Thrombin clotting time

The anticoagulant activity of dextran derivatives were assessed by measuring the thrombin clotting time (ThNIH units) of freshly prepared platelets from plasma in the presence of the CMD, CMDB, CMDBSSu and CMDSu polymers and of human thrombin (1094 NIH units mL 1). The anticomplementary activity was expressed as the amount of polymer that inhibits 50% formation of the alternative and classical pathway C3 convertase [220,290,291]. 

Thrombin clotting time 70 to 120 seconds 1 50 to 600 seconds depending on indication for anticoagulation... 

We now report results concerning the interactions between these two proteins and two of these polystyrene derivatives sulfonated polystyrene (PSSO3) and sulfonate-glutamic acid sulfonamide polystyrene (PSSO2GIU). The adsorption of each protein was studied either in purified system or in plasma and the binding constants were determined. Moreover, the catalysed formation of thrombin-anti-thrombin III complex was examined and compared with the antithrombic activity measured through thrombin clotting times of plasma preincubated with these polymers. 

The antithrombic activity of the polymers was first compared through the thrombin clotting times of platelet poor plasma (PPP) incubated with various amounts of suspended resin. The results were translated into the amount of inactivated thrombin as previously described and are reported in Fig. 4. These curves show that the inactivation of the same thrombin activity in plasma requires approximately 3 times more PSSO3 than PSSO2GIU. 

Prothrombin time (PT), activated partial thromboplastin time (aPTT), and Thrombin clotting time (TCT)... 

The last of the fat-soluble vitamins to be identified was vitamin K, found by Dam to be an anti-hemorrhagic factor for young chicks, distinct from vitamin C. Its structure was determined by Dam in collaboration with Karrer. Interest in the vitamin was intensified when it was discovered (Link, 1941) that dicoumarol, present in spoiled sweet clover, was the agent producing hypothrombinemia (giving prolonged blood-clotting time) in cattle. Since vitamin K is structurally similar to dicoumarol, the vitamin was presumptively implicated in thrombin formation. This has been fully substantiated by recent work on the role of vitamin K in the synthesis of prothrombin in the liver. 

Pharmacology Enoxaparin, tinzaparin, and dalteparin are LMWHs. These agents enhance the inhibition of Factor Xa and thrombin by binding to and accelerating antithrombin activity. They preferentially potentiate the inhibition of Factor Xa, while only slightly affecting thrombin and clotting time (activated partial thromboplastin time [APTT] or PT). 

Mechanism of Action An anticoagulant that binds specifically and directly to thrombin, inhibiting free circulating and clot-bound ihmmhinT herapeuticEffect Prolongs the clotting time of human plasma. 

FIGURE S.4 Relative fibrin-clotting and amidolytic activity of thrombin as a function of the concentration of desalted fermented anchovy sauce (dFAS). Anticoagulation activity was assessed by the increase in the fibrin clotting time (empty circles) and the release of p-nitroaniline (closed circles). Data are presented as the mean SD (n —3). Source Kim et at. (2004). Permission has been obtained for the use of copyrighted material from Elsevier B.V. 

Fig. 3. Plasma clotting time as a function of amount of copolymer in contact. 1 — 0.1 ml of a suspension of copolymer was incubated with 0.2 ml plasma for 20 min, 0.1 ml thrombin solution was added 2 — 0.1 ml of the copolymer suspension was incubated for 20 min with 0.2 ml plasma, the copolymer filtered from the solution, and to this solution were then added 0.1 ml buffer solution and thrombin solution 93)...

The sorbed heparin fully retains its anticoagulant activity the thrombin time for both sorbed heparin and heparin in solution is 20 + 2 s/mg heparin. The clotting time of blood in contact with the gel is proportional to the amount of heparin sorbed and significantly higher than that characteristic for the non-heparinized gel. Heparin may be repeatedly sorbed after it has been removed with saturated NaCl solution. 

A dose-proportional curve was also noted in ecarin clotting time (ECT) (46). ECT is measured based on the conversion from prothrombin to meizothrombin mediated by ecarin, the venom of the snake. Thrombin inhibitors can inhibit... 

Callas D, Fareed J. Comparative anticoagulant effects of various thrombin inhibitors, as determined in the ecarin clotting time method. Thromb Res 1996 83 463-468. 

Bivalirudin is a direct thrombin inhibitor that has found utility for reducing the rate of acute reocclusion in patients treated with PCI. It is preferential to heparin in PCI when HIT is present. This drug is a derivative of hirudin, which is a dedicated thrombin inhibitor with no other in vivo activities of significance. The molecule is semisynthetic the C-terminal of hirudin is linked by a polyglycine spacer to the tetrapeptide region of the N-terminal that reacts with the thrombin active site (22). It is monitored by the activated clotting time test. Its pharmacologic properties are shown in Table I. 

Fig. 7 C Plasma clotting time measurements, including measurements of plasma recalcification time [PRT], plasma thromboplastin-catalyzed clotting time [PTT], and thrombin-catalyzed clotting time [TT]...

Heparin therapy may be monitored by its increases in clotting time in the APTT, although this method for measuring heparin is difficult to standardize. Heparin is more specifically assayed by its effect on factor Xa inactivation by antithrombin. Such factor Xa-based heparin assays usually employ purified factor Xa as a reagent and factor X-deficient substrate plasma as the source of antithrombin. The prolongation of the clotting time that results from the heparin in the patient s plasma is compared with pooled normal plasma that is known to be free of heparin. Many variations of this heparin assay are available. Heparin assays can use thrombin rather than factor Xa, however, the low-molecular-weight heparins are not reliably measured in thrombin-based assays. 

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