P508 Association between clinical outcome and post induction CT-P13 trough levels at week 14, in patients with inflammatory bowel disease. Preliminary results in an observational multicentric study

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Background: CT-P13 became the first Infliximab (IFX) biosimilar approved for the treatment of Inflammatory Bowel Disease (IBD) in 2013. Measurement of IFX trough levels has been suggested as a new approach to tailor the therapy. Few studies have evaluated in clinical practice the relationship between primary failure after induction therapy (10–30%) and trough levels of CT-P13. Our aim is to evaluate the usefulness of systematically testing trough levels of CT-P13 at week 14.

Methods: We conducted a multicentric observational study including all adult patients with IBD treated with CT-P13, excluding patients on CT-P13 to prevent post-surgical recurrence. Induction dose was 5mg/kg at week 0, 2 and 6. Trough levels were measured in week 14 using enzyme-linked immunoabsorbent assay (ELISA) (Promonitor-IFX; Progenika Biopharma®). In Crohn's Disease (CD) a decrease ≥3 points in Harvey-Bradshaw index (HBI) was considered partial response (PR) and a HBI lower than 5 was considered clinical remission (CR). In Ulcerative Colitis (UC) a decrease ≥3 points in Partial Mayo Index (MI) was considered PR and CR was a MI lower than 3.

Results: We included 80 patients with a median age of 47.55±13.6 (62.7% males). CD patients (49) had a basal HBI of 7.88±4.01. UC patients (31) had a basal MI of 6.55±2.11. Patients had previous treatment with antiTNF drugs in 38.5%, and 83.1% with immunomodulators (IMM). We associated IMM to CT-P13 in 59% of our patients.

Median trough levels at week 14 were 4.36 (CD 4.04 and UC 4.85). No differences were found between patients with concomitant IMM (4.40) or without it (4.31); naïve (3.97) and no naïve anti-TNF patients (5.07).

Postinduction trough levels in patients with NR were 2.897, PR 4.57 and CR 4.87. Patients with primary failure presented lower CT-P13 trough levels compared with patients in CR, although no statistical significance was found (p=0.539).

Considering less than 3μg/ml as infratherapeutic, only 39.7% of patients reached therapeutic levels (36.3% CD, 44.8% UC). NR had 33.3% of patients (CD = UC), PR 48% of patients (41.6% CD, 43.85% UC) and CR 36.3% (36.3% CD and 40% UC).

Conclusions: The median CT-P13 trough level in week 14 was 4.36 μg/ml. No statistically significant differences were found between CD/UC, naïve/not naive to antiTNF therapy.

Association of inmunomodulators did not increased CT-P13 postinduction levels.

Up to 60% of patients had infratherapeutic (<3μg) CT-P13 postinduction levels.

There were no statistically significant differences between therapeutic or infratherapeutic levels and clinical response at week 14.

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