Z Arkir

Infliximab and adalimumab drug levels in Crohn's disease: contrasting associations with disease activity and influencing factors

Discriminative drug level thresholds for disease activity endpoints in patients with Crohns disease. have been consistently demonstrated with infliximab, but not adalimumab.

PTH-074 The Presence of Total Anti-Drug Antibodies to Biologic Drugs Does not Adversely Affect Long-Term Outcomes in Crohn’s Disease Patients with Adequate Drugs Levels and Absent Free Anti-Drug Antibodies

Introduction The use of therapeutic drug monitoring (TDM) for anti-TNF drugs has become increasingly widespread over recent years. It is now used in many centres to guide clinical decisions regarding dose optimisation, the use of concomitant immunomodulators as well as switching or withdrawal of treatment.1 TDM usually includes the measurement of serum trough levels of infliximab (IFX) or adalimumab (ADA) as well as anti-drug antibodies (ADAb). There are two different approaches to measuring ADAb; some techniques measure total ADAb (drug-ADAb complexes as well as free ADAb), whilst other measure only free ADAb. However, the clinical relevance of the differing data generated by these techniques is not yet fully understood. Methods A prospective evaluation of trough drug levels and ADAb was performed using our standard ELISA assay (LISA TRACKER, Theradiag) in 145 IBD patients on anti-TNF agents between January and May 2014. This technique measures only free ADAb. The samples were also anaylsed using an ELISA assay that measures total ADAb (IDKmonitor, Immundiagnostik). Long term outcomes were evaluated for 21 (17 IFX, 4 ADA) patients with Crohn’s disease (CD) who were found to have negative free ADAb but positive total ADAb. Outcome assessments were made by review of a prospectively maintained database, with a mean follow-up period of 22 months. Clinical outcome measures included; the need to escalate/switch/withdraw biologic treatment, infusion/injection-site reactions, documented clinical flare (HBI > 5) and need for steroid treatment. Biochemical outcome measures included; CRP > 5 mg/L and faecal calprotectin >150 ug/g. The subsequent development of positive free ADAb and subtherapeutic/undetectable drug levels were also collected as outcome measures. Results Anti-drug antibody (ADAb) detection: Of the 21 CD patients with positive total ADAb and negative free ADAb at the time of initial sampling, 3 (14%) went on to subsequently develop positive free ADAb during the follow-up period. Sixteen patients (75%) were taking concomitant immunomodulators, including all 3 patients who subsequently developed free ADAb. The mean IFX trough level in patients who went on to develop free ADAb was 1.05 ug/ml, compared to 4.04 ug/ml in those who did not. Outcomes: All 3 (100%) of the patients who developed positive free ADAb subsequently went on to have subtherapeutic or undetectable drug levels and required a switch in anti-TNF therapy. Two of the 3 (67%) had a flare in disease activity with an elevated faecal calprotectin. Two (67%) also developed significant infusion reactions. Of the remaining 18 patients who did not subsequently developed free ADAb, only one patient (6%) required a switch in anti-TNF, 4 (22%) developed clinical flares and 3 (17%) required steroid treatment. None of the 18 patients who remained free ADAb negative had undetectable drug levels during the follow-up period. Conclusion Long-term outcomes were not shown to be adversely affected by the presence of total ADAb, in the absence of free ADAb and adequate drug levels. However, patients who subsequently developed free ADAb and subtherapeutic or undetectable drug levels had unfavourable long-term outcomes. The presence of total ADAb does not appear to accurately predict the development of free ADAb. This data supports the use of ELISA techniques which measure free ADAb as well as drug levels. Our study and other similar work,2 suggests that quantification of drug-ADAb complexes (total ADAb) appears to be less relevant to long-term clinical outcomes and therefore, less informative to clinical decision making. References 1 Ben-Horin S, Chowers Y. Tailoring anti-TNF therapy in IBD: drug levels and disease activity. Nature Reviews Gastroenterology & Hepatology 2014;11:243–255. 2 van schouwenburg, et al. Long-term measurement of anti-adalimumab using pH-shift-anti-idiotype antigen binding tests shows predictive value and transient antibody formation.Ann Rheum Dis. 2013;72:1680–6. Disclosure of Interest None Declared

