Enoxaparin does not ameliorate liver fibrosis or portal hypertension in rats with advanced cirrhosis.

BACKGROUND & AIMS: Recent studies suggest that heparins reduce liver fibrosis and the risk of decompensation of liver disease. Here, we evaluated the effects of enoxaparin in several experimental models of advanced cirrhosis. METHODS: Cirrhosis was induced in male Sprague-Dawley (SD) rats by: (i) Oral gavage with carbon tetrachloride (CCl4ORAL ), (ii) Bile duct ligation (BDL) and (iii) CCl4 inhalation (CCl4INH ). Rats received saline or enoxaparin s.c. (40 IU/Kg/d or 180 IU/Kg/d) following various protocols. Blood biochemical parameters, liver fibrosis, endothelium- and fibrosis-related genes, portal pressure, splenomegaly, bacterial translocation, systemic inflammation and survival were evaluated. Endothelial dysfunction was assessed by in situ bivascular liver perfusions. RESULTS: Enoxaparin did not ameliorate liver function, liver fibrosis, profibrogenic gene expression, portal hypertension, splenomegaly, ascites development and infection, serum IL-6 levels or survival in rats with CCl4ORAL or BDL-induced cirrhosis. Contrarily, enoxaparin worsened portal pressure in BDL rats and decreased survival in CCl4ORAL rats. In CCl4INH rats, enoxaparin had no effects on hepatic endothelial dysfunction, except for correcting the hepatic arterial dysfunction when enoxaparin was started with the CCl4 exposure. In these rats, however, enoxaparin increased liver fibrosis and the absolute values of portal venous and sinusoidal resistance. CONCLUSIONS: Our results do not support a role of enoxaparin for improving liver fibrosis, portal hypertension or endothelial dysfunction in active disease at advanced stages of cirrhosis. These disease-related factors and the possibility of a limited therapeutic window should be considered in future studies evaluating the use of anticoagulants in cirrhosis.

Comparative subcutaneous repeated toxicity study of enoxaparin products in rats.

Enoxaparin is a low-molecular-weight heparin widely used for the prevention and treatment of thromboembolism. With the development of several enoxaparin biosimilars, real medical concerns about their safety and efficacy have been raised. This repeated dose toxicity study consists of preclinical toxicological evaluation of a biosimilar biological version of enoxaparin, the drug product "Enoxa", compared to the enoxaparin reference drug product, "Lovenox". Eighty white Wistar rats were treated with "Enoxa" versus the reference product, using subcutaneous therapeutic and toxic doses, varying from 3.5 to 100 mg/kg/day. Dose levels were adjusted and ultimately fixed at 3.5 and 20 mg/kg/day as therapeutic and toxic doses, respectively. A sodium chloride solution (0.9%) was used as the control, and the comparative study was conducted over periods of 14 and 28 days. Comparable effects were observed with few adverse effects at the administration dose of 20 mg/kg/day, for both enoxaparin biosimilar and reference products. Interestingly, mortality started only at high doses of 40 mg/kg/day and reached 25% at 100 mg/kg/day for both products. These results, as part of the recommended biosimilarity monitoring, demonstrated comparable toxicity profiles of "Enoxa" and "Lovenox" products in rats. Continuing investigation of biosimilarity on humans to confirm safety and efficacy is suggested.

Peripheral treatment with enoxaparin exacerbates amyloid plaque pathology in Tg2576 mice.

