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Coagulation Specialist, Department of Pathology, University of California Davis Medical Center, Sacramento, CA
Clinical Coordinator, Department of Pharmaceutical Services, University of California Davis Medical Center; Associate Clinical Professor of Pharmacy, University of California at San Francisco
Assistant Professor, Department of Pathology, University of California Davis Medical Center
Anticoagulation Specialist, Department of Pharmacy, University of California Davis Medical Center
Professor and Vice Chair, Department of Pathology, University of California Davis Medical Center
Associate Clinical Professor of Surgery, University of California Davis Medical Center
Reprints: John T Owings MD, University of California Davis Medical Center, 2315 Stockton Blvd., Rm. 4209, Sacramento, CA 95817-2201, fax 916/734-7755, john.owings{at}ucdmc.ucdavis.edu
BACKGROUND: Previous studies have indicated the variability of anti-Xa activity in different sources of heparin and the variability of different methods used for measuring anti-Xa activity. Manufacturers of low-molecular-weight heparins (LMWHs) determine each lot's anti-Xa activity against the World Health Organization standard, but little information is known about anti-Xa activity variation between lots of LMWH and the impact on reported anti-Xa activity in patient samples.
OBJECTIVE: To determine the variation of plasma anti-Xa activity in patients receiving enoxaparin when different lots of enoxaparin are used for test calibration.
METHODS: We obtained 7 lots of enoxaparin containing approximately 10 000 IU/mL and one lot containing approximately 15 000 IU/mL of anti-Xa activity. For each lot, a 2.0 anti-Xa IU/mL dilution was prepared and a calibration curve performed using a chromogenic method. To test the variation in reported results between the different calibration lots, 20 patient samples were tested. Nineteen patients receiving enoxaparin and one patient not receiving enoxaparin (negative control) were tested in a blinded fashion, and the changes in light absorbance recorded. Anti-Xa activity results from tested plasmas were then extrapolated from each enoxaparin lot calibration curve.
RESULTS: Using Student's paired t-test, there were statistically significant differences between the plasma anti-Xa activities generated from the various enoxaparin lots. In the range of 0.5-1.0 IU/mL of anti-Xa activity, 3 (4.2%) samples had a >0.2 IU/mL difference (maximum difference 0.33 IU/mL) in anti-Xa activity between 2 lots of enoxaparin. For samples that had supratherapeutic anti-Xa activities (1.0-1.5 IU/mL anti-Xa activity), there was a wider variation (>0.2 IU/mL) in anti-Xa activity, which may have resulted in a dosing change.
CONCLUSIONS: The statistical differences in plasma anti-Xa activities noted between enoxaparin lots are not clinically significant. However, anti-Xa activities in the upper therapeutic and supratherapeutic ranges (>1.0 IU/mL of anti-Xa activity) resulted in a deviation of >0.3 IU/mL in reported anti-Xa activity, which may result in dosing changes.
Key Words: anti-Xa activity, enoxaparin, lot variability, low-molecular-weight heparin
Published Online, February 24, 2004. www.theannals.com, DOI 10.1345/aph.1D245
This article has been cited by other articles:
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  S. A Spinler, A. K Wittkowsky, E. A Nutescu, and M. A Smythe Anticoagulation Monitoring Part 2: Unfractionated Heparin and Low-Molecular-Weight Heparin Ann. Pharmacother., July 1, 2005; 39(7): 1275 - 1285. [Abstract] [Full Text] [PDF]
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