PTH-083 Selective monitoring of antitnf drug levels and antibodies will reduce short-term prescribing costs and provide early personalised tailoring of antitnf therapy in routine ibd practice

Introduction Clinical trial results suggest that measurement of antiTNF drug levels (ATL) and antibodies (ATA) may have a cost-saving as well as clinically beneficial effect in patients with IBD. We aimed to assess whether selective monitoring of ATL and ATA reduces prescribing costs and how it affects clinical decisions in ordinary clinical practice. Method ATL and ATA were assayed in 47 (19%) of our 247 antiTNF-treated IBD patients (Crohn’s disease 41, ulcerative colitis 4 and pouchitis 2; (on infliximab 45, on adalimumab 2)) because of either secondary loss of response (n = 11) or a dosage of infliximab (IFX) exceeding 5 mg/kg every 8 weeks (n = 36). ATL and ATA were measured by automated LISA-TRACKER assay (Theradiag, France) at Viapath, St Thomas’ Hospital. For each patient, the outcomes of decisions about therapeutic strategy based on clinical assessment alone were compared against those based on assay results combined with clinical criteria. AntiTNF prescribing and surgery costs were predicted for the ensuing 4 months for the two decision-making strategies, assuming that infliximab phials were shared. Results Outcomes of the decisions taken are summarised in the Table. Prescribing costs estimated for the subsequent 4 months (17 weeks) for clinically based decisions were £225,825 and for assay based strategies were £209,772 (£3525 assay costs included). Predicted total cost savings using the assay based decisions, taking into account referrals for surgery and for trial drugs, were £16,053 in 4 months. Clinically based decisions led to more patients staying on antiTNFs, while assay-based decisions caused more patients to be switched to an alternative antiTNF, recruited to trials and referred for surgery. In 19/47 patients, both decision-making approaches gave the same outcome.Abstract PTH-083 Table 1 N = 47 Continue antiTNF in same dose Increase antiTNF dose or frequency Reduce antiTNF dose or frequency Stop antiTNF therapy Switch to alternative antiTNF Transfer to clinical trial drug Surgery Clinically based decisions 25 6 6 0 9 0 1 Assay based decisions 14 5 6 2 13 3 4 Conclusion Measurement of antiTNF drug levels and antibodies in selected patients should produce short-term cost savings in ordinary clinical practice. Longer follow-up is needed to assess the clinical impact of the decisions made using these assays in combination with clinical criteria, but is likely to amplify the savings they make possible. Disclosure of interest None Declared.

Su1206 Association Between Crohn's Disease Activity and Therapeutic Drug Monitoring of Thiopurines and Infliximab Comparing Free and Total Antidrug Antibody Measurement

Introduction Therapeutic drug monitoring (TDM) of infliximab (IFX) is useful in patients with Crohn’s disease (CD). Therapeutic cut-offs to predict active disease and the influence of thiopurines on drug levels (DL) according to 6-thioguanine nucleotide (TGN) are not defined. There is limited data on the utility of free anti-drug antibodies (ADAb) against total ADAb. We assessed the utility of TDM of IFX in CD using a commercially available ELISA and investigated the influence of TGNs on DL and free/total ADAb. Method Prospective evaluation of trough DL and ADAb using Lisa-Tracker, ((LT), Theradiag, France) and Immundiagnostik ELISA, ((IM), Germany) in 79 CD patients (male = 40) between January and May 2014. Only free ADAb is detected with LT assay, whereas IM assay measures total ADAb (semiquantitative). Total ADAb results were calculated using the cut off control. Results of TDM were assessed with respect to faecal calprotectin (FC), C-reactive protein (CRP) and clinical activity (Harvey Bradshaw Index, (HBI) Results Higher DL were observed amongst patients in remission (HBI 245 pmol/8 × 10 8 ) was not associated with ADAb (p = 0.5). TGN quartile analysis did not identify a value associated with DL (p > 0.5), nor was a therapeutic TGN associated with higher DL (p = 0.7). Conclusion IFX DL were inversely related to disease activity. A cut-off of 3.0–5.7 μg/mL was associated with active disease depending on the definition used. The presence of free ADAb was associated with active inflammation, whereas the presence of total ADAb was not. There was no relationship between TGN and DL or ADAb, although most patients were adequately dosed. This study highlights the limitations and utility of TDM in IBD. Disclosure of interest B. Warner: None Declared, M. Ward: None Declared, E. Johnston: None Declared, P. Irving Speaker Bureau of: AbbVie, MSD, Takeda, Warner Chilcott, Shire, Ferring and Tillotts Pharma.

