Clinical Pharmacokinetics and Pharmacodynamics of Desmoteplase.

Desmoteplase is a bat (Desmodus rotundus) saliva-derived fibrinolytic enzyme resembling a urokinase and tissue plasminogen activator. It is highly dependent on fibrin and has some neuroprotective attributes. Intravenous administration of desmoteplase is safe and well tolerated in healthy subjects. Plasma fibrinolytic activity is linearly related to its blood concentration, its terminal elimination half-life ranges from 3.8 to 4.92 h (50 vs. 90 µg/kg dose). Administration of desmoteplase leads to transitory derangement of fibrinogen, D-dimer, alpha2-antiplasmin, and plasmin and antiplasmin complex which normalize within 4-12 h. It does not alter a prothrombin test, international normalized ratio, activated partial thromboplastin time, and prothrombin fragment 1.2. Desmoteplase was tested in myocardial infarction and pulmonary embolism and showed promising results versus alteplase. In ischemic stroke trials, desmoteplase was linked to increased rates of symptomatic intracranial hemorrhages and case fatality. However, data from "The desmoteplase in Acute Ischemic Stroke" Trials, DIAS-3 and DIAS-J, suggest that the drug is well tolerated and its safety profile is comparable to placebo. Desmoteplase is theoretically a superior thrombolytic because of high fibrin specificity, no activation of beta-amyloid, and lack of neurotoxicity. It was associated with better outcomes in patients with significant stenosis or occlusion of a proximal precerebral vessels. However, DIAS-4 was stopped as it might have not reached its primary endpoint. Due to its promising properties, desmoteplase may be added into treatment of ischemic stroke with extension of the time window and special emphasis on patients presenting outside the 4.5-h thrombolysis window, with wake-up strokes and strokes of unknown onset.

Engineered microparticles and nanoparticles for fibrinolysis.

Fibrinolytic agents including plasmin and plasminogen activators improve outcomes in acute ischemic stroke and thrombosis by recanalizing occluded vessels. In the decades since their introduction into clinical practice, several limitations of have been identified in terms of both efficacy and bleeding risk associated with these agents. Engineered nanoparticles and microparticles address some of these limitations by improving circulation time, reducing inhibition and degradation in circulation, accelerating recanalization, improving targeting to thrombotic occlusions, and reducing off-target effects; however, many particle-based approaches have only been used in preclinical studies to date. This review covers four advances in coupling fibrinolytic agents with engineered particles: (a) modifications of plasminogen activators with macromolecules, (b) encapsulation of plasminogen activators and plasmin in polymer and liposomal particles, (c) triggered release of encapsulated fibrinolytic agents and mechanical disruption of clots with ultrasound, and (d) enhancing targeting with magnetic particles and magnetic fields. Technical challenges for the translation of these approaches to the clinic are discussed.

Functionalized carriers for the improved delivery of plasminogen activators.

Various plasminogen activators have been routinely used for the treatment of thrombotic diseases. However, these agents possess various problems e.g. short half life and other bleeding complications. To improve the effectiveness as well as to reduce the side effects of these drugs, various modifications have been made. For example, fibrin specific plasminogen activators have been developed. However, these agents also demonstrated various bleeding complications, clinically. Nowadays, so many carrier systems have been explored to improve the activity of these agents. Novel carriers not only improve the effectiveness of these drugs but also reduce the side effects. In the present review, we discuss novel carrier based strategies to improve the delivery of the plasminogen activators to site of thrombus.

The effects of age and gender on the pharmacokinetics and pharmacodynamics in healthy subjects of the plasminogen activator, lanoteplase.

