P546 Which are the optimal adalimumab trough levels associated with biological remission in patients with inflammatory bowel disease?

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Background: Anti-TNF trough levels have been associated with clinical outcomes in inflammatory bowel disease (IBD). Several therapeutic algorithms based on therapeutic drug monitoring have been proposed. Such algorithms require knowing the optimal drug trough level therapeutic window. However, there are few data about which levels of Adalimumab (ADA) are associated with remission. The aim of this study was to evaluate the relationship between ADA trough levels (ADA-TL) and faecal calprotectin (FC) and to determine the optimal ADA-TL associated with biological remission (BR).

Methods: Prospective observational study including IBD patients under ADA treatment in steady state. ADA-TL, anti-ADA antibodies and biological markers (FC and C-reactive protein [CRP]) were measured. BR was defined as FC <250μg/g along with CRP <5mg/L.

Results: 49 samples from 34 patients were included: 94% corresponded to crohn's disease, 61% were female, 14% smokers, 25% under intensified treatment, 74% on concomitant immunosuppressive treatment and 45% were naïve to anti-TNF.

There was a statistically significant inverse correlation between ADA-TL and biomarkers of inflammation (FC: R=−0.54, p=0.0002; CRP: R=−0.32, p=0.02).

The proportion of cases in BR was significantly higher in those with the highest ADA-TL (ADA-TL<9.5 mg/L: BR 7.1%; ADA-TL 9.5–11.8mg/L: BR 38.5%; ADA-TL >11.8 mg/L: BR 71.4%; p=0.002).

The performance of ADA-TL to identify BR can be considered fair: the area under de curve was 0.79. The accuracy qualities of 2 cut-off points of AD-TL to predict BR, one that prioritizes the sensibility (9.5mg/L), and another that prioritizes the specificity (12mg/L), are shown in Table 1.

Conclusions: There is an inverse correlation between ADA trough levels and FC values. ADA trough levels below 9.5mg/L are associated with a low probability of biological remission.

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