referred to as thiopurine compounds, are commonly used in the management of inflammatory bowel disease. However, patients receiving these drugs are prone to developing adverse drug reactions or therapeutic resistance. Achieving predefined levels of two major thiopurine metabolites, 6-thioguanine nucleotides and 6-methylmercaptopurine, is a long-standing clinical practice in ensuring therapeutic efficacy; however, their correlation with treatment response is sometimes unclear. Various genetic markers have also been used to aid the identification of patients who are thiopurine-sensitive or refractory. The recent discovery of novel Asian-specific DNA variants, namely those in the NUDT15 gene, and their link to thiopurine toxicity, have led clinicians and scientists to revisit the utility of Caucasian biomarkers for Asian individuals with inflammatory bowel disease. In this review, we explore the limitations associated with the current methods used for therapeutic monitoring of thiopurine metabolites and how the recent discovery of ethnicity-specific genetic markers can complement thiopurine metabolites measurement in formulating a strategy for more accurate prediction of thiopurine response. We also discuss the challenges in thiopurine therapy, alongside the current strategies used in patients with reduced thiopurine response. The review is concluded with suggestions for future work aiming at using a more comprehensive approach to optimize the efficacy of thiopurine compounds in inflammatory bowel disease.

Thiopurine Optimization Through Combination With Allopurinol in Children With Inflammatory Bowel Diseases

OBJECTIVES

Thiopurines are commonly used in the maintenance of remission for children with inflammatory bowel diseases (IBDs). Variation in drug metabolism may affect hepatotoxicity or therapeutic effect. We aimed to describe our center's experience with thiopurine optimization through the use of reduced thiopurine dosing in combination with allopurinol upon hepatotoxicity, drug metabolite levels, and clinical outcomes in children with IBD.

METHODS

Patients aged 2 to 21 years with IBD treated with the combination of thiopurines/allopurinol between 2008 and 2015 were retrospectively reviewed. Patients previously treated with antitumor necrosis factor therapy were excluded. Demographic data, transaminase levels (aspartate transaminase, alanine transaminase), drug metabolites levels (6-thioguanine [6-TG], 6-methylmercaptopurine), physician global assessment, and corticosteroid use were recorded at baseline, 6, and 12 months.

RESULTS

Fifty-two patients (29 girls, 56%) met inclusion criteria. Thirty-two of 52 (62%) remained on the combination for 12 months. In those remaining on the thiopurine/allopurinol combination, median alanine transaminase and aspartate transaminase levels were reduced (P < 0.001) and median 6-TG levels were increased (P < 0.001) at both 6 and 12 months. Corticosteroid use was decreased at both 6 (P < 0.001) and 12 months (P < 0.001) compared to use at baseline. Remission rates also improved at both 6 (P = 0.013) and 12 months (P = 0.003). Twenty of the 52 patients (38%) had discontinued the thiopurine/allopurinol combination within 12 months of initiation with 17 of 52 (33%) initiating antitumor necrosis factor therapy.

CONCLUSIONS

Low-dose thiopurines in combination with allopurinol improved hepatotoxicity and increased 6-TG levels in children with IBD. Corticosteroid use was reduced and remission rates improved in those patients remaining on this combination for 1 year. However, approximately 40% of patients required a change in therapy within 12 months.

Adherence to infliximab therapy in inflammatory bowel disease patients in a real-life setting

OBJECTIVE

To assess adherence to infliximab (IFX) therapy in inflammatory bowel disease patients, to investigate reasons for non-adherence and to identify predictors for non-adherence.

METHODS

This observational study was conducted in two French referral university hospitals between 1 September and 31 October, 2011. Patients were systematically asked if they had already delayed or missed an IFX perfusion since the beginning of the treatment and about the reasons for their non-adherence.

RESULTS

Of the 162 included patients (121 Crohn's disease [CD], 41 ulcerative colitis), 87 (53.7%) reported a delay of at least one IFX injection and 14 (8.6%) missed at least one IFX perfusion since the beginning of the treatment. The overall non-adherence rate was 54.3%. Pooling all misses, the main reasons for non-adherence were pregnancy (33.3%), intentional non-adherence (20%) and forgetfulness (13.3%). Pooling all delays, the main reasons for non-adherence were professional constraints (46.9%), infections (17.3%) and travels (14.3%). Perineal disease was associated with IFX delays (P = 0.0007, odds ratio 4.0), whereas active CD/UC was associated with IFX misses (P = 0.0258, OR = 5.4).

CONCLUSIONS

The overall non-adherence rate for IFX use was 54.3%. Professional constraints and intentional non-adherence were the leading causes of non-adherence. Perineal disease and active CD were negatively related to adherence.

Inflammatory bowel disease: adherence to immunomodulators in a biological therapy era

BACKGROUND

Combination therapy, with anti-tumor necrosis factor-α agents and immunomodulators, is the most effective option to induce and maintain remission in inflammatory bowel disease (IBD). Infliximab, with its administration features, determines particular conditions of adherence; the same is not possible with thiopurines. Nevertheless, research on adherence to these treatments is scarce. Nonadherence worsens the prognosis of IBD.

AIM

(a) Assess adherence to immunomodulators and (b) determine therapeutic nonadherence predictors.

PATIENTS AND METHODS

We included all IBD outpatients consecutively evaluated over a 6-month period in our center. Participants completed a study-specific questionnaire on IBD, IBD therapeutic adherence (Morisky Medication Adherence Scale-8-item), Therapeutics Complexity questionnaire, Beliefs about Medication questionnaire, and Hospital Anxiety and Depression Scale.

