Quantitative Analysis of MOR-1 Internalization in Spinal Cord of Morphine-Tolerant Mice.

The biological process of opioid analgesic tolerance remains nowadays elusive. In particular the mechanism by which opioid receptor desensitization occurs has not been completely elucidated to date. One possible hypothesis involves the internalization of MOR. Here, we describe a simple in vitro protocol to investigate the localization of MOR-1 after repeated morphine administration in the spinal cord of morphine-tolerant mice, using western blotting and immunofluorescence techniques.

Strategies to develop highly drug-tolerant cell-based neutralizing antibody assay: neutralizing antidrug antibodies extraction and drug depletion.

Aim: Drug interference poses great analytical challenges for cell-based neutralizing antidrug antibodies (NAb) assay. The work aimed to improve assay drug tolerance through biotin-drug extraction with acid dissociation method optimization and developing new approach. Results: The NAb extraction with biotin-drug extraction with acid dissociation approach has been optimized by reducing biotinylated drug leaching and improving NAb elution efficiency, resulting in drug tolerance of up to 160 µg/ml. To circumvent the low acid elution efficiency of NAb from drug, a novel drug depletion approach was developed, which combined acid dissociation and drug targeted crosslinked capture, achieved drug tolerance up to 400 µg/ml. At last, a strategy workflow for sample pretreatment approach selection and optimization was established for improving drug tolerance of NAb assay. Conclusion: We demonstrated that reduced biotinylated drug leaching and the high NAb elution efficiency was critical for improving assay drug tolerance. Drug depletion offers an alternative approach to overcome low NAb elution efficiency.

Drug Tolerant Anti-drug Antibody Assay for Infliximab Treatment in Clinical Practice Identifies Positive Cases Earlier.

A subgroup of patients treated with infliximab lose response to the treatment and one reason for this is the development of anti-drug antibodies (ADA). If used optimally, measuring drug and ADA level could lead to a more personalized and efficient treatment regime, and enable identification of ADA-positive patients before the underlying disease flares or allergic reactions occur. With the use of a drug-tolerant ADA assay which can detect ADA irrespective of drug levels in the sample, we determined the impact of ADA on treatment failure to infliximab. The aims of this study were to estimate the real-life optimal serum infliximab (sIFX) level and set a clinical threshold value for a drug-tolerant ADA assay. Trough levels of sIFX were measured with ELISA. Free ADA was measured with two drug-sensitive methods (ELISA and a bioassay) and one drug-tolerant method (PandA). Two real-life cohorts treated with infliximab were included; a cross-sectional cohort including patients with inflammatory rheumatic diseases (n = 270) and a prospective cohort of rheumatoid arthritis (RA) patients (n = 73) followed for 1 year. Normal range of sIFX was estimated from the prospective cohort and an arbitrary optimal drug level was set to be between 1 and 6 µg/mL. Using this range, optimal sIFX was found in only 60% (163/270) of the patients in the cross-sectional cohort. These patients had significantly better treatment response than those with a drug level under 1 µg/mL, who had an ADA frequency of 34% (19/56) using the drug-tolerant method. In the prospective cohort, the drug-tolerant assay could identify 34% (53/155 samples) as ADA positive in samples with sIFX level >0.2 µg/mL. ADA were seldom detected in patients with >1 µg/mL sIFX, with three interesting exceptions. A clinically relevant ADA threshold was determined to be >3 RECL as measured with the drug-tolerant assay. In a real-life setting, there was a substantial number of patients with suboptimal drug levels and a proportion of these had ADA. Both too low and too high drug levels correlated with worse disease, but for different reasons. Adding a drug-tolerant assay enabled detection of ADA earlier and regardless of drug level at time of sampling.

High ionic strength dissociation assay (HISDA) for high drug tolerant immunogenicity testing.

