Low plasma edoxaban concentrations during therapeutic drug monitoring: a single-center retrospective study

In our therapeutic drug monitoring (TDM) laboratory, over one-third of approximately 350 analyzed samples from patients on edoxaban were < 12 ng/mL, which is below concentrations reported in clinical trials. Our study aimed to explore the effect of factors potentially associated with low edoxaban concentrations in patients monitored with TDM. A retrospective cohort study of previously analyzed edoxaban plasma concentrations collected at Karolinska University Hospital between November 2017 and May 2023 was performed. Low concentration was defined as < 12 ng/mL (30 mg) and < 16 ng/mL (60 mg). Fifty samples from 34 individuals were included. No significant difference in trough concentration between 30 and 60 mg dose group was found. Low concentrations were observed in 42% of samples. Higher estimated glomerular filtration rate (eGFR) was found among patients with low edoxaban concentrations (p = 0.004); however, the correlation between eGFR and concentration was weak (rho =  - 0.4; p < 0.05). Off-label dose reduction (n = 4) and drug-drug interactions (DDIs) (n = 4) were found in cases with low concentrations. In a TDM-setting, low trough concentrations of edoxaban were frequently observed. Potential explanations include normal renal function, drug-drug interactions, and off-label dose reductions. These findings suggest that TDM may be beneficial in selected clinical scenarios. However, the study is limited by its small sample size and selected study population.