Alzheimer's disease (AD) is a complex, progressive neurological disorder characterized by the formation of extracellular amyloid plaques composed of ß-amyloid protein (Aß), the key component in pathogenesis of AD. Peripheral administration of enoxaparin (ENO) reportedly reduces the level of Aß and the amyloid plaques in the cortex of amyloid precursor protein (APP) transgenic mice. However, the exact mechanism of these effects is unclear. Our previous studies indicated that ENO can inhibit APP processing to Aß in primary cortical cells from Tg2576 mice by downregulating BACE1 levels. This study examines whether ENO-induced reduction of amyloid load is due to the decreased APP processing to Aß in Tg2576 mice. Surprisingly, our results indicated that ENO significantly increases the Aß42/Aß40 ratio in cortex and enhances the amyloid plaque load in both cortex and hippocampus, although overall APP processing was not influenced by ENO. Moreover, ENO stimulated the aggregation of both Aß40 and Aß42 in vitro. Although ENO has been reported to improve cognition in vivo and has potential as a therapeutic agent for AD, the results from our study suggest that ENO can exacerbate the amyloid pathology, and the strategy of using ENO for the treatment of AD may require further assessment. © 2016 Wiley Periodicals, Inc.

Hepatotoxicidad secundaria a enoxaparina / Enoxaparin-induced hepatotoxicity

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Structural and functional analyses of biosimilar enoxaparins available in Brazil.

Biosimilar enoxaparins have been available for clinical use in Brazil since 2009. Although their use has reduced costs of treatment expenses, their implementation still raises some concerns about efficiency, safety, regularity and reproducibility of batches. We undertook structural and functional analyses on over 90 batches of pharmaceutical-active ingredient, and 330 ones of the final products of biosimilar enoxaparins available in the Brazilian market between 2009 and 2014. Besides a nationwide-scale analysis, we have also employed methods that go beyond those recommended by the standard pharmacopeias. We have used high-resolution 2D NMR, detailed assessment of the anticoagulant and antithrombotic properties, check of side effects in experimental animals after continuous administration, and analyses of individual composing oligosaccharides. The 1D 1H NMR spectra of all batches of biosimilar enoxaparins are fairly coincident, and the resultant average spectrum is quite identical to that from the original drug. This structural equality was also assured by highly resolved 2D NMR spectra. The anticoagulant activity, determined by diverse assays and the in vivo antithrombotic and bleeding effects of the biosimilar version were confirmed as equal as of the parental enoxaparins. Structure and function of the composing oligosaccharides were identical in both enoxaparin types. No side effect was observed after continuous subcutaneous administration to rats for 30 days at the dose of 2 mg kg⁻¹ body weight. Biosimilar enoxaparins available in Brazil fulfilled the requirement of the five items defined by FDA-USA for approval of this type of drug.

Effectiveness of dabigatran etexilate for thromboprophylaxis of mechanical heart valves.

OBJECTIVE: Warfarin reduces risk of stroke in patients with mechanical heart valves but increases risk of hemorrhage and is difficult to use. Dabigatran etexilate, a new oral direct thrombin inhibitor, is safe and effective in reducing risk of stroke among patients with atrial fibrillation. No data exist in the setting of mechanical heart valves. We tested the hypothesis that dabigatran etexilate is as effective as heparin for thromboprophylaxis of mechanical valves in a porcine heterotopic aortic valve model. METHODS: Thirty swine underwent implantation of modified bileaflet mechanical valved conduit bypassing the ligated, native descending thoracic aorta. Animals randomly received no anticoagulation (n = 10), enoxaparin 2 mg/kg subcutaneously twice daily (n = 10), or dabigatran etexilate 20 mg/kg orally twice daily. Primary end point was amount of valve thrombus at 30 days. Secondary end points included quantitative measurement of platelet deposition on valve prosthesis, thromboelastography, and hemorrhagic and embolic events. RESULTS: At 30 days, we observed 638 ± 895 mg thrombus in no anticoagulation group, 121 ± 128 mg in enoxaparin group, and 19 ± 31 mg in dabigatran etexilate group (P = .01 enoxaparin vs dabigatran etexilate). Fewer platelets were deposited on valves in dabigatran etexilate group (2.7 × 10(8)) than in enoxaparin group (1.8 × 10(9), P = .03). No major or occult hemorrhagic or embolic events were observed. By thromboelastographic analysis, dabigatran etexilate produced less prolongation of K value (P = .01) and less decreases in angle (P = .01) and maximum amplitude (P = .001) than enoxaparin. CONCLUSIONS: Dabigatran etexilate is as effective as enoxaparin for short-term thromboprophylaxis of mechanical valves. It prevents valve thrombus and platelet deposition at 30 days without increased adverse events. These promising results serve as a foundation for prospective clinical trials with dabigatran etexilate as an alternative to warfarin in patients with bileaflet mechanical aortic valves.

