October 12, 2009

Dear ACCP Members,

Last week, the US Food and Drug Administration (FDA) revised the USP unit for unfractionated heparin. The new standards went into effect on October 1, 2009, with the first product reaching the market in mid-October 2009.

The changes in USP standards for unfractionated heparin will improve the consistency and quality of heparin and make it more consistent with international standards that have been in effect for some time. As a result of this new standard, there also likely will be an average decrease in potency of 6 to 10% of one USP heparin unit.

On September 30, 2009, the American College of Chest Physicians (ACCP) convened a large group of US, Canadian, and European experts in parenteral anticoagulants and thrombosis and other peer-agencies to discuss this issue and how it may impact the ACCP antithrombotic guidelines. The group indicated that, currently, there is in vitro data suggesting the 6 to 10% reduction of potency and no data on the effect of this change on patients or on common laboratory tests, such as the APTT or ACT. Furthermore, the same doses of heparin that will now become available in North America, labeled as “USP units,” have been used for many years as International Units, without apparent ill effect.

Based on this expert discussion, the ACCP antithrombotic guideline recommendations will not be revised as a result of the changes in heparin potency resulting from the new manufacturing standards. However, guideline authors and other convening experts emphasize the following:

• For therapeutic use, physicians may or may not notice that larger doses of heparin are required to achieve “therapeutic” levels of anticoagulation. Clotting tests, such as the APTT, the ACT, or the TCT, should be used to guide heparin infusions.


• In cases where fixed doses of heparin are used with clinical monitoring but without laboratory monitoring (such as extracorporeal circuits), increased heparin doses may or may not be required to maintain circuit patency.


• In cases where fixed doses of heparin are used without laboratory or clinical monitoring, physicians may or may not note reduced efficacy. This may particularly impact those clinicians who use large, weight-adjusted, fixed doses of heparin for the treatment of acute venous thromboembolism.

The ACCP will reconvene this group to review new data in 3 months, will send notification of any guideline changes to its members, and will post changes to its Web site at www.chestnet.org.

For more information about the new USP standards related to unfractionated heparin, please refer to the FDA Web site at: http://www.fda.gov/Drugs/default.htm.

Sincerely,

Mark Crowther, MD, MSc
Professor And Chair - Hematology And Thromboembolism
McMaster University
Vice Chair, Thrombosis
Antithrombotic Therapy and Prevention of Thrombosis: ACCP Evidence-based Clinical Practice Guidelines, 9th Edition

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