AIMS: To investigate the influence of age and gender on the intravenous pharmacokinetics and pharmacodynamics of the plasminogen activator, lanoteplase. METHODS: Forty healthy subjects (10 each of young males, elderly males, young females and elderly females) received a single bolus 10 kU kg(-1) intravenous dose of lanoteplase. Plasma from blood serially collected for 24 h post-dose was analyzed for lanoteplase (antigen), fibrinogen, plasminogen and α2-antiplasmin concentrations, plasma plasminogen activation activity (PPAA) and rapid plasminogen activator inhibitor (PAI-1). RESULTS: Lanoteplase mean total systemic clearance (CL(t)) values ranged from 1.9 to 2.8 l h(-1) and mean steady-state volume of distribution (V(ss)) values ranged from 12.3 to 15.6 l. Age-by-gender interactions were observed for lanoteplase CL(t) (P= 0.04), but no differences were observed for V(ss) or elimination half-life. Elderly females had a 27% lower mean CL(t) than young females (95% CI for the difference 0.17, 1.27 l h(-1)) and 32% lower CL(t) than elderly males (95% CI for the difference 0.15, 1.65 l h(-1)). PPAA AUC/dose values did not show an age-by-gender interaction. Haemostasis parameters indicated only a slight degree of systemic plasminogen activation. CONCLUSIONS: Elderly females had a lower mean lanoteplase CL(t) than elderly males and young females. However, no difference was observed between young and elderly females for the AUC/dose of PPAA. In addition, there were no age-related or gender-related differences observed in the other pharmacodynamic parameters measured.

Targeting of a mutant plasminogen activator to circulating red blood cells for prophylactic fibrinolysis.

Chemical coupling to carrier red blood cells (RBCs) converts tissue type plasminogen activator (tPA) from a problematic therapeutic into a safe agent for thromboprophylaxis. The goal of this study was to develop a more clinically relevant recombinant biotherapeutic by fusing a mutant tPA with a single-chain antibody fragment (scFv) with specificity for glycophorin A (GPA) on mouse RBCs. The fusion construct (anti-GPA scFv/PA) bound specifically to mouse but not human RBCs and activated plasminogen; this led to rapid and stable attachment of up to 30,000 copies of anti-GPA scFv/PA per mouse RBC that were thereby endowed with high fibrinolytic activity. Binding of anti-GPA scFv/PA neither caused RBC aggregation, hemolysis, uptake in capillary-rich lungs or in the reticuloendothelial system nor otherwise altered the circulation of RBCs. Over 40% of labeled anti-GPA scFv/PA injected in mice bound to RBC, which markedly prolonged its intravascular circulation and fibrinolytic activity compared with its nontargeted PA counterpart, anti-GPA scFv/PA, but not its nontargeted PA analog, prevented thrombotic occlusion in FeCl(3) models of vascular injury. These results provide proof-of-principle for the development of a recombinant PA variant that binds to circulating RBC and provides thromboprophylaxis by use of a clinically relevant approach.

Rituximab penetrates full-thickness retina in contrast to tissue plasminogen activator control.

PURPOSE: To assess whether intravitreal rituximab 1 mg/0.1 cc penetrates the retina of Dutch-belted rabbits. METHODS: Two right eyes of two rabbits were injected with intravitreal rituximab 1 mg/0.1 mL, and one right eye of one rabbit was injected with intravitreal tissue plasminogen activator (tPA) 12.5 microg/0.1 mL, as a protein control. The three left eyes received no intravitreal injections. The rabbits were killed; the eyes were enucleated and immediately frozen at -80 degrees C. Rituximab was detected using rabbit antihuman IgG (whole molecule) peroxidase conjugated antibody. tPA was detected using an antihuman IgG with a sheep antihuman tPA antibody conjugated with peroxidase. RESULTS: There was staining in all retinal layers of the two eyes injected with intravitreal rituximab, and no staining of the retina in the eye injected with intravitreal tPA. The three control eyes showed no staining in any retinal layer. CONCLUSION: Intravitreal rituximab at a dose of 1 mg/0.1 cc penetrates the retina of Dutch-belted rabbits while the control intravitreal tPA at a dose of 12.5 microg/0.1 cc does not.