Complexation of a poly-L-arginine with low molecular weight heparin enhances pulmonary absorption of the drug.

PURPOSE: This study tests the hypothesis that complexation between a cationic polymer, poly-L-arginine (PLA), and an anionic drug, low molecular weight heparin (LMWH), enhances pulmonary absorption and reduces the epithelial toxicity. MATERIALS AND METHODS: Enoxaparin, a LMWH, was complexed with PLAs of different molecular weights at varying concentrations. The resulting complexes were characterized by measuring particle size and zeta potential, and by quantitating the interactions between PLA and enoxaparin using an azure A assay. Changes in transepithelial electrical resistance (TEER) and cytotoxicity induced by enoxaparin-PLA complex were investigated in Calu-3 cells. Pulmonary absorption of LMWH was determined by measuring plasma anti-factor Xa levels. A bronchoalveolar lavage (BAL) study was performed to investigate if the PLA-based formulations caused any cellular or biochemical changes in the lungs. RESULTS: The particle size of enoxaparin-PLA complexes decreased and the zeta potential values of the complex became less negative as the concentration of positively charged PLA in the complex increased. In vitro experiments suggest that addition of enoxaparin-PLA complex to the apical side of a polarized cell monolayer results in a significant increase in permeability to 14C-mannitol and a decrease in TEER. Pulmonary formulations of enoxaparin plus 0.0125% or 0.0625% PLA of molecular weight 93 kDa led to a twofold increase in the relative bioavailability of LMWH compared to the control (enoxaparin plus normal saline). The BAL study showed that the enoxaparin-PLA complex formulation did not elicit any significant increases in marker enzyme activities compared to the normal saline-treated or untreated control groups. CONCLUSION: PLA could be used as a carrier for the pulmonary delivery of LMWH.

Oral dabigatran etexilate vs. subcutaneous enoxaparin for the prevention of venous thromboembolism after total knee replacement: the RE-MODEL randomized trial.

BACKGROUND: Oral anticoagulants, such as dabigatran etexilate, an oral, direct thrombin inhibitor, that do not require monitoring or dose adjustment offer potential for prophylaxis against venous thromboembolism (VTE) after total knee replacement surgery. METHODS: In this randomized, double-blind study, 2076 patients undergoing total knee replacement received dabigatran etexilate, 150 mg or 220 mg once-daily, starting with a half-dose 1-4 hours after surgery, or subcutaneous enoxaparin 40 mg once-daily, starting the evening before surgery, for 6-10 days. Patients were followed-up for 3 months. The primary efficacy outcome was a composite of total VTE (venographic or symptomatic) and mortality during treatment, and the primary safety outcome was the incidence of bleeding events. RESULTS: The primary efficacy outcome occurred in 37.7% (193 of 512) of the enoxaparin group versus 36.4% (183 of 503) of the dabigatran etexilate 220 mg group (absolute difference, -1.3%; 95% CI, -7.3 to 4.6) and 40.5% (213 of 526) of the 150 mg group (2.8%; 95% CI, -3.1 to 8.7). Both doses were noninferior to enoxaparin based on the pre-specified noninferiority criterion. The incidence of major bleeding did not differ significantly between the three groups (1.3% versus 1.5% and 1.3% respectively). No significant differences in the incidences of liver enzyme elevation and acute coronary events were observed during treatment or follow-up. CONCLUSIONS: Dabigatran etexilate (220 mg or 150 mg) was at least as effective and with a similar safety profile as enoxaparin for prevention of VTE after total knee-replacement surgery.

Bridging therapy in patients on long-term oral anticoagulants who require surgery: the Prospective Peri-operative Enoxaparin Cohort Trial (PROSPECT).