Aim: Antidrug antibody (ADA) assessment may be challenged in studies that involve the administration of high doses of biotherapeutics and/or with long half-lives. In such cases, ADA assays with optimized drug tolerance are desired. Material & Methods: We evaluated the use of MgCl2 to develop high ionic strength dissociation assays in two investigational examples (bridging enzyme-linked immunosorbent ADA assays) to attain high drug tolerance while maintaining best possible structural integrity of ADAs. Results: Both ADA-bridging assays treated with MgCl2 showed improved drug tolerance and higher signal-to-blank values compared with overnight incubation or acid treatment. Conclusion: The use of MgCl2 treatment in ADA-bridging assays provides a sensitive, drug tolerant and easy-to-use alternative in cases where acid dissociation is not possible or unwanted.

Toward comparability of anti-drug antibody assays: is the amount of anti-drug antibody-reagent complexes at cut-point (CP-ARC) the missing piece?

Immunogenicity testing is a mandatory and critical activity during the development of therapeutic proteins. Multiple regulatory guidelines provide clear recommendations on appropriate immunogenicity testing strategies and required bioanalytical assay performances. Unfortunately, it is still generally accepted that a comparison of the immunogenicity of different compounds is not possible due to apparent performance differences of the used bioanalytical methods. In this perspective, we propose the 'cut-point anti-drug antibody-reagents complex' (CP-ARC) concept for technical comparability of the bioanalytical methods. The feasibility and implementation in routine assay development is discussed as well as the potential improvement of reporting of bioanalytical immunogenicity data to allow comparison across drugs. Scientific sound comparability of the bioanalytical methods is the first step toward comparability of clinical immunogenicity.

Efficacy of Granulocyte and Monocyte Adsorptive Apheresis in Patients With Inflammatory Bowel Disease Showing Lost Response to Infliximab.

BACKGROUND AND AIMS: In inflammatory bowel disease [IBD] patients, antibody-to-infliximab [ATI] generation is responsible for loss of response [LOR] and infusion reaction [IR] to infliximab. An immuno-therapeutic approach is considered an option to overcome LOR. Granulocyte/monocyte adsorptive apheresis [GMA] using an Adacolumn has been shown to have clinical efficacy together with immunomodulatory effects in IBD patients. METHODS: We developed an ATI-CAI assay utilizing a C1q immobilized plate and applied it to measure ATI in patients who were receiving infliximab, including 56 with sustained response, 76 with LOR and six with IR. Furthermore, 14 patients with LOR and two with paradoxical skin reactions who received infliximab + GMA combination therapy were analysed. RESULTS: Fourteen patients with LOR, seven with Crohn's disease and seven with ulcerative colitis, showed significantly improved clinical indices [p = 0.0009], and decreased ATI [p = 0.0171] and interleukin-6 [p = 0.0537] levels at week 8 following initiation of infliximab + GMA therapy. Nine patients who received combination therapy achieved remission, which was maintained to week 24 with infliximab alone. Additionally, cutaneous lesions in two patients with IR were improved. ATI-CAI assay efficiency was not influenced by infliximab concentration during the test. Pre- and post-infliximab infusion ATI levels were not different. Patients with ATI greater than the 0.153 µg/mL cut-off value were likely to experience LOR [odds ratio 3.0]. CONCLUSIONS: Patients who received infliximab + GMA therapy appeared to regain clinical response to infliximab by a decrease in ATI level. Furthermore, the concentration of infliximab in the test did not influence ATI measurement, but was associated with clinical response.

Approaches to improve drug tolerance and target tolerance in the assessment of neutralizing anti-drug antibodies.