Tratamiento fibrinolítico con activador del plasminógeno tisular. Resultados en la práctica clínica con un modelo de actuación multidisciplinario / Fibrinolytic treatment with tissue plasminogen activator. Outcomes in clinical practice with a multidisciplinary model of intervention

Introducción y objetivo. El tratamiento del infarto cerebral agudo con activador del plasminógeno tisular (rt-PA) se ha aplicado hasta ahora de forma restrictiva en grandes centros con unidades de ictus de agudos. El objetivo de este estudio es determinar la seguridad y eficacia de este tratamiento en un centro sin experiencia previa siguiendo un modelo multidisciplinario. Pacientes y métodos. Estudio prospectivo y observacional que incluyó pacientes con ictus isquémico agudo de menos de 3 h de evolución tratados con rt-PA endovenoso desde enero de 2004 a diciembre de 2006. Se valoraron variables basales, complicaciones hemorrágicas, respuesta al tratamiento y evolución funcional mediante la escala de Rankin modificada a (mRS) los 3 meses. El tratamiento y control se aplicó siguiendo un protocolo multidisciplinario con una dirección compartida por los servicios de Medicina Intensiva y Neurología. Resultados. Se trataron 46 pacientes, con una edad media de 67 ± 12 años (63% hombres). NIH pretratamiento: 13,6 ± 4,7; mediana: 13,5; rango: 5-22. El tiempo entre el inicio de los síntomas y la llegada al hospital fue de 53 ± 27 min, y el tiempo puerta-aguja, de 69 ± 27 min. A las 24 h, un 48% de los pacientes había mejorado en la escala NIH > 4 puntos. Se observaron un total de 10 transformaciones hemorrágicas (21,7%), ninguna de ellas sintomática. A los tres meses, un 54,3% de los pacientes era independiente funcionalmente (mRS: 0-2). La mortalidad a los 90 días fue del 13,1%. Conclusión. La administración de rt-PA a pacientes con ictus isquémico agudo en la práctica asistencial siguiendo un protocolo multidisciplinario es segura y con una evolución neurológica comparable a ensayos y estudios clínicos

Introduction and aims. Until now treatment of acute cerebral infarction with tissue plasminogen activator (rt-PA) has been applied to a limited extent in large medical centres with acute stroke units. The aim of this study is to determine the safety and effectiveness of this treatment in a centre with no previous experience following a multidisciplinary model. Patients and methods. We conducted a prospective, observation-based study involving patients who were treated with intravenous rt-PA within 3 hours of suffering an acute ischaemic stroke between January 2004 and December 2006. Basal variables, haemorrhagic complications, response to treatment and functional progress were evaluated using the modified Rankin Scale (mRS) at 3 months. Treatment and control were applied following a multidisciplinary protocol implemented by the Intensive Medicine and Neurology services. Results. In all, 46 patients were treated, their mean age being 67 ± 12 years (63% males). NIH pre-treatment: 13.6 ± 4.7; median: 13.5; range: 5-22. Time elapsed between the onset of symptoms and arrival at the hospital was 53 ± 27 min, and door-to-needle time was 69 ± 27 min. At 24 hours, 48% of patients had improved their scores on the NIH scale > 4 points. A total of 10 haemorrhagic transformations (21.7%) were observed, none of which were symptomatic. At three months, 54.3% of patients were functionally independent (mRS: 0-2). Mortality rate at 90 days was 13.1%. Conclusions. Administration of rt-PA to patients with acute ischaemic stroke in health care practice following a multidisciplinary protocol is safe and has a neurological progression that is comparable to clinical trials and studies

Recombinant Desmodus rotundus salivary plasminogen activator crosses the blood-brain barrier through a low-density lipoprotein receptor-related protein-dependent mechanism without exerting neurotoxic effects.

