Highly variable anticoagulant response after subcutaneous administration of high-dose (12,500 IU) heparin in patients with myocardial infarction and healthy volunteers

Gerinnungsdiagnostik im klinischen Alltag – Teil 2

Während bei einer Vitamin-K-Antagonisten-Therapie die Therapieüberwachung (International Normalized Ratio [INR]) obligat ist, gilt dies für direkte orale Antikoagulanzien (DOAK) oder niedermolekulares Heparin (NMH) nur in ausgewählten klinischen Szenarien. Bei DOAK steht die Bestimmung von Tal- und Spitzenspiegeln des Medikaments im Plasma im Vordergrund, bei NMH die Anti-Xa-Aktivität. Der Zeitpunkt der Probenabnahme in Relation zur Einnahme ist für die Bewertung essenziell. Eine neu aufgetretene Thrombozytopenie im Rahmen stationärer Behandlungen ist häufig. Einordnung der Grunderkrankung, Tag des Auftretens sowie Erfassung medikamentöser Einflüsse und ihrer Dynamik ermöglichen oft die Eingrenzung der Ursache. Die Thrombophilietestung nach venöser Thromboembolie wird aufgrund fehlender therapeutischer Konsequenz zunehmend seltener durchgeführt. Ein Antiphospholipidsyndrom darf aber nicht übersehen werden, da sowohl die Therapiedauer als auch die Wahl des Antikoagulans davon abhängen.

Sulfated poly-amido-saccharides (sulPASs) are anticoagulants in vitro and in vivo

Anticoagulant therapeutics are a mainstay of modern surgery and of clotting disorder management such as venous thrombosis, yet performance and supply limitations exist for the most widely used agent - heparin. Herein we report the first synthesis, characterization, and performance of sulfated poly-amido-saccharides (sulPASs) as heparin mimetics. sulPASs inhibit the intrinsic pathway of coagulation, specifically FXa and FXIa, as revealed by ex vivo human plasma clotting assays and serine protease inhibition assays. sulPASs activity positively correlates with molecular weight and degree of sulfation. Importantly, sulPASs are not degraded by heparanases and are non-hemolytic. In addition, their activity is reversed by protamine sulfate, unlike small molecule anticoagulants. In an in vivo murine model, sulPASs extend clotting time in a dose dependent manner with bleeding risk comparable to heparin. These findings support continued development of synthetic anticoagulants to address the clinical risks and shortages associated with heparin.

Development of Selective FXIa Inhibitors Based on Cyclic Peptides and Their Application for Safe Anticoagulation

Coagulation factor XI (FXI) has emerged as a promising target for the development of safer anticoagulation drugs that limit the risk of severe and life-threatening bleeding. Herein, we report the first cyclic peptide-based FXI inhibitor that selectively and potently inhibits activated FXI (FXIa) in human and animal blood. The cyclic peptide inhibitor (K_i = 2.8 ± 0.5 nM) achieved anticoagulation effects that are comparable to that of the gold standard heparin applied at a therapeutic dose (0.3-0.7 IU/mL in plasma) but with a substantially broader estimated therapeutic range. We extended the plasma half-life of the peptide via PEGylation and demonstrated effective FXIa inhibition over extended periods in vivo. We validated the anticoagulant effects of the PEGylated inhibitor in an ex vivo hemodialysis model with human blood. Our work shows that FXI can be selectively targeted with peptides and provides a promising candidate for the development of a safe anticoagulation therapy.

Heparin-Mimicking Polymers: Synthesis and Biological Applications

Heparin is a naturally occurring, highly sulfated polysaccharide that plays a critical role in a range of different biological processes. Therapeutically, it is mostly commonly used as an injectable solution as an anticoagulant for a variety of indications, although it has also been employed in other forms such as coatings on various biomedical devices. Due to the diverse functions of this polysaccharide in the body, including anticoagulation, tissue regeneration, anti-inflammation, and protein stabilization, and drawbacks of its use, analogous heparin-mimicking materials are also widely studied for therapeutic applications. This review focuses on one type of these materials, namely, synthetic heparin-mimicking polymers. Utilization of these polymers provides significant benefits compared to heparin, including enhancing therapeutic efficacy and reducing side effects as a result of fine-tuning heparin-binding motifs and other molecular characteristics. The major types of the various polymers are summarized, as well as their applications. Because development of a broader range of heparin-mimicking materials would further expand the impact of these polymers in the treatment of various diseases, future directions are also discussed.

