P088 Serum drug and antibody level monitoring of infliximab and vedolizumab: Use in the proactive management of IBD
Authors: Ryan Burkholder , Mark Porta 
Published: July 2019

BACKGROUND:
There has been debate regarding monitoring therapeutic drug levels in order to maximize clinical, endoscopic, and histologic response, despite studies proving benefit of this approach. There are 2 approaches to monitoring. Reactive drug monitoring, the more common practice, obtains drug levels when patients show evidence of active disease such as worsening clinical symptoms, mucosal ulceration, or elevated biomarkers. Proactive drug monitoring involves early, frequent assessment of drug and antibody levels even as disease is in remission. This quality improvement study is aimed at establishing serial drug level and antibody monitoring for Infliximab and Vedolizumab infusions.

METHODS:
All patients receiving Infliximab and Vedolizumab at our infusion clinic were considered, and patients not receiving the appropriate scheduled therapy were removed from the analysis. An order to obtain routine drug trough and antibody levels prior to each infusion was placed into the EMR infusion therapy plan for both Infliximab and Vedolizumab. Patient drug and antibody levels, before and 4 months after therapy plan change, were reviewed and compared to the recommended goal trough levels. Changes in therapy and compliance with clinic follow up appointments were also reviewed.

RESULTS:
A total of 34 patients receiving Infliximab and 21 patients receiving Vedolizumab were included in this analysis. In the Infliximab group, 7 (20%) patients were found to be at the recommended serum trough level. 13 (38%) patients were found to be non-compliant with clinic follow up or infusion treatments.16 (47%) patients had no prior monitoring prior to therapy plan change. Additionally, 2 (6%) patients had high antibody levels and receiving scheduled infusions with no clinic follow up for over 1 year. In the Vedolizumab group, 6 (29%) patients were at the recommended serum trough level. 2 (10%) patients were found to be non-compliant. 19 (90%) patients had no prior monitoring prior to therapy plan change.

CONCLUSION(S):
Given the limited number of targeted therapies currently available, maximization of therapy is key to achieving and maintaining disease control. In this analysis, a majority of our patients receiving anti-TNF infusion therapy were below the therapeutic drug level goal. There is a significant amount of non-compliance with clinic follow up and infusion visits in our patient population. Multiple patients had not been seen in clinic for over one year but continued to get infusion therapy at regular intervals. They were found to have a significant elevation of antibodies with no detectable drug level. With therapeutic drug monitoring, we are able to identify these patients and re-establish clinic follow up. Antibody formation against Anti-TNF therapy is more frequent in patients losing therapy response, associated with lower trough levels, and increases risk of infusion-related reactions. It is well studied that non-compliance is associated with refractory disease and increased risk for antibody formation. The added costs of monitoring may be an initial drawback; however, the addition of therapeutic drug monitoring can act as an objective guide for maximizing and maintaining therapeutic response in patients—ultimately delivering high value care.