OP006 Correlation of durability of response, serum trough concentrations and outcome parameters: long-term follow-up of the Trough Concentration Adapted Infliximab Treatment (TAXIT) trial
Pouillon L.*1, Ferrante M.1, Van Assche G.1, Rutgeerts P.1, Noman M.1, Vande Casteele N.2, Gils A.3, Vermeire S.1
1University Hospitals Leuven, Department of Gastroenterology and Hepatology, Leuven, Belgium 2University of California San Diego, Department of Medicine, La Jolla, CA, United States 3University of Leuven, Department of Pharmaceutical Sciences, Leuven, Belgium
The Trough Concentration Adapted Infliximab Treatment (TAXIT) randomized controlled trial  showed that targeting patients' infliximab trough concentrations in a 3–7 μg/mL window resulted in a more efficient use of the drug in patients with inflammatory bowel disease (IBD). However, following dose optimization, continued concentration-based dosing was not superior to clinically-based dosing for achieving a co-primary endpoint of clinical and biological remission after 1 year.
This was a retrospective analysis of the long-term outcome of all 226 patients who completed the TAXIT maintenance phase. Durability of response to infliximab was correlated with serum trough concentrations and important quality of care outcome parameters, including need for IBD-related hospitalization, need for abdominal surgery and steroid use.
With a median follow-up of 41 months after the completion of the TAXIT trial, 167/215 (78%) patients were still on continued treatment with infliximab, and 48/215 (22%) patients needed to stop (11 patients were lost to follow-up). Among the 48 patients who discontinued infliximab, 10/27 (37%) randomized previously to the clinically-based dosing arm did so within 1 year, compared to 2/21 (10%) patients randomized to the concentration-based dosing arm (p<0.05).
Among the 167 patients who continued infliximab, the dosing scheme was intensified in 56 patients and de-intensified in 27 patients, compared to the end of the TAXIT maintenance phase. Median trough concentrations of infliximab at the end of follow-up were 4.73 μg/mL (IQR=3.3–6.42). Five patients developed immunogenicity within 1 year after TAXIT and all had been randomized to the clinically-based dosing arm. In patients continuing on infliximab, the rates of IBD-related hospitalization (16/167 patients or 9.6%), abdominal surgery (4/167 patients or 2.4%) and steroid use (6/167 patients or 3.6%) during the entire follow-up period were very low and significantly better than in patients who had to discontinue infliximab.
Continuation of infliximab Discontinuation of infliximab p-value (n=167) (n=48) Hospitalization 16 (9.6%) 16 (33.3%) <0.001 Abdominal surgery 4 (2.4%) 10 (20.8%) <0.001 Steroid use 6 (3.6%) 16 (33.3%) <0.001
In this long-term follow-up of the TAXIT trial, infliximab discontinuation occurred earlier in patients treated in the clinically-based dosing arm than in patients treated in the concentration-based dosing arm. Targeting infliximab trough concentrations to a therapeutic window led to a highly durable treatment response, and was associated with very good outcomes including very low (<5%) surgical rates and steroid use.
 Vande Casteele et al, (2015), Trough concentrations of infliximab guide dosing for patients with inflammatory bowel disease, Gastroenterology