What Is the Most Effective Blood Thinner for Treating Patients with Blood Clots in the Veins?. Ann Intern Med. 2003;138:I-63. doi: 10.7326/0003-4819-138-9-200305060-00004
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Published: Ann Intern Med. 2003;138(9):I-63.
When blood clots form in veins (blood vessels that carry blood back to the heart), serious and even fatal complications can occur. Doctors use blood thinners to promote clot breakdown and prevent additional clots. For many years, the most commonly used blood thinner has been a drug known as unfractionated heparin. To be effective, unfractionated heparin must be injected every 6 hours (or given continuously through a needle in a vein). This requires hospitalization and careful daily monitoring of the dose to confirm effective blood thinning. More recently, another preparation of heparin, low-molecular-weight heparin (LMWH), has been introduced. It can be given at home, requires less frequent injections, and does not require daily monitoring of the dose. However, LMWH is about 10 times as expensive as unfractionated heparin. Several studies have suggested that LMWH is more effective than unfractionated heparin. Since the implications for cost and effectiveness are important, doctors need to be confident that these studies fairly compare unfractionated heparin and LMWH. The problem is that to make a fair comparison, researchers must be certain that the correct dose of unfractionated heparin was administered. This depends on accurate laboratory tests. Over the past 25 years, many different laboratory tests have been used, each having a different standard for effective blood thinning dose.
To find out whether previous studies had carefully considered the potential influence of variations in laboratory tests in concluding that LMWH is more effective than unfractionated heparin.
The researchers searched the medical literature from 1984 to 2001 to identify published articles that randomly assigned patients to receive either LMWH or unfractionated heparin and then evaluated how the researchers decided on the correct dose of unfractionated heparin.
15 journal articles were identified. Only 3 of these articles described the specific laboratory methods used to evaluate the degree of blood thinning caused by a particular dose of unfractionated heparin, while 10 articles simply assumed that a standard evaluation of blood thinning was effective. Only 3 articles reported exactly how the dose of unfractionated heparin was adjusted.
The researchers did not compare clinical outcomes between studies with and without careful attention to methods for monitoring blood thinning.
Although this study identifies the possibility of unfairness in previous comparisons between unfractionated heparin and LMWH, it does not prove that unfractionated heparin is as good as or better than LMWH in treating patients with blood clots in the veins.
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