• Crohn's disease
• inflammatory bowel disease
• anti-TNF therapy
• infliximab
• adalimumab
• IBD
• gastrointesinal endoscopy
• radiation enteritis

The efficacy of infliximab and adalimumab for the treatment of Crohn's disease has been shown in randomised controlled trials and corroborated in observational studies. However, one of the most worrying aspects of biological therapies for patients and clinicians is the variable but relevant proportion of patients on long-term treatment in whom there is a loss of response. From studies evaluating the incidence of loss of response to infliximab in patients with Crohn's disease (including more than 2000 patients and more than 6000 patient-years of follow-up), it is estimated that approximately 40% will lose response to infliximab, and the annual risk for loss of response to infliximab is calculated to be about 13% per patient-year of treatment.1 Similarly, data from a systematic review on the loss of response and need for adalimumab dose intensification in adult and paediatric patients with Crohn's disease showed that the mean percentage of patients who lost response to adalimumab was 18.2% among a total of 955 primary responders, with a calculated annual risk of 20.3% per patient-year. The mean percentage of patients who needed escalation of the adalimumab dose was 21.4% and the annual risk was 24.4% per patient-year.2 Loss of response and intolerance are the main reasons for switching from one anti-tumour necrosis factor (TNF) agent to another. However, constraints in hospital budgets or changes in the personal situation of patients may also lead to consideration of a change in treatment from an intravenous to a subcutaneously administered drug.

In their paper published in this issue of Gut, …