Infliximab therapeutic drug monitoring (TDM) in IBD can significantly reduce unnecessary use of the TNF inhibitor and has the potential to offer substantial cost savings, Austraian research shows.
A study of all public TDM of infliximab for IBD across Australia between 1 July 2016 and 31 July 2017 has shown infliximab use could be reduced by about 30%.
The TDM was performed at NSW Health Pathology – the only public diagnostic service for infliximab TDM during the study period.
Of 618 patient samples that were considered in the analysis, the most common reason for testing was secondary loss of response (LOR) in about half the samples (49.8%).
A further 40.5% of testing episodes were in patients on maintenance therapy in remission.
The study found 25.4% of samples had a trough drug level (TL) <2 mg/L warranting further testing for anti-drug antibodies (ATI).
Subtherapeutic infliximab levels and high titre ATI, suggesting continuing or dose intensifying infliximab therapy would not be effective, were found in 8.1% of cases.
Patients with secondary LOR were found to have significantly lower median infliximab levels across all IBD phenotypes and a higher likelihood of having high titre ATI compared with those in remission.
In patients in remission, 16.6% of samples showed a supra-therapeutic TL >10mg/L where infliximab dose reduction should be possible.
“Overall, we identified unnecessary use in a total of 19.3% (35/181) cases where testing was proactive, and 38.9% (96/247) where testing was reactive,” the study authors said.
“Identification of unnecessary IFX use in the context of secondary LOR would have hypothetically saved 46,300mg of IFX in this cohort, calculated as one IFX infusion avoided for each patient’s real-life dosing regimen. This equates to a saving of $266,155.55 in IFX drug costs alone.”
“For those on maintenance therapy in remission with supratherapeutic levels, 17,500mg of IFX use could potentially be avoided over the following six months of therapy, equivalent to a cost saving of $100,598.75. The total IFX use avoided would be 66,300mg, with a cost saving of $381,125.55.”
The cost of testing during the study period was $52,730.
“Thus, the total hypothetical cost savings made by unnecessary use being avoided through IFX TDM was $328,395.55. This equates to $531.38 saved per testing episode over this 13 months period in Australia.”
The researchers, including head of IBD service at Liverpool Hospital Associate Professor Susan Connor, said their study supports the vital role that TDM plays in dose optimisation for patients and rational use of an expensive medication.
“Approximately 30% of patients undergoing TL testing could have avoided prolonged IFX therapy or high IFX doses that would not have offered them any clinical value.”
The findings are consistent with those of the Australian Inflammatory Bowel Diseases Consensus Working Group which supports the role of TDM in optimising anti-TNF agents, especially in situations of treatment failure.