RESULTS

A total of 112 patients under azathioprine were considered; 49.1% were also under anti-tumor necrosis factor-α. Self-assessed questionnaire showed that 70.5% were adherent to immunosuppression. Similar adherence was found with and without infliximab (68.4%-monotherapy vs. 72.7%-combination therapy; P=0.61). Nonintentional nonadherence was documented in 57.6%; 42.4% reported voluntary nonadherence. Nonadherence was higher in male patients [odds ratio (OR): 3.79; 95% confidence interval (CI): 1.2-11.95; P=0.023], younger patients (OR: 0.93; 95% CI: 0.87-0.98; P=0.01), nonsmokers (OR: 4.90; 95% CI: 1.22-19.73; P=0.025), and those who had depression (OR: 2.22; 95% CI: 1.36-3.62; P=0.001). Most of the IBD patients believed in the necessity of maintaining immunosuppression (86.7%), but 36.6% reported concerns about drugs.

CONCLUSION

Nonadherence to thiopurines plays a significant role in IBD. Nonetheless, it does not increase with association with biological agents. Involuntary nonadherence is higher. Male sex, younger age, nonsmoker, and presence of depression were independent predictors of nonadherence to immunomodulators. More than one-third of IBD patients had concerns about drugs. Optimizing the discussion on patients' concerns to overcome perceptual barriers related to drugs may obviate the negative course of IBD related to nonadherence.

International variation in medication prescription rates among elderly patients with inflammatory bowel disease

BACKGROUND AND AIMS

The elderly represent a growing demographic of patients with IBD. No study has previously described variations in care or medication prescriptions in senior patients with IBD. We compared prescription rates among elderly patients with IBD in four countries using health administrative data.

METHODS

Databases from the United States (US), United Kingdom (UK), Denmark and Canada were queried. Variation in prescription rates between countries was assessed in patients ≥65y with prevalent IBD who had ≥1 prescription for an IBD-related medication in a given quarter between 2004 and 2009. Patients were identified using previously-reported, validated algorithms. Country-specific rates were compared in each quarter using Fisher's exact test.

RESULTS

In patients with Crohn's disease, Canada and US had higher prescription rates for oral 5-ASA (P<0.0001 in all quarters) and infliximab (P<0.05 in 22/24 quarters), while the US had higher rates of thiopurine usage (P<0.05 in 23/24 quarters). Canada had greater rates of methotrexate prescriptions (P<0.05 in 21/24 quarters analyzed). In patients with ulcerative colitis (UC), rates of oral steroid usage was lowest in the US (P<0.05 in 22/24 quarters) and oral 5-ASA use was highest in the US and Canada (P<0.0001 in all quarters). Canada and Denmark used more rectal therapy than the US. Infliximab usage in UC was significantly higher in the US and Canada after 2006.

CONCLUSIONS

Significant variation in medication prescription rates exists among countries. Future research should assess whether these differences were associated with disparities in outcomes and health care costs.

Factors associated with thiopurine non-adherence in patients with inflammatory bowel disease

BACKGROUND

Medication non-adherence seems to be a particular problem in younger patients with inflammatory bowel disease (IBD) and has a negative impact on disease outcome.

AIMS

To assess whether non-adherence, defined using thiopurine metabolite levels, is more common in young adults attending a transition clinic than adults with IBD and whether psychological co-morbidity is a contributing factor. We also determined the usefulness of the Modified Morisky 8-item Adherence Scale (MMAS-8) to detect non-adherence.

METHODS

Seventy young adults [51% (36) male] and 74 [62% (46) male] adults were included. Psychological co-morbidity was assessed using the Hospital Anxiety Depression Scale (HADS) and self-reported adherence using the MMAS-8.

RESULTS

Twelve percent (18/144) of the patients were non-adherent. Multivariate analysis [OR, (95% CI), P value] confirmed that being young adult [6.1 (1.7-22.5), 0.001], of lower socio-economic status [1.1 (1.0-1.1), <0.01] and reporting higher HADS-D scores [1.2 (1.0-1.4), 0.01] were associated with non-adherence. Receiver operator curve analysis of MMAS-8 scores gave an area under the curve (95% CI) of 0.85 (0.77-0.92), (P < 0.0001): using a cut-off of <6, the MMAS-8 score has a sensitivity of 94% and a specificity of 64% to predict thiopurine non-adherence. Non-adherence was associated with escalation in therapy, hospital admission and surgeries in the subsequent 6 months of follow up.

CONCLUSIONS

Non-adherence to thiopurines is more common in young adults with inflammatory bowel disease, and is associated with lower socio-economic status and depression. The high negative predictive value of MMAS-8 scores <6 suggests that it could be a useful screen for thiopurine non-adherence.

The impact of introducing thioguanine nucleotide monitoring into an inflammatory bowel disease clinic

BACKGROUND

Thioguanine nucleotides (TGNs) are the active product of thiopurine metabolism. Levels have been correlated with effective clinical response. Nonetheless, the value of TGN monitoring in clinical practice is debated. We report the influence of introducing TGN monitoring into a large adult inflammatory bowel disease (IBD) clinic.

PATIENTS AND METHODS

Patients with IBD undergoing TGN monitoring were identified from Purine Research Laboratory records. Whole blood TGNs and methylated mercaptopurine nucleotides were hydrolysed to the base and measured using HPLC. Clinical and laboratory data were obtained retrospectively.

