*Purpose: Enoxaparin 1 mg/kg subcutaneously every 12 hours for therapeutic anticoagulation is known to increase rates of supratherapeutic anti-Xa levels in lung transplant recipients (LTRs). Since enoxaparin is renally eliminated, this risk may be higher in patients with renal impairment. Our protocol uses enoxaparin 0.8 mg/kg every 12 hours in LTRs. This study aims to evaluate anti-Xa levels using the current protocol and whether these levels are impacted by renal function.

*Methods: This single center, retrospective analysis included LTRs from 11/2017-8/2020 who received therapeutic enoxaparin with an anti-Xa level (drawn 3-6 hours post-injection after ≥3 doses). Therapeutic anti-Xa levels were defined as 0.6-1.0 IU/mL. LTRs with creatinine clearance (CrCl) <30 mL/min were excluded. The primary outcome was incidence of therapeutic anti-Xa levels in the cohort. The secondary outcome was incidence of therapeutic anti-Xa levels based on renal function, with renal dysfunction defined as CrCl <60 mL/min.

*Results: Of 109 LTRs, 29 were included. The study cohort was median 62[56-66] years old, 78.9[67.1-86.7] kg, 65.5% male, and 48.3% received a double lung transplant. Indications for anticoagulation were venous thromboembolism (79.3%) and atrial fibrillation (20.7%). Twelve (41.4%) had CrCl <60 mL/min. Overall, the mean anti-Xa was 0.85±0.36 IU/mL, with 41.3%, 20.7%, and 37.9% in a therapeutic, subtherapeutic, and supratherapeutic range, respectively. The mean dose among LTRs with and without renal dysfunction was similar (p=0.86), however, the mean anti-Xa in the renal dysfunction group was significantly higher (p=0.005, Table). LTRs with renal dysfunction were more likely to have an anti-Xa in the supratherapeutic range (Figure).

*Conclusions: A majority of LTRs did not achieve therapeutic anti-Xa levels on enoxaparin 0.8 mg/kg every 12 hours. This may be attributed to the high incidence of supratherapeutic anti-Xa levels among LTRs with renal dysfunction. A dose reduction in this population may be warranted. Further research is needed to determine the optimal enoxaparin dose in LTRs with renal impairment.

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