Increased unfractionated heparin requirements with decreasing body mass index in pregnancy

BACKGROUND

Pregnant women receiving low-molecular-weight heparin for therapeutic anticoagulation are often converted to unfractionated heparin in anticipation of labor. We aim to characterize the impact of maternal body mass index on attainment of target anticoagulation during the conversion process.

METHODS

We conducted a five-year retrospective study of a pregnancy cohort converted from low-molecular-weight heparin to unfractionated heparin in the third trimester. Patient demographics, anticoagulation regimens, and clinical outcomes were extracted from the medical record. Nonparametric statistical methods were used for analysis by body mass index (<30, 30-35, and >35).

RESULTS

Thirty-one subjects were evenly distributed by body mass index (p = 0.97). Linear regression revealed an inverse correlation between patient body mass index and unfractionated heparin dose needed to achieve therapeutic anticoagulation (p = 0.04). Subjects with body mass index > 35 attained therapeutic activated partial thromboplastin time levels at 18 U (Units)/kg/h, while subjects with body mass index < 30 required 25 U/kg/h (p = 0.02).

CONCLUSION

Higher doses of unfractionated heparin are needed to achieve anticoagulation in patients with body mass index < 30 during pregnancy. This paradoxical relationship may be explained by physiologic characteristics that increase unfractionated heparin elimination, including diminished adiposity and increased renal clearance.

Poly(vinyl sulfonate) Facilitates bFGF-Induced Cell Proliferation

Heparin is a highly sulfated polysaccharide and is useful because of its diverse biological functions. However, because of batch-to-batch variability and other factors, there is significant interest in preparing biomimetics of heparin. To identify polymeric heparin mimetics, a cell-based screening assay was developed in cells that express fibroblast growth factor receptors (FGFRs) but not heparan sulfate proteoglycans. Various sulfated and sulfonated polymers were screened, and poly(vinyl sulfonate) (pVS) was identified as the strongest heparin-mimicking polymer in its ability to enhance binding of basic fibroblast growth factor (bFGF) to FGFR. The results were confirmed by an ELISA-based receptor-binding assay. Different molecular weights of pVS polymer were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. The polymers were able to facilitate dimerization of FGFRs leading to cell proliferation in FGFR-expressing cells, and no size dependence was observed. The data showed that pVS is comparable to heparin in these assays. In addition, pVS was not cytotoxic to fibroblast cells up to at least 1 mg/mL. Together this data indicates that pVS should be explored further as a replacement for heparin.

Low-dose intravenous heparin infusion in patients with aneurysmal subarachnoid hemorrhage: a preliminary assessment

OBJECT

Aneurysmal subarachnoid hemorrhage (aSAH) predisposes to delayed neurological deficits, including stroke and cognitive and neuropsychological abnormalities. Heparin is a pleiotropic drug that antagonizes many of the pathophysiological mechanisms implicated in secondary brain injury after aSAH.

METHODS

The authors performed a retrospective analysis in 86 consecutive patients with Fisher Grade 3 aSAH due to rupture of a supratentorial aneurysm who presented within 36 hours and were treated by surgical clipping within 48 hours of their ictus. Forty-three patients were managed postoperatively with a low-dose intravenous heparin infusion (Maryland low-dose intravenous heparin infusion protocol: 8 U/kg/hr progressing over 36 hours to 10 U/kg/hr) beginning 12 hours after surgery and continuing until Day 14 after the ictus. Forty-three control patients received conventional subcutaneous heparin twice daily as deep vein thrombosis prophylaxis.

