Long term efficacy and safety of allopurinol and azathioprine or 6-mercaptopurine in patients with inflammatory bowel disease

Low-dose azathioprine or mercaptopurine in combination with allopurinol can bypass many adverse drug reactions in patients with inflammatory bowel disease

BACKGROUND

The thiopurine drugs, azathioprine and mercaptopurine (MP), are established treatments for IBD. However, therapeutic failure caused by adverse drug reactions occurs frequently.

AIM

To study combination of allopurinol with reduced-dose thiopurine in an attempt to avoid adverse drug reactions in the treatment of IBD.

METHODS

Patients with drug reactions to full-dose thiopurines were recruited for combination therapy in two IBD centres in this retrospective study. Dosing was guided by measuring thiopurine methyltransferase (for UK patients) or thioguanine nucleotides and methyl-6MP (Australian patients). Response was monitored by clinical activity indices.

RESULTS

Of 41 patients, 25 had non-hepatic and 16 had hepatitic reactions. Clinical remission was achieved in 32 patients (78%) with a median follow-up of 41 weeks (range 0.5-400). Patients who did not respond to combination therapy tended to fail early with the same adverse reaction. The relative risk of having an adverse reaction with methyl-6MP in the top interquartile range was 2.7 (1.3-28) times that with methyl-6MP in the lower three quartiles (95% confidence interval).

CONCLUSION

The combined experience from our centres is the largest reported experience of this combination therapy strategy in IBD, and the first to provide evidence for benefit in thiopurine and allopurinol co-therapy to avoid non-hepatitic adverse drug reactions.

Optimizing conventional therapies for inflammatory bowel disease

Conventional therapies remain the mainstay of treatment for most patients with inflammatory bowel disease (IBD), with only a minority of patients requiring biologic therapies. Recently, attention has focused on optimizing dosing strategies for biologic agents; however, of equal importance are recent advances in the optimization of conventional IBD therapies. Newer aminosalicylate formulations demonstrate similar efficacy with a reduced pill burden and less frequent dosing, while new corticosteroid preparations may retain efficacy with a significantly improved safety profile. The limited indications for antibiotics and probiotics have been further refined by recent data, although uncertainties remain. Advances in the understanding of thiopurine metabolism continue to improve dose optimization and the potential for deliberate therapeutic manipulation with adjunctive therapies. An improved knowledge of intracellular methotrexate metabolism may translate to similar opportunities in the future. This article discusses recent advances relevant to clinical practice today.