The Clinical and Cost-Effectiveness of 4 Enzyme-Linked Immunosorbent Assay Kits for Monitoring Infliximab in Crohn Disease Patients: Protocol for a Validation Study

Background Currently, treatment decisions for people with Crohn disease are based on clinical judgment and trial and error. Consequently, people may continue to receive high drug dosages and experience unnecessary toxicity when it is possible to reduce or discontinue without a detrimental effect on clinical outcomes. Therapeutic drug monitoring (TDM) involves regularly testing blood samples for drug and antibody levels that could help clinicians identify the optimal treatment strategy and pre-empt treatment failure. However, heterogeneity in the assays can lead to a discrepancy in results and difficulties in decision-making. Standardization of the kits, and therefore results, would allow clinicians to optimize the use of biologics. Currently, there is also a lack of evidence for the cost-effectiveness of TDM using commercial test kits. Objective This study aims to analyze the clinical and cost-effectiveness of 4 commercial enzyme-linked immunosorbent assay (ELISA) kits (LISA TRACKER, IDKmonitor, Promonitor, and RIDASCREEN) to generate evidence which could support a recommendation for wider adoption in the National Health Service. Methods We propose to carry out a prospective-retrospective predictive biomarker validation study using the blood samples and clinical/utilization data collected during the ongoing SPARE trial (NCT02177071). A total of 200 stored samples from people with Crohns disease who respond to treatment with infliximab will be used along with clinical and cost data from the trial. We will investigate the relationship between the drug and antidrug antibody levels with the main clinical outcomes (relapse rate at 2 years and time spent in remission), as well as resource utilization and quality of life. Results Funding is being sought to conduct this research. Conclusions This is the first study to compare the 4 ELISA kits for monitoring infliximab in patients with Crohn disease. It aims to address the uncertainties in the potential benefits of using the technologies for TDM. International Registered Report Identifier (IRRID) PRR1-10.2196/11218

Wide variation in the use and understanding of therapeutic drug monitoring for anti-TNF agents in inflammatory bowel disease: an inexact science?

ABSTRACT Background: We aimed to understand the way in which therapeutic drug monitoring (TDM) is used, understood and interpreted for anti-TNF agents in IBD. Research design and methods: We designed an 18-question survey that included 5 TDM-based clinical scenarios, for which the ‘most appropriate’ responses were based on the BRIDGe groups ‘Anti-TNF Optimizer’. This resource combines TDM evidence with expert consensus. Results: We received 110 complete responses: 50 (45%) consultants, 30 (27%) trainees, 25 (23%) IBD nurse specialists and 5 (5%) gastroenterology pharmacists. Over half (61, 55%) only carry out TDM in non-response. The remainder use TDM routinely, including during stable maintenance therapy for patients in remission. Lower therapeutic thresholds used were variable. Most (82, 75%) were unsure whether their laboratory uses a drug-tolerant or drug-sensitive antidrug antibody assay and few (15, 14%) understand the difference. Consultants, high-frequency users (> 3requests/month) and clinicians with larger anti-TNF cohorts (> 100) were significantly more likely to select the ‘most appropriate’ answer to at least 1 of the 5 TDM-based clinical scenarios. Conclusions: There exists marked heterogeneity in the practical use, understanding and interpretation of biologic TDM. Biologic decision-making, informed by TDM, should involve consultation with experienced clinicians who are frequent TDM users, ideally, as part of a multidisciplinary, biologics-focused IBD meeting. Abbreviations: TDM: therapeutic drug monitoring; CNS: clinical nurse specialist; ELISA: enzyme-linked immunosorbent assay; RIA: radioimmunoassays; HMSA: homogenous mobility shift assays; BSG: British Society of Gastroenterology.