RESULTS

One hundred and eighty-nine patients with 608 available TGN results were identified. In non-responders, TGNs directed treatment change in 39/53 patients. When treatment was changed as directed by TGN, 18/20 (90%) improved vs. 7/21 (33%) where the treatment decision was not TGN-directed, p < 0.001. Where treatment change was directed at optimisation of thiopurine therapy, 14/20 achieved steroid-free remission at 6 months vs. 3/10 where the TGN was ignored, (p = 0.037). Six per cent of patients were non-adherent, 25% under-dosed and 29% over-dosed by TGN. Twelve per cent of patients predominantly methylated thiopurines, this group had low TGN levels and high risk of hepatotoxicity. In responders, adherence and dosing issues were identified and TGN-guided dose-reduction was possible without precipitating relapse. Mean cell volume (MCV), white blood cell count (WBC) and lymphocyte counts were not adequate surrogate markers. MCV/WBC ratio correlated with clinical response, but was less useful than TGN for guiding clinical decisions.

CONCLUSIONS

Monitoring TGNs enables thiopurine therapy to be optimised and individualised, guiding effective treatment decisions and improving clinical outcomes.

Split-dose administration of thiopurine drugs: a novel and effective strategy for managing preferential 6-MMP metabolism

BACKGROUND

Mercaptopurine and azathioprine (AZA) are efficacious in treating IBD. 6-tioguanine (6-TGN) levels correlate with therapeutic efficacy, whereas high 6-methylmercaptopurine (6-MMP) levels are associated with hepatotoxicity and myelotoxicity. Some IBD patients exhibit dose-limiting preferential 6-MMP production, which may lead to undesired side effects and impact efficacy.

AIM

To review the outcomes of thiopurine split-dosing in patients with preferential 6-MMP metabolism.

METHODS

A retrospective chart review of 179 IBD patients treated at the Cedars-Sinai IBD Center with AZA or mercaptopurine was performed. Preferential 6-MMP metabolisers with 6-MMP levels greater than 7000 pmol/8 × 10(8) erythrocytes who underwent split-dosing were identified and assessed for biochemical and clinical responses to these dose modifications.

RESULTS

A total of 20 of 179 patients met the criteria for preferential 6-MMP metabolism and underwent thiopurine split-dosing. Dividing the total daily thiopurine dose led to a reduction in 6-MMP levels (11785 vs. 5324 pmol/8 × 10(8) erythrocytes; P < 0.0001) without negatively affecting clinical disease activity or 6-TGN levels (239 vs. 216 pmol/8 × 10(8) erythrocytes; P = N.S.) and led to resolution of 6-MMP associated side effects (elevated transaminases, leucopenia and flu-like symptoms) in all but two patients. After mean follow-up of 36 months, 12 patients remained in clinical remission on split-dose mercaptopurine. Five of the remaining eight patients escalated to anti-TNF therapy, two progressed to surgery, and one switched to tioguanine therapy.

CONCLUSION

Split-dose administration of mercaptopurine/AZA represents an alternative option in IBD patients with preferential 6-MMP metabolism who might otherwise require steroid exposure or escalation of therapy.

Factors associated with nonadherence to thiopurines in adolescent and adult patients with inflammatory bowel disease

OBJECTIVES

We hypothesised that nonadherence to thiopurines is more common in adolescents than in adults with inflammatory bowel disease.

METHODS

We sought factors associated with thiopurine nonadherence defined by thiopurine metabolite levels.

RESULTS

Multivariate logistic regression confirmed that adolescents (odds ratio [OR] 4.6 [95% confidence interval [CI] 1.9-11.5]; P < 0.01) compared with adults, patients with Crohn disease (OR 3.3 [CI 1.1-10.5] P = 0.04) compared with ulcerative colitis, and patients living in more socially deprived areas (OR 1.03 [CI 1.0-1.1] P = 0.02) were more likely to be nonadherent to thiopurines.

CONCLUSIONS

Adolescents are more frequently nonadherent than adults: prospective studies are required to determine the reasons for nonadherence in adolescents.

Common misconceptions about 5-aminosalicylates and thiopurines in inflammatory bowel disease

Misconceptions are common in the care of patients with inflammatory bowel disease (IBD). In this paper, we state the most commonly found misconceptions in clinical practice and deal with the use of 5-aminosalicylates and thiopurines, to review the related scientific evidence, and make appropriate recommendations. Prevention of errors needs knowledge to avoid making such errors through ignorance. However, the amount of knowledge is increasing so quickly that one new danger is an overabundance of information. IBD is a model of a very complex disease and our goal with this review is to summarize the key evidence for the most common daily clinical problems. With regard to the use of 5-aminosalicylates, the best practice may to be consider abandoning the use of these drugs in patients with small bowel Crohn’ s disease. The combined approach with oral plus topical 5-aminosalicylates should be the first-line therapy in patients with active ulcerative colitis; once-daily treatment should be offered as a first choice regimen due to its better compliance and higher efficacy. With regard to thiopurines, they seem to be as effective in ulcerative colitis as in Crohn’ s disease. Underdosing of thiopurines is a form of undertreatment. Thiopurines should probably be continued indefinitely because their withdrawal is associated with a high risk of relapse. Mercaptopurine is a safe alternative in patients with digestive intolerance or hepatotoxicity due to azathioprine. Finally, thiopurine methyltransferase (TPMT) screening cannot substitute for regular monitoring because the majority of cases of myelotoxicity are not TPMT-related.

Clinical usefulness of therapeutic drug monitoring of thiopurines in patients with inadequately controlled inflammatory bowel disease

BACKGROUND

Circulating concentrations of 6-thioguanine nucleotide (6-TGN) and 6-methyl mercaptopurine (6-MMP) are associated with thiopurine efficacy and may predict toxicity. This study aimed to examine retrospectively the utility of measuring metabolite concentrations in patients with inflammatory bowel disease (IBD) who had continuing symptoms despite stable thiopurine treatment.

