Monitoring Enoxaparin with Antifactor Xa Levels in Obese Patients.

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To characterize antifactor Xa peak levels (as therapeutic, subtherapeutic, and supratherapeutic) in morbidly obese patients receiving treatment doses of enoxaparin, using a therapeutic range of 0.5-1.1 units/ml, and to assess the occurrence of bleeding complications in these patients. Retrospective cohort study. Community hospital. Ninety-nine morbidly obese patients (body mass index [BMI] higher than 40 kg/m(2) or total body weight more than 150 kg) who received at least three doses of the standard treatment dosage of enoxaparin and had steady-state antifactor Xa peak levels between April 2009 and January 2014. Data were collected from patients' medical records on age, sex, height, weight, BMI, serum creatinine concentration, creatinine clearance (using lean body weight as well as adjusted body weight), antifactor Xa level, and time of blood collection for measurement of antifactor Xa level. Enoxaparin therapy was monitored by using antifactor Xa levels; steady-state enoxaparin antifactor Xa levels were measured 4 hours after administration of the third dose for peak level monitoring. The primary outcome was the proportion of patients whose steady-state antifactor Xa peak values were in the therapeutic (0.5-1.1 units/ml), subtherapeutic, and supratherapeutic ranges. The secondary outcome was occurrence of major bleeding. Univariate regression analysis was performed to identify the correlation between baseline patient characteristics and antifactor Xa levels. Most of the patients (50 [50.5%]) had supratherapeutic levels, 35 (35.4%) had levels within the therapeutic peak range (0.5-1.1 units/ml), and 14 (14.1%) had subtherapeutic levels. No bleeding was observed in any of the 99 patients. Univariate analysis revealed a negative association between antifactor Xa levels and serum creatinine concentration (r = -0.262, p=0.009). Based on the results of this study, monitoring antifactor Xa levels is warranted to ensure the safety and efficacy of enoxaparin in the obese patient population (defined as a total body weight more than 150 kg or BMI higher than 40 kg/m(2)). Enoxaparin dose individualization and antifactor Xa level monitoring need further validation with clinical outcomes.