Aim: Neutralizing anti-drug antibody (NAb) assays are inherently prone to the interference from drug and its soluble target, potentially resulting in erroneous results. An effective approach to improve drug tolerance of an NAb assay is pretreatment of samples with acid to dissociate immune complexes of NAb and drug, followed by separating NAbs from circulating drug before testing them in the assay. Methods and Results: The acid pretreatment conditions were optimized to improve drug tolerance of cell-based and non-cell-based NAb assays. NAbs were further separated from circulating drug either through direct drug removal or purification of NAb from the sample. In addition, an integrated experimental strategy was implemented to simultaneously improve drug and its soluble target tolerance for reliable NAb assessment. Conclusion: The approaches described herein would enable the development of reliable NAb assays that overcome drug and its target interference for more precise and sensitive NAb assessment.

Universal antibiotic tolerance arising from antibiotic-triggered accumulation of pyocyanin in Pseudomonas aeruginosa.

Pseudomonas aeruginosa is an opportunistic pathogen that often infects open wounds or patients with cystic fibrosis. Once established, P. aeruginosa infections are notoriously difficult to eradicate. This difficulty is in part due to the ability of P. aeruginosa to tolerate antibiotic treatment at the individual-cell level or through collective behaviors. Here, we describe a new phenomenon by which P. aeruginosa tolerates antibiotic treatment. In particular, treatment of P. aeruginosa with sublethal concentrations of antibiotics covering all major classes promoted accumulation of the redox-sensitive phenazine pyocyanin (PYO). PYO in turn conferred general tolerance against diverse antibiotics for both P. aeruginosa and other gram-negative and gram-positive bacteria. This property is shared by other redox-active phenazines produced by P. aeruginosa. Our discovery sheds new insights into the physiological functions of phenazines and has implications for designing effective antibiotic treatment protocols.

Time to antibody detection and associated factors for presence of anti-drug antibodies in pediatric inflammatory bowel disease patients treated with anti-TNF therapy.

BACKGROUND: Loss of response in pediatric inflammatory bowel disease patients treated with biologic medications can be due to development of anti-drug antibodies. Natural history of anti-drug antibodies development has not been well described in pediatric inflammatory bowel disease. The primary aim of this study was to describe a single-center experience for the temporal onset of anti-drug antibodies detection. METHODS: We performed a retrospective, single-center chart review of pediatric inflammatory bowel disease patients at the Division of Pediatric Gastroenterology, Hepatology, and Nutrition at Rainbow Babies and Children's Hospital from 2010 to 2015. Patients were treated with infliximab or adalimumab and had at least two evaluations for anti-drug antibodies with the homogenous mobility shift assay. Demographics, laboratory and medication data, and clinical disease activity were collected. RESULTS: A total of 75 subjects are included in the analysis. Eighty-one percent of subjects were treated with infliximab. Eleven subjects developed anti-drug antibodies; average time to anti-drug antibodies detection was 13.2 ± 7.3 months. Longer duration of inflammatory bowel disease, L1 location in Crohn's disease, and not having immunomodulatory therapy before biologic was associated with higher risk of antibody detection. Antibody detection occurred more frequently with infliximab vs. adalimumab. Time-to-antibody detection for infliximab and adalimumab was 14.83 and 23.48 months, respectively. CONCLUSION: Chances of anti-drug antibodies detection in the infliximab group were higher than the adalimumab group. Time-to-antibody detection was 8.65 months longer in patients who received adalimumab when compared to infliximab. These results may have implications for long-term therapy and help guide use of concomitant immunomodulators.

Tolerability of Ig20Gly during onboarding in patients with primary immunodeficiency diseases.