METHODS

Concentrations of 6-TGN and 6-MMP were measured in lysates of washed red cells by high-performance liquid chromatography in peripheral blood drawn from 63 symptomatic patients with IBD (63% men, mean age 37, range 14-74 years, 67% Crohn's disease, 33% ulcerative colitis) treated with azathioprine or 6-mercaptopurine. Short-term clinical outcomes were examined.

RESULTS

6-TGN concentrations weakly correlated with the thiopurine dose (r = 0.28, P = 0.08). On weight-based criteria, 50% of patients were underdosed. However, metabolite patterns suggested 7 (11%) patients were noncompliant, 18 (29%) were being underdosed, 33 (52%) were refractory to treatment with either appropriate (41%) or elevated (11%) metabolite concentrations, and 6 (10%) had a raised 6-MMP:6-TGN ratio consistent with aberrant thiopurine metabolism. The clinical outcome improved in 40 of 46 (87%) of patients in whom the course of action taken was as recommended by a metabolite-directed algorithm, while 3 of 17 patients (18%) improved where discordant actions were taken (P = 0.0001; Fisher's exact test). Fifteen patients (24%) avoided inappropriate escalation of therapy.

CONCLUSIONS

Dose-optimization or toxicity-avoidance strategies frequently result from metabolite testing in patients with inadequate efficacy from thiopurines, with evidence of better outcomes. Thiopurine metabolite testing is a potentially powerful tool for optimizing thiopurine usage in IBD.

Adherence to adalimumab therapy in Crohn's disease: a French multicenter experience

BACKGROUND

We evaluated adherence to adalimumab therapy in Crohn's disease (CD).

METHODS

This was an observational multicenter study conducted in four French university hospitals between April 4, 2008 and January 1, 2010. Patients were systematically asked, at each clinical visit, whether or not they delayed or missed an injection of adalimumab over the past 3 months. Patients were also asked about the reasons for their nonadherence.

RESULTS

Of the 108 patients analyzed, 33 (30.6%) delayed the administration of at least one injection and 16 (14.8%) missed at least one injection over the past 3 months. The main reasons for overall nonadherence were: forgetfulness (24.6%), infection (24.6%), and travel (20%). Other reasons for nonadherence were intentional nonadherence (10.8%), pharmaceutical supply issues (9.2%), side effects (7.7%), pregnancy (1.5%), and CD-related hospitalization (1.5%). Adalimumab regimen of 40 mg every other week was a positive predictor for injection delays (P = 0.02, odds ratio [OR] = 3.76, 95% confidence interval [CI], 1.28-11.05), whereas having at least one relapse in the past 12 months was associated with fewer delays (P = 0.02, OR = 0.37, 95% CI, 0.15-0.87). [correction made here after initial online publication]. Disease duration over 90 months negatively predicted failure to inject adalimumab (P = 0.009, OR = 0.17, 95% CI, 0.05-0.64).

CONCLUSIONS

The overall nonadherence rate for adalimumab use was 45.4%. Most of the reasons for nonadherent behaviors could be avoided. An adalimumab regimen of 40 mg every other week was negatively related to adalimumab adherence; both the occurrence of at least one relapse in the past 12 months and disease duration over 90 months were positively related to adherence.

A prospective evaluation of the impact of allopurinol in pediatric and adult IBD patients with preferential metabolism of 6-mercaptopurine to 6-methylmercaptopurine

BACKGROUND

6-mercaptopurine (6-MP) is used for the induction and maintenance of remission of inflammatory bowel disease (IBD). 6-MP is converted into 6-methylmercaptopurine (6-MMP) or 6-thioguanine nucleotides (6-TGN) intracellularly. Treatment response in IBD patients correlates with 6-TGN levels. This study prospectively evaluated the effect of allopurinol on 6-MP metabolites in adult and pediatric IBD patients. Additionally, we quantified the prevalence of preferential metabolism towards 6-MMP through a retrospective analysis of IBD patients.

METHODS

Twenty patients (10 adult; 10 pediatric) with evidence of preferential metabolism towards 6-MMP, (6-TGN<250 pmol/8×10⁸ RBCs and 6-MMP>5000 pmol/8×10⁸ RBCs) were prospectively treated with allopurinol 100 mg daily and up to 100 mg of 6-MP. 6-MP dose was adjusted after a 3-week metabolite measurement.

RESULTS

The median dose of 6-MP for adults decreased from 100mg daily (range: 37.5-150 mg) to 25mg daily (range: 12.5-50 mg). The median dose of 6-MP for pediatric patients decreased from 50 mg (range: 25-50 mg) to 10.7 mg (range: 10.7 to 21.4 mg). Mean 6-TGN levels in all subjects increased from 197.4 (± 59) to 284.8 (± 107) pmol/8×10⁸ RBCs (p=0.0005). Mean 6-MMP levels in all subjects decreased from a mean of 7719.8 (± 4716) to 404.8 (± 332) pmol/8×10⁸ RBCs (p=0.0004). There were no complications associated with allopurinol therapy. Eighty-eight (30.9%) of 285 IBD patients had evidence of preferential metabolism towards 6-MMP. The proportion of preferential metabolism was equal in adults and pediatric patients.

CONCLUSION

Our results indicate that the addition of allopurinol safely shifts metabolite production in both adult and pediatric IBD patients and that there is a high prevalence of preferential metabolism towards 6-MMP among IBD patients.

