Anti-xa activity after enoxaparin prophylaxis in hospitalized patients weighing less than fifty-five kilograms.
Thromb Res. 2013 Dec;132(6):761-4
Authors: Rojas L, Aizman A, Ernst D, Acuña MP, Moya P, Mellado R, Cerda J
INTRODUCTION: Low-molecular-weight heparins are commonly used for the prophylaxis of thromboembolic disease. In contrast to therapeutic doses, recommended prophylactic doses are fixed (i.e., 40mg/day enoxaparin). Dosing of patients with extreme body weights has not been well studied, especially dosing of low weight patients.
OBJECTIVES: To establish the anti-Xa activity that results from 40mg/day enoxaparin in inpatients with body weight ≤55kg.
PATIENTS/METHODS: Cross-sectional study including inpatients older than 18years, with body weight ≤55kg, and whose treating physician found indication for 40mg/day enoxaparin. We excluded patients with renal failure and those using oral anticoagulants. Anti-Xa activity was measured 3hours after the second dose of enoxaparin. Statistical analyses were conducted to determine the effect of body weight on anti-Xa levels.
RESULTS: Average age was 72.5years (interquartile range, 30) and median body weight was 49.7kg (interquartile range, 7). Twenty-five percent of patients weighed ≤45kg, 37.5% weighed 46-50kg, and 37.5% weighed 51-55kg. The mean anti-Xa activity was 0.54±0.18IU/ml, and 60% of the patients exhibited activity ≥0.5IU/ml. Weight and anti-Xa activity inversely correlated (Spearman's rho=-0.428, p=0.001). Patients weighing ≤45kg exhibited higher anti-Xa activity (0.61±0.18IU/ml, p=0.008) than heavier patients and an odds ratio of 8 for anti-Xa level ≥0.5IU/ml (95% CI: 1.42-45.06).
CONCLUSIONS: Anti-factor Xa activity rises significantly when body weight decreases. Patients of low weight, especially those weighing <45kg, exhibited an anti-Xa activity higher than the desired range for thromboembolic prophylaxis.
PMID: 24521789 [PubMed - in process]