BACKGROUND: The subcutaneous immune globulin (SCIG) 20% product, Ig20Gly, was shown to be efficacious and well tolerated in 2 phase 2/3 North American and European studies at infusion volumes up to 60 mL/site and rates up to 60 mL/h/site in patients with primary immunodeficiency diseases. OBJECTIVE: To assess patient experience after switching to Ig20Gly with fast infusion rates and large infusion volumes/site in the North American study. METHODS: In this analysis of the open-label phase 2/3 study in which patients aged ≥2 years received weekly Ig20Gly infusions for up to approximately 1.3 years, tolerability and infusion parameters were assessed throughout the study for all patients and by prestudy treatment regimen (intravenous [IV] switchers or SC switchers). RESULTS: Overall, 61% of patients reached the infusion rate of ≥60 mL/h/site and continued at this rate for 1 or more subsequent infusions; the median infusion number when patients first reached ≥60 mL/h/site was 3. No association was found between higher infusion volumes or rates and increased incidences of local and systemic adverse events (AEs) in the total population and patients younger than 16 years. Infusion parameters and tolerability were generally comparable regardless of the route of prestudy treatment (IV or SC switchers); however, IV switchers experienced lower rates of local AEs than SC switchers and had a slightly higher median infusion volume per site and longer infusion duration vs SC switchers. CONCLUSION: High Ig20Gly infusion rates of at least 60 mL/h/site and volumes ≥60 mL/site were well tolerated during onboarding and throughout treatment, regardless of prestudy treatment. TRIAL REGISTRATION: ClinicalTrials.gov Identifier NCT01218438.

Neutralizing Antibody Assay Development with High Drug and Target Tolerance to Support Clinical Development of an Anti-TFPI Therapeutic Monoclonal Antibody.

Immunogenicity is a major challenge for protein therapeutics which can potentially reduce drug efficacy and safety and is often being monitored by anti-drug antibody (ADA) and neutralizing antibody (NAb) assays. Circulating targets and residual drugs in matrices can have significant impacts on accuracy of results from ADA and NAb assays, and sufficient drug and target tolerance for these assays are necessary. Here, we report the development of a competitive ligand binding (CLB) NAb assay for an anti-TFPI (tissue factor pathway inhibitor) monoclonal antibody (PF-06741086) with high drug and target tolerance to support ongoing clinical studies. A double acid affinity capture elution approach was used to mitigate drug interference, and a robust target removal strategy was employed to enhance target tolerance. The validated NAb assay has sensitivity of 313 ng/mL, drug tolerance of 50 µg/mL, and target tolerance of 1200 ng/mL. A step-by-step tutorial of assay development is described in this manuscript along with the rationale for using a high drug/target tolerant NAb assay. The NAb assay cut point factor obtained was 0.78. Other assay performance characteristics, e.g., precision and selectivity, are also discussed. This validated method demonstrated a superior drug and target tolerance to warrant specific and precise characterization of the NAb responses in support of ongoing clinical studies.

Immunogenicity of Golimumab and its Clinical Relevance in Patients With Ulcerative Colitis.

BACKGROUND: Antidrug antibody (ADA) detection with standard bridging enzyme immunoassays (EIA) can yield false-negative results or underestimate titers through drug interference. A more sensitive assay was needed to determine clinical impact of antigolimumab antibodies. METHODS: A high-sensitivity, drug-tolerant EIA (DT-EIA) was developed and cross-validated against the original EIA, and samples from induction/maintenance studies in golimumab-treated patients with ulcerative colitis were analyzed for ADAs using both methods. Immunogenicity results were compared, and pharmacokinetic, efficacy, and safety associations were evaluated. RESULTS: An 8-fold increase in ADA-positive patients (21.8% DT-EIA vs 2.8% EIA) reflected DT-EIA improved sensitivity and drug tolerance. Most newly detected ADA-positive patients (using DT-EIA) had low antibody titers, whereas most with high antibody titers were ADA-positive with original EIA. With DT-EIA, week 44 median trough serum golimumab concentrations among ADA-positive patients were approximately half vs ADA-negative (0.51 vs 0.85 µg/mL [50 mg q4w]; 0.85 vs 1.60 µg/mL [100 mg q4w]). Antidrug antibody impact on golimumab concentrations was more notable at titers ≥1:100. During induction, ADAs had no notable impact on efficacy. During maintenance, proportions of patients maintaining clinical response through week 54 were lower using DT-EIA: 38.1% ADA-positive and 52.8% ADA-negative. Antidrug antibody status had no impact on injection-site reaction incidence. CONCLUSIONS: A more sensitive DT-EIA identified higher proportions of ADA-positive patients. A trend of decreasing drug concentrations with increasing ADA titers was observed. Pharmacokinetic impact was better elucidated with DT-EIA. Although development of ADA did not preclude efficacy, a trend toward decreased efficacy in ADA-positive vs ADA-negative patients was observed during maintenance treatment. Antidrug antibody status did not impact safety.