Pharmacogenomics in the treatment of inflammatory bowel disease

In recent years, the benefits of early aggressive treatment paradigms for inflammatory bowel disease have emerged. Symptomatic improvement is no longer considered adequate; instead, the aim of treatment has become mucosal healing and altered natural history. Nonetheless, we still fail to achieve these end points in a large number of our patients. There are many reasons why patients fail to respond or develop toxicity when exposed to drugs used for inflammatory bowel disease, but genetic variation is likely to account for a significant proportion of this. Some examples, notably thiopurine methyltransferase polymorphism in thiopurine treatment, are already established in clinical practice. We present a review of the expanding literature in this field, highlighting many interesting developments in pharmacogenomics applied to inflammatory bowel disease and, where possible, providing guidance on the translation of these developments into clinical practice.

Initial clinical experience with allopurinol-thiopurine combination therapy in pediatric inflammatory bowel disease

BACKGROUND

Thiopurines are a mainstay of immunomodulator therapy in inflammatory bowel disease (IBD). Despite their efficacy, some patients may have a poor response due to inability to achieve adequate levels of the active metabolite, 6-thioguanine (6-TGN). Others experience hepatotoxicity, which correlates with excessive 6-methylmercaptopurine (6-MMP) levels. Two adult studies have demonstrated successful manipulation of thiopurine metabolism with allopurinol, a xanthine oxidase inhibitor, to achieve more optimal thiopurine levels. The aim was to retrospectively characterize the utility of allopurinol to optimize thiopurine metabolite levels in pediatric IBD patients.

METHODS

Thirteen patients received allopurinol daily (100 mg in patients >or=30 kg and 50 mg <30 kg), and their thiopurine dose was simultaneously reduced to 25%-50% of the previous maintenance dose. Metabolite levels and other screening labs were checked 2-4 weeks later.

RESULTS

The mean azathioprine dose was decreased from 148.1 to 59.6 mg daily (60% of the mean original dose). The mean 6-TGN level increased from 173 to 303 pmol/8 x 10(8) red blood cell count (RBC) (P = 0.03), and the mean 6-MMP level decreased from 7888 to 2315 pmol/8 x 10(8) RBC (P < 0.001). Elevated transaminase levels improved or resolved in all patients. Two patients experienced reversible neutropenia. At the conclusion of the study 9 patients (69%) remained on combination therapy with a mean duration of follow-up of 162.8 +/- 119.2 days.

CONCLUSIONS

Combination therapy successfully shunted thiopurine metabolites to a more favorable pattern. Reversible neutropenia was the most common side effect (2 patients). Long-term prospective studies are needed in this patient population.

Thiopurine-induced myelotoxicity in patients with inflammatory bowel disease: a review

AIM

Probably, the most important and potentially lethal adverse event of azathioprine (AZA) and mercaptopurine (MP) is myelosuppression. Our aim was to conduct a review of AZA/MP-induced myelotoxicity in inflammatory bowel disease (IBD) patients.

METHODS

Bibliographical searches were performed in MEDLINE/EMBASE. The studies evaluating thiopurine-induced myelotoxicity in patients with IBD were reviewed. The cumulative incidence and the incidence rate of AZA/MP-induced myelotoxicity were calculated by a meta-analysis.

RESULTS

In total, 66 studies (8,302 patients) were included. The cumulative incidence of AZA/MP-induced myelotoxicity was 7% (95% confidence interval [CI] 6-8%). The incidence rate (per patient and year of treatment) of the drug-induced myelotoxicity was 3% (95% CI 3-4%). The risk was roughly similar with AZA and with MP (7%vs 9%). The duration of AZA/MP treatment in patients with myelotoxicity ranged from 12 days to 27 yr. The cumulative incidence of infections among AZA/MP-induced myelotoxicity patients was 6.5%. The cumulative incidence of severe myelotoxicity was 1.1% (incidence rate 0.9%). Three deaths were reported due to myelotoxicity (cumulative incidence 0.06%, 95% CI 0.02-0.17%). The risk of death among patients who developed myelotoxicity was 0.94% (95% CI 0.32-2.70%).

CONCLUSION

The incidence rate of myelotoxicity in IBD patients receiving AZA/MP is approximately 3% per patient and year of treatment. Although bone marrow toxicity may develop at any time after starting the therapy, this happens more frequently during the first months. The incidence rate of severe myelotoxicity is less than 1% per patient and year of treatment, and the mortality risk is less than 0.1% (which means that the risk of death among IBD patients who develop myelotoxicity is approximately 1%).

A triangulation study of the clinician and patient experiences of the use of the immunosuppressant drugs azathioprine and 6-mercaptopurine for the management of inflammatory bowel disease

AIM

The aim of this study was to explore the service for patients with inflammatory bowel disease taking or having taken azathioprine or 6-mercaptopurine in the last three years, at two District General Hospitals within the same Trust.

BACKGROUND

Published data confirm that the use of azathioprine and 6-mercaptopurine is effective in the control of inflammatory bowel disease. However, there are inconsistencies in dosing regimes, blood monitoring and duration of therapy. Regimes used have been largely based on clinicians' personal preference leading to inconsistencies in practice.

METHODS

A questionnaire, designed to elicit the experience of treatment regimes, blood monitoring and access to information was sent to 130 patients taking or having taken azathioprine or 6-mercaptopurine in the last three years. A further questionnaire was sent to 94 general practitioners and interviews were conducted with 10 hospital doctors initiating treatment.

RESULTS

The study demonstrated lack of clarity in the prescribing methods, the monitoring regimes being offered, variation in information given to patients and consequent patient knowledge.

