Venous thromboembolism (VTE) is common following lung transplantation. Enoxaparin is an approved therapy for VTE and anti-factor Xa (AXAL) can be used to monitor enoxaparin activity. Some studies have demonstrated elevated AXALs are associated with an increased risk of hemorrhage. Having identified a high incidence of supratherapeutic AXALs in lung transplant recipients, we aimed to elucidate the relationship between enoxaparin dose and AXAL in this patient population.
We identified post-lung transplantation patients with VTE receiving therapeutic enoxaparin who had AXAL measured. Standard enoxaparin dosing was defined as 0.9–1.1 mg/kg. After identifying a high incidence of supratherapeutic AXALs, we implemented “non-standard” dosing of 0.8 mg/kg. Multivariable linear regression analysis was used to examine the association between enoxaparin dose and AXAL; age, BMI, and creatinine clearance were included as covariates.
In the cohort, 18 patients received standard and 8 patients received non-standard enoxaparin dosing. 12 of 18 patients (67%; 95% CI 43% to 91%) receiving standard dosing had supratherapeutic AXALs versus 0 of 8 patients (0%; 95% CI 0 to 37%) receiving lower non-standard dosing (p = 0.002). AXALs were significantly different between the two groups; the mean AXAL was 1.3 IU/ml (95% CI 1.06 to 1.53) in the standard group versus 0.79 IU/mL (95%CI 0.67 to 0.91) in the non-standard group (p = 0.008). After controlling for covariates, for each 0.1mg/kg increase in enoxaparin, the mean AXAL increased by 0.18 IU/mL (95% CI: 0.05 to 0.31; p = 0.011; model r2 = 0.53).
Standard dosing of enoxaparin in lung transplant recipients is associated with a high incidence of supratherapeutic anti-Xa levels. To correlate this finding with risk of hemorrhage requires further study.