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Thrombosis Guidelines Emphasize Difficult Choices for Pregnant Women

Wednesday, June 25, 2008 General News J E 4
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NORTHBROOK, Ill., June 24 New evidence-based guidelinesaddress the prevention and management of thrombosis in key patient populationsand reinforce recommendations related to the routine use of preventivetherapies. Published as a supplement in the June issue of CHEST, thepeer-reviewed journal of the American College of Chest Physicians (ACCP),Antithrombotic and Thrombolytic Therapy: ACCP Evidence-Based Clinical PracticeGuidelines, Eighth Edition was developed by an international panel of90 experts and includes more than 700 of the most comprehensiverecommendations related to the prevention, treatment, and long-term managementof thrombotic disorders. The guidelines include chapters on the challenges inpreventing and treating thrombosis in pregnant women and children, and onmanaging peri- and postoperative patients, while also reinforcing previousguidelines related to the routine use of preventive therapies, includingaspirin.

"For years, clinicians have faced challenges in preventing and managingthrombosis in women who are pregnant or patients who require surgery," saidguidelines panel chair Jack Hirsh, MD, FCCP, Henderson Research Center,Hamilton, ON, Canada. "The new guidelines address many troublesome issues inantithrombotic therapy and provide clinicians with a variety of options forcare in special patient groups." Antithrombotic and thrombolytic therapies areused to prevent and treat thrombosis or blood clotting that arises inarteries, veins, and the heart.

Pregnant Women

The new ACCP guidelines address challenging issues facing women who arepregnant or wish to become pregnant while undergoing long-term antithrombotictherapy. Pregnant women taking vitamin K antagonists (VKA), such as theanticoagulant warfarin, have an increased risk for birth defects andmiscarriage and are, therefore, advised to stop taking VKAs before 6 weeks offetal gestation. However, some pregnant women with certain types of mechanicalheart valves may be continued on VKA therapy because of concerns about theeffectiveness of alternative anticoagulants in preventing stroke and valvethrombosis. For other women taking VKAs who become pregnant, the guidelinesrecommend substituting low-molecular-weight heparin (LMWH) or unfractionatedheparin (UFH). The guidelines recommend two options for doing this: (1)continuing VKA but performing frequent pregnancy tests to determine whenpregnancy has been achieved, followed by the substitution of LMWH or UFH astherapy; or (2) substituting VKAs with LMWH or UFH prior to conception.Although the second option eliminates the potential for fetal exposure to VKA,it provides additional challenges. LMWH and UFH are more expensive than VKAsand must be administered through a once- or twice-daily injection as opposedto a once daily oral dose of VKAs. In addition, long-term use of LMWH or UFHcan be associated with osteoporosis.

"If women substitute heparin prior to pregnancy and have difficultiesconceiving, they may find themselves taking the medication for a much longertimeframe than expected," said guideline coauthor Shannon Bates, MD, McMasterUniversity and Henderson Research Centre, Hamilton, Ontario, Canada. "This isnot only inconvenient but also increases treatment costs and may be associatedwith long-term risks for the mother."

Children

Recommendations related to childhood stroke, one of the top ten causes ofdeath in children, and congenital heart disease have been substantiallyexpanded since the previous guideline. Arterial ischemic stroke (AIS), usuallycaused by embolism or thrombosis, is difficult to diagnose in children becauseunderlying health conditions are markedly different than those in adult strokeand up to 15% of children with AIS have no apparent risk factors. Theguidelines recommend that children with AIS receive initial antithrombotictherapy until underlying causes can be determined, followed by maintenan
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