Monitoring of patients with IBD treated with azathioprine or 6-MP

Dr John Marshall is a professor and director in the Division of Gastroenterology at McMaster University and editor in chief of the Journal of the Canadian Association of Gastroenterology.

How to monitor a patient with inflammatory bowel disease (IBD) receiving long-term treatment with azathioprine or 6-mercaptopurine (6-MP)

John Marshall, MD, MSc: I think it is fair to say first that we are using less thiopurine now than we were 5, 10, or certainly 20 years ago because we have other options available for treatment of IBD. But we do certainly have patients who are on long-time thiopurine therapy, either with 6-MP or with azathioprine. I think in terms of how we follow these patients, there are some immediate things we need to monitor, which would include the complete blood count (CBC) and liver enzymes at minimum every 2 to 3 months.

Typically, before we start people on these agents we have done thiopurine methyltransferase (TPMT) testing. At our center it is done by genotype, but at other centers it could be done by phenotype. It is not a perfect test for predicting complications of thiopurines, but it helps to identify a high-risk subset of patients. We are really going forward to follow this bloodwork every 2 to 3 months.

It is fair to say that thiopurines have some other health concerns that need some other monitoring or consideration. There is a small, but I think significant, increase in risk of nonmelanoma skin cancer, which for us ideally means involving a dermatologist for annual skin examinations. In Canada, we have difficulty accessing dermatologists for these sorts of assessments, so at minimum we are advising patients of this risk, asking them to do their own skin checks, and advising them against excess sun exposure and measures to prevent that.

Of course, there is also an increased risk of lymphoma that has been associated with long-time thiopurine use. We do not really have a good strategy for monitoring that, but I think being aware of it and having a low index of suspicion when patients develop symptoms is the way to go.