PTU-065 Four-Way Comparison of Elisa Methods Available for the Measurement of Infliximab and Anti-Infliximab Antibody in IBD Patients

Introduction Commercial assays are now widely available and in routine use for the therapeutic drug monitoring of Infliximab (IFX) and anti-Infliximab antibody (ADAb). Although results generated using these assays are used to guide clinical decision making, there is no standardisation and data assessing the comparability between these assays is lacking. Methods A prospective evaluation of IFX drug levels and ADAb was performed using our standard ELISA assay; LISA TRACKER (Theradiag) and also Promonitor (Proteomika), IDKmonitor (Immundiagnostik) and RIDASCREEN IFX (R-Biopharm AG / KU Leuven) ELISA assays. 105 samples from 102 IBD patients were analysed for IFX, free ADAb (LT/PRO) and total ADAb (ID) automated on eRobot and Grifols Triturus analysers. LT, PRO and RS kits were provided at no cost.Method comparisons were performed using difference plots and Passing Bablok analysis. Results A summary of IFX drug level comparison data is shown in the image below. The distribution of bias between methods was variable (-6.7% to +87.8%) with PRO and ID showing scattered, bimodal distributions of %bias. A consistent, proportional relationship was observed between LT and RS results. Free ADAb were detected in 4/105 (3.8%) samples using LT and 3/105 using PRO. All patients with detectable free ADAb had undetectable IFX drug levels. Conversely, total ADAb were detected in 23/105 (21.9%) samples but IFX drug levels were sub-therapeutic (<1.0 ug/mL) in only 6/23 (26.1%) of these and therapeutic (>2.0 ug/mL) in the majority of cases (13/23).Abstract PTU-065 Figure 1 Conclusion These results show that there is significant variation in IFX drug levels obtained when using different CE marked ELISA assays and as such, results are not directly comparable. Although the clinical utility of measuring total ADAb is yet to be established, a significant proportion of patients tested will be positive for total ADAb irrespective of therapeutic IFX drug levels. In the absence of assay standardisation and external quality assurance, laboratory providers and clinicians should ensure that assays currently in routine use are fit for purpose. Disclosure of Interest None Declared

Sa1972 Factors Influencing Infliximab and Adalimumab Antibody Formation and 6 Month Retrospective Follow up in a Tertiary IBD Centre