CONCLUSION

Azathioprine and 6-mercaptopurine are increasingly being used successfully in inflammatory bowel disease, sparing the use of steroids and maintaining remission over a longer period. A review of the current literature has informed and made possible a suggested blood-monitoring regime.

RELEVANCE TO CLINICAL PRACTICE

The adoption of a protocol-led service, managed by the nurse specialist, incorporating guided self-management by patients should be considered. A shared-care approach with the patient and general practitioner with rapid access to secondary care would provide a robust system.

Adherence to thiopurine treatment in out-patients with Crohn's disease

BACKGROUND

High frequency of incomplete or non-response to azathioprine (AZA) and/or mercaptopurine (MP) limit their use in Crohn's disease (CD). Non-adherence is considered to be of relevance for ineffectiveness.

AIM

To assess adherence to thiopurines in CD out-patients treated in a single gastroenterology practice.

METHODS

Patients were eligible for inclusion if they received AZA/MP for at least 3 months. After follow-up of 3 months, adherence to AZA/MP was assessed by quantitation of relevant thiopurine metabolite levels in red blood cells as well as by patients' self-report using standardized questionnaire.

RESULTS

Sixty-five patients were prospectively included. Six patients (9.2%) had metabolite profiles indicative of non-adherence. Self-assessed questionnaire revealed non-adherence in four of 56 patients (7.1%). Therapeutic drug monitoring (TDM) and self-assessment as two independent methods had a concordance rate of 75%. Metabolite levels and self-assessed adherence were not significantly different between patients in remission compared with those with active disease.

CONCLUSIONS

Out-patients with CD treated in a single gastroenterology practice had a satisfactory adherence (>90%) to thiopurine therapy. Different measures of adherence (TDM and self-report) applied to the same patient suggest comparable levels. TDM appears to be a reliable tool to assess adherence to thiopurines in clinical practice.

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.

How adherent to treatment with azathioprine are patients with Crohn's disease in long-term remission?

BACKGROUND

Patients with longstanding quiescent Crohn's disease on azathioprine usually maintain an excellent quality of life but are also concerned about long-term safety. This may affect adherence to treatment. The aim of the present study was to assess the adherence to azathioprine in a cohort of patients with Crohn's disease in long-term remission.

METHODS

Thirty patients with Crohn's disease in remission on azathioprine for > or =48 months were enrolled in the study. All were asked to record the number of azathioprine tablets they consumed daily. Notes were kept every other month for 6 months. Adherence was defined as consumption of > or =80% of medication.

RESULTS

Most patients (18/28, 74.3%) were not adherent to treatment. The mean (+/-SD) daily dose of azathioprine in adherent and nonadherent patients was 145 +/- 45 mg and 102 +/- 20 mg, respectively. However, there were no significant differences between the 2 groups in the mean IBDQ score and mean Crohn's Disease Activity Index (CDAI) score, both throughout the entire study and at each time point of the study. Male gender, single status, and consumption of >5 concomitant medications were associated with nonadherence.

CONCLUSIONS

Most patients with Crohn's disease in longstanding remission had low self-reported adherence to azathioprine. Both male gender and single status were associated with nonadherence to azathioprine, whereas disease factors were not related to self-reported adherence. Patients considered nonadherent to treatment maintained disease remission and a quality of life similar to patients who were adherent to treatment.

[Monitoring of thiopurine methyltransferase and thiopurine metabolites to optimize azathioprine therapy in inflammatory bowel disease]

Determination of the activity of thiopurine methyltransferase (TPMT) and of thiopurine metabolites (6-thioguanine and 6-methylmercaptopurine nucleotides) could be useful for individualized monitoring of azathioprine (AZA) and 6-mercaptopurine (6-MP) doses. TPMT activity in the general population follows a trimodal distribution, in which approximately 0.3% of the population is homozygotic for the low-activity allele. A notable correlation has been observed between the low TPMP activity genotype or phenotype and the risk of myelotoxicity. Patients with a high TPMT activity genotype or homozygous phenotype should receive immunosuppressive doses that have clearly been demonstrated to be effective. In contrast, in patients with a low TPMT activity genotype or homozygous phenotype, the use of AZA/6-MP should be contraindicated or only very small doses should be administered. Importantly, TPMP deficiency explains only some cases of myelotoxicity and consequently periodic laboratory testing should be performed in patients receiving AZA/6-MP, even though TPMP function may be normal. Currently, the utility of routine thiopurine metabolite determinations in patients undergoing AZA/6-MP therapy has not been established and this practice should be limited to specific situations such as lack of response to thiopurine therapy or the occurrence of thiopurine-related adverse effects. Randomized trials comparing the routine strategy of AZA/6-MP dosing (based exclusively on the patient's weight) versus individualized monitoring (based on quantification of TPMP activity and/or thiopurine metabolites) are required before definitive conclusions on the most effective alternative can be drawn.

Medication-taking behavior in a cohort of patients with inflammatory bowel disease

Recent studies have shown a low adherence rate to maintenance treatment in patients with inflammatory bowel disease (IBD). We sought to assess the medication-taking behavior in a cohort of patients with IBD. We prospectively included IBD patients from the outpatient clinic who agreed to answer a questionnaire about prescribed treatment and adherence. Physicians registered clinical data including prescribed medications. Two hundred fourteen patients (115 Crohn's disease/99 ulcerative colitis) were included. The most prescribed medications were oral mesalazine (56.5%) and immunomodulators (41.1%). Forty-three percent of patients admitted to occasionally forgetting to take their medication but only 7.5% of them did it voluntary. Oral mesalazine and azathioprine were the drugs with the poorest compliance, with nonadherence rates of 45% and 25% of the total prescribed doses, respectively. The only factor associated with a better adherence was a more complicated course of the disease-steroid dependency, steroid refractoriness, need for infliximab treatment, hospitalization, or surgery (P=.02). Twenty percent of patients admitted to self-medicating. An important proportion of patients with IBD admit to forget some doses of the prescribed medication in the setting of a specialized unit of a referral centre.

