P523 New guidance on therapeutic drug monitoring; potential clinical and cost implication

Abstract

Background: Biologic drugs are effective treatments in IBD, the use of therapeutic drug monitoring (TDM) is rapidly becoming part of routine clinical practice. The American Gastroenterology Association (AGA) and the Australian gastro association have recently published guidance recommending the use of therapeutic drug monitoring in clinical practice. Recommendations on the minimum trough level (TL) for Infliximab differ between these two guidelines. The AGA recommends a level >5 mug/ml, whilst the Australian guidance suggests > 3 mug/ml. To date there are no published recommendations from ECCO or BSG. In patients with active disease and sub-therapeutic TL we shorten the dose interval from 8 to 4 weeks. Aim(s): To review the clinical and cost implications of introducing these guidelines into clinical practice at a large district general hospital. Method(s): We maintain a prospective IBD database and have used TDM routinely since 2014. Data on TDM from 2016 to 2017 were reviewed. Age, sex, disease type, and activity were reviewed. Results of drug levels in the active disease and remission group were compared and the cost implications of intensifying treatment to achieve recommended trough levels calculated. The costs were calculated for escalating all patients below recommended levels to dosing every 4 weeks. Result(s): Biosimilar infliximab (Remsima) TL data were available for 167 patients. Mean age = 42, range 18-81. 133 (80%) had Crohn's disease and 34 (20%) UC. One hundred and eighteen had inactive disease at the time of TDM, whilst 49 had active disease. Of those with inactive disease 78 of 118 (66%) had an Infliximab TL <3 mug/ml and 104 of 118 (88%) a TL <5 mug/ml. In patients with active disease 33 of 49 (67%) had a TL <3 mug/ml and 40 of 49 (82%) a level <5 mug/ml . Across both groups antibodies were present in 125 (74%). The annual cost for maintaining all 167 patients on Remsima (5 mg/kg) was calculated at 521,040. If all patients with a TL <3 had treatment intensified the annual drug cost would be 925,080 (+77%). If all patients <5 mug/ml were intensified the annual cost rises to 1,045,200 (+100%). If only patients with active disease and <3 mug/ml were escalated the annual cost rises to 641,160 (+23%) and 666,640 (+28%) if those <5 mug/ml were escalated. Conclusion(s): In our cohort of 167, 62% (n = 104) of patients had a TL below the recently published recommended guidelines (5 mug/ml) yet were in a clinical remission. Therefore following these guidelines would lead to a significant increase in drug spend which may not translate into improved clinical outcomes; since in this cohort only 24% with sub-therapeutic levels had active disease. Escalating only those with active disease may represent a more acceptable financial solution but too will lead to an increase in drug spend.