BACKGROUND: The peri-operative management of patients on oral anticoagulants (OACs) is a common clinical problem. Our aim was to determine the incidence of major bleeding during peri-operative administration of treatment-dose enoxaparin and the impact of the extensiveness of the procedure on the risk of bleeding. METHODS: We performed a prospective cohort study of 260 patients at 24 North American sites on OACs for atrial fibrillation or a history of deep vein thrombosis (DVT) requiring invasive or surgical procedures whose treating physician felt that bridging therapy was required. Warfarin was withheld, and once-daily s.c. enoxaparin (1.5 mg kg(-1)) was given peri-operatively. Patients were followed for 28 days after OAC was therapeutic. RESULTS: Major bleeding was observed in nine of 260 patients (3.5%, 95% CI: 1.6-6.5). The bleeding risk varied markedly by extensiveness of procedure: the incidence of major bleeding for invasive procedures, minor surgery and major surgery was 0.7% (95% CI: 0.02-3.7), 0% (95% CI: 0-5.0), and 20.0% (95% CI: 9.1-35.7), respectively. There were five thromboembolic events in total (1.9%, 95% CI: 0.6-4.4). There were four arterial events (2.3%, 95% CI: 0.6-5.7) in 176 patients with atrial fibrillation, and one venous event (1.0%, 95% ci: 0.03-5.7) in 96 patients with prior DVT/ CONCLUSIONS: Bridging therapy with once-daily therapeutic-dose enoxaparin administered primarily in an outpatient setting has a low incidence of major bleeding for patients undergoing invasive procedures and minor surgery. Further studies are needed to optimize the bridging strategy for patients undergoing major surgery.

Monotherapy with enoxaparin for the prevention of recurrent venous thromboembolism.

This study aimed to determine whether a weight-adjusted dose of subcutaneous enoxaparin is as effective and safe as oral acenocoumarol for the secondary prophylaxis of pulmonary embolism. Three hundred and eighty consecutive noncancer outpatients hospitalized with an episode of symptomatic pulmonary embolism selected treatment with acenocoumarol or enoxaparin at a dose of 1 mg/kg once daily after being informed of the type of administration and expected frequency of laboratory monitoring for both medicinal products. Endpoints were symptomatic recurrent thromboembolic events evaluated by standard objective testing, and a composite endpoint of recurrent venous thromboembolism, major bleeding, and death from any cause. One hundred and ninety-nine patients (52%) chose acenocoumarol therapy and 181 chose enoxaparin monotherapy. Four patients in the enoxaparin group (2.2%) and six patients in the acenocoumarol group (3%) had an objective thromboembolic recurrence (hazard ratio, 1.35; 95% confidence interval, 0.38-4.79; P = 0.64). Nine patients in the enoxaparin group (5.0%) had a hemorrhagic complication compared with 11 in the acenocoumarol group (5.5%) (P = 0.81). The hospital length of stay was shorter with enoxaparin compared with acenocoumarol (11 versus 16 days, P = 0.0001). Enoxaparin is as effective and safe as acenocoumarol in the secondary prevention of recurrent thromboembolic disease and is associated with shorter hospitalization.

Once-daily enoxaparin in the outpatient setting versus unfractionated heparin in hospital for the treatment of symptomatic deep-vein thrombosis.

