P449 Cost Effectiveness of a Proactive Therapeutic Drug Monitoring Strategy in Patients with Inflammatory Bowel Disease Receiving Infliximab

Abstract

Introduction: Proactive therapeutic drug monitoring (TDM) is widely used in clinical practice, however, has not been clearly demonstrated to result in improved anti-TNF therapy outcomes compared with clinically-based dosing strategies. While the use of proactive TDM incurs additional assayrelated costs this strategy may be cost-effective due to TDM-driven anti- TNF therapy dose de-escalation and discontinuation. Aims & Methods: We aimed to assess whether use of proactive-TDM is a cost-effective strategy in routine clinical practice. As a pilot project, a proactive TDM strategy was utilised in our unit with infliximab (IFX) levels and antibody-to-infliximab (ATI) levels, assessed at trough, in all inflammatory bowel disease (IBD) patients receiving IFX therapy. Baseline demographics including IFX dosing schedules and use of concomitant immunomodulators were documented. Patients were grouped based on disease activity status with remission defined by any one of the following criteria: faecal calprotectin < 150 mug/mg, C reactive protein < 5 mg/L, absence of active disease at endoscopy performed within 3 months of TDM assessment or physician's impression of disease remission at the time of TDM assessment. Trough IFX and ATI levels were documented for all patients. Patients with IFX levels outside the therapeutic range of 3-7 mug/mL had IFX therapy dosing adjusted as appropriate. IFX dose adjustments were not protocolised and were at attending physicians discretion. IFX dosing regimens following proactive TDM were documented and the net effect on IFX infusions number over the subsequent year extrapolated. Increase or decrease in drug-related costs on an annualised basis were then estimated. Result(s): N=108 patients were included ([median age 36 years, 46% were female, 36% ulcerative colitis, 60% Crohn's disease, 4% IBD-U) 35% were receiving concomitant immunomodulators. 56% of patients were in remission at the time of TDM assessment. 44%, 30% and 26% of patients had IFX levels < 3 mug/mL, 3-7 mug/mL and > 7 mug/mL respectively. IFX levels were significantly lower in patients with active disease compared with those in remission (p=0.008). Following proactive TDM assessment, 37%, 11%, 36%, 13%, 2% and 1% of patients had no treatment change, therapy discontinuation, interval shortening, interval lengthening, dose increase and dose decrease respectively. Cost-effectiveness analysis focused on patients in remission (n=59). The use of proactive TDM-based IFX dosing resulted in a projected annualised reduction of 19.5 and 28.5 infusions due to IFX discontinuation and interval lengthening respectively; the projected annualised increase in infusions was 39.1 and 4.3 due to IFX interval shortening and dose increase respectively. This resulted in a net projected reduction of 4.7 IFX infusions per annum. Utilising publicly available list prices for originator and biosimilar IFX and accounting for TDM assay cost (2065 Euro), projected cost savings resulting from proactive-TDM use were 9105.0 and 6840.7 Euro per annum respectively. Conclusion(s): Proactive TDM in IBD patients in remission resulted in a modest reduction in the projected annualised number of infusions in our unit with consequent minor drug-related cost savings. Proactive-TDM encouraged cost-effective prescribing of IFX, however, the effect was minor. The frequency at which proactive TDM should be performed and whether subsequent rounds of proactive-TDM would continue to deliver similar cost savings is uncertain and requires further evaluation.