P611 Relation between AntiTNF levels during the induction and clinical and radiological outcomes in perianal Crohn´s disease

Background Perianal Crohn's disease(PCD) significantly impacts quality of life with poor long-term prognosis. Anti-tumor necrosis factor(anti-TNF) therapy improves fistula closure rates. However, achieving permanent closure remains challenging. Our aim is to evaluate the relation between antiTNF(infliximab (IFX) and adalimumab(ADA) serum concentrations at induction(w2 and 6), and clinical and radiological outcomes at w24 and w52 Methods We conducted a single tertiary center, retrospective, cohort study including patients with an established diagnosis of PCD treated with antiTNF because of perianal activity. Variables related to their PCD(phenotype, location, fistulas type) were collected. Regarding treatment, we collected serum levels at week 2,6,24 and 52, concomitant treatment and setons presence. We defined clinical response as the absence of drainage on physical examination and clinical remission as the absence of external fistula openings. Radiological response was defined as the absence of T2 hypersignal, gadolinium enhancement, abscess and proctitis in pelvic MRI Results 65 patients were included, baseline characteristics are in Table1. None of the demographic characteristics collected were statistically significant related to clinical or radiological response although non smokers(p=0.01), ileal(p=0.02) and non-stricturing disease(p=0.01) had statistically significant higher drug levels. Taking into account the clinical response at w52, IFX mean levels at w2 were 25.8µg/mL(SD 4.1) in non responders and 30.9µg/mL(SD 14) in responders(p=0.39). At w6 they were 17.2µg/mL(SD 12.2) and 19.4µg/mL(SD 13.8) respectively(p=0.7). ADA mean levels at w2 were 13.3µg/mL(SD 7.7) in non responders and 14µg/mL(SD 6.3) in responders(p=0.87). At w6 they were 10.1µg/mL(SD 3.3) and 12µg/mL(SD 6.1) respectively(p= 0.59). For radiological response at w52 IFX mean levels at w2 were 27µg/mL(SD 15.3) in non responders and 32.7µg/mL(SD 14.5) in responders(p=0.45). At w6 the mean levels were 15.9µg/mL(SD 6.7) and 23.7µg/mL(SD 14.8) respectively(p=0.27). In ADA group the mean levels at w2 were 14.8µg/mL(SD 7.6) in responders and only one patient did not respond. At w6 ADA mean levels were 12.3µg/mL(SD 5.9) in non responders and 12.7µg/mL(SD 6.2) in responders(p=0.94). Early response at w24 was related with a long-term response at w52, 89.9% of the patients who responded at w52, had already responded at w24. Conclusion In our study we observed that almost 90% of the patients who had an early response also responded at w52, so trying to achieve an early response should be an aim in clinical practice. Despite the limited number of patients, our study shows a trend in the relationship between higher antiTNF levels and clinical and radiological response rates