BACKGROUND AND PURPOSE: Desmoteplase, a recombinant form of the plasminogen activator DSPAalpha1 from Desmodus rotundus, may offer improved clinical benefits for acute ischemic stroke treatment over the current therapy, recombinant tissue plasminogen activator (rtPA). Accumulating evidence suggests that clinical use of rtPA could be limited by unfavorable properties, including its ability to cross the blood-brain barrier (BBB), thus potentially adding to the pro-excitotoxic effect of endogenous tPA in cerebral parenchyma. Here, to investigate whether desmoteplase may display a safer profile than the structurally-related tPA, both agents were compared for their ability to cross the BBB and promote neurotoxicity. METHODS: First, the passage of vascular DSPA and rtPA was investigated in vitro in a model of BBB, subjected or not to oxygen and glucose deprivation. Second, we studied DSPA- and rtPA-mediated effects in an in vivo paradigm of excitotoxic necrosis. RESULTS: The rtPA and desmoteplase cross the intact BBB by LRP-mediated transcytosis. Under conditions of oxygen and glucose deprivation, translocation rates of both compounds increased; however, unlike rtPA, desmoteplase transport remained LRP-dependent. Additionally, neither intracerebral nor intravenous desmoteplase administration enhanced NMDA-induced excitotoxic striatal damage in vivo. Interestingly, intravenous but not intrastriatal coadministration of desmoteplase and rtPA reduced the pro-excitotoxic effect of rtPA. CONCLUSIONS: We show that desmoteplase crosses the BBB but does not promote neuronal death. Moreover, intravenous administration of desmoteplase antagonizes the neurotoxicity induced by vascular rtPA. This action may be caused by competition of desmoteplase with rtPA for LRP binding at the BBB, thus effectively blocking rtPA access to the brain parenchyma.

Plasminogen activators: a comparison.

Thrombolytic drugs play a crucial role in the management of patients with acute myocardial infarction, pulmonary embolism, deep vein thrombosis, arterial thrombosis, acute thrombosis of retinal vessel, extensive coronary emboli, and peripheral vascular thromboembolism. Recognition of the importance of fibrinolytic system in thrombus resolution has resulted in the development of different fibrinolytic agents. Now a days several newer plasminogen activators with different pharmacokinetic and pharmacodynamic properties have been developed to treat thrombotic disease, which are fibrin specific with prolonged half-life and can be administered as a single bolus.

Therapeutic potential of monteplase in acute myocardial infarction.

Thrombolysis with conventional thrombolytic agents prior to percutaneous coronary intervention (PCI) has had no impact on the treatment of acute myocardial infarction (AMI). However, the development of mutant tissue type plasminogen activators (mt-PA) has prompted us to reassess the combination of thrombolysis and PCI. Monteplase is a newly developed mt-PA that can be administered as a single intravenous bolus injection. The results of the COMA (COmbining Monteplase with Angioplasty) trial, suggest that monteplase administration prior to emergent PCI in AMI improves 6-month outcomes and possibly the long-term prognosis of myocardial infarction. Combining monteplase administration on presentation at a community hospital with prompt transfer to a tertiary center for PCI would be an ideal strategy for the treatment of AMI.

Technology evaluation: desmoteplase, PAION/Forest.

PAION GmbH, under license from Schering AG, is developing desmoteplase, a recombinant form of the anticlotting salivary plasminogen activator of the vampire bat Desmodus rotundus (DSPAalpha-1), for the potential treatment of acute ischemic stroke. The drug is currently undergoing phase II clinical trials.

Tissue plasminogen activator levels after single intracisternal injection in patients with subarachnoid hemorrhage.

Tissue plasminogen activator (tPA) levels were investigated in the cisternal fluid of patients with subarachnoid hemorrhage treated with single intracisternal injection of recombinant tPA during radical surgery for ruptured aneurysms. Seven patients received different doses of tPA: two of 400 microg/ml, three of 500 microg/ml, one of 700 microg/ml, and one of 800 microg/ml in a total amount of 20 ml distilled water at pH 7. Cerebrospinal fluid samples were taken directly from the cisternal fluid at 15-minute incubation after injection, immediately after irrigation during surgery, and by lumbar tap 2 days after surgery. Cisternal tPA levels decreased to about 60% of the mean injected doses after 15-minute incubation. Simple linear regression analysis showed these tPA levels after incubation correlated with the initial doses. After copious irrigation with Ringer solution at pH 8, tPA levels decreased rapidly without correlation with the initial doses. After spinal drainage for 2 days, tPA levels further decreased by an order of 10(-4) to 10(-6) from the initial dose. These values were still greater than normal controls. The final values of tPA levels were not related to the initial dose. None of the patients suffered from systemic or wound complications. Cisternal tPA injection with increased doses and irrigation may be beneficial for the selective rapid removal of blood clots with controllable safety.

