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Intravenous Lovenox and PTT: Response

In response to Dana Haas’ question about IV Lovenox (Enoxaparin, low molecular weight heparin, LMWH) and the PTT, while it is true the PTT is relatively insensitive to LMWH, it is slightly prolonged. 
According to Lovenox Prescribing Information, a standard IV bolus of 30 mg followed by a 1 mg/kg SC injection results in a mean PTT of 50 seconds and a mean anti-Xa heparin level of 1.16 IU/mL 3 to 5 hours after administration. The anti-Xa heparin half-life is 4.5 to 7 hours depending on duration of therapy. There is measurable anti-Xa heparin activity at 12 hours, considered the trough period. Contrary to Dana’s experience, I believe LMWH half-life exceeds that of standard unfractionated heparin, however the kinetics of unfractionated heparin vary by the individual.

LMWH dosing and effects become increasingly important as we switch from standard heparin to LMWH and now Arixtra (synthetic pentasaccharide). The Heme-onc and Path residents at UAB tell me only about 1 in 10 patients needing heparin anticoagulation now receives standard heparin. Geo.

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