P149 Therapeutic drug monitoring of Vedolizumab for patients with inflammatory bowel disease: real world experience

Introduction Vedolizumab (VDZ) is a humanised monoclonal IgG-1 antibody that is used in the treatment of inflammatory bowel disease (IBD). Unlike with anti-TNF therapy the benefit of therapeutic drug monitoring (TDM) of VDZ remains debatable. A number of trials have suggested that VDZ trough levels post induction of >18–20 μg/ml are associated with better clinical outcomes.1 2 However, data regarding levels in the maintenance phase is less convincing but likely to be lower.1 Real-world data is lacking, and the use of Vedolizumab drug monitoring is not widely used outside tertiary centres. The aim of this study was to evaluate our current practice at a busy London district general hospital. Methods A retrospective study of all patients undergoing VDZ TDM at our unit between July 2017 and December 2019. Data collected included indication and timing of level, value and whether the level resulted in a change in management. Results 67 patients were established on VDZ between July 2017 and December 2019. 15 patients (22.4%) had VDZ levels performed with 4 patients undergoing more than one level during this time giving a total of 22 levels performed. Levels were undertaken in the majority of patients for secondary loss of response (LOR) (16/22). A small number were taken during maintenance (4/22), post induction (1/22), and after recapturing response (1/22). Out of the 22 drug levels analysed, 10 (45.5%) were classified as trough levels (within 1 week of a VDZ infusion). Trough levels ranged between 5 μg/ml and 32.7 μg/ml with a median of 15.8 μg/ml. We used a cut-off of 18 μg/ml when interpreting levels. All trough levels taken were performed due to LOR. 6 (60%) levels taken in 4 patients were <18 μg/ml with the remaining 4 levels ≥18 μg/ml. The outcomes of the 4 patients who had sub-therapeutic trough levels were analysed. 2 patients recaptured response after either a course of corticosteroids or optimising 5-ASA therapy. 2 were switched to other therapeutic options (Infliximab and Ustekinumab). A further 3 non-trough levels (in 2 patients) analysed were sub-therapeutic. 1 recaptured response after optimisation and 1 responded to a 3 month period of escalated 4-weekly VDZ therapy. All patients with levels ≥18 μg/ml have continued VDZ therapy with good response. Conclusions In our real-world setting, using a cut-off of <18 μg/ml for levels carried out in LOR is helpful in identifying the need to either escalate/optimise or switch agent. However, VDZ levels are being underutilised and are only being taken as trough in 45.5% of patients. There remains uncertainty as to how maintenance levels should be interpreted and national guidance after more studies would be welcome. References Papamichael K, Cheifetz A, Melmed G, et al. Appropriate Therapeutic Drug Monitoring of Biologic Agents for Patients With Inflammatory Bowel Diseases. Clinical Gastroenterology and Hepatology 2019;17:1655–1668. Ward M, Sparrow M and Roblin X. Therapeutic drug monitoring of vedolizumab in inflammatory bowel disease: current data and future directions. Therapeutics Advances in Gastroenterology. 2018:11;1–10.