BACKGROUND: Once- and twice-daily low-molecular-weight heparin administered in hospital have been shown to be effective and safe for treating deep-vein thrombosis. The aim of this study was to compare the efficacy and safety of deep-vein thrombosis treatment using once-daily subcutaneous enoxaparin in the outpatient setting with intravenous unfractionated heparin in hospital. METHODS: This randomized, parallel-group, open-label study was conducted in 18 centers in 4 countries. In total, 298 patients with symptomatic deep-vein thrombosis who were eligible for home treatment were randomized to treatment with enoxaparin in the outpatient setting (1.5 mg/kg subcutaneously once-daily) or unfractionated heparin in hospital (5000 IU bolus and 1250 IU/hour intravenous infusion) for > or =5 days. Clinical endpoints were assessed during a 6-month follow-up period. RESULTS: Among all patients treated with enoxaparin, there was a trend towards fewer recurrent deep-vein thromboses (1.3% vs. 5.4%; p = 0.060) and pulmonary emboli (1.3% vs. 4.1%; p = 0.17) compared with patients treated with unfractionated heparin. When considering a post-hoc combined endpoint of deep-vein thrombosis and pulmonary embolism, significantly fewer events occurred in the enoxaparin group than in the unfractionated-heparin group (2.7% vs. 8.8%; p = 0.026). The incidences of bleeding events and adverse events in the enoxaparin and unfractionated-heparin groups were similar. CONCLUSIONS: Once-daily subcutaneous enoxaparin in the outpatient setting is at least as effective and as well tolerated as in-hospital intravenous unfractionated heparin for treatment of deep-vein thrombosis.

Efficacy and safety of bemiparin compared with enoxaparin in the prevention of venous thromboembolism after total knee arthroplasty: a randomized, double-blind clinical trial.

In this randomized, multicenter, controlled, double-blind, sequential trial, 381 patients undergoing primary total knee replacement were randomly assigned to receive subcutaneous injections of either 3500 IU anti-factor Xa of bemiparin sodium, first dose 6 h after surgery, or 40 mg of enoxaparin, first dose 12 h before surgery, followed by daily doses for 10 +/- 2 days, for the prophylaxis of venous thromboembolism. The primary efficacy endpoint was venous thromboembolism up to postoperative day 10 +/- 2, defined as deep vein thrombosis detected by mandatory bilateral venography, documented symptomatic deep vein thrombosis and/or documented symptomatic pulmonary embolism. The primary safety endpoint was major bleeding. Eighty-seven percent of all randomized patients (333 of 381 patients) were evaluable for efficacy. The incidence of venous thromboembolism was 32.1% (53 of 165 patients) in the bemiparin group and 36.9% (62 of 168 patients) in the enoxaparin group. The absolute risk difference was 4.8% in favor of bemiparin [95% confidence interval (CI), -15.1% to 5.6%; non-inferiority P-value: 0.02; superiority P-value: 0.36]. The incidence of proximal deep vein thrombosis was 1.8% (three of 165 patients) in the bemiparin group and 4.2% (seven of 168 patients) in the enoxaparin group. Major bleeding occurred in six patients (three in each group). There were no deaths during the study. This trial shows that bemiparin started postoperatively is as effective and safe as enoxaparin started preoperatively in the prevention of venous thromboembolism in patients undergoing total knee replacement.

Enoxaparin monotherapy without oral anticoagulation to treat acute symptomatic pulmonary embolism.

Conventional anticoagulation for symptomatic pulmonary embolism consists of continuous intravenous unfractionated heparin as a "bridge" to oral anticoagulation. This strategy requires 5 days or more of intravenous heparin while oral vitamin K antagonists gradually achieve a therapeutic effect. Oral vitamin K antagonists require frequent blood testing to optimize dosing, and their interactions with other medications and foods make regulation difficult. Therefore we tested a different approach to therapy: long-term enoxaparin monotherapy. We randomized 60 symptomatic pulmonary embolism patients in a 2:1 ratio to 90 days of enoxaparin as monotherapy without warfarin (N=40) or to intravenous unfractionated heparin as a "bridge" to warfarin, target INR 2.0-3.0 (N=20). Enoxaparin patients received 1 mg/kg twice daily for 14 days during the acute phase followed by randomized assignment during the chronic phase to 1.0 mg/kg vs. 1.5 mg/kg once daily. In an intention-to-treat analysis, 3 of the 40 enoxaparin patients developed recurrent venous thromboembolism compared with 0 of 20 standard therapy patients (p = 0.54). One of the 40 enoxaparin patients had a major hemorrhagic complication compared with 2 of the 20 standard therapy patients (p = 0.26). Median hospital length of stay was shorter with enoxaparin compared to standard therapy (4 vs. 6 days) (p = 0.001). Following our study we can conclude that extended 3-month treatment with enoxaparin as monotherapy for symptomatic, acute pulmonary embolism is feasible and warrants further study in a large clinical trial.