Review article: how to control and improve adherence to therapy in inflammatory bowel disease

Any chronic disease is a risk situation for non-adherence to treatment. This results in suboptimal medication, and poor disease control. Adherence and compliance are directly related to therapeutic success, which is further complicated in inflammatory bowel disease patients. There is a wide array of circumstances that increase the likelihood of non-compliance in a given patient: difficult-to-follow treatment schedules (multiple doses and multiple drugs), insufficient patient information, longer evolution of the disease and inactive disease. Depression, male gender, active employment and living alone are also associated with poorer adherence to therapy. Monitoring drug intake is possible in many circumstances, directly or indirectly (urinary salicylate levels; erythrocyte metabolites and increased mean corpuscular volume and bilirubin in patients under azathioprine; blood levels of ciclosporin or tacrolimus). However, such measures are probably better utilized for dose adjustment and not for the identification of non-compliant patients. High-risk patients are a target group in which pre-emptive intervention could ensure better compliance. If the question of non-adherence arises, for instance, as a possible cause of therapy failure, the patient should be carefully approached. This should take into consideration factors that may be corrected and, most importantly, should aim at building a better patient-doctor relationship.

Evolution of thiopurine use in pediatric inflammatory bowel disease in an academic center

OBJECTIVES

We evaluated how our use of thiopurines was altered by determination of thiopurine methyltransferase (TPMT) level and drug dose adjustment guided by a 6-mercaptopurine metabolite assay. We further examined whether these resulted in better selection of the drug dose, improved control of disease, and decreased corticosteroid use in pediatric inflammatory bowel disease (IBD).

PATIENTS AND METHODS

This is a retrospective review of 101 pediatric patients with IBD receiving a stable dose of azathioprine (AZA) for 4 months or longer. The study group (n = 64) consisted of patients who received AZA and had metabolite levels measured. The comparison group (n = 37) consisted of patients who were receiving AZA before the availability of metabolite measurement. The TPMT level was measured in study group patients before starting AZA.

RESULTS

Patients with normal TPMT level received a higher starting dose of AZA than in patients who were heterozygous for TPMT deficiency (1.7 vs 0.9 mg/[kg x d], P < 0.0001). Study group patients received a higher starting dose (1.6 vs 1.2 mg/[kg x d], P = 0.001) and a higher final dose of AZA (2.4 vs 1.7 mg/[kg x d], P < 0.0001) compared with patients in the comparison group. These patients also had more dose adjustments (0.8 vs 0.4 mg/kg, P < 0.002). The number of disease exacerbations per patient per year was 55% less in the study group (95% CI, 17%-76%, P < 0.0001). The study group patients received less prednisone (P < 0.0001) and had lower disease activity scores (P < 0.05). There was no difference between groups in infliximab use or surgery rate.

CONCLUSIONS

Azathioprine dose adjustment using a 6-mercaptopurine metabolite assay was associated with use of higher doses, improved control of disease and decreased corticosteroid use in pediatric patients with IBD.

Pharmacoeconomic analyses of azathioprine, methotrexate and prospective pharmacogenetic testing for the management of inflammatory bowel disease

OBJECTIVES

To compare the cost effectiveness of azathioprine (AZA), methotrexate (MTX) and no immunosuppression for maintaining remission of moderate to severe inflammatory bowel disease (IBD) in New Zealand Caucasians, and to determine whether prospective testing for poor metabolisers of AZA by genotype or phenotype is cost effective.

METHODS

Pharmacoeconomic models were developed to compare treatment costs and effects (QALYs) in theoretical populations of 1,000 IBD patients over a 1-year period. Efficacy and tolerability profiles for AZA and MTX were taken from the literature. The costs (year 2004 values) of the drugs and treatment of adverse effects were estimated from New Zealand drug and service costs. Representations of the patients' health-related quality of life (HR-QOL) were obtained from clinicians via the EQ-5D health state classification system and valued using the New Zealand EQ-5D social tariff. The effects of genotyping or phenotyping a population for thiopurine methyltransferase (TPMT) status were compared using the prevalence of TPMT deficiency in Caucasians, the relative risks of neutropenia and the associated costs.

RESULTS

Net cost savings (vs no immunosuppressant treatment) of approximately 2.5 million and 1 million New Zealand dollars were realised for AZA and MTX, respectively, for the theoretical 1,000 patients, and AZA generated 877 QALYs compared with 633 for MTX. Phenotype and genotype testing generated net cost savings (vs no testing) of 120,000 and 11,000 New Zealand dollars, respectively. Savings related to phenotype tests were greater because of the lower assay costs of phenotype testing and a greater likelihood of pre-empting neutropenia.

CONCLUSION

Our model suggests that both MTX and AZA may generate significant net cost savings and benefits for patients with IBD in New Zealand, with AZA likely to be more cost effective than MTX. Prospective testing for poor metabolisers of AZA may also be cost effective, with phenotype testing likely to be more cost effective than genotype testing.

Azathioprine metabolite measurements: its use in current clinical practice

Azathioprine (AZA) is one of the oldest immunosuppressive agents available today. It is used as an immunomodulator in different disciplines such as hematology, dermatology, rheumatology, gastroenterology, and transplant. The present article presents a summary of AZA metabolism and the role of AZA metabolite measurements in the current clinical practice.

