Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.5 (thrombin)
 33,306 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Low molecular weight heparins are increasingly prescribed in France. Prepared from standard heparin by depolymerisation, they show a markedly decreased anti IIa activity and a anti Xa/anti IIa ratio ranging from 2 to 4. Their mode of action in the coagulation system is still not well known and it is difficult to explain the mechanism of their antithrombotic effect, demonstrated in vivo. They seem to inhibit the first traces of thrombin and then counteract the priming and amplification of coagulation. Their fibrinolytic activity is also a disputed question, but seems to be lower than that of standard heparin. The pharmacological studies show a venous as well as arterial antithrombotic activity of a low molecular weight heparin on several animal models, a lower but not negligible bleeding risk as compared to unfractionated heparin. Furthermore heparin fragments have a weak interaction with platelets, which allow to foresee a greater efficacy of LMWH than standard heparin in arterial thrombosis. Some very rare cases of thrombocytopenia in patients treated with LMW heparins have been recently reported. The compared pharmacokinetics of heparins gave proof of a renal elimination of low molecular weight heparin and a bio availability of about 90% after subcutaneous injection. Many clinical studies allowed to define indications of heparin fragments in prophylactic treatment after surgery as well as in medical patients and in curative treatment in case of deep vein thrombosis. However, others studies must be carried out to define the real efficacy of such a treatment during pulmonary embolism, disseminated intravascular coagulation and myocardial infraction, or during thrombotic complications after vascular surgery.
 ...
PMID:[The new heparins]. 131 47

The pharmacodynamic parameters of a low molecular weight heparin (LMWH, CY 216) and their inter-individual variations were investigated. In a cross over study 100 anti-factor Xa IC U/kg were injected, one week apart, to 12 healthy volunteers by intravenous (IV) or subcutaneous (SC) route. The pharmacological effects were followed by performing activated partial thromboplastin time (APTT), thrombin clotting time (TCT) and a chromogenic anti-factor Xa assay. The main pharmacodynamic parameters were calculated from the anti-factor Xa activity disappearance curves. Five to ten min after IV injection, the APTT ranged between 56 and 98 sec (baseline 40 sec), the TCT between 28 and 99 sec (baseline 19 sec) and the anti-factor Xa activity between 1.58 and 2.28 IC U/ml. The anti-factor Xa activity half-life ranged between 1.5 and 2.9 h. After SC injection, there were no detectable APTT and TCT prolongations; the maximum anti-factor Xa activity ranged between 0.36 and 0.88 IC U/ml and the half life between 1.5 and 6.4 h. These results indicate that, as for standard heparin, there are large inter-individual variations in the anticoagulant responses to a given dose of CY 216 an observation which may have clinical implications.
 ...
PMID:Pharmacodynamics of CY 216 in healthy volunteers: inter-individual variations. 216 Apr 14

A pilot study has been conducted in ten consecutive patients undergoing femoro-popliteal reconstruction or distal vascular surgery under epidural anaesthesia. Immediately before arterial cross-clamping, enoxaparin (E) (75 anti-Xa IU.kg-1) was injected intravenously (i.v.). During surgery, washing of the saphenous or polytetrafluoroethylene (PTFE) graft has been performed using enoxaparin. Enoxaparin (75 anti-Xa IU.kg-1) was administered subcutaneously (S.C.) 8 hours after the i.v. injection, and then every 12 hours during 10 days. The patency of the vascular reconstruction and the side-effects of E administration were evaluated clinically before and during surgery, then by a daily clinical examination. Echo-Doppler and/or arteriography were also performed preoperatively and on the 10th postoperative day. Haematocrit, platelet count, activated partial thromboplastin time, prothrombin time, thrombin time, fibrinogen and anti-Xa activity were assessed. None of the patients developed venous or arterial thrombosis and all the by-pass grafts remained patient. Only one minor surgical bleeding occurred on the first post operative day, despite anti-Xa levels in the expected range. One patient developed minor haematomas at the injection site. No bleeding was observed. Further randomized studies comparing LMWH and UH are required in order to substantiate these preliminary clinical and biological findings.
 ...
PMID:[Peri- and postoperative use of low molecular weight heparin in peripheral vascular surgery]. 216 91

The effect of different heparins and a synthetic pentasaccharide on the inhibition of intrinsic prothrombinase and of its generation was studied by a new technique, using a defibrinated prothrombin poor human plasma, supplemented with phospholipids and calcium. Prothrombinase activity was evaluated on purified prothrombin with a chromogenic substrate. This technique is designed to bypass the interference of massive endogenous thrombin generation on the measurement of prothrombinase activity. We first validated the specificity of the technique by using specific Xa and IIa inhibitors. Then, the inhibition of prothrombinase generation and the inhibition of generated prothrombinase were both studied. The results showed that anti-Xa activity measured on exogenous bovine factor Xa added to plasma was not correlated with the inhibition of prothrombinase generation or prothrombinase activity. The concentrations required for unfractionated heparin (the 4th International Standard: 4th IS UH), 1st International Standard Low Molecular Weight Heparins (1st IS LMWH), enoxaparin, Fraxiparine, and pentasaccharide in order to inhibit preformed prothrombinase were significantly higher than those necessary to inhibit prothrombinase generation. These data suggest that anti-Xa activity of unfractionated heparin and its derivatives does not completely reflect the extent of the inhibition of intrinsic prothrombinase generation by UH, LMWH, and pentasaccharide. On the other hand, anti-IIa activity of heparins could be responsible for the inhibition of prothrombinase generation. The action of pentasaccharide devoid of anti-IIa activity on prothrombinase generation appears related to its indirect effect on the formation of initial thrombin traces. This new technique provides a tool to study the essential role played by thrombin during the early steps of coagulation.
 ...
PMID:The inhibition of intrinsic prothrombinase and its generation by heparin and four derivatives in prothrombin poor plasma. 216 62

