title: The relationship between anti-factor Xa level and clinical outcome in patients receiving enoxaparine low molecular weight heparin to prevent deep vein thrombosis after hip replacement.
abstract: Studies in experimental animals have demonstrated that there is a relationship between levels of low molecular weight (LMW) heparin and both bleeding and inhibition of thrombosis. The relationship between these outcomes and ex vivo anti-factor Xa levels has been examined in 163 patients undergoing total hip replacement who were given prophylaxis once daily with a LMW heparin (enoxaparine). Fifty patients received 60 mg of enoxaparine and 113 received 40 mg, both regimens being administered subcutaneously once daily. Blood samples for anti-factor Xa levels were collected 12 hours after the injection on the day of surgery and on days 1, 3 and 6, postoperatively. The incidence of wound hematoma was 5.3% when the maximum anti-factor Xa level was less than or equal to 0.2 units per ml, but increased to 24.5% when the anti-factor Xa level exceeded 0.2 units per ml, P = 0.0008. The incidence of postoperative thrombosis was low (6.3%) if the minimum anti-factor Xa level exceeded 0.1 units per ml, but increased to 14.6% when less than or equal to 0.1 units per ml, and to 18.8% if the anti-factor Xa level was less than or equal to 0.05 units per ml. Regression analysis revealed that there was a statistically significant relationship between anti-factor Xa level and wound hematoma, P = 0.002 and anti-factor Xa level and thrombosis, P = 0.03. These findings suggest that when enoxaparine is administered as a once daily subcutaneous injection, the 12 hour anti-factor Xa level should not exceed 0.2 units per ml to minimize bleeding and levels greater than 0.05 units per ml should be obtained to optimize efficacy.
authors.affiliation: Department of Medicine, McMaster University, Hamilton, Ont., Canada.
authors.forename: M N
authors.initials: MN
authors.lastname: Levine
authors.forename: A
authors.initials: A
authors.lastname: Planes
authors.forename: J
authors.initials: J
authors.lastname: Hirsh
authors.forename: M
authors.initials: M
authors.lastname: Goodyear
authors.forename: N
authors.initials: N
authors.lastname: Vochelle
authors.forename: M
authors.initials: M
authors.lastname: Gent
mesh_terms: D065427:Factor Xa Inhibitors; D006406:Hematoma / Q000209:etiology; D006495:Heparin, Low-Molecular-Weight / Q000627:therapeutic use*; D006622:Hip Prosthesis / Q000009:adverse effects*; D006801:Humans; D011183:Postoperative Complications / Q000517:prevention & control*; D013924:Thrombophlebitis / Q000517:prevention & control*
chemical_list: D065427:Factor Xa Inhibitors; D006495:Heparin, Low-Molecular-Weight