Renal Function, Peak Anti‐Xa Levels and Enoxaparin Dosing

Background: Low molecular weight heparin is administered in a fixed, weight‐adjusted dose without laboratory monitoring in the majority of patients. However, there is still uncertainty regarding optimum dosing in patients with renal impairment. Aim: To examine the association between peak anti‐Xa levels and creatinine clearance in patients treated with enoxaparin. Method: Prospective study of hospitalised patients receiving enoxaparin 1 mg/kg twice daily. Peak anti‐Xa levels were measured after patients received at least 3 doses of SC enoxaparin and were compared in 3 patient groups according to baseline creatinine clearance (Group 1: Crcl ≤ 30 rnUmin; Group 2: Crcl < 30 and ≤ 60 mL/min; Group 3: Crcl < 60 mL/min). Results: 50 patients were studied (54% male). Peak anti‐Xa levels after a mean of 5.2 doses of enoxaparin were within or above the recommended therapeutic range (0.6‐1.0 unit per mL) in 96% of patients ( 48/50). At this time, five of the seven patients (71.4%) in Group 1 had peak anti‐Xa levels < 1.0 unit per mL, compared with 15/19 (78.9%) in Group 2 and 7/24 (29.2%) in Group 3. Mean peak anti‐Xa levels were 1.58 ± 0.54 unit per mL, 1.25 ± 0.38 unit per mL and 0.93 ± 0.28 unit per mL in Groups 1, 2 and 3 respectively, p = 0.001. Conclusion: Patients with reduced creatinine clearance who were receiving enoxaparin 1 mg/kg twice daily achieved significantly higher peak anti‐Xa levels compared with those with normal creatinine clearance. Dose reduction and/or routine laboratory monitoring of enoxaparin should be considered in patients with impaired renal function.