Endothelial damage after treatment with low-molecular weight heparins--a morphological study.

OBJECTIVE: Recent studies failed to show long-term benefit with low-molecular weight heparins (LMWH) in unstable coronary heart disease. A previous study of vascular effects of the cytostatic agent 5-fluorouracil (5-FU) showed that dalteparin prevented thrombosis induced by 5-FU but endothelial damage was not ameliorated and was present also in animals treated with dalteparin only. This study investigates the influence of LMWH currently in clinical use on arterial endothelium in vivo. DESIGN: Eighty rabbits in four groups were treated with dalteparin, enoxaparin, tinzaparin and saline, respectively. Arterial endothelium was examined after 3, 14, 30 and 60 days with scanning electron microscopy. RESULTS: All three groups treated with LMWH showed moderate damage to the endothelium, with contracted vessel wall and endothelial cells, cell membrane damage, denudation of subendothelium and adhering platelets. Contrarily, the control group exhibited a normal endothelium. CONCLUSION: Morphologic examination of arterial endothelium shows that all investigated LMWH exert a moderate toxic effect on endothelial cells. The clinical impact of these observations, e.g. concerning effect of long-term LMWH treatment, needs to be further elucidated.

Clinical experiences with low-molecular weight heparins in pediatric patients.

The courses of 79 children (2 weeks to 19 years old) treated with two different low-molecular weight heparins (LMWHs)--nadroparin (n=66) and enoxaparin (n=13)--were retrospectively analysed. In 62 patients, LMWHs were given for short-term prophylaxis (1-2 weeks) during immobilization after surgery or trauma. Thirteen children with thromboembolic events received long-term prophylaxis with LMWHs for 2-18 months--six after thrombolytic therapy and seven after therapy with unfractionated heparin (UFH). Because of thromboembolic events, four patients were initially treated with LMWHs. In all patients with short-term prophylaxis, no thrombosis occurred. After thrombolytic therapy, three children had no reocclusion, two had no thrombus apposition and one had complete recanalization. In the seven patients treated with LMWHs after UFH, four had no reocclusion, two had recanalization and one had reocclusion. In all patients receiving LMWHs for initial treatment of thrombosis, no thrombus apposition, but also no recanalization, occurred. For short-term prophylaxis, nadroparin was used independent of the body weight and without determination of anti-factor Xa (anti-FXa) activity. Long-term prophylaxis was given mainly as doses of 45-100 anti-FXa U/kg resulting in anti-FXa activities between 0.2 and 0.4 U/ml. For treatment of thrombosis, doses of 200-300 anti-FXa U/kg corresponded to 0.5-1.0 anti-FXa U/ml. Side effects--slight gastrointestinal bleeding and temporary reversible hair loss--were seen in two patients. In conclusion, LMWHs proved to be efficacious and safe especially in prophylaxis of thromboembolic events in children.

The TETAMI trial: the safety and efficacy of subcutaneous enoxaparin versus intravenous unfractionated heparin and of tirofiban versus placebo in the treatment of acute myocardial infarction for patients not thrombolyzed: methods and design.

Patients with acute myocardial infarction (AMI) who do not receive early reperfusion therapy are at high risk of reinfarction or death, and the efficacy and safety of antithrombotic therapy in this group of patients has not been evaluated. Enoxaparin is a low-molecular-weight heparin (LMWH) that has previously been shown to reduce the incidence of ischemic events in patients with unstable angina or non-Q-wave MI. The principal aims of the TETAMI study are to investigate the efficacy and safety of treatment with enoxaparin or tirofiban (a glycoprotein IIb/IIIa receptor antagonist) alone or in combination for 2 to 8 days in patients with AMI who are not eligible for early reperfusion therapy. In this 2 by 2 factorial design study approximately 900 patients will be randomly assigned, in a blinded manner, to one of four treatments: enoxaparin alone, enoxaparin plus tirofiban, unfractionated heparin (UFH), or UFH plus tirofiban, with appropriate matched placebos. The primary end point is the composite of death, recurrent AMI, and recurrent angina, analyzed at 30 days after AMI. The design and methods of the TETAMI study are described in this article.

