Anti-Xa monitoring for low-molecular-weight heparin (LMWH) is currently recommended in obese, renally impaired, and pregnant patients. Substantial evidence indicates solid organ transplant (SOT) patients are at an increased risk for renal impairment, thus representing a population at risk for LMWH accumulation. The purpose of this study was to review our experience with LMWH dosing and monitoring in a cohort of transplant recipients.

This was a retrospective, single center review of 96 SOT patients receiving enoxaparin treatment and anti-Xa monitoring. The percent of patients with supratherapeutic anti-Xas (>1 IU/mL) was determined, as was the relationship between enoxaparin dosages and anti-Xa levels and bleeding. Bleeding was defined by the following criteria: a) identification of hematomas though radiographic imaging b) a reduction in Hgb ≥ 3 g/dL during enoxaparin administration; or c) hemoccult positivity.

The cohort had a mean age of 62 years, creatinine clearance of 59 ml/min, and was composed primarily of lung transplant recipients (73%). The mean enoxaparin dose was 0.82 ± 0.18 mg/kg every 12 hours, which resulted in a mean anti-Xa level of 0.98 ± 0.32 IU/mL. Despite the reduced initial enoxaparin dose, 44% of patients experienced a supratherapeutic anti-Xa level. Patients with supratherapeutic anti-Xas had higher doses than those within the therapeutic range (0.89 mg/kg vs. 0.77 mg/kg; p=0.002). As shown in Figure 1, the majority of dosages of >0.85 mg/kg resulted in supratherapeutic anti-Xa levels. Bleeding was identified in 23% of patients, owing primarily to reduction in hemoglobin, however no major bleeds occurred.

Supratherapeutic anti-Xa levels are common in transplant patients receiving enoxaparin therapy. Empirically reduced dosing of enoxaparin and monitoring may warrant consideration in this population.

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