Background: Therapeutic drug monitoring of infliximab is commonly performed based on trough concentration. However, doses and dosing intervals may be adapted to patient outcomes, and this trough concentration target may correspond to a large range of exposures in terms of the area under the concentration-time curve (AUC). The objectives of this study were to assess the real-life exposure to intravenous infliximab in patients with Crohn disease in remission at year 1 and to assess the evolution of exposure in patients who switched to subcutaneous infliximab.
Methods: The authors conducted a retrospective observational pharmacokinetic study in patients with Crohn disease who had available infliximab concentrations during intravenous and subcutaneous infliximab maintenance therapy as per the standard of care. Infliximab exposure parameters (AUCs and trough concentrations, C0) were compared for different dosing regimens of intravenous infliximab before (intravenous) and after (subcutaneous) the switch.
Results: A total of 113 patients had 383 intravenous infliximab concentrations. Dosing intervals ranged from 4 to 12 weeks. The median/range/CV% C0, AUC0-t, and AUC0-8weeks were 5.3 mcg/mL [<LLoQ-49.6]/71.6%, 37,792 mcg.h/mL [4971-116,366]/33.1%, and 41,582 mcg.h/mL [7953-232,048]/43.9%, respectively. Forty-one patients had available paired C0 after both intravenous and subcutaneous administration. A poor correlation was found between preswitch intravenous infliximab C0 and postswitch subcutaneous infliximab C0.
Conclusions: In this study, the authors suggested that in patients treated with IV IFX, different targets of C0 should be proposed according to treatment schemes and that AUC0-t might be a relevant determinant of clinical remission. Moreover, exposure did not remain stable throughout the switch from IV to SC IFX in any patient. These variations may depend on the intravenous dosing interval before switching.
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