Anti-factor X Activity Levels with Continuous Intravenous Infusion and Subcutaneous Administration of Enoxaparin after Coronary Artery Bypass Grafting: a Randomized Clinical Trial

BACKGROUND: Low-molecular-weight heparin enoxaparin is widely used in pharmacological thromboprophylaxis after coronary artery bypass grafting (CABG). The aim of this study was to compare anti-factor X activity (anti-Xa) levels when the thromboprophylactic dose of enoxaparin was provided after CABG, with two different administration routes: continuous intravenous infusion (CIV) and subcutaneous bolus (SCB) injection. We hypothesized that the current standard method of SCB administration might lead to lower anti-Xa levels than recommended in other patient groups, due to reduced bioavailability.

METHODS: In this prospective, randomized, controlled clinical trial, 40 patients scheduled for elective CABG were randomized to receive 40 mg of enoxaparin per day either as CIV or SCB for 72 h. Enoxaparin was initiated 6-10 h after CABG. Anti-Xa levels were measured 12-14 times during the study period. The primary outcome i.e. the maximum anti-Xa concentration over 0-24 h (Cmax0-24h ), was calculated from these measured values. Secondary outcomes were Cmax25-72h and the trough concentration of anti-Xa after 72 h of enoxaparin initiation (C72h ).

RESULTS: Twenty patients were randomized to the CIV-group and 19 to the SCB-group. The median anti-Xa Cmax0-24h was significantly lower in the CIV-group than in the SCB-group: 0.15 [interquartile range (IQR) 0.13-0.19] IU/mL versus 0.25 (IQR 0.18-0.32) IU/mL, p < 0.005. The median anti-Xa Cmax25-72h was 0.12 (IQR, 0.1-0.17) IU/mL versus 0.23 (IQR 0.19-0.31) IU/mL, respectively, p < 0.005. At 72 h, there was no difference between the groups in their anti-Xa levels.

CONCLUSIONS: In this low-risk CABG patient population, SCB administration of a thromboprophylactic dose of enoxaparin provided anti-Xa levels that are considered sufficient for thromboprophylaxis in other patient groups. CIV administration resulted in lower anti-Xa levels compared to the SCB route.