How are thiopurines used and monitored by Swedish gastroenterologists when treating patients with inflammatory bowel disease?

Therapeutic drug monitoring in inflammatory bowel disease: implementation, utilization, and barriers in clinical practice in Scandinavia

BACKGROUND AND AIMS

Therapeutic drug monitoring (TDM) may optimize biologic and thiopurine therapies in inflammatory bowel disease (IBD). The study aimed to investigate implementation and utilization of TDM in Scandinavia.

METHODS

A web-based questionnaire on the use of TDM was distributed to Scandinavian gastroenterologists via the national societies.

RESULTS

In total, 297 IBD physicians prescribing biologic therapies, equally distributed between community and university hospitals, were included (response rate 42%) (Norway 118 (40%), Denmark 86 (29%), Sweden 50 (17%), Finland 33 (11%), Iceland 10 (3%)). Overall, TDM was applied during biologic therapies by 87%, and for TNF-inhibitors >90%. Among the users, reactive and proactive TDM were utilized by 90% and 63%, respectively. Danish physicians were significantly less inclined to use TDM compared to other Scandinavian countries; (58% vs 98%); OR 0.03 [0.01-0.09], p < 0.001). Reactive TDM was commonly applied at primary (74%) and secondary (99%) treatment failure. Proactive TDM was used by 80% during maintenance therapy and 56% during induction and more commonly utilized in Norway (p < 0.001), and by physicians managing >10 IBD patients/week (p = 0.005). TDM scenarios were interpreted in accord with available evidence but with discrepancies for proactive TDM. The main barriers to TDM were lack of guidelines (51%) and time lag between sampling and results (49%). TDM of thiopurines was routinely used by 87%.

CONCLUSION

TDM of biologic and thiopurine therapies has been broadly implemented into clinical practice in Scandinavia. However, physicians call for TDM guidelines detailing indications and interpretations of test results along with improved test response times.

Monitoring thiopurine metabolites in inflammatory bowel disease

Thiopurines (azathioprine and mercaptopurine) are one of the immunosuppressive mainstays for the treatment of inflammatory bowel disease. In spite of its widespread use, thiopurine metabolism is still not fully understood, and a significant proportion of patients suffer toxicity or lack of efficacy. Different enzymatic pathways with individual variations constitute a pharmacogenetic model that seems to be suitable for monitoring and therapeutic intervention. This review is focused on current concepts and recent research that may help clinicians to rationally optimise thiopurine treatment in patients with inflammatory bowel disease.

Association between thiopurine S-methyltransferase polymorphisms and thiopurine-induced adverse drug reactions in patients with inflammatory bowel disease: a meta-analysis

Purpose

Thiopurine drugs are well established treatments in the management of inflammatory bowel disease (IBD), but their use is limited by significant adverse drug reactions (ADRs). Thiopurine S-methyltransferase (TPMT) is an important enzyme involved in thiopurine metabolism. Several clinical guidelines recommend determining TPMT genotype or phenotype before initiating thiopurine therapy. Although several studies have investigated the association between TPMT polymorphisms and thiopurine-induced ADRs, the results are inconsistent. The purpose of this study is to evaluate whether there is an association between TPMT polymorphisms and thiopurine-induced ADRs using meta-analysis.

Methods

We explored PubMed, Web of Science and Embase for articles on TPMT polymorphisms and thiopurine-induced ADRs. Studies that compared TPMT polymorphisms with-ADRs and without-ADRs in IBD patients were included. Relevant outcome data from all the included articles were extracted and the pooled odds ratio (OR) with corresponding 95% confidence intervals were calculated using Revman 5.3 software.

Results

Fourteen published studies, with a total of 2,206 IBD patients, which investigated associations between TPMT polymorphisms and thiopurine-induced ADRs were included this meta-analysis. Our meta-analysis demonstrated that TPMT polymorphisms were significantly associated with thiopurine-induced overall ADRs and bone marrow toxicity; pooled ORs were 3.36 (95%CI: 1.82–6.19) and 6.67 (95%CI: 3.88–11.47), respectively. TPMT polymorphisms were not associated with the development of other ADRs including hepatotoxicity, pancreatitis, gastric intolerance, flu-like symptoms and skin reactions; the corresponding pooled ORs were 1.27 (95%CI: 0.60–2.71), 0.97 (95%CI: 0.38–2.48), 1.82 (95%CI: 0.93–3.53), 1.28 (95%CI: 0.47–3.46) and 2.32 (95%CI: 0.86–6.25), respectively.