New directions in thrombolytic therapy.

Although current thrombolytic agents have proven their clinical benefit, the failure to rapidly reperfuse some patients and the persistent bleeding risk represent areas for improvement in therapy. In the past two years, the field has been advanced by the regulatory approval of agents with greater ease of administration, continued development of new agents and exploration of the use of more advanced antiplatelet therapies in combination with thrombolytic agents. Finally, a new class of directly acting fibrinolytic agents is available.

Argatroban and alteplase in patients with acute myocardial infarction: the ARGAMI Study.

ARGAMI was designed to assess safety and efficacy of argatroban compared with heparin as adjunctive treatment to alteplase in the treatment of patients with acute myocardial infarction. ARGAMI consisted of an open-dose finding study (35 patients) followed by a placebo-controlled study with double dummy technique and 2:1 (argatroban:heparin) randomization. An argatroban dosage of 100 microg/kg bolus plus 3 microg/kg/min infusion for 72 hours was selected for the randomized study in which 82 patients were allocated to argatroban and 45 to heparin (5000 U intravenous bolus, 1000 U/h infusion). Patency of the infarct-related artery (Thrombolysis in Myocardial Infarction [TIMI] grade 2 or 3 flow) after 90 minutes was obtained in 62 patients (76%) allocated to argatroban versus 37 patients (82%) allocated to heparin (p=ns). Angiograms after 24 hours and 5 to 10 days showed low reocclusion rates in both groups. Bleeding complications were observed in 16 patients allocated to argatroban (19.5%) and in 9 patients allocated to heparin (20.0%). One patient allocated to heparin suffered from hemorrhage stroke. Argatroban, given as adjunctive treatment to alteplase, is tolerated well in patients with acute myocardial infarction. Safety and efficacy of the combination alteplase and argatroban (with this dose regimen) are similar to those of alteplase and heparin.

[Increased efficacy of thrombolytic therapy in acute myocardial infarction by improved properties of new thrombolytic agents]. / Effizienzsteigerung der Thrombolysetherapie des akuten Myokardinfarktes durch verbesserte Eigenschaften neuer Thrombolytika.

Thrombolysis is a milestone in the therapy of acute myocardial infarction due to its ubiquitous availability and ease of application. The recombinant form of tissue-type plasminogen activator (rt-PA) has been proven to be superior over first generation fibrinolytic agents (streptokinase, urokinase, APSAC) with respect to efficacy and side effects and the front-loaded regimen has meanwhile become the "gold"-standard of thrombolytic therapy. Biochemically modified mutants of wild-type t-PA, e.g. r-PA (reteplase), n-PA (lanoteplase), and TNK-t-PA have altered biochemical and pharmacokinetic characteristics which make them more easy to use (as double or single bolus injection) and share a theoretical efficacy benefit. This article describes these specific characteristics focussing on clot-selectivity and PAI-1 resistance of the new mutants of wild-type t-PA and their possible clinical efficiency.

Loco-regional thrombolysis for deep vein thrombosis: fact or fiction? A study of hemostatic parameters.