RESULTS

Patients in the 2 groups were balanced in terms of baseline characteristics. In the heparin group, activated partial thromboplastin times were normal to mildly elevated; no clinically significant hemorrhages or instances of heparin-induced thrombocytopenia or deep vein thrombosis were encountered. In the control group, the incidence of clinical vasospasm requiring rescue therapy (induced hypertension, selective intraarterial verapamil, and angioplasty) was 20 (47%) of 43 patients, and 9 (21%) of 43 patients experienced a delayed infarct on CT scanning. In the heparin group, the incidence of clinical vasospasm requiring rescue therapy was 9% (4 of 43, p = 0.0002), and no patient suffered a delayed infarct (p = 0.003).

CONCLUSIONS

In patients with Fisher Grade 3 aSAH whose aneurysm is secured, postprocedure use of a low-dose intravenous heparin infusion may be safe and beneficial.

Heparin-grafted dialysis membrane allows minimal systemic anticoagulation in regular hemodialysis patients: a prospective proof-of-concept study

This prospective, multicenter, proof-of-concept study aimed to evaluate the possibility to reduce the ordinary heparin dose and the systemic anti-Xa activity during hemodialysis (HD) sessions using a new heparin-grafted HD membrane. In 45 stable HD patients, the use of a heparin-grafted membrane with the ordinary heparin dose was followed by a stepwise weekly reduction of dose. Reduction was stopped when early signs of clotting (venous pressure, quality of rinse-back) occurred during two out of three weekly HD sessions. Heparin dose was decreased for 67% of patients resulting in the lowering of these patients' anti-Xa activity by 50%. Dose reductions were achieved with both types of heparin (low-molecular-weight heparin: 64 ± 14 to 35 ± 12 IU/kg, P < 0.0001; unfractionated heparin: 82 ± 18 to 46 ± 13 IU/kg, P < 0.0001) resulting in a decrease of anti-Xa activity at dialysis session end (low-molecular-weight heparin: 0.51 ± 0.25 to 0.25 ± 0.11 IU/mL, P < 0.0001; unfractionated heparin: 0.28 ± 0.23 to 0.13 ± 0.07 IU/mL, P < 0.0001). Failure to further decrease heparin dose was related to signs of clotting in blood lines (57% of sessions), in dialyzer (9%), or both (34%). Significant reduction of heparin dose and anti-Xa activity at the end of HD sessions was possible in stable HD patients using heparin-grafted membrane. HD patients who require low anti-Xa activity at the end of HD sessions might benefit from a heparin-grafted membrane to reduce bleeding risk and other heparin adverse events.

Airway obstruction due to a pre-vertebral haematoma following difficult central line insertion--implications for ultrasound guidance and review of the literature

We describe a case of airway obstruction secondary to a large pre-vertebral cervico-mediastinal haematoma following failed attempts at insertion of an internal jugular central venous line. The need for a high index of suspicion to diagnose this injury and early aggressive intervention to manage it are outlined. The role of ultrasound guidance in preventing such a complication is reviewed, as well as other possible mechanisms of haematoma development.

Heparin resistance in acute coronary syndromes

BACKGROUND

Maintaining a therapeutic level of anticoagulation with unfractionated heparin remains a major challenge for clinicians because of the wide variability of patient responses, which may be explained by variable binding of heparin to plasma proteins. Direct thrombin inhibitors may offer an advantage in more predictable anticoagulation.

METHODS

Plasma samples from normal volunteers, stable coronary artery disease (CAD) patients, unstable angina patients, and acute myocardial infarction patients were obtained. A fixed concentration of heparin (.13 U/ml) or bivalirudin (1.6 microg/ml) was added to plasma from each of the four study groups and measurement of the APTT was performed. In addition, a pool of plasma from patients with acute MI was diluted in pooled normal plasma, and heparin or bivalirudin was added to the plasma preparation and APTT measurements performed.

