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Rapid Responses to:
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Electronic letters published:
![[Read Rapid Response]](/icons/misc/sectionDOWN.gif){kind=icon}
Re: Limitations of studies analyzed
In response
Anticoagulation in Pregnancy: What we learn from guidelines for other conditions.
Improved safety of low molecular weight heparins.
Limitations of studies analyzed
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Amir Qaseem, MD, PhD, MHA American College of Physicians
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aqaseem{at}acponline.org Amir Qaseem
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All the studies included in the review had exclusion criteria and these exclusion criteria were applied to both groups (LMWH and UFH). As a result, the results drawn from comparison from these trials refer to highly selected patient population in both groups. Conflict of Interest:None declared |
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Amir Qaseem, MD ACP, Snow, Vincenza
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aqaseem{at}acponline.org Amir Qaseem, et al.
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Our recommendations are based on only evidence from randomized controlled trials. That is why the studies that were mentioned in the letters comparing the efficacy of LMWH vs. UFH as well as for safety of heparin and warfarin during pregnancy were not mentioned in the guideline. However, LMWH is more cost-effective compared to UFH. Although there are many studies evaluating prophylactic use of LMWH in pregnant women, the evidence is scarce for treating DVT or PE in pregnant women. Conflict of Interest:None declared |
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Emmanuel M Bhaskar, M.D Sri Ramachandra Medical College & Research Institute,Porur,Chennai-600116,India
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drmebchennai{at}rediffmail.com Emmanuel M Bhaskar
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In the guideline, observations regarding safety of heparin and warfarin during pregnancy needs further clarification. Neither warfarin nor heparin is completely safe in pregnancy.The American college of cardiology recommendations regarding anticoagulation for pregnant women with mechanical heart valves tell us these interesting facts[1]: 1.Warfarin is generally safe during the first 6 weeks of gestation and in the second trimester.The risk of fetal embryopathy is maximum between 6 and 12 weeks of gestation. The drug is also safe in the third trimester ,but needs to be discontinued after 36 weeks of gestation. 2.Unfractionated heparin(UHF) is safe since it does not cross the placenta and has no significant teratogenicity. However it is associated with a higher incidence of thromboembolic complications compared to warfarin. Due to increase in the levels of factor VIII and fibrinogen during pregnancy the response of activated partial thromboplastin time(aPTT) is often blunted. 3.Low molecular weight heparin(LMWH) causes lower incidence of thrombocytopenia, more predictable response than UHF and is associated with decreased risk of osteoporosis. However increase in the volume of distribution of LMWH as pregnancy advances makes it necessary to monitor anti-Xa levels. Chan and collegues in their systamatic review observe that warfarin is generally safe in pregnant women with mechanical heart valve except between 6 and 12 weeks of gestation during which substitution with heparin is required[2]. To conclude,data from pregnant women with mechanical prosthesis reveal that warfarin therapy is not completely harmful and heparin has its own limitations. References: 1.Robert O Bonow, Blase A Carabello, Kanu Chatterje, Antonio C deLeon, David P Faxon, Michael D.Freed, et al.ACC/AHA 2006 Guidelines for the management of patients with valvular heart disease. J Am Coll Cardiol 2006;48:1-148 2.Wee Shian Chan, Sonia Anand, Jeffrey Ginsberg. Anticoagulation of pregnant women with mechanical heart valves: a systamatic review of the literature. Arch Intern Med 2000;160:191-6. Conflict of Interest:None declared |
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Richard Schreiber, M.D., F.A.C.P. Internists of Central Pa, Ltd.
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rschreiber{at}hsh.org Richard Schreiber
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I am surprised that the recently published guidelines regarding treatment of venous thromboembolic disease do not include some comments regarding the added safety of low-molecular-weight heparins (lmwh’s) compared to unfractionated heparin (UFH). There is clearly a lower incidence of heparin induced thrombocytopenia (HIT) with lmwh’s (ref. 1, 2, 3). The reduced likelihood of thrombocytopenia also decreases the chance of the devastating and life-threatening consequences of warfarin skin necrosis (ref. 4). Indeed, the price of one case of heparin induced thrombocytopenia quickly offsets the increased initial acquisition cost of lmwh. Other savings accrue when using lmwh, such as decreased costs for IV solutions, lab tests, and nursing time when lmwh is used, even in the inpatient setting, compared to UFH. In the 12 or so years that I have prescribed lmwh, I have seen 2 cases of readily reversible thrombocytopenia attributable to lmwh, and no cases of thrombotic HIT, whereas I routinely see at least one case per year of severe, sometimes life threatening HIT induced by UFH. To me the data regarding the safety and efficacy of lmwh’s are far more convincing than as represented in the currently published guidelines. As Dr. Russell Hull told us at the 1997 ACP convention, “heparin is outdated therapy.” Why are we still using UFH at all? Richard Schreiber, M.D., F.A.C.P. 1. Warkentin, TE, Levine, MN, Hirsh, J, et al (1995) Heparin-induced thrombocytopenia in patients treated with low-molecular-weight heparin or unfractionated heparin. N Engl J Med 332,1330-1335. 2. Lee, DH, Warkentin, TE Frequency of heparin-induced thrombocytopenia. Warkentin, TE Greinacher, A eds. Heparin-induced thrombocytopenia 3rd ed. 2004,107-148 Marcel Dekker. New York, NY. 3. Lindhoff-Last, E, Nakov, R, Misselwitz, F, et al Incidence and clinical relevance of heparin-induced antibodies in patients with deep vein thrombosis treated with unfractionated heparin or low-molecular- weight heparin. Br J Haematol 2002;118,1137-1142. 4. Srinivasan, AF, Rice, L, Bartholomew, JR, et al Warfarin-induced skin necrosis and venous limb gangrene in the setting of heparin-induced thrombocytopenia. Arch Intern Med 2004;164,66-70. Conflict of Interest:I serve on the speakers' bureau for Sanofi-Aventis pharmaceuticals. |
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Christopher Hughes, MD St. Clair Memorial Hospital
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cmh{at}cmhughesmd.com Christopher Hughes
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I am always suspicious when told that the use of LMWH products results in less hemorrhagic complications than IV UFH because it is so contrary to my clinical experience. I am also well aware that, as Hippocrates noted, "Experience is delusory." So my question goes to the original studies analyzed for these guidelines. How many of the underlying studies had no exclusion criteria? In other words, were patients entered into protocols only after screening for chronic kidney disease, age or other criteria that lead to a greater frequency of hemorrhagic complications? If not, that's great and forget I said anything. If so, should the guidelines reflect this more explicitly? Thanks, Conflict of Interest:None declared |
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