Antidepressant treatment resistance is associated with increased inflammatory markers in patients with major depressive disorder.

BACKGROUND: One third of patients with major depressive disorder (MDD) fail to respond to currently available antidepressant medications. Inflammation may contribute to treatment non-response through effects on neurotransmitter systems relevant to antidepressant efficacy. In post-hoc analyses, increased concentrations of inflammatory markers prior to treatment predict poor antidepressant response. However, limited data exists on whether depressed patients with multiple failed treatment trials in their current episode of depression exhibit increased inflammation. METHODS: Plasma concentrations of inflammatory markers were measured in unmedicated, medically stable patients with MDD (n = 98) and varying numbers of adequate antidepressant treatment trials in the current depressive episode as measured by the Massachusetts General Hospital Antidepressant Treatment Response Questionnaire. Covariates including age, sex, race, education, body mass index (BMI) and severity of depression were included in statistical models where indicated. RESULTS: A significant relationship was found between number of failed treatment trials and tumor necrosis factor (TNF), soluble TNF receptor 2 (sTNF-R2) and interleukin (IL)-6 (all p < 0.05 in multivariate analyses). Post hoc pairwise comparisons with correction for multiple testing revealed that patients with 3 or more failed trials in the current episode had significantly higher plasma TNF, sTNF-R2 and IL-6 compared to individuals with 0 or 1 trial (all p < 0.05). High sensitivity c-reactive protein was also associated with a greater number of treatment failures, but only in models with BMI excluded. CONCLUSIONS: Measuring inflammatory markers and targeting inflammation or its downstream mediators may be relevant for depressed patients with multiple failed antidepressant treatment trials in their current depressive episode.

A transgenic mouse model for HLA-B*57:01-linked abacavir drug tolerance and reactivity.

Adverse drug reactions (ADRs) are a major obstacle to drug development, and some of these, including hypersensitivity reactions to the HIV reverse transcriptase inhibitor abacavir (ABC), are associated with HLA alleles, particularly HLA-B*57:01. However, not all HLA-B*57:01+ patients develop ADRs, suggesting that in addition to the HLA genetic risk, other factors may influence the outcome of the response to the drug. To study HLA-linked ADRs in vivo, we generated HLA-B*57:01-Tg mice and show that, although ABC activated Tg mouse CD8+ T cells in vitro in a HLA-B*57:01-dependent manner, the drug was tolerated in vivo. In immunocompetent Tg animals, ABC induced CD8+ T cells with an anergy-like phenotype that did not lead to ADRs. In contrast, in vivo depletion of CD4+ T cells prior to ABC administration enhanced DC maturation to induce systemic ABC-reactive CD8+ T cells with an effector-like and skin-homing phenotype along with CD8+ infiltration and inflammation in drug-sensitized skin. B7 costimulatory molecule blockade prevented CD8+ T cell activation. These Tg mice provide a model for ABC tolerance and for the generation of HLA-B*57:01-restricted, ABC-reactive CD8+ T cells dependent on both HLA genetic risk and immunoregulatory host factors.

Long-Term Outcome of Infliximab Optimization for Overcoming Immunogenicity in Patients with Inflammatory Bowel Disease.