Absence of transplacental passage of the low molecular weight heparin enoxaparin.

BACKGROUND: Venous thromboembolism (VTE) during pregnancy and puerperium remains a major cause of maternal morbidity and mortality. The use of low molecular weight heparin (LMWH) constitutes a promising alternative for the prevention of VTE instead of unfractionated heparin as it can be administered subcutaneously once daily and without coagulation measurement. Unfortunately, the safety of LMWHs administration for the mother and fetus has not been well established. STUDY DESIGN: In order to examine the safety of enoxaparin to the fetus, 24 women were recruited and 40 mg of enoxaparin was administered in 14 of them. All 24 women were going to have an early termination of pregnancy due to major fetal malformations. Maternal blood samples were drawn before and after the injection of enoxaparin, while fetal blood samples were taken only after the drug administration. Anti-IIa and anti-Xa activities were measured. RESULTS: A statistically significant increase of anti-Xa activity in the mothers studied was pointed out, while there was no detection of anti-IIa and anti-Xa activities in the fetuses. CONCLUSIONS: Since no anti-IIa and anti-Xa activities were detected in the fetuses' blood samples, it is concluded that enoxaparin does not cross the placenta and therefore appears safe for the fetus.

Comparison of enoxaparin, hirulog, and heparin as adjunctive antithrombotic therapy during thrombolysis with rtPA in the stenosed canine coronary artery.

A canine model of electrolytic injury-induced coronary artery thrombosis and rtPA-induced thrombolysis was used to evaluate the relative antithrombotic efficacy of enoxaparin (a low molecular weight heparin), conventional therapy (heparin or heparin plus aspirin), and hirulog (a direct thrombin inhibitor), when used as adjunctive therapy during thrombolysis. After 60 min of clot aging, adjunctive therapy was begun at doses which elevated APTT approximately 2-fold over baseline. Fifteen minutes after the start of adjunctive therapy, recombinant tissue plasminogen activator (rtPA) was administered (100 microg/kg i.v. bolus + 20 microg/kg/min for 60 min). Adjunctive therapy continued for 1 h after termination of rtPA and blood flow was monitored for two additional hours. Enoxaparin (1 mg/kg i.v. bolus + 30 microg/kg/min, n = 10 for each treatment group) was the only adjunctive treatment that significantly increased the total minutes of flow (143 +/- 25 min out of a possible 240 min, vs 54 +/- 25 min for vehicle, p <0.05) and decreased thrombus mass (6.0 +/- 1.3 mg vs 11.8 +/- 3.2 mg for vehicle). Although hirulog (2 mg/kg i.v. bolus + 40 microg/kg/min) did not significantly increase the minutes of flow (120 +/- 27 min, p <0.06) or decrease thrombus mass (8.7 +/- 1.7 mg) compared to vehicle, these values were not significantly different than those measured in the enoxaparin group. However, the results with hirulog were achieved at the expense of a significantly greater increase in template bleeding time than that measured during enoxaparin treatment. Minutes of flow for heparin (50 U/kg i.v. bolus + 0.6 U/kg/min) and heparin plus aspirin (5 mg/kg i.v. bolus) were 69 +/- 20 and 60 +/- 23 min, respectively; thrombus masses were 8.2 +/- 1.3 and 7.3 +/- 1.0 mg, respectively. In summary, enoxaparin was more effective than conventional therapy in this model in terms of vessel patency and thrombus mass, and was as effective as hirulog, at least at a dose of hirulog that only modestly impaired hemostasis. Therefore, enoxaparin may prove to be a safe and effective alternative agent for adjunctive therapy during thrombolysis with rtPA.