Introduction Infliximab(IFX) and adalimumab(Ada) are established treatments for IBD.However, immunogenicity can lead to anti-drug antibodies(ADAb) which is associated with a poor clinical response.Little is known regarding the factors which influence ADAb formation or the long term outcomes. Methods Patients with detectable ADAb between May 2012 and October 2014 were identified.Assays had been performed using LISA-Tracker DUO Kits which detects free drug levels(DLs) and ADAb only.Patients were analysed for disease phenotype, prior anti-TNF treatment and ADAb formation,and the use of concomitant immunomodulation(IM). Results 330 IFX DLs and ADAb levels from 199 patients and 143 Ada DLs and ADAb levels from 105 patients were analysed.21 positive ADAb, 19 IFX(9.5%) and 2 Ada(1.9%),were detected with a median ADAb of 141.8 U/ml(range 11–200),all DLs were >1.0μg/ml. 47.6% were male, age range 21–84,median 33.85.7% had Crohn’s Disease.In the majority of patients DL and ADAb were measured due to loss of response(66.7%). 6/19 patients who had IFX ADAb had prior exposure to IFX and 1 had prior exposure to Ada.Time to antibody detection ranged from 2–140 weeks(median 14).Of the 6 patients who had previous exposure to IFX,median time to ADAb detection was 6 weeks.Both patients who developed Ada ADAb had prior exposure to Ada,one also had prior exposure to IFX. 18/21 patients were prescribed concomitant IM(2 methotrexate, 16 thiopurines).8/16 on thiopurines had subtherapeutic TGNs( 8 RBC). IFX ADAb group(n = 19):11 patients were switched to Ada, all of whom had a clinical response(mean HBI at week 26 = 2.1, no ADAb detected). 1 was switched out of class to vedolizumab and responded well. 3 stopped biologic treatment,1 patient continued on IFX at their own request and 1 patient was dose escalated but failed to respond. 2 patients had concomitant IM optimised,1 of whom on subsequent ADAb testing showed loss of ADAb. Ada ADAb group(n = 2):1 patient stopped anti-TNF due to recurrent infections and the other was lost to follow up. Conclusion 42.9% of patients with ADAb had been exposed to anti-TNF previously,all with a gap of >6 months prior to repeat exposure suggesting this is a risk factor for earlier ADAb formation. All patients switched to Ada from IFX responded well without developing ADAb,highlighting that switching to another anti-TNF is an acceptable option before switching out of class. Our use of concomitant IM is high but 50% of this cohort had subtherapeutic TGNs.The 2 patients in whom a thiopurine was optimised achieved clinical remission while remaining on IFX. However the level at which TGNs should be targeted in this context is still unclear Disclosure of Interest B. Warner: None Declared, E. Johnston: None Declared, J. Digby-Bell: None Declared, Z. Arkir: None Declared, N. Unsworth: None Declared, S. Anderson: None Declared, J. Sanderson: None Declared, P. Irving Grant/research support from: PI has been advisor to, in receipt of educational or research grants from, or invited lecturer for Abbvie, Falk, Ferring, Genetech, Hospira, Merck, Pharmacosmos, Shire, Takeda, Tillotts, Topivert, Vifor and Warner Chilcott, Paid instructor for: as above

PTH-090 Laboratory experience of anti-tnf drug monitoring in routine practice – perspective from the first uk centre

Introduction Therapeutic drug monitoring (TDM) of Infliximab (IFX) and Adalimumab (ADAL) has been in use in our centre since 2012. Here we present the TDM experience of our laboratory service at Viapath, St Thomas’ Hospital. Method Anti-TNF requests received between June 2012 and January 2015 were reviewed. All assays were performed using LISA-TRACKER Duo kits automated on eRobot (Theradiag, France). These assays measure free drug and anti-drug antibody (ADAb) and therefore inhibition studies were performed on samples with detectable drug levels (>1 ug/ml) and positive ADAb. Results were classified according to drug levels (DL) and ADAb status. Results The laboratory analysed 2424 (17% internal) samples for IFX (Median DL 3.8 ug/mL, IQR 1.2–6.3) and 1335 (21% internal) samples for ADAL (Median DL 5.2 ug/mL, IQR 3.4–7.3) from IBD patients. Prevalence of detectable antibodies was higher in IFX (10%) than ADAL (4.1%) samples. External requests originated from >90 different hospitals. Number of requests received for both assays doubled from 2013 to 2014 with batch frequency consequently decreasing from fortnightly to weekly.Abstract PTH-090 Table 1 Therapeutic DL (>2 ug/mL) Intermediate DL (1.0–2.0 ug/mL) Subtherapeutic DL (<1 ug/mL) Infliximab 1614 (67%) 249 (10%) 561 (23%) Anti-Infliximab antibody positive (>10 ng/mL) 0 0 245 (44%) Therapeutic DL (>5 ug/mL) Subtherapeutic DL (<5 ug/mL) Adalimumab 691 (52%) 644 (48%) Anti-Adalimumab antibody positive (>10 ng/mL) 0 53 (8%) 40 patients had IFX >1 ug/ml and were antibody positive. 16 of these patients were confirmed to have switched to ADAL due to loss of response to IFX therapy. Detectable DL observed in these cases was due to cross reactivity of ADAL with the IFX assay. 11 patients had false positive drug levels and 4 patients had borderline antibodies due to non specific binding. 1 patient had sample collected around infusion. 4 patients had subtherapeutic ADAL (1.1–1.4 ug/ml) and were antibody positive. 1 of these patients was confirmed to have switched to IFX due to loss of response to ADAL therapy. Detectable DL observed in this case was due to cross reactivity of IFX with the ADAL assay. 3 patients had false positive results for ADAL. From the data, it was evident that some centres monitored patients with serial measurements and made subsequent changes to therapy. 63 patients (IFX) and 52 patients (ADAL) had an average of 7 and 3 repeat measurements taken respectively. Conclusion Anti-TNF testing has been embedded in several IBD centres as a way of optimising therapy however variation in TDM practices was observed highlighting the need for national guidance. Significant increase in test requesting suggests assay based treatment strategies combined with clinical assessment is now an accepted practice in IBD. Disclosure of interest Z. Arkir: None Declared, N. Unsworth: None Declared, G. Richards: None Declared, Z. Odho: None Declared, P. Irving Speaker Bureau of: MSD, Abbvie and Takeda.

