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Management of thromboembolic disease involves administration of anticoagulants, thrombolytics or antiplatelet agents to lyse or prevent thrombus extension. Despite widespread use and decades of experience with some of these agents, much is unknown about the effects of dose and plasma concentration on patient response. Unfractionated heparin (UFH) improves outcome in many thromboembolic disorders when administered to a target activated partial thromboplastin time (aPTT) or plasma heparin concentration. UFH exhibits dose-dependency both with absorption from subcutaneous sites and elimination. Doses based on bodyweight or estimated blood volume attain therapeutic aPTTs faster than fixed or standard doses. Low molecular weight heparins (LMWHs) were developed to increase the anti-factor Xa:anti-factor IIa activities. Several different LMWHs are as effective as UFH in treating deep venous thrombosis. Evidence fails to support a relationship between anti-factor Xa activity and either thrombosis evolution or bleeding. No comparisons have been made between bodyweight-based and anti-factor Xa activity-based doses. The dose of orally administered warfarin is adjusted to achieve a target International Normalised Ratio (INR). Maintenance doses are estimated on the basis of the patient's INR during the first 3 days of therapy: the dose required to achieve an optimal INR decreases with age > 50 years. The thrombolytic agents are administered in standard doses to achieve rapid thrombolysis with minimal alteration in systemic haemostasis. Accelerated intravenous alteplase may result in the highest rate of coronary artery reperfusion. Nevertheless, standard doses of streptokinase, anisoylated plasminogen streptokinase complex and alteplase result in similar 1-month mortality rates. The minimal advantage seen with alteplase is offset by higher rates of stroke. Future trials will focus on administration strategies achieving rapid thrombolysis, while minimising the risk of serious bleeding. With the antiplatelet agents, unpredictability in the pharmacokinetic parameters of different products has confounded interpretation of published reports. Optimal aspirin (acetylsalicylic acid) administration would include administration of an initial dose of 160 to 325mg after an acute vascular event, followed by maintenance dosages of approximately 75 mg/day for prophylaxis or treatment. Ticlopidine does not exhibit a relationship between either plasma concentration or dose and adverse effects, while pharmacodynamic effects may be dose-, but not plasma concentration-, dependent. The correlation between the concentration of dipyridamole and some of its antiplatelet effects may be the strongest amongst all the antiplatelet agents. However, unfortunately all clinical trials used standard doses and the current consensus is that dipyridamole alone is not an effective antiplatelet agent.
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PMID:Pharmacokinetic optimisation of the treatment of embolic disorders. 771 62

We propose that anti-platelet thienopyridines, such as ticlopidine or clopidogrel, are thrombolytic owing to endothelial release of prostacyclin (PGI2) and tissue plasminogen activator (t-PA). In this study we used anaesthetised Wistar rats with extracorporal circulation in which arterial blood superfused thrombi which adhered to a strip of collagen. Weight of thrombi was continuously monitored. When administered intravenously, clopidogrel or its R enantiomer deprived of anti-platelet action, both at doses of 3 mg x kg(-1), produced lost in weight of thrombi by 14.1 +/- 1.3% or 16.0 +/- 1.4% (n = 9), and at doses 10 mg x kg(-1) by 28.3 +/- 2.3% or 30.4 +/- 1.9% (n = 8), respectively. Maximum of thrombolysis occurred 30-45 min following the drug administration. Ticlopidine at a dose of 30 mg x kg(-1) reduced weight of thrombi by 33.7 +/- 1.7% (n = 32). Thrombolytic action of ticlopidine was accompanied by a rise in 6!keto-PGF1alpha blood levels from 0.42 +/- 0.10 to 1.58 +/- 0.29 ng x ml(-1) and t-PA antigen plasma levels from 4.70 +/- 1.00 to 12.90 +/- 1.15 ng x ml(-1) (n = 7). Five out of eleven tested thienopyridine congeners with pyrimidine or pyrimidinone instead of pyridine rings had thrombolytic potencies similar to that of clopidogrel (ED30s at a range of 6.2-11.4 mg x kg(-1)). A substantial increase in thrombolytic potency (ED30s at a range of 0.3-2.1 mg x kg(-1)) was observed for congeners in which thienyl ring was condensed with an additional cyclopentyl, cyclohexyl or cycloheptyl structures or in which thienopyridine complex was replaced for a pyridopyrimidine one. We claim that thienopyridines, independently of their delayed anti-platelet action, do produce immediate thrombolysis in vivo. This new activity emulates capacity of their native, non-metabolised molecules to release prostacyclin and tissue plasminogen activator. We have also shown that structural changes in molecules of thienopyridines may intensify their thrombolytic potency.
