Balsalazide and azathioprine or 6-mercaptopurine

Impact of Genetic Polymorphisms on 6-Thioguanine Nucleotide Levels and Toxicity in Pediatric Patients with IBD Treated with Azathioprine

BACKGROUND

Thiopurine-related toxicity results in discontinuation of therapy in up to 30% of patients with inflammatory bowel disease. Although thiopurine S-methyltransferase (TPMT) is implicated in toxicity, not all toxicity can be attributed to TPMT polymorphisms. We investigated the effects of polymorphisms of genes involved in thiopurine and folate metabolism pathways on 6-thioguanine nucleotide levels and toxicity.

METHODS

Retrospective clinical data and blood samples were collected from 132 pediatric patients with inflammatory bowel disease treated with azathioprine. Eighty-seven genetic polymorphisms of 30 genes were screened using the MassARRAY system, and 70 polymorphisms of 28 genes were selected for further analysis.

RESULTS

TPMT genotype (P < 0.001), concurrent use of mesalazine (P = 0.006), ABCC5 (rs2293001) (P < 0.001), ITPA (rs2236206 and rs8362) (P = 0.010 and P = 0.003), and ABCB1 (rs2032582) (P = 0.028) were all associated with the ratio of 6-thioguanine nucleotides to azathioprine dose. ADK (rs10824095) (P = 0.004, odds ratio [OR] = 6.220), SLC29A1 (rs747199) (P = 0.016, OR = 5.681), and TYMS (rs34743033) (P = 0.045, OR = 3.846) were associated with neutropenia. ABCC1 (rs2074087) (P = 0.022, OR = 3.406), IMPDH1 (rs2278294) (P = 0.027, OR = 0.276), and IMPDH2 (rs11706052) (P = 0.034, OR = 3.639) had a significant impact on lymphopenia.

CONCLUSIONS

This study describes genetic polymorphisms in genes whose products may affect pharmacokinetics and which may predict the relative likelihood of benefit or risk from thiopurine treatment. These findings may serve as a basis for personalized thiopurine therapy in pediatric patients with inflammatory bowel disease, although our data need to be validated in further studies.

Relationship between azathioprine dosage, 6-thioguanine nucleotide levels, and therapeutic response in pediatric patients with IBD treated with azathioprine

BACKGROUND

Azathioprine (AZA) is commonly used to treat IBD either alone or in combination with mesalazine. However, there are relatively few studies concerning the relationship between AZA dose, thiopurine metabolite levels, and therapeutic response in pediatric patients treated with both AZA and mesalazine.

METHODS

We retrospectively investigated the relationship between AZA dose, thiopurine metabolite levels, and therapeutic response in 137 pediatric patients with IBD treated with AZA using multilevel analysis. Additional factors affecting metabolite levels and therapeutic response were also analyzed.

RESULTS

A positive correlation was observed between AZA dosage and 6-thioguanine nucleotide (6-TGN) level (P < 0.0001). Variant TPMT genotype (P < 0.001) and concomitant use of mesalazine (P < 0.001) were predictors of higher 6-TGN levels. Leukopenia (P = 0.025) and lymphopenia (P = 0.045) were associated with higher levels of 6-TGN. Poor AZA compliance affected median 6-TGN levels (P < 0.001). The frequency of patients with median 6-TGN levels >235 pmol per 8 × 10(8) red blood cells was the highest in the sustained therapeutic response group (P = 0.015). Age, sex, IBD type, and duration of AZA therapy did not influence 6-TGN levels or therapeutic effect.

CONCLUSIONS

AZA dosage is positively correlated with 6-TGN level. Higher 6-TGN levels are related to leukopenia, lymphopenia, and concurrent use of mesalazine. These results provide the rationale for monitoring metabolites to optimize drug dosing and minimize drug-related toxicity. In addition, maintenance of 6-TGN levels within a beneficial therapeutic range by direct monitoring should be helpful in attaining therapeutic efficacy, although this possibility should be verified in prospective studies.

Monitoring and safety of azathioprine therapy in inflammatory bowel disease

Azathioprine is the most common drug used to maintain clinical remission in inflammatory bowel disease. This drug is also important as a steroid-sparing agent in steroid-dependent and chronically active inflammatory bowel disease. Nevertheless, many questions remain concerning the optimal treatment regimens of azathioprine. The dose of azathioprine has to be reduced or the therapy has to be discontinued frequently because of drug-induced toxicity. In this review, we discuss monitoring of thiopurines, adverse events, malignant complications and how to use azathioprine safely and usefully.