Our purpose was to determine the relative contribution of the antifactor Xa and antithrombin activities of heparin to its antithrombotic potency. The antithrombotic activities of unfractionated heparin (UH), two low molecular weight heparins (LMWH, CY 216 and CY 222) with increasing anti-factor Xa/antithrombin ratio and a synthetic pentasaccharide (PS) with high affinity to antithrombin III and no antithrombin activity were evaluated. In the Wessler-thromboplastin model, the most potent antithrombotic agent, on a weight basis, was UH followed by CY 216, CY 222 and the PS which was 40 times less potent than UH. On an antithrombin unit basis, the antithrombotic potencies of UH, CY 216 and of CY 222 were equivalent. Thus, in this model, the antithrombotic effect results from the catalytic action of UH or LMWH on thrombin inhibition. In the Wessler-serum model, on a weight basis, the antithrombotic effectiveness of UH was unchanged, those of CY 216 and CY 222 were doubled, and that of the PS was increased 10 times. On an anti-factor Xa unit basis, CY 216 was as effective as UH, and PS as effective as CY 222. On an antithrombin unit basis, CY 216 and CY 222 were equivalent and more potent than UH. Thus, in this model, the antifactor Xa activity of heparin becomes important for its antithrombotic property. After a single subcutaneous injection of 1000 antifactor Xa U/kg, the antithrombotic effects of UH were maintained for more than 14 h in the two models. After injection of the same dose of CY 216 significant antithrombotic effects were observed only for 9 h, in the Wessler-thromboplastin model but for 18 h in the Wessler-serum model. At that time, no detectable antithrombin activity was measurable in the plasma while 0.11 units of antifactor Xa activity/ml was detected. Thus, the relative contribution of the anti-factor Xa and antithrombin activities to the antithrombotic effect of a LMWH differs according to the nature of the thrombogenic stimulus.
 ...
PMID:Antithrombotic potencies of heparins in relation to their antifactor Xa and antithrombin activities: an experimental study in two models of thrombosis in the rabbit. 222 52

The pharmacodynamic properties of a new LMWH (alfa-LMWH) were investigated in 8 healthy volunteers after single subcutaneous administrations of 7,500, 15,000 and 30,000 anti-XaU doses at weekly intervals. Anti-Xa and anti-IIa heparin activities were monitored together with aPTT, thrombin time, bleeding time and euglobulin lysis time. No relevant changes in bleeding time or major side-effects were ever recorded. A group of 26 patients submitted to gynaecological surgery were then investigated to determine the dosage schedule for prophylaxis of post-operative deep vein thrombosis. Two subgroups received daily subcutaneous doses of 7,500 and 15,000 anti-XaU alfa-LMWH respectively, beginning 2 h before surgery; the third subgroup received 5,000 IU calcium heparin three times daily over the seven postoperative days. The following tests were peri-operatively monitored: anti-Xa heparin activity, aPTT, PT, fibrinogen, Antithrombin III. No differences in intra-operative bleeding or side-effects were recorded. On the basis of the levels of anti-Xa heparin activity and the negligible effects on aPTT, the dose of 7500 anti-XaU was selected at single daily administration for thromboprophylaxis in gynecological surgery.
 ...
PMID:Pharmacodynamic effects on blood coagulation of a new low molecular weight heparin (alfa-LMWH) in healthy volunteers and gynecological surgery patients. 276 58

Thirty healthy volunteers underwent a pharmacokinetic study to control the effect of calcium heparin and low-molecular-weight heparin on coagulation factors. Activated partial thromboplastin time (aPTT), thrombin time (TT) and inhibition of activated factor X (Xa) were checked after a single subcutaneous administration of calcium heparin, 5000 IU (CH group); low-molecular-weight heparin 7500 AXaU (LMWH-LD group); and LMW heparin, 15,000 AXaU (LMWH-MD group). The mean values of aPTT rose significantly only after administration of LMW heparin (15,000 AXaU), while no relevant variations were observed after CH and LMWH-LD administration. The effects on TT were also very small and not relevant to an anticoagulant response. The Xa inhibitory effect exerted by the two LMW heparin doses proved substantially higher and longer-lasting than the effect of unfractioned heparin. A statistically significant Xa inhibition was still present 24 h after LMWH-MD administration and 16-20 h after LMWH-LD administration, while 6 h after CH administration no effect was detectable. The laboratory results confirm the marked antithrombophylic action, without relevant anticoagulant effects, already attributed by other authors to the new LMW heparin under study.
 ...
PMID:Time-course of anti-Xa effects of calcium heparin and low-molecular-weight heparin given s.c.: insights for thrombosis prevention. 285 Sep 3