Utility of azathioprine metabolite measurements in post-transplant recurrent autoimmune and immune-mediated hepatitis

Patients with post-transplant immune-mediated hepatitis (IMH) and recurrent autoimmune hepatitis (RAIH) have a poor outcome and a higher need for retransplantation. Azathioprine (AZA) is used as adjunctive immunosuppression after transplantation; optimizing its dose may be a key point in preserving graft function. Complications of high AZA dosing make dose escalation potentially problematic. Our aim was to correlate AZA metabolite levels with therapeutic effects, toxicity, and adherence to medication in children with IMH and RAIH. Charts of 14 patients were retrospectively reviewed. The post-transplant diagnosis was based on liver biopsy and autoimmune markers. AZA was prescribed after establishing the post-transplant diagnosis. AZA was started at 1.1 (1.0-1.8) mg/kg/day. Routine biochemical studies, tacrolimus levels, 6-thioguanine (6-TG) and 6-methylmercaptopurine levels were assessed every 8 wk. AZA dose was routinely adjusted to achieve 6-TG levels between 235 and 450 pmol per 8 x 10(8) RBC. A total of 92 samples from 14 patients were reviewed. Four patients were excluded because of non-adherence. AZA dose was increased by 245% resulting in eight of 10 patients in the target range; no hepatic or bone marrow toxicity was observed. ALT levels and steroid requirements were significantly reduced (p < 0.05). The AZA dose required to achieve target 6-TG levels was significantly greater in children <10 yr. AZA metabolite testing in children post-liver transplant is useful in assessing adherence to medication and it is potentially helpful in optimizing medication dosing. In younger children the AZA dose requirements were two to four times higher than previously reported standard doses.

The utility of 6-thioguanine metabolite levels in managing patients with inflammatory bowel disease

OBJECTIVES

We aimed at determining the utility of measuring 6-thioguanine (6-TG) and 6-methylmercaptopurine (6-MMP) in inflammatory bowel disease (IBD) patients on azathioprine (AZA) or 6-mercaptopurine (6-MP), whether the described therapeutic range for 6-TG (235-400 pmol/8 x 10(8) red blood cells, RBC) correlated with clinical remission or leukopenia, and if 6-MMP level was a marker for hepatotoxicity (>5,700 pmol/8 x 10(8) RBC).

METHODS

Study eligibility included an IBD diagnosis of >6 months and either active disease or disease remission of <6 months and the use of AZA/6-MP for >10 wk consecutively. Metabolite levels were evaluated against clinical status, CBC, and hepatic parameters.

RESULTS

Seventy-four of 166 AZA/6-MP users were eligible. 6-TG levels >235 pmol/8 x 10(8) RBC were found in 22/59 (38%) with active disease and in 7/15 with remission (47%, p= 0.16). There was a trend of higher 6-TG levels among those in remission versus those with active disease (mean 325 +/- 284 vs 223 +/- 159 pmol/8 x 10(8) RBC, p= 0.2). No hepatotoxicity was observed, although 12.2% had 6-MMP levels > 5,700 pmol/8 x 10(8) RBC. The correlation between 6-MP dose and 6-TG levels was weak (r = 0.22, p= 0.08). The 6-TG level did not correlate with WBC. There were five instances, each of markedly low levels of both 6-TG and 6-MMP, suggesting noncompliance and of marked 6-MMP levels versus 6-TG.

CONCLUSIONS

There was a poor correlation between 6-TG levels and remission. Nonetheless, the measurements of these levels are helpful when patients are on high doses but not achieving remission since noncompliance or metabolism favoring 6-MMP can be established.

Thioguanine-nucleotides do not predict efficacy of tioguanine in Crohn's disease

BACKGROUND

6-Thioguanine-nucleotides seem to be the active metabolites of thiopurine therapy, and their monitoring has been considered a useful tool for optimizing response in inflammatory bowel diseases. Tioguanine (thioguanine) therapy results in much higher levels of 6-thioguanine-nucleotide levels when compared with azathioprine or mercaptopurine.

AIM

To elucidate the influence of 6-thioguanine-nucleotide and methylated 6-thioguanine-nucleotide levels under tioguanine on efficacy and toxicity in Crohn's disease.

METHODS

6-Thioguanine-nucleotide and methylated 6-tioguanine-nucleotide levels were measured regularly in 26 Crohn's disease patients treated with tioguanine. Nucleotide levels were related to efficacy and toxicity.

RESULTS

6-Thioguanine-nucleotide levels rose very high [median 1241 pmol/8 x 10(8) red blood cells (range 313-1853)]. Methylated 6-thioguanine-nucleotide levels were detected in all patients [491 pmol/8 x 10(8) red blood cells (154-1775)]. 6-Thioguanine-nucleotide and methylated 6-thioguanine-nucleotide concentrations correlated significantly (r = 0.7, P < 0.0001). Nucleotide levels from patients achieving remission (n = 14) did not differ significantly from non-remitters (n = 12) [6-thioguanine-nucleotide: 1077 (599-2160) vs. 1210 (534-4665); methylated 6-thioguanine-nucleotide: 510 (214-1222) vs. 421 (145-1284)]. One patient with intermediate thiopurine S-methyltransferase activity experienced bone marrow toxicity upon dose escalation parallel with excessively high thioguanine-nucleotide levels.

CONCLUSIONS

6-Thioguanine-nucleotide as well as methylated 6-thioguanine-nucleotide levels under tioguanine therapy were not related to efficacy. This suggests that monitoring of 6-thioguanine-nucleotide levels is not a useful tool to predict response to thiopurines.