Breaking the rules - the benefits of co-prescribing allopurinol and thiopurines : clinical practice

The thiopurines, azathioprine and 6-mercaptopurine, have been used to treat inflammatory bowel disease (Crohn's disease (CD) and Ulcerative Colitis (UC)) for decades. Cochrane reviews have confirmed that azathioprine is effective in Crohn's disease both for induction (OR=2.4) and maintenance of remission (OR=2.3). Although less effective in UC, it also helps induce remission (OR=1.6) and maintain that remission once achieved. This leads to both reduced hospitalisation rates and a reduced need for surgery. In addition, patients are much more likely to become steroid-free if they are taking a thiopurine. Traditionally, azathioprine has been prescribed as a weight based dose (eg 2-2.5mg/kg/day) with adjustments made if there is any evidence of bone marrow suppression on full blood count (FBC) monitoring. With this approach azathioprine has over a 40% rate of remission after 12 months treatment for Crohn's disease. The question is what to do with patients who do not respond to weight based dosing. The majority of these patients are not actually refractory to thiopurines and the recent availability of drug levels has shown us why.