A104 A STUDY OF POST-INDUCTION INFLIXIMAB TROUGH LEVELS DEMONSTRATES MOST PEDIATRIC IBD PATIENTS ARE BEING UNDERDOSED

Abstract

Abstract Background Infliximab (IFX) is widely used for induction and maintenance of remission in pediatric inflammatory bowel disease (PIBD). Post induction IFX trough levels are a predictor of clinical and biochemical remission at week 52. Aims - evaluate the effectiveness of infliximab (IFX) induction regimens in attaining therapeutic post induction IFX trough levels in 2 PIBD cohorts. - investigate baseline laboratory values and patient factors as predictors of post-induction levels. Methods 78 patients from Vancouver, Canada [Cohort 1 (C1) originator IFX; variable dose induction regimen] and 62 patients from Glasgow, Scotland [Cohort 2 (C2) replication cohort - biosimilar IFX; standard induction of 5mg/kg at 0, 2 and 6 weeks, with 8 weekly maintenance] were included in the study. Baseline characteristics and laboratory values from time of IFX initiation were recorded. Mann-Whitney U Testing was utilized to analyse the relationship between IFX trough levels and lab parameters. Results The median pre-dose 4 trough in C1 & C2 was 4.25mg/L (IQR 7.8) and 1.85mg/L (IQR 3.38) respectively. In C1 patients who had a trough level <3mg/L pre-dose 4, 62% (20/32) had already had a dose adjustment documented. The IFX dose of 50% (39/78) of C1 patients and 65% (40/62) of C2 patients was escalated following the pre-dose 4 IFX level. TABLE 1 Baseline median albumin (Alb) was significantly lower and replicated in both cohorts in those with low pre-dose 4 IFX levels: IFX trough <0.8mg/L C1: Alb 30g/L vs 37.5g/L in IFX ≥0.8mg/L, p=0.002 C2: Alb 34.5g/L vs 37g/L in IFX ≥0.8mg/L, p=0.02 IFX trough <3.0mg/L C1:Alb 34.5g/L vs 38g/L in IFX ≥3.0mg/L, p= 0.05 C2:Alb 35g/L vs 37g/L in IFX ≥3.0mg/L, p=0.04 IFX trough <5.0mg/L C1:Alb 35g/L vs 39g/L in IFX ≥5.0mg/L, p=0.006 C2:Alb 35g/L vs 37g/L in IFX ≥5.0mg/L, p=0.45 In the combined cohort (C1 + 2), patients with baseline albumin ≤30g/L had significantly lower IFX levels pre-dose 4 than those with albumin >30g/L (1.4mg/L vs 3.55mg/L, p=0.0003). In patients with an albumin ≤30g/L, 23% (6/26) achieved a dose 4 trough level of ≥3.0mg/L, however only 1/6 patients received a standard induction regime meaning only 4% (1/26) of patients had a trough ≥3.0mg/L on standard treatment. Conclusions Standard IFX induction regimen is ineffective in achieving relevant post-induction trough levels (>5 mg/L) in the majority of PIBD patients regardless of IFX type. We suggest that optimization of initial IFX prescribing based on baseline albumin (i.e. a higher dose given to patients with albumin < 30g/L) and subsequent levels will improve post-induction trough levels and consequently clinical outcomes for a greater proportion of patients. Funding Agencies None