RESULTS

In heparin-treated plasma samples, mean APTT values were 443 +/- 137% baseline for normal volunteers, 347 +/- 116% for patients with stable CAD, 290 +/- 124% for patients with unstable angina (p < 0.05), and 230 +/- 120% for patients with acute MI (p < 0.05). APTT did not differ across the four groups treated with bivalirudin. There was a much higher degree of variability in APTT values in heparin treated controls (272%-671%, SD approximately 30%) compared to bivalirudin treated controls (284-499%, SD approximately 12%). When the "acute MI pool" was diluted in pooled normal plasma at fixed concentrations of either bivalirudin (1.6 mug/ml) or heparin (0.13 U/ml), there was a sharp decrease in heparin activity from 407% baseline (at 0% acute MI pool) to values as low as 126% baseline (at 100% acute MI pool). A markedly different pattern was seen in the bivalirudin treated samples, where a trend towards decreased APTT values was seen only at the 100% acute MI pool.

CONCLUSION

Both heparin variability and resistance may limit optimal antithrombotic therapy with heparin in patients with ACS and constitutes a potential advantage of direct antithrombin blockade with bivalirudin.

Role of low-molecular-weight heparins in the management of patients with unstable angina pectoris and non-Q-wave acute myocardial infarction

The development of effective approaches to the management of the unstable coronary syndromes has resulted from an improved understanding of interactions between the vascular wall, platelets, and coagulation factors, and of their response to pharmacologic and mechanical interventions. Furthermore, the occurrence of frequent adverse events after discharge in patients with unstable coronary artery disease (CAD) treated with these therapies alone would argue that, for many of these patients, such stabilization is not the end of the therapeutic pathway; rather, these therapies are for many a preparation for ultimate revascularization, to preserve myocardium and minimize periprocedural complications. The low-molecular-weight heparins with their unique pharmacology offer a new option in the therapy of patients with unstable CAD. There is now extensive experience in the use of several of the low-molecular-weight heparins, particularly dalteparin and enoxaparin, in the management of patients with unstable angina. Several trials have investigated the questions raised by these observations, taking advantage of the unique pharmacologic properties of the low-molecular-weight heparins for both acute inpatient use and prolonged outpatient administration. Although differences in study design preclude direct comparison between the available low-molecular-weight heparins, in these trials low-molecular-weight heparins have been shown to be effective alternatives to conventional heparin for the management of patients with unstable angina and non-Q-wave infarction. These include several small-scale trials and the larger FRagmin during InStability in Coronary artery disease (FRISC), Fragmin in Unstable Coronary Artery Disease (FRIC), Efficacy and Safety of Subcutaneous Enoxaparin in Non-Q-Wave Coronary Events (ESSENCE), FRISC II, and Thrombolysis in Myocardial Infarction (TIMI)-11B trials. Thus, the low-molecular-weight heparins appear to be a superior alternative to traditionally administered intravenous unfractionated heparin. They are more predictable in action, do not require frequent activated partial thromboplastin time (aPTT) measurements and dosage adjustments, are easier to administer, and are potentially more efficacious. With their proven efficacy, predictability of action, and convenience of administration and dosing, there are very good reasons for selecting them as first-line therapies for patients presenting with unstable angina and non-Q-wave myocardial infarction.

Activated partial thromboplastin time (aPTT) monitoring to achieve therapeutic anticoagulation before and after introducing a nomogram for adjunctive heparin treatment with thrombolytic therapy for acute myocardial infarction

In patients with acute myocardial infarction (AMI) receiving thrombolytic therapy and i.v. unfractionated heparin, anticoagulant levels are frequently outside the target range. We evaluated the effects on anticoagulant levels before (group A) and after (group B) the introduction of a heparin nomogram in consecutive AMI-patients, receiving thrombolytic therapy and adjunctive heparin treatment. The target activated partial thromboplastin time (aPTT) was defined as 60-90 s. During the first 72 h after admission, the total number of aPTTs within the target range and the time taken to achieve the range were compared. The incidence of bleeding complications was assessed. Group A consisted of 56 and group B of 55 patients. The number of patients within the target range at 72 h (44 versus 51; chi2=4.51; P=0.034) was significantly higher in group B. No difference was found between total aPTTs within the target range (26% in group A versus 30% in group B; P=ns). Bleeding complications were slightly less in group B (7 versus in group A versus 2 patients in group B; P=ns). We concluded that the introduction of a nomogram resulted in significantly more patients with aPTTs within the target range. However, a substantial number of aPTTs before and after introduction of the nomogram were outside the target range. Moreover, this retrospective study shows that previously acquired prospective data (which showed a marked improvement of anticoagulation using a heparin nomogram) are not necessarily reproduced in the real life clinical setting.