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PMID:Thrombolysis by thienopyridines and their congeners. 1119 41

The developments and trends of hemostatic and antithrombotic drugs in Japan were investigated chronologically for the last 50 years after the 2nd World War. 1. Hemostatic drugs are classified into three groups ; capillary stabilizers, blood coagulants and antifibrinolytics. l) As to capillary stabilizers, flavonoid (rutin, 1949), adrenochrome derivative (carbazochrome, 1954) and conjugated estrogen (Premarin, 1964) were introduced therapeutically. Especially, the soluble types of adrenochrome compounds (Adona 1956, S-Adchnon, 1962) were devised and used widely in Japan. 2) Drugs concerning blood coagulation, thrombin, introduced in 1953, and hemocoagulase, a snake venom introduced in 1966, were used clinically. V.K. groups producing various coagulation factors were introduced as V.K1 (Phytonadione, 1962) and V.K2 (rnenatetrenone,1972), and they were admitted in "The Japanese Pharmacopoeia"editions 8 and 14, respectively). 3) Regarding antifibrinolytic drugs, Japanese researchers have made remarkable contributions. e-Aminocapronic acid (Ipsilon, 1962) and tranexamic acid (Transamin, 1965) were developed and used for various abnormal bleedings or hemorrhage associated with plasmin over-activation. tranexamic acid also proved to suppress inflammations of the throat such as tonsillitis, pharyngitis or laryngitis. 2. Antithrombotic drugs are also divided into three groups; anticoagulants, antiplatelet drugs and fibrinolytics.1) The anticoagulants used therapeutically by injection are heparins (Na-salt, 1951; Ca-salt, 1962) and low-molecular-weight heparins such as dalteparin (1992), parnaparin (1994) and reviparin (1999). The low molecule compounds are superior to the original heparins in reducing the risk of bleeding. As oral anticoagulants, coumarin derivatives, dicumarol (1950), ethylbiscoumacetate (1954), phenylindandione (1956) and warfarin (1962) are known. Warfarin potassium is the main drug for oral therapy of thromboembolism lately. Gabexate mesilate (1989) and nafamostat mesilate (1989) were developed in Japan and used for DIC and acute pancreatitis to inhibit protease enzymes. Argatroban is a unique antithrombin product developed by Japanese researchers in 1990, and is used for vascular or cerebral thrombosis. After noticing in 1968 that aspirin inhibits platelet aggregation and prevents myocardial infraction, projects for developing antiplatelet drugs were initiated worldwide. Ticlopidine, originally developed in France, was introduced in 1981 and prevailed widely in Japan for reducing the risk of thrombotic stroke. Aspirin itself was recognized by the FDA (USA) as an antithrombotic drug in 1988, and was also approved by Japanese authorities in 2000. PGE1 clathrate compounds have also been developed as antiplatelet drugs; alprostadil alfadex for injection (1979), and limaprost alfadex for oral use (1988). The PGI2 product, beraprost sodium, for oral use followed them in 1992. Other antiplatelet drugs with unique mechanisms explored in Japan: Ozagrel (1988), which inhibits TXA2 synthetase, cilostazol (1988), which inhibits cAMP phosphodiesterase, and sarpogrelate (1993), which blocks 5HT in platelets, are the notable drugs in this field. Ethyl icosapentate, from fish oil, is available for antiplatelet therapy. Concerning the fibrinolytic system, plasminogen activators are useful for thromboembolism. The streptokinase from bacterial origin developed in the USA and Europe was not introduced, and urokinase (1965) was the first plasminogen activator developed in Japan. Then tissue plasminogen activators (t-PA) tisokinase (cell culture, 1991), alteplase (genetical recombination, 1991), nateplase (genetical recombination, 1996), monteplase (1998) and pamiteplase (1998) were developed and approved for acute myocardial infarction. Nasaruplase (prourokinase, cell culture,1991) was also approved for the same indication. While the development of the hemostatic drugs ceased in the 1960s, avid project studies for antithrombotic drugs including fibrinolytics began in the 1980s and are progressing now towards new molecular targets. This may be due to the increasing tendency of cardiovascular thromboembolic diathesis in Japan. (The figures in parentheses are the years approved by the Japanese Ministry of Health, Labor and Welfare.)
