Abstract Background Increasing therapeutic options for inflammatory bowel disease (IBD) calls for tools to aid choice of sequencing. We investigated if pharmacokinetic (PK) and pharmacodynamic (PD) failure mechanisms prompting therapy change influenced subsequent outcomes when switching to a different biologic drug class. Methods Retrospective cohort study at a tertiary, Danish IBD center including all patients treated with first TNF-inhibitors, followed by vedolizumab, and then ustekinumab, as defined by national treatment regulations at time of study. Clinical and objective disease remission were defined by validated indices (HBI, SCCAI, Mayo, SES-CD). Treatment failure was defined by the treating physician and supported by clinical disease activity scorings and objective disease activity evaluations. Drug trough levels and anti-drug antibodies were measured at manifest treatment failure in routinely collected biobanked samples. PK-PD failure was defined according to maintenance drug concentrations: infliximab 8.0 µg/mL, adalimumab 12.0, golimumab 1.4, vedolizumab 15. Primary treatment failure despite dose intensification was ascribed to PD. Primary endpoints were steroid-free treatment persistence and one-year remission. Results The study included 112 patients switching from TNF-inhibitors to vedolizumab (infliximab n=61, adalimumab n=32, golimumab n=16, certolizumab pegol n=3) and 31 subsequently to ustekinumab. Treatment persistence on vedolizumab did not differ between patients discontinuing TNF-inhibitors due to PK (n=28, 31%) or PD (n=63, 69%) (mean 989 days [554-1,424] vs. 951 [659-1,242], p=0.93). One-year steroid-free clinical and objective remission rates on VDZ were also comparable between PK-PD groups (29% vs 35%, p=0.63 and 35% vs. 43%, p=0.48, respectively). Furthermore, treatment persistence on ustekinumab was neither different between patients having initially discontinued TNF-inhibitors due to PK or PD (1,553 [997-2,110], n=11) vs. 1,200 [762-1,639], n=14; p=0.42), nor later discontinued vedolizumab due to PK or PD (1,305 [832-1,778], n=11 vs. 1,323 [785-1,862], n=15; p=0.43). Clinical and objective remission on ustekinumab was also similar between these groups. Sensitivity analysis using other thresholds to define PK or PD failure were congruent to the above findings. Sensitivity analyses with exclusion of primary non-responders and multivariate analyses correcting for potential confounders also supported the findings. Conclusion Our study does not show evidence for inferior outcomes during subsequent sequencing to biologics with different modes of action in patients switching due to PK failures as compared to those with PD failure. Choice of sequencing may thus take into account other aspects such as efficacy, safety and costs.
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