PB0459 - The Impact of Gastrointestinal Surgeries on peak plasma anti-Xa Direct Oral Anticoagulant levels

Background: Direct oral anticoagulants (DOACs) are first line therapy in venous thromboembolism (VTE), and non-valvular atrial fibrillation. Gastrointestinal (GI) surgeries involving removal or rearrangement of the proximal GI tract may alter DOAC absorption, and thereby its anticoagulant effect, but data is lacking.

Aims: (1) To compare peak plasma anti-Xa DOAC levels (PPDL) post-GI surgery in our cohort to expected levels from pharmacokinetic studies. (2) To assess the rates of VTE, arterial thrombosis (AT), major bleeding (MB) and all-cause mortality.

Methods: We performed a single-center retrospective review of all patients anticoagulated with anti-Xa DOACs, who underwent a GI surgery with removal or rearrangement of the proximal GI tract and had a PPDL measured between January 2014 and June 2022. PPDLs were measured using anti-Xa assays calibrated to the respective DOAC. PPDLs were compared to the expected levels and clinical outcomes were calculated as events per 100 person years with 95% confidence intervals (CI).

Results: Our cohort consisted of 61 patients with a mean age of 58.7 years, of which 63.9% were female, and 57.3% had cancer (Table 1). The median PPDLs on therapeutic Apixaban (n=38) and Rivaroxaban (n=17) were 139 (interquartile range (IQR) 102.5 to 188.5) ng/mL and 261.5 (IQR 160 to 340.75) ng/mL, respectively (Figure 1). In total, 71.2% of PPDLs were in the expected range, including 84.6% on Apixaban and 45.0% on Rivaroxaban. The total rate of recurrent VTE, AT, MB and all-cause mortality were 2.26 (95% CI 0.87 to 5.23), 0.95 (95% CI 0.16 to 0.31), 1.42 (95% CI 0.36 to 3.86) and 4.91 (95% CI 2.32 to 9.47), respectively per 100-person years.

Conclusion(s): After proximal GI surgery, 71.2% of PPDLs were in the expected range on therapeutic anti-Xa DOACs, with Apixaban twice as often in range compared to Rivaroxaban. Rates of VTE, AT and MB were low.