The effect of a low molecular weight heparin (Fragmin) (20-80 U/kg) was studied in 10 healthy male volunteers after intravenous administration. Clotting abnormalities are extensive shortly after injection, lasting for 1-2 hours depending on heparin dosage. Dilute thrombin time, showing a close correlation to anti-F-Xa activity, is as sensitive as anti-F-Xa. The parallel time course of dilute thrombin time and anti-F-Xa activity clearly demonstrates that LMWH has an effect on F-IIa lasting as long as that of F-Xa. After subcutaneous administration clotting abnormalities are only slight with 40-60 U/kg, in contrast to the intravenous study. The platelet system remains unchanged.
 ...
PMID:Human pharmacological studies of a defined low molecular weight heparin fraction (Fragmin) evidence for a simultaneous inhibition of factor Xa and IIa (thrombin). 316 30

Standard heparin and a LMWH, CY222 do not cross the placenta nor alter fetal coagulation when injected into the pregnant ewe. We found that another LMWH, Pharmuka-10169 (PK-10169) alters fetal coagulation without crossing the placenta in the pregnant sheep. To characterize this anticoagulant we measured the in vitro and in vivo effects of 125I-PK-10169 in maternal and fetal plasmas following administration of PK-10169 to the mother or fetus. The fetal anticoagulant activity was not neutralizable by protamine sulphate and was attributable to the inhibition of thrombin but not factor Xa. In vitro, the fetal anticoagulant activity had properties similar to dermatan sulphate; both catalyzed the inhibition of thrombin but not factor Xa by sheep plasma; and neither was neutralizable by protamine sulphate. These effects were due to the enhanced neutralization of thrombin by heparin cofactor II. We conclude that PK-10169 does not cross the placenta, but does induce the release of an endogenous dermatan sulphate-like substance which alters fetal coagulation.
 ...
PMID:A low molecular weight heparin alters the fetal coagulation system in the pregnant sheep. 375 Feb 64

The present trial was designed to comparatively investigate the pharmacokinetic profile and evaluate the apparent bioavailability pattern of three already marketed low molecular mass heparins (LMMHs): dalteparin (Fragmin), nadroparin (Fraxiparin), and enoxaparin (Lovenox) given by subcutaneous route. The study was carried out in 20 healthy young volunteers given, according to a cross over design, a single subcutaneous injection of the doses recommended for the prophylaxis of deep vein thrombosis (commercial preparations, prefilled syringes): dalteparin 2,500 IU (= 2,500 IU anti-Xa), nadroparin 7,500 ICU (= 3,075 IU anti-Xa), enoxaparin 20 mg (= 2,000 IU anti-Xa) and enoxaparin 40 mg (= 4,000 IU anti-Xa). Of the markers used, activated partial thromboplastin time (APTT), thrombin clotting time (TCT), Heptest, anti-thrombin (aIIa) activity and anti-Xa (aXa) activity, the most pertinent parameter (from a biodynamic viewpoint) is plasma aXa activity. We demonstrated that dalteparin, nadroparin and enoxaparin exhibit statistically significantly different pharmacokinetic and overall disposition patterns. Normalized to the same injected dose (1,000 IU aXa), the relative actual amount of plasma anti-Xa activity generated by enoxaparin is 1.48 times greater (p < 0.001) than that of nadroparin and 2.28 times greater (p < 0.001) than that of dalteparin while the plasma amount induced by nadroparin is 1.54 times greater (p < 0.001) than that of dalteparin. The apparent total body clearance of enoxaparin doses (CL/F = 16.7 +/- 5.5 and 13.8 +/- 3.2 ml/min) is significantly smaller than those of nadroparin (CL/F = 21.4 +/- 7.0 ml/min; p < 0.01) and dalteparin (CL/F = 33.3 +/- 11.8 ml/min; p < 0.001) while dalteparin apparent clearance is about 1.5-fold greater (p < 0.001) than that of nadroparin. These LMMHs also differ by their renal excretion pattern: more fragments exhibiting an anti-Xa activity are recovered in urine following enoxaparin doses (6.4 and 8.7% of the dose, respectively) than following nadroparin (3.9%) and dalteparin (3.4%) injection. These differences in the disposition profiles explain why the apparent elimination half life t1/2 values of the LMMHs compared here are different: dalteparin: 2.8 h; nadroparin: 3.7 h; and enoxaparin: 4.1 h. Whether or not these differences may contribute to explain the different safety/efficacy balance of each of these antithrombotic medications remains to be discussed and needs further studies.
 ...
PMID:Comparison of the pharmacokinetic profiles of three low molecular mass heparins--dalteparin, enoxaparin and nadroparin--administered subcutaneously in healthy volunteers (doses for prevention of thromboembolism). 749 71


1 2 3 4 5 6 Next >>