P303 Biologic Therapeutic Drug Monitoring in Patients with Inflammatory Bowel Disease: Are we aiming high?

Robertson, A.(1);Hawkins, I.(1);Wilkinson, S.(2);Patel, R.(3);

(1)Lakes District Health Board, House Officer, Rotorua, New Zealand;(2)Lakes District Health Board, Gastroenterology Nurse Specialist, Rotorua, New Zealand;(3)Lakes District Health Board, Consultant Gastroenterologist, Rotorua, New Zealand;


Infliximab and Adalimumab are the only funded biologic therapies for inflammatory bowel disease (IBD) in New Zealand. We hypothesised that clinicians are aiming for higher drug trough levels to mitigate for the absence of alternative therapies.


Retrospective study of IBD patients at Lakes DHB from 2016 to 2021. Data collected using the IBD patient register and electronic patient records. Change in management included dose escalation, de-escalation and switching biologic. Analyses were performed using chi-square and student t-test. Target trough levels are Infliximab >5 mg/L and Adalimumab>7.5 mg/L. We defined high trough levels as greater than double the suggested target levels (Infliximab >10mg/L, Adalimumab>15mg/L).


197 patients in the IBD register. 79 (40.1%) receiving biologic therapy (Infliximab 31 [39.2%], Adalimumab 48 [60.8%]).Therapeutic drug monitoring (TDM) performed in 61 (77.2%) biologic patients with a total of 129 TDM results available. Mean trough levels: Infliximab 7.7 (sd 9.2) mg/L, Adalimumab 5.7 (sd5.8) mg/L.


High trough levels were seen more with Infliximab use, reflecting its increased use as a 2nd line agent and a final option to optimise medical management prior to considering surgery. Fewer changes to management were seen with high trough levels indicating improved clinical outcomes and acceptability of high levels within our practice.