Low molecular weight heparin as an adjunct to thrombolysis for acute myocardial infarction: the FATIMA study. Fraxiparin Anticoagulant Therapy in Myocardial Infarction Study Amsterdam (FATIMA) Study Group

OBJECTIVE

To investigate the feasibility of fixed dose, weight adjusted subcutaneous low molecular weight heparin (LMWH), with monitoring of anti-Xa levels and assessment of coronary patency rates after three to five days, thereby giving an initial indication of its safety and efficacy.

DESIGN

In 30 patients with acute myocardial infarction, LMWH (nadroparine) was given as a body weight adjusted intravenous bolus with thrombolysis (rt-PA infusion) and in weight adjusted subcutaneous doses at six hours, and every 12 hours thereafter for 72 hours. The target range was defined prospectively as 0.35-0.70 anti-factor Xa activity (aXa) units. The aXa level was measured every six hours. Coronary angiography was performed in all patients within five days after the start of thrombolytic treatment to determine patency (TIMI 2 and 3 flow) of the infarct related artery.

RESULTS

The mean (SEM) aXa level over 72 hours was 0.52 (0.08) U/ml; from 12 hours onwards 88% of all aXa measurements were within the target range. At angiography, a patent infarct related artery was present in 24 of the 30 patients. No major bleeding complications occurred, though minor bleeding complications were observed in two patients.

CONCLUSIONS

This small study indicates that LMWH is feasible as an adjunct to thrombolysis in patients with acute myocardial infarction. The aXa levels were within the target range and patency rates at three to five days were around 80%, with no major bleeding complications.

Randomized trial of low molecular weight heparin (dalteparin) in prevention of left ventricular thrombus formation and arterial embolism after acute anterior myocardial infarction: the Fragmin in Acute Myocardial Infarction (FRAMI) Study

OBJECTIVES

The present trial investigated the efficacy and safety of dalteparin in the prevention of arterial thromboembolism after an acute anterior myocardial infarction (MI).

BACKGROUND

Left ventricular (LV) thrombus formation is associated with increased risk of arterial embolism in patients with an acute MI. Thrombolytic and antiplatelet therapy do not prevent thrombus formation.

METHODS

A total of 776 patients were enrolled in a multicenter, randomized, double-blind, placebo-controlled trial of subcutaneous dalteparin (150 IU/kg body weight every 12 h during the hospital period). Thrombolytic therapy and aspirin were administered in 91.5% and 97.6% of patients, respectively. The primary study end point was the composite of thrombus formation diagnosed by echocardiography and arterial embolism on day 9 +/- 2.

RESULTS

Of 517 patients with echocardiographic recordings available for end point analysis, thrombus formation or embolism, or both, was found in 59 (21.9%) of 270 patients (59 with thrombus, none with embolism) in the placebo group and 35 (14.2%) of 247 patients (34 with thrombus, 1 with embolism) in the dalteparin group (p = 0.03). The risk reduction of thrombus formation associated with dalteparin treatment was 0.63 (95% confidence interval 0.43 to 0.92, p = 0.02). Analyses of all randomized patients (388 in each group) revealed no significant difference between the placebo and dalteparin groups with respect to arterial embolism (6 vs. 5 patients), reinfarction (8 vs. 6 patients) and mortality rates (23 vs. 23 patients, p = NS for all). Dalteparin was associated with an increased risk of hemorrhage: major in 11 dalteparin group patients (2.9%) verus 1 placebo group patient (0.3%, p = 0.006); minor in 52 dalteparin group patients (14.8%) versus 8 placebo group patients (1.8%, p < 0.001).

CONCLUSIONS

Dalteparin treatment significantly reduces LV thrombus formation in acute anterior MI but is associated with increased hemorrhagic risk.