Loco-regional thrombolysis for deep-vein thrombosis (DVT) has been claimed to be equally effective and safe compared with systemic thrombolysis. It is not known whether a loco-regional thrombolytic effect exists and of what it might consist. To investigate this issue, we studied eight patients with DVT undergoing loco-regional thrombolysis with 20 mg alteplase infused over 4 h in a dorsal foot-vein of the affected leg, while the leg was kept tightly bandaged; alteplase infusions were repeated every 24 h, the number of therapy cycles (TC) was seven, and full-dose heparin was given. For coagulation analyses, 'loco-regional' blood samples were taken from a vein of the affected leg and 'systemic' samples were taken from an antecubital vein. After a median number of six TC, good partial reperfusion was achieved in 4/8 patients, moderate partial reperfusion in 2/8, major bleedings occurred in 2/8, and minor bleedings in 1/8 patients. During the first TC, recombinant tissue-type plasminogen activator (rtPA) activity and antigen, as well as FgDPs and d-dimers, were elevated significantly loco-regionally over systemic values, and a complete breakdown of plasmin-inhibitor activity occurred with only a slight systemic reduction; no other differences were found. During successive TC, differences in rtPA-activity and -antigen levels decreased, and no significant differences were found for all other parameters. Thus, a local fibrinolytic effect was demonstrable during loco-regional thrombolysis for DVT; the magnitude of this effect diminished during successive TC, giving rise to the hypothesis that the fibrinolytic efficacy may be decreased due to growing, antifibrinolytic activity. The preserved, loco-regional plasmin-inhibitor activities during the later TC, in contrast to the complete breakdown during the first TC, suggest that part of the enhanced antifibrinolytic activity is due to loco-regionally increased plasmin-inhibitor activity. The ultimate goal of loco-regional thrombolysis, the induction of local fibrinolysis without systemic effects, has not, however, been achieved.

The contribution of residues 192 and 193 to the specificity of snake venom serine proteinases.

Snake venom serine proteinases, which belong to the subfamily of trypsin-like serine proteinases, exhibit a high degree of sequence identity (60-66%). Their stringent macromolecular substrate specificity contrasts with that of the less specific enzyme trypsin. One of them, the plasminogen activator from Trimeresurus stejnegeri venom (TSV-PA), which shares 63% sequence identity with batroxobin, a fibrinogen clotting enzyme from Bothrops atrox venom, specifically activates plasminogen to plasmin like tissue-type plasminogen activator (t-PA), even though it exhibits only 23% sequence identity with t-PA. This study shows that TSV-PA, t-PA, and batroxobin are quite different in their specificity toward small chromogenic substrates, TSV-PA being less selective than t-PA, and batroxobin not being efficient at all. The specificity of TSV-PA, with respect to t-PA and batroxobin, was investigated further by site-directed mutagenesis in the 189-195 segment, which forms the basement of the S(1) pocket of TSV-PA and presents a His at position 192 and a unique Phe at position 193. This study demonstrates that Phe(193) plays a more significant role than His(192) in determining substrate specificity and inhibition resistance. Interestingly, the TSV-PA variant F193G possesses a 8-9-fold increased activity for plasminogen and becomes sensitive to bovine pancreatic trypsin inhibitor.

A study of the ability of tissue plasminogen activator to diffuse into the subretinal space after intravitreal injection in rabbits.

PURPOSE: Intravitreal injections of tissue plasminogen activator have been used to lyse fibrin from blood in the subretinal space, despite the lack of proof that tissue plasminogen activator can diffuse across the retina. We tested whether tissue plasminogen activator injected into the vitreous could penetrate the neural retina and enter the subretinal space. METHODS: We injected a mixture of 50 microg of tissue plasminogen activator (70 kD) labeled with fluorescein isothiocyanate and rhodamine B isothiocyanate-labeled dextran, which has a lower molecular weight (20 kD), into the midvitreous cavity of one eye in each of 18 rabbits. The eyes were enucleated after 3, 6, and 24 hours, and cryosections were examined with epifluorescent microscopy to determine the distribution of the labeled molecules. We also evaluated tissue plasminogen activator pharmacokinetics in one eye each of 18 rabbits in which a subretinal clot was induced by injecting autologous blood (50 microL) into the subretinal space through the sclera. Fluorescein isothiocyanate-labeled tissue plasminogen activator was injected into the vitreous 2 days after induction of the subretinal clot. RESULTS: Fluorescein isothiocyanate-labeled tissue plasminogen activator was present at the vitreal surface of the retina in a linear array in all 36 eyes studied, whereas the rhodamine B isothiocyanate-labeled dextran had diffused throughout the neural retina in the same sections. No fluorescein isothiocyanate signal was observed in the neural retina or in the subretinal clot. Vitreous hemorrhage caused by retinal perforation was observed in all eyes with intraretinal hemorrhage in which fluorescein isothiocyanate fluorescence was seen in the neural retina and inside the clot. CONCLUSION: Intravitreal tissue plasminogen activator did not diffuse through the intact neural retina to reach a subretinal clot. This study demonstrates no scientific rationale for the intravitreal tissue plasminogen activator treatment of submacular hemorrhage without vitreous hemorrhage presumably caused by an overlying retinal break.

