IBD: Switching metabolism-can two drugs be better than one?

Randomised clinical trial: efficacy, safety and dosage of adjunctive allopurinol in azathioprine/mercaptopurine nonresponders (AAA Study)

BACKGROUND

Thiopurine hypermethylation towards 6-methylmercaptopurine (6MMP) instead of 6-thioguanine nucleotides (6TGN) is associated with inefficacy in patients with IBD. Allopurinol reverses such hypermethylation.

AIMS

To prospectively determine efficacy of allopurinol-thiopurine combination and to compare 2 doses of allopurinol.

DESIGN

In a multicentre, double-blind trial, patients with clinically active or steroid-dependent IBD and thiopurine shunting were randomised to 50 or 100 mg/d allopurinol and 25% of their screening thiopurine dose, which was subsequently optimised, aiming for 6TGN of 260-500 pmol/8x10⁸ RBCs. The primary endpoint was steroid-free clinical remission at 24 weeks.

RESULTS

Of 73 patients, 39 (53% [95% CI 42-65]) achieved steroid-free remission, (54% with 50 mg/d and 53% with 100 mg/d). 81% were able to discontinue steroids. Therapeutic 6TGN levels were achieved in both groups. Final thiopurine doses were lower with 100 mg/d allopurinol (P < 0.005). 6MMP: 6TGN ratio decreased from mean 64 to 4 (P < 0.001), being higher with 50 mg/d (6 ± 1.83) than for 100 mg/d ([1 ± 0.16], P = 0.003). Three patients on 50 mg/d failed to sustain low ratios at 24 weeks. Toxicity was minimal; three patients on 50 mg/d allopurinol developed transient leukopenia. Alanine aminotransferase concentrations decreased (P < 0.001) similarly in both arms. Faecal calprotectin levels at study end were lower in patients who achieved the primary endpoint (median 171 [85-541] vs 821[110-5892] ug/g, P = 0.03).

CONCLUSIONS

Low-dose allopurinol-thiopurine combination safely reverses shunting and optimises 6TGN with associated improvement in disease activity. 100 mg/d allopurinol is preferable due to greater metabolite profile stability and lower thiopurine dose without additional toxicity.

Pharmacology and Optimization of Thiopurines and Methotrexate in Inflammatory Bowel Disease

Improving the efficacy and reducing the toxicity of thiopurines and methotrexate (MTX) have been areas of intense basic and clinical research. An increased knowledge on pharmacodynamics and pharmacokinetics of these immunomodulators has optimized treatment strategies in inflammatory bowel disease (IBD). This review focuses on the metabolism and mode of action of thiopurines and MTX, and provides an updated overview of individualized treatment strategies in which efficacy in IBD can be increased without compromising safety. The patient-based monitoring instruments adapted into clinical practice include pretreatment thiopurine S-methyltransferase testing, thiopurine metabolite monitoring, and blood count measurements that may help guiding the dosage to improve clinical outcome. Other approaches for optimizing thiopurine therapy in IBD include combination therapy with allopurinol, 5-aminosalicylates, and/or biologics. Similar strategies are yet to be proven effective in improving the outcome of MTX therapy. Important challenges for the management of IBD in the future relate to individualized dosing of immunomodulators for maximal efficacy with minimal risk of side effects. As low-cost conventional immunomodulators still remain a mainstay in pharmacotherapy of IBD, more research remains warranted, especially to substantiate these tailored management strategies in controlled clinical trials.

The role and advances of immunomodulator therapy for inflammatory bowel disease

Immune modulating drugs such as thiopurines (azathioprine and 6-mercaptopurine) and methotrexate has been a mainstay for treatment of inflammatory bowel disease (IBD) for decades. However, despite widely used in IBD, questions still remain concerning the most rational treatment regimens of these agents. Results from a range of recent studies necessitate increased awareness on how to best use these potent drugs in the clinic. As controversy still remains regarding the most appropriate use of immunomodulators, this review is based on scrutinizing the current literature, with emphasis on randomized controlled trials and Cochrane reviews, focusing on aspects that can lead to optimal and evidence-based thiopurine and methotrexate treatment strategies in IBD.

Thiopurine metabolite measurement leads to changes in management of inflammatory bowel disease

BACKGROUND

The thiopurines azathioprine and 6-mercaptopurine are recommended for maintenance of remission in inflammatory bowel disease (IBD). Measurement of concentrations of the metabolites 6-thioguanine nucleotide and 6-methylmercaptopurine helps delineate interindividual variation in metabolism that may underlie variability in efficacy and toxicity.

AIMS

We aimed to perform a retrospective observational study to determine the utility of thiopurine metabolite testing following its introduction into South Australia.

METHODS

All patients having thiopurine metabolite tests done at Flinders Medical Centre between November 2008 and January 2010 were identified. Case notes of patients with testing done in the context of treatment for IBD were interrogated to determine the reason for testing, clinical context and outcome.

RESULTS

One hundred and fifty-one patients were identified with thiopurine metabolite testing for IBD with 157 testing episodes. Eighty (51.0%) had testing done for flare or inefficacy, 18 (11.5%) for adverse effects, 5 (3.2%) for a combination of inefficacy and adverse effects, and 54 (34.4%) for routine or other reasons. Testing was followed by improved outcomes of increased efficacy, reduced toxicity or change to alternative therapy in 55.0% of the inefficacy/flare group, 27.8% of the suspected adverse reaction group, 60.0% of the combination group, and 13.0% of the routine/other group. Allopurinol was used as cotherapy in 16 patients and led to marked improvements in metabolite concentrations.

CONCLUSIONS

Thiopurine metabolite testing has quickly become established in South Australia. When used for inefficacy or adverse effects, it often leads to improved outcomes. Prospective studies are needed to determine whether routine testing to guide dosing is of benefit.

Recent advances using immunomodulators for inflammatory bowel disease

Use of the immunomodulators thiopurines and methotrexate (MTX) in the treatment of inflammatory bowel disease (IBD), i.e., Crohn's disease and ulcerative colitis (UC), is considered to be good clinical practice. However, despite being administered to a considerable number of IBD patients over the years, questions remain about the most rational treatment regimens of azathioprine (AZA), 6-mercaptopurine (6-MP), and MTX, and results from a range of recent studies necessitate increased attention to how to optimize the use of these immunomodulators. First and foremost, it is of utmost importance to define the subgroup of IBD patients in need of immunomodulators, including those in need of combination therapy with biologic agents, especially because some side effects may be rather severe. Second, colorectal cancer is observed more often in IBD patients than in the background population. However, a recent nationwide Dutch study pointed to a preventive effect of thiopurines. Finally, the need for an appropriate approach to the discontinuation of immunomodulators is emphasized. Since controversy continues regarding the most appropriate use of immunomodulators, this paper is focusing on pharmacokinetics, pharmacogenetics, and therapeutic blood testing, as well as the occurrence of adverse events, when using AZA, 6-MP, and MTX in an attempt to determine a more up-to-date and rational treatment regimen in IBD.