Antiplatelet and anticoagulant use after myocardial infarction

Coronary thrombosis leading to myocardial infarction is a complex process involving the interaction of the arterial wall, the coagulation cascade, and platelets. Increased understanding of the molecular biology of thrombosis has prompted an evolution in antithrombotic therapy, from the early use of warfarin following myocardial infarction to agents targeting specific receptors or modulators in the thrombotic process. The complexity of thrombosis allows for numerous sites of pharmacologic intervention; the multiple pathways leading to platelet aggregation and thrombin formation provide the opportunity for combined therapies. This review presents the current clinical data on antiplatelet, anticoagulant, and specific antithrombin therapies following myocardial infarction.

Shortened hospitalization by means of adjusted-dose subcutaneous heparin for deep venous thrombosis

Adjusted-dose subcutaneous unfractionated heparin (SC heparin) was used in the initial management of deep venous thrombosis (DVT) to allow shortened hospital stay. Of 78 patients screened, 41% were eligible and 18 (23%) were enrolled. Follow-up venous ultrasound examination was performed 6 weeks after discharge. Of enrolled patients, 16 (89%) completed the protocol. Hospital length of stay was 2 days in protocol patients compared with 5 days for patients receiving conventional inpatient heparin with a continuous intravenous infusion (p = 0.0009). Very high heparin doses (mean 42,000 to 62,000 U daily, given in three divided doses every 8 hours) and a median time of 21 hours were required initially to achieve a target activated partial thromboplastin time (aPTT) > 55 seconds. Subsequently many patients had supratherapeutic levels, yet there were no bleeding complications. Four patients (25%) did not show improvement at follow-up ultrasound in spite of aPTTs > 55 seconds after the second injection. Clot regression was evident in remaining patients. Hospital cost savings were offset partially by the need for time- and labor-intensive outpatient monitoring after hospital discharge.

Heparin as an adjuvant to thrombolytic therapy in acute myocardial infarction

For the treatment of acute myocardial infarction, heparin has been a topic of continuing debate for the past four decades. After review of the available data, the American College of Cardiology/American Heart Association Guidelines for the Early Management of Patients with Acute Myocardial Infarction, published in 1990, recommended intravenous heparin administration together or immediately after thrombolytic therapy to maintain the activated partial thromboplastin time approximately 1.5 to 2.0 times the control value for 24 to 72 hours. Over the past five years, with the proven benefits or thrombolytic therapy and antiplatelet therapy, investigators have been in search of the ideal thrombolytic agent as well as the best adjunctive antithrombotic strategy. We review a number of angiographic patency trials as well as the major thrombolytic mortality reduction trials in which adjunctive heparin therapy was directly assessed. These trials established the need for intravenous heparin administration with tissue plasminogen activator, but, on the other hand, do not substantiate the need for either subcutaneous or intravenous heparin use with streptokinase. New data from a large scale trial emphasizes the importance of maintaining the aPTT in the 55-70 second range to prevent bleeding complications and optimize clinical outcomes.

Contemporary use of and future roles for heparin in antithrombotic therapy

Although heparin therapy is an established component of the prevention and treatment of thromboembolic disease, recent advances have resulted in improvements in the clinical use of this agent. Studies have shown that weight-based dosing influences significantly both the time to reach a therapeutic intensity of anticoagulation and the incidence of thromboembolic recurrence. It is now considered the standard of care. A growing understanding of the variability among activated partial thromboplastin time (aPTT) reagents and the influence of these differences on aPTT outcomes has led to the use of reagent-specific therapeutic ranges for heparin monitoring. Many practitioners now choose to adjust the therapeutic range to correspond to heparin serum concentrations of 0.2-0.4 U/mL rather than the more common practice of prolonging aPTT to 1.5-2.5 times the mean normal aPTT. Pharmaceutical companies have developed low molecular weight heparins to minimize adverse effects associated with unfractionated heparin. More specific thrombin inhibitors are also under investigation with the aim of improving clinical outcomes in coronary syndromes now treated with heparin. Low molecular weight heparins or specific thrombin inhibitors are unlikely to replace unfractionated heparin in the near future. Therefore, optimum dosing and appropriate monitoring of heparin are critically important in the management of thromboembolic disease.

