Adalimumab Drug Levels at Secondary Loss of Response Do Not Predict Response to Dose-intensification in Crohn's Disease: A Retrospective, International Multicenter Study.

Background: The exposure-response relationship is less established for adalimumab (ADA) compared with infliximab in inflammatory bowel disease (IBD). Evidence supporting therapeutic drug monitoring post dose-intensification of ADA is limited. We aimed to explore the association between ADA drug levels and Crohn's disease (CD) activity at loss of response, and at 6 and 12 months post dose-intensification.

Methods: We performed a retrospective study of adult patients with CD receiving dose-intensified weekly ADA following secondary loss of response at 3 tertiary centers across 5 years. ADA trough levels were analyzed using a drug-sensitive enzyme-linked immunosorbent assay at loss of response, and 6 and 12 months after dose-intensification. Rates of clinical remission, objective remission (C-reactive protein <5 mg/L, fecal calprotectin <150 µg/g, or absence of inflammation at endoscopy or imaging), and ADA failure were investigated.

Results: A total of 131 CD patients were included, with a median disease duration of 9 (interquartile range, 4-17) years. 51% were biologic exposed prior to ADA and 50% received concomitant immunomodulators. Baseline drug levels measured at secondary loss of response did not discriminate between subsequent responders and non-responders at either 6 or 12 months post dose-intensification. However, both higher drug levels at 6 and 12 months and a higher increment from baseline were associated with improved outcomes. On receiver-operating characteristic analyses, post-escalation ADA drug levels >10.7 µg/mL (area under the receiver-operating characteristic curve [AUROC], 0.66; P = .013) and >10.9 µg/mL (AUROC, 0.67; P = .032) were associated with objective remission at 6 and 12 months, respectively.

Conclusions: Drug levels following dose-intensification rather than at the time of secondary loss of response were associated with subsequent CD remission.