Non-therapeutic anti-FXa levels are common among medical ward patients treated with enoxaparin

Thromboembolism is treated with a weightadjusted enoxaparin dose without the need for laboratory monitoring. This study aims to determine the prevalence of sub and supra-therapeutic anti-factor Xa (aFXa) levels among medical ward patients treated with enoxaparin, and to identify potential factors associated with non-therapeutic aFXa levels. aFXa levels were measured in a cohort of medical ward patients treated with curative enoxaparin regimen (1 mg/kg bid) in the Ha'emek Medical Center in the northeastern area of Israel. The relative risk (RR) ratio for sub and supra-therapeutic aFXa levels was estimated in demographic and clinical subgroups. Of the 294 included patients, only 78.6% had therapeutic aFXa levels, while 13.3% and 8.1% had sub and supra-therapeutic levels, respectively. On univariate analysis, females, smoking, BMI=30, and cancer were significantly associated with supra-therapeutic aFXa levels; fibrates and warfarin use were significantly associated with sub-therapeutic aFXa levels (P<0.05). On multivariate analysis, females and patients with cancer were independently at increased risk for supra-therapeutic levels RR 3.35(95% CI 1.50, 7.48), RR 3.61(95% CI 1.50, 8.70), respectively. Fibrates and warfarin were associated with sub-therapeutic levels RR 2.99(95% CI 1.44, 6.20), RR 3.42(95% CI 1.73, 6.76), respectively. Standard curative enoxaparin regimen is associated with increased risk for supra-therapeutic aFXa levels in females and patients with cancer and subtherapeutic levels in patients treated with fibrates and warfarin. This may suggest the need for anticoagulation monitoring in high-risk patients with these conditions.