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The Influence of Obesity on Choice of Biologic Agent in Rheumatoid Arthritis

In rheumatoid arthritis we have a wide range of options available to us when we progress to a biologic treatment option. We have little to differentiate between these agents based on the clinical trials. We often make our choices based on minor hints from clinical features, comorbidities, or cost considerations.

Body mass index (BMI) and obesity are clinical features which have not been prominent in influencing our decisions regarding biologic agent. Obesity has been recognised as a predictor of reduced response to TNF inhibitors. Suggestions of differences between the treatment response to different TNF inhibitors have been inconsistent. 

It is in this setting that Dr Gianfrancesco and colleagues used the RISE registry to explore the effects of biologic drugs based on BMI, Abstract #0588, Poster Session B, on Sunday. They included 15,139 individuals with rheumatoid arthritis. Disease activity was assessed using the clinical disease activity index (CDAI). I like the use of CDAI for the purpose of biologic comparisons as it does not include CRP, and so avoids the undue differential influence of certain biologic agents on CRP. Longitudinal targeted maximum likelihood estimation was used to calculate the average treatment effect (ATE) to evaluate differences between biologic agents.

They found no overall difference between TNF inhibitor and non-TNF inhibitor biologics over 12 months, either in the overall population, nor in obese or non-obese individuals. However, it is when they looked at individual non-TNF biologics that things became interesting. They found that abatacept use (vs TNF inhibitor) resulted in significantly larger decreases in CDAI in obese individuals (ATE 3.70 (95%CI 2.26, 5.15) for TNF inhibitor vs abatacept). In contrast, they found that tocilizumab (vs TNF inhibitor) resulted in significantly larger decreases in CDAI in non-obese individuals (ATE 4.05 (95%CI 2.90, 5.21) for TNF inhibitor vs tocilizumab).

These results are interesting, and suggest that when other factors are equal there may be a rationale to preferring abatacept in obese individuals and tocilizumab in non-obese individuals.


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