Conclusions

Our meta-analysis demonstrated an association of TPMT polymorphisms with overall thiopurine-induced ADRs and bone marrow toxicity, but not with hepatotoxicity, pancreatitis, flu-like symptoms, gastric intolerance and skin reactions. These findings suggest that pretesting the TPMT genotype could be helpful in clinical practice before initiating thiopurine therapy. However, white blood cell count analysis should be the mainstay for follow-up.

Genotyping should be considered the primary choice for pre-treatment evaluation of thiopurine methyltransferase function

BACKGROUND AND AIMS

A pre-treatment determination of the thiopurine S-methyltransferase (TPMT) genotype or phenotype can identify patients at risk of developing severe adverse reactions from thiopurine treatment. The risk of misclassifying a patient might be dependent on the method used. The aim of this study was to investigate the concordance between TPMT genotyping and phenotyping.

METHODS

The data consist of 7195 unselected and consecutive TPMT genotype and phenotype determinations sent to the division of Clinical Pharmacology, Linköping, Sweden. TPMT activity was measured in red blood cells (RBC) and the genotype determined by pyrosequencing for the three most common TPMT variants (TPMT *2, *3A, *3C).

RESULTS

TPMT genotyping identified 89% as TPMT wild type (*1/*1), 10% as TPMT heterozygous and 0.5% as TMPT defective. The overall concordance between genotyping and phenotyping was 95%, while it was 96% among IBD patients (n=4024). Genotyping would have misclassified 8% of the TPMT defectives as heterozygous as compared to 11% if only TPMT activity had been measured. 11% of the heterozygous patients had a normal TPMT activity (>8.9 U/ml RBC) and 3% of the TPMT wild-type patients had an intermediate TPMT activity (2.5-8.9 U/ml RBC).

CONCLUSIONS

There is a risk for TPMT misclassification when only genotyping or phenotyping is used, but it is not reasonable to check both in all patients. Since TPMT genotyping is the more reliable test, especially in TPMT heterozygotes, we suggest that genotyping should be considered the primary choice for the pre-treatment evaluation of TPMT function before initiation of thiopurine therapy.

Thiopurine methyltransferase genotype and thiopurine S-methyltransferase activity in Greek children with inflammatory bowel disease

BACKGROUND

Azathioprine (AZA) and 6-mercaptopurine (6MP) are used in the treatment of pediatric inflammatory bowel disease (IBD). Genetic variations in thiopurine S-methyltranfarase (TPMT) gene have been correlated with enzyme activity and with the occurrence of adverse events to AZA and 6MP. The aim of the present study was to examine the sensitivity and specificity of TPMT genotyping for TPMT enzymatic activity, reducing harm from thiopurine by pretesting, and the association of thiopurine toxicity with TPMT status in children with IBD.

METHODS

TPMT red blood cell (RBC) activity was measured by using a radiochemical method and genotype was determined for the TPMT alleles *2, *3A, *3B and *3C in 108 thiopurinetreated pediatric IBD patients with a mean age of 11.3 years (range 3-16).

RESULTS

Significant TPMT activity differences between wild-type and heterozygous and homozygous mutated subjects were observed. We divided TPMT activity into three categories according to frequency distribution: low (16.67%), intermediate (25.92%) and high (57.41%). The whole population included a total of 77.78% of homozygous wild-type subjects, 15.74% heterozygous variants, 1.85% homozygous variants and five (4.63%) compound heterozygous variant TPMT*3B/*3C. The overall concordance rate between TPMT genotypes and phenotypes was 88.2%. Seven carriers of at least one variant allele and low or intermediate TPMT activity developed adverse effects.

CONCLUSIONS

Our findings suggest that carriers of at least one variant allele and both intermediate and absent TPMT activity have an increased risk of developing thiopurine-induced myelotoxicity compared with individuals with normal genotype and TPMT activity.