Current clinical use of reteplase for thrombolysis. A pharmacokinetic-pharmacodynamic perspective.

Clinical evaluation of a new thrombolytic agent should start with a dose that provides adequate efficacy and has an acceptably low bleeding risk; this results in a narrow therapeutic window at the upper end of the dose-response curve. Angiographic patency of the infarct-related artery is still the clinical surrogate end-point for mortality in phase II dose-ranging studies. There is experimental and clinical evidence that the area under the concentration-time curve (AUC) for plasminogenolytic activity of a thrombolytic agent is positively correlated with patency of the infarct-related artery. Dose-ranging studies of the novel recombinant plasminogen activator reteplase in healthy volunteers enabled computation of a linear regression curve by which a clinical starting dose could be calculated for an adapted target AUC that would be clinically effective. Pharmacokinetic analysis also revealed that the half-life of reteplase is 4 times longer than that of the reference thrombolytic alteplase, thus allowing bolus injection. The suggested single bolus starting dose of 10U was supported by results from studies in a canine model of coronary thrombolysis. The feedback of insufficiently high patency rates compared with the increased efficacy of front-loaded and accelerated alteplase demanded optimisation strategies for reteplase. Animal experiments suggested that a double bolus regimen of reteplase would be preferable to doubling the single bolus dose. Pharmacokinetic modelling suggested a time interval of 30 min between the 2 bolus injections. Selection of the tested double bolus regimens was conservative and empirical. First, the previously tested single bolus of 15U was divided to 10 + 5U; secondly, the second bolus dose was increased to 10U. This strategy proved to be successful. The current dosage recommendation for reteplase is a double bolus intravenous injection of 10 + 10U, each over 2 min, 30 min apart. This produces a reduction in mortality in patients with acute myocardial infarction that is equivalent to that produced by front-loaded and accelerated infusion of alteplase.

Comparative time course of thrombolysis induced by intravenous boluses and infusion of staphylokinase and tissue plasminogen activator in a rabbit arterial thrombosis model.

Staphylokinase (SAK), a protein with known profibrinolytic properties, has recently given encouraging results in acute myocardial infarction and in peripheral arterial occlusion. The aims of this study were to compare SAK with alteplase (recombinant tissue plasminogen activator rt-PA) in a rabbit arterial thrombosis model, in terms of femoral blood flow kinetics during and after thrombolysis, and to examine the biological effects of systemic fibrinolysis in vivo. We compared two modes of intravenous rt-PA administration, two modes of intravenous SAK administration and three different SAK dose regimens in a rabbit model of femoral artery thrombosis. The main finding was that the infusion of SAK following a single bolus administration gave statistically higher blood flow values than the infusion of the same dose of rt-PA following a single bolus administration (P < 0.05). In this experimental model, we also confirmed that SAK is a fibrin-specific and plasminogen-saving fibrinolytic agent at doses below 0.5 mg/kg. However, at higher doses (1.0 and 1.5 mg/kg), which are above usual therapeutic doses, SAK significantly reduced fibrinogen levels in a dose- and time-dependent manner (P < 0.05). These results indicate that SAK compares favorably with rt-PA in an rabbit arterial thrombosis model, yielding higher blood flow values. Moderate-dose SAK seems to be a fibrin-specific plasminogen activator, but in our model very high doses were associated with a decrease of fibrinogen.