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PMID:[A 50-year history of new drugs in Japan-the development and trends of hemostatics and antithrombotic drugs]. 1457 69

About 80% of strokes are ischaemic. Approximately 12% of patients die within 3 months following stroke, and another 20% are institutionalised or become highly dependent. In early 2013, what is the harm-benefit balance of antithrombotic treatments used in the acute phase of ischaemic stroke? To answer this question, we reviewed the available data using the standard Prescrire methodology. Clinical trials of aspirin in the acute phase of ischaemic stroke consist mainly of two randomised trials including a total of 40 541 patients. After 1 to 6 months, 13 deaths or sequelae resulting in dependence are prevented when 1000 patients are treated with aspirin during the acute phase. Aspirin increases the risk of symptomatic intracranial haemorrhage when it is introduced less than 24 hours after treatment with alteplase. Abciximab, an injectable antiplatelet agent, showed no tangible clinical benefit in 5 randomised placebo-controlled trials in a total of 1275 patients. Clopidogrel and prasugrel, two other antiplatelet agents, have not been evaluated in this setting. However, in case of allergy to aspirin, clopidogrel is a useful alternative in other situations associated with a risk of arterial ischaemia. In a randomised trial including 458 patients, cilostazol and aspirin were similarly effective after 3 months of follow-up, but cilostazol caused cardiac arrhythmias. Ticlopidine has too many adverse effects to consider it a useful drug. Anticoagulant therapy during the acute phase of stroke has an unfavourable harm-benefit balance, including in patients with stroke secondary to cardiac embolism. Low-molecular-weight heparin reduces the risk of pulmonary embolism but has no impact on overall mortality. The aim of thrombolysis is to unclog the affected artery. Intravenous alteplase administration is the best-assessed thrombolytic method. Twelve randomised trials have compared intravenous thrombolysis with alteplase versus no thrombolytic therapy in 7012 patients. Among patients treated within 3 hours after stroke onset, 41% survived without sequelae after alteplase administration, versus 32% in the absence of thrombolysis; alteplase had no statistically significant impact on mortality at the end of follow-up. Efficacy appeared to be similar in patients over 80 years old.The harm-benefit balance may also be favourable when thrombolysis is started more than 3 hours after stroke onset, but when it is initiated more than 4.5 hours after stroke onset, it increases mortality. Four randomised trials showed that intra-arterial thrombolysis with urokinase or pro-urokinase had a beneficial effect, versus no thrombolysis, in a total of 356 patients. In a randomised trial including 362 patients, intra-arterial thrombolysis did not have a better harm-benefit balance than intravenous thrombolysis. Among the various physical and mechanical methods used to remove or dissolve clots, the best-evaluated is ultrasound plus intravenous alteplase thrombolysis; initial results with this procedure warrant further clinical trials. Rapid intervention and patient selection are both crucial in optimising the harm-benefit balance of intravenous alteplase thrombolysis. This treatment should only be used when management begins within the first hours following stroke symptom onset, and when there are no risk factors for bleeding, especially intracranial bleeding. For other patients, aspirin is the only antithrombotic drug known to reduce, albeit only slightly, the risk of death and sequelae following ischaemic stroke.
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PMID:Antithrombotic drugs and ischaemic stroke. 2442 42