PTH-091 Measurement of tnf-alpha drug levels and free versus total anti-drug antibodies using three commercially available assays

Introduction Commercial assays are now available for therapeutic drug monitoring (TDM) of anti-TNF drugs and antibodies (ADAb). Utility of free versus total ADAb assays remains debatable, further complicated by lack of assay standardisation. Here we report analytical comparison of 3 commercially available assays for Infliximab (IFX) and Adalimumab (ADAL) drug levels (DL) and ADAb. Method Prospective evaluation of IFX and ADAL DL and ADAb was performed using our local LISA-TRACKER (LT) assay automated on e-Robot in IBD patients. Samples were also analysed by Immundiagnostik (IM, Germany) and Promonitor (PM, Spain) ELISA automated on Grifols Triturus. LT and PM utilises a specific bridging ELISA to quantitatively measure free-ADAb whereas IM utilises a dissociation step to enable detection of total-ADAb generating semi-quantitative results. IFX assays measure free drug but differ in microtitre plate coating and secondary detection reagents. Data was analysed using Passing Bablok and bias plots. LT and PM kits were provided at no cost. Results Summary of DL comparisons shown below:Abstract PTH-091 Table 1 Infliximab range: 1.30 – 16.70 ug/mL Immundiagnostik (n = 76) Promonitor (n = 63) Passing Bablok Bias Passing Bablok Bias Lisa-Tracker IM=1.24–0.38 8.00% PM=1.16LT – 0.43 –1.71% Immundiagnostik IM= 0.94PM-0.15 –4.82% Adalimumabrange: 0.2–19.9 ug/mL (n = 78) (n = 58) Lisa-Tracker IM=1.73LT-0.06 79.60% PM=1.47LT+1.25 74.00% Immundiagnostik IM=0.84PM+1.27 –0.30% Samples analysed in different batches showed different kit biases against each other for IFX. Batch 1 showed that LT assay had 43.9% positive bias against ID kit whereas batch 2 demonstrated –26% negative bias. Both LT and ID kits used had different lot numbers. This change in bias was not observed in ADAL assays which showed consistent and systematic bias. PM kit showed concentration dependent bias changes within the same assay. 4 patients tested (n = 79) IFX ADAb positive with undectable DL with one exception where total/free ADAb was negative using ID and PM assays. A further 17 patients tested total ADAb positive using IM with detectable DL (0.5–9.2 ug/mL). 1 patient tested ADAL ADAb positive using LT, PM and ID assays however ID and PM assays produced positive resuts on a further 4 specimens, all with ADAL DL >5 ug/mL. Conclusion Although commercial assays are now available, our data highlights the need for assay standardisation. Free ADAb assays were in agreement however ADAb positivity was higher using ID assay. Significance of total ADAb positivity is unknown. Results for both IFX and ADAL confirm that DL are not transferable from one assay to another and as such, common therapeutic cut-offs will not be applicable. Further work is warranted to establish the cause of batch-to-batch variation observed. Disclosure of interest Z. Arkir: None Declared, N. Unsworth: None Declared, B. Warner: None Declared, G. Richards: None Declared, P. Irving Speaker Bureau of: MSD, Abbvie and Takeda.