BACKGROUND: Preliminary data suggest that treatment optimization can reverse immunogenicity and regain response in patients with IBD and secondary loss of response (SLR) to anti-TNF therapy due to antidrug antibodies. However, data regarding the long-term outcome of these patients are scarce. AIMS: We aimed to investigate drug retention in IBD patients of whom infliximab was optimized to overcome immunogenicity and variables associated with drug retention. METHODS: This was a retrospective, multicenter study of consecutive IBD patients with antibodies to infliximab (ATI), based on either proactive or reactive therapeutic drug monitoring, who underwent infliximab optimization (increasing dose, shortening interval, adding an immunomodulator, or combination) to overcome immunogenicity from September 2012 to July 2015; they were followed through December 2015. ATI were analyzed using the drug-tolerant Prometheus homogeneous mobility shift assay. Drug retention was defined as no need for drug discontinuation due to SLR or serious adverse event. RESULTS: Our cohort consisted of 22 patients (Crohn's disease, n = 15). At the end of follow-up [median, (IQR): 17.3 (10.5-32.8) months] 77% (15/22) of patients were still on drug. Univariable Cox proportional hazards regression analysis identified first detectable ATI titer as the only variable associated with drug retention (HR: 0.89; 95% CI: 0.82-0.98, p = 0.016). Receiver-operating characteristic analysis identified an ATI titer < 8.8 U/mL associated with drug retention. CONCLUSIONS: In real-life clinical practice, optimization of infliximab therapy can prevent drug discontinuation in approximately 3/4 of patients with ATI, especially in those with low titers. Large prospective studies are needed to confirm these data.

Feedback from the European Bioanalysis Forum: focus workshop on current analysis of immunogenicity: best practices and regulatory hurdles.

European Bioanalysis Forum Workshop, Lisbon, Portugal, September 2016: At the recent European Bioanalysis Forum Focus Workshop, 'current analysis of immunogenicity: best practices and regulatory hurdles', several important challenges facing the bioanalytical community in relation to immunogenicity assays were discussed through a mixture of presentations and panel sessions. The main areas of focus were the evolving regulatory landscape, challenges of assay interferences from either drug or target, cut-point setting and whether alternative assays can be used to replace neutralizing antibody assays. This workshop report captures discussions and potential solutions and/or recommendations made by the speakers and delegates.

Endotoxin tolerance induced by lipopolysaccharide preconditioning protects against surgery­induced cognitive impairment in aging mice.

Postoperative cognitive dysfunction (POCD) is a clinical syndrome characterized by varying degrees of cognitive functional decline in patients following major surgery. Inflammation and a dysregulated innate immune system exert broad effects in the periphery and central nervous system, yet the mechanisms underlying POCD remain poorly understood and without effective therapy. It has been reported that modulation of the dysregulated inflammatory response with low­dose lipopolysaccharide (LPS) preconditioning, a phenomenon additionally referred to as endotoxin tolerance, has the potential to reduce neuroinflammation, blood­brain barrier disruption, and cognitive impairment in a number of disease states. Therefore, it was hypothesized that endotoxin tolerance induced by LPS preconditioning may protect against surgery­induced cognitive impairment in aging mice. Using a mouse model of surgery­induced cognitive decline, the present study demonstrated that exploratory laparotomy caused a significant impairment in hippocampal­dependent memory. Notably, one application of low­dose LPS preconditioning at 24 h prior to surgery improved the cognitive impairment and abolished the signs of neuroinflammation in the hippocampus following surgery. However, LPS injection at 6 h or immediately prior to surgery did not confer such beneficial effects, suggesting that the effects of LPS­induced endotoxin tolerance may depend on the time of application. In conclusion, the results of the present study suggested that low­dose LPS preconditioning may markedly alleviate surgery­induced neuroinflammation and cognitive impairment in aging mice, which may provide a novel approach to preventing POCD and, potentially, other forms of memory impairment.

Evaluation of periprocedural hypersensitivity reactions.

