Effects of low-molecular-weight heparin on platelets as compared with commercial heparin

Five subjects were injected with 5,000 IU of commercial heparin and low-molecular-weight heparin at an interval of 20 days after each injection. Both heparins produced the same platelet factor 4 release immediately after administration (commercial heparin 114.6 +/- 21.6 ng/ml, low-molecular-weight heparin 113.1 +/- 22.1 ng/ml). However, commercial heparin induced a more evident potentiating effect on ADP-induced platelet aggregation and was still present 60 min after injection. Low-molecular-weight heparin had a higher anti-Xa-specific activity than that determined by activated partial thromboplastin time. The opposite was true for the commercial preparation.     

Preventing pulmonary embolism with heparin in low doses

Wide use of heparin as prophylaxis in selected persons at high risk of thrombosis promises to reduce the incidence of pulmonary embolism dramatically. Administered in low doses, heparin prevents deep-vein thrombosis yet avoids bleeding complications and the need for laboratory monitoring.     

国产低分子量肝素钠在血液透析抗凝中的应用

目的：研究国产低分子量肝素钠（ＬＭＷＨＮａ）和普通肝素钠（ＳＨＮａ）在血液透析（血透）中的抗凝效果及对尿素氮和肌酐清除能力的影响，并观察其不良反应。方法：６２例慢性肾功能衰竭（肾衰）维持性血透患者自身对照，分两个阶段分别用ＬＭＷＨＮａ和ＳＨＮａ抗凝透析各４次，每周２次～３次，３周～４周内完成；比较透析器凝血程度、血室容积下降率、活化部分凝血活酶时间（ＡＰＴＴ）、抗Ⅹａ因子（ＦⅩａ）活性、尿素氮和肌酐清除下降率的改变，观察动、静脉穿刺点压迫止血时间、肝功能、肾功能、血常规的变化以及不良反应。结果：与ＳＨＮａ比较，ＬＭＷＨＮａ在透析中抗ＦⅩａ活性明显增强，但对ＡＰＴＴ的影响不如ＳＨＮａ明显；透析结束后动、静脉穿刺点压迫止血的时间缩短；透析器凝血情况有所改善，血室容积下降率、尿素氮和肌酐清除下降率与ＳＨＮａ比较均无显著性差异；使用中未发生明显的与药物有关的不良反应。结论：透析中用国产ＬＭＷＨＮａ可达到与ＳＨＮａ相似的抗凝效果，而出血倾向明显减少     

小剂量肝素和低分子肝素治疗恶性血液病血栓前状态的临床研究

目的探讨D-二聚体(D-dimer,D-D)在恶性血液病患者中的临床意义,以及使用小剂量肝素和低分子肝素后的变化.方法正常对照20例.恶性血液病45例,分为3组:①单纯化疗组(15例);②小剂量肝素组(15例);③低分子肝素组(15例).采用酶联免疫吸附测定(ELISA)双抗夹心法对45例恶性血液病进行了D-D测定.结果恶性血液病组D-D较对照组明显增高,差异具有统计学意义(P<0.01),使用小剂量肝素和低分子肝素后D-D含量较初诊时明显降低(P<0.05),且低分子肝素组较小剂量肝素组降低更为明显(P<0.05).结论恶性血液病患者D-D含量可早期发现血栓前状态,低分子肝素较小剂量肝素具有更明显降低D-D含量的作用.低分子肝素改善血栓前状态有效、安全.     

Inhibition of platelet-dependent thrombosis by low molecular weight heparin (CY222): comparison with standard heparin

We have compared the relative antithrombotic and antihemostatic effects of the very low molecular weight heparin CY222 with standard unfractionated heparin (SH) in a baboon model of platelet-dependent thrombosis. Thrombus formation was induced by placement of a thrombogenic device in an exteriorized femoral arteriovenous shunt under conditions of intermediate-shear blood flow. The device consisted of a collagen-coated cannular segment positioned proximal to two regions of expanded diameter exhibiting disturbed flow and stasis. Thrombus formation was measured in real time by indium 111-labeled platelet imaging. The collagen-coated surface accumulated thrombi composed largely of platelets, and the regions of disturbed flow were morphologically rich in fibrin and red cells. SH and CY222 were administered by continuous infusion for 1 hour. Although both heparin preparations abolished thrombus formation in the low-shear fibrin-rich regions at plasma levels less than 0.5 anti-Xa U/ml, platelet deposition onto the collagen surface was not reduced by either SH or CY222 at that dosage. These findings were consistent with previously observed therapeutic benefits of this level of anti-Xa activity in venous, but not arterial, thrombosis. Platelet deposition on the collagen was reduced in a dose-dependent manner by both SH and CY222 administered at doses between 1 and 5 anti-Xa U/ml. It is important to note that although heparin preparations produced profound and equivalent antithrombotic effects for platelet-dependent thrombus formation at comparable levels of anti-Xa activity, SH prolonged both the coagulation time and the bleeding time substantially more than did CY222.(ABSTRACT TRUNCATED AT 250 WORDS)     

Anticoagulation monitoring part 2: Unfractionated heparin and low-molecular-weight heparin

OBJECTIVE: To review the availability, mechanisms, limitations, and clinical application of point-of-care (POC) devices used in monitoring anticoagulation with unfractionated heparin (UFH) and low-molecular-weight heparins (LMWHs). DATA SOURCES: Articles were identified through a MEDLINE search (1966-August 2004), device manufacturer Web sites, additional references listed in articles and Web sites, and abstracts from scientific meetings. STUDY SELECTION AND DATA EXTRACTION: English-language literature from clinical trials was reviewed to evaluate the accuracy, reliability, and clinical application of POC monitoring devices. DATA SYNTHESIS: The activated partial thromboplastin time (aPTT) and activated clotting time (ACT) are common tests for monitoring anticoagulation with UFH. Multiple devices are available for POC aPTT, ACT, and heparin concentration testing. The aPTT therapeutic range for UFH will vary depending upon the reagent and instrument employed. Although recommended by the American College of Chest Physicians Seventh Conference on Antithrombotic and Thrombolytic Therapy, establishing a heparin concentration-derived therapeutic range for UFH is rarely performed. Additional research evaluating anti-factor Xa monitoring of LMWHs using POC testing is necessary. CONCLUSIONS: Multiple POC devices are available to monitor anticoagulation with UFH. For each test, there is some variability in results between devices and between reagents used in the same device. Despite these limitations, POC anticoagulation monitoring of UFH using aPTT and, more often, ACT is common in clinical practice, particularly when evaluating anticoagulation associated with interventional cardiology procedures and cardiopulmonary bypass surgery.