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P517. Evaluating Adalimumab drug and antibody levels as predictors of clinical and laboratory response in Crohn's disease patients

Y. Mazor1, U. Koplov2, D. Ben Hur1, R. Almog1, M. Waterman1, S. Ben-Horin2, Y. Chowers1, 1Rambam Health Care Campus, Department of Gastroenterololgy, Israel, 2Chaim Sheba Medical Center, Tel Hashomer, Gastroenterology, Tel Aviv, Israel

Background

Adalimumab is effective for treatment of Crohn's disease (CD). Anti-drug antibodies and low trough serum concentrations have been implicated as predisposing factors for treatment failure. We aimed to assess Adalimumab and anti-Adalimumab antibody (AAA) serum levels and correlate them with clinical response and serum C-reactive protein (CRP).

Methods

Sera from 121 Adalimumab-treated CD patients, with treatment duration of at least 8 weeks, were obtained. Demographic data and clinical response (CR) were recorded and classified as complete, partial or none. Serum Adalimumab and AAA were measured. Receiver operator characteristic (ROC) analysis was preformed to find drug and antibody thresholds for predicting disease activity. Univariate Wilcoxon rank sum tests comparing drug levels, antibody levels, CRP and disease activity were performed. Finally, multivariate regression was utilized to explore the correlation between drug levels, AAA, and disease activity.

Results

161 serum samples were obtained, 94 at trough. Adalimumab >5 µg/ml was predictive of normal CRP (AUC 0.772 for all patients, AUC 0.776 for only trough level measurements, p < 0.005). AAA only did not predict normal CRP or clinical remission, but all patients with trough AAA >5 µg/ml had elevated CRP (RR 16.185, p < 0.005). On multivariate regression, correlation between drug levels, CRP, and clinical response was preserved at AAA levels <5 µg/ml, but not above these levels.

Conclusion

Adalimumab serum concentration >5 µg/ml was correlated with normal CRP and CD remission. This correlation is lost when the patient has AAA >5 µg/ ml, suggesting a neutralizing effect of high AAA.