BACKGROUND: Identifying the cause of periprocedural hypersensitivity reactions (HSRs) remains challenging because of the multitude of medications involved. Antibiotics are the most common cause in the United States, whereas neuromuscular blocking agents are most common in Europe. OBJECTIVE: To identify causative agents for periprocedural HSRs. METHODS: This study was a 7-year retrospective medical record review of patients evaluated between December 2009 and January 2017 at a drug allergy center in Bronx, New York for periprocedural HSRs, defined as occurring soon before, during, or soon after a medical procedure or operation with or without general anesthesia. Demographics, description of historical HSRs, results of testing to potential causative medications, and tolerance of subsequent anesthesia were reviewed. RESULTS: Thirty-four patients completed a comprehensive evaluation. Skin testing identified an IgE-mediated cause in 22 patients (64.7%). The most common causative class of medications was induction agents (n = 9 [36%]), with midazolam being the most frequently implicated (n = 6 [3 positive skin test results, 3 equivocal skin test results]). Cefazolin was the most common agent identified (n = 8 [32%]) followed by ondansetron (n = 3 [12%]). Sixteen of 22 contacted patients were exposed to subsequent anesthesia, including 3 patients with negative evaluations. One patient experienced a mild urticarial HSR. CONCLUSION: Induction agents were the most common causative agents in our patients, which differs from other studies. Given the variability in evaluations of periprocedural HSRs across the United States with data published on small sample sizes, there is a need to establish national guidelines to standardize evaluations and to create a national registry to allow for data sharing.

[Adherence in specific immunotherapy]. / Adhärenz in der spezifischen Immuntherapie.

Allergies are steadily gaining in importance in the Western world. For over one hundred years, immunology has been the only causal treatment. Specific immunotherapy (SIT) aims at the cure of allergy or at least freedom from allergy symptoms. In association with this, adherence poses a complex problem. Both treatment applications commonly used in Germany-sublingual and subcutaneous immunotherapy-show poor persistence on the part of the patients. In most cases, SIT is not carried out to the end of the recommended duration and instead is discontinued prematurely. Corresponding figures from 3­year studies in the literature range from 41- 93% for uncompleted SLIT and from 40-77% for uncompleted SCIT. Patient adherence is subject to influencing factors of various dimensions that are interdependent in complex relationships. The physician-patient relationship is just as decisive a factor for treatment success as the patient's understanding of allergy, treatment, and the importance of adherence.

Infliximab Optimization Based on Therapeutic Drug Monitoring in Pediatric Inflammatory Bowel Disease.

BACKGROUND: Infliximab (IFX) is an effective treatment for the management of moderate to severe inflammatory bowel disease (IBD). Low-serum IFX levels are associated with the development of antibodies to IFX (ATI), which subsequently associated with clinical relapse and increased morbidity. The primary purpose of this study is to examine the relation between dose and interval to IFX level. Secondary goal is to evaluate the relation between IFX level and ATI in a pediatric IBD population. METHODS: We performed a retrospective chart review of all children diagnosed with IBD and treated with IFX at a tertiary care pediatric IBD center. We performed our analysis based on prescribed dosing intervals and rounded dose up to 5 or 10 mg/kg as indicated in clinical practice. RESULTS: Our study included 278 samples from 129 children on IFX. ATI were detected in 37 samples (13.3%). Low IFX levels (<3 µg/mL) were detected in 37.2% of children receiving IFX. Samples with ATI present had significantly lower levels of IFX than samples in which ATI were not present. For the dose 5 mg/kg, Q6 dosing had significantly higher IFX levels than Q8 dosing (P = 0.009). Higher IFX levels were seen with interval shortening rather than dose escalation. CONCLUSIONS: We demonstrate that low IFX levels are associated with development of immunogenicity to IFX as measured by ATI. We demonstrate that interval shortening rather than dose escalation results in higher IFX levels. We suggest that given the high number of IFX levels below 3 µg/mL in patients, early IFX level evaluation or primary initiation of Q6 week dosing be considered.