Antithrombotic therapy for acute myocardial infarction

Antithrombotic therapy is clearly beneficial in the treatment of acute myocardial infarction, but the optimal regimen is controversial. Treatment with aspirin leads to substantial and significant reductions in rates of mortality, reinfarction and stroke in patients with acute myocardial infarction, and the benefits are additive with those of thrombolytic therapy. It is unclear whether heparin confers additional net benefits over aspirin alone. In patients receiving aspirin and thrombolytic therapy, there is no mortality benefit from adding delayed subcutaneous heparin, no consistent patency benefit from adding immediate intravenous heparin and no reduction in mortality from adding immediate intravenous heparin, at least for patients treated with streptokinase. However, heparin is consistently associated with increased rates of intracranial and other serious bleeding events when used with both aspirin and thrombolytic therapy. Existing data support the need for further large-scale trials of current and newer antithrombotic regimens in acute myocardial infarction to assess the balance of benefits and risks of these regimens compared with that for aspirin alone. In patients not receiving thrombolytic therapy, randomized trial data are currently insufficient to adequately compare the benefits and risks of adding heparin to aspirin alone. The First American Study of Infarct Survival (ASIS-1) will directly compare the balance of risks and benefits of aspirin alone, aspirin plus intravenous heparin and aspirin plus intravenous hirudin in patients with acute myocardial infarction not receiving thrombolytic therapy.

Drug interactions with thrombolytic agents. Current perspectives

Thrombolytic agents are widely used for the treatment of acute thromboembolic diseases, especially acute myocardial infarction (AMI). These compounds include streptokinase, anistreplase, alteplase, urokinase and, although not commercially available yet, saruplase (prourokinase). The therapeutic window of these compounds is relatively small and subtherapeutic or toxic plasma concentrations may have serious clinical implications (insufficient thrombolysis, reocclusion and bleeding). Among the factors that affect the pharmacokinetics and pharmacodynamics of thrombolytic agents, comedication is especially relevant since these drug interactions are partly predictable and sometimes preventable. Based on knowledge of the pharmacology of thrombolytic agents and general mechanisms by which pharmacokinetic drug interactions occur, interactions with alteplase and saruplase are expected. The clearance of alteplase is dependent on hepatic blood flow (HBF), and scientific evidence is emerging that saruplase is also a high-clearance compound. Each pharmacological agent that alters HBF and is given concurrently with one of these agents can change the plasma concentrations of those thrombolytics. Although there are no published data confirming drug-induced changes in the metabolism of alteplase or saruplase by this mechanism in humans, indirect supportive evidence (clinical observations and animal experiments) is available. An overview is presented of the anticipated effects of compounds that are frequently coadministered with thrombolytic agents on the pharmacokinetics of the thrombolytics with high-clearance properties. Since the clearance of these thrombolytics may be strongly affected by hypoperfusion of the liver as a result of cardiogenic haemodynamic failure, the role of circulatory changes in potential drug-drug interactions is also discussed. Pharmacodynamic drug interactions are highly relevant in the treatment of acute thrombotic lesions and are still being evaluated to further optimise treatment strategies. As most of these treatments exist as combinations of thrombolytic, antithrombin and antiplatelet compounds, beneficial effects are partly offset by bleeding complications. Changes in the pharmacokinetics and/or pharmacodynamics of thrombolytic agents may have serious consequences. It becomes imperative for the practising physician to be aware of benefits and risks of interactions with thrombolytic agents and especially of the fact that the principal way by which the pharmacokinetics of alteplase and, presumably, saruplase can be affected is by drug- and/or haemodynamic failure-induced changes of HBF.

Failure of fixed dose intravenous heparin to suppress increases in thrombin activity after coronary thrombolysis with streptokinase

OBJECTIVES

This study was designed to define the extent of inhibition of thrombin activity achieved with conjunctive fixed dose intravenous sodium heparin compared with fixed dose subcutaneous calcium heparin in patients receiving intravenous streptokinase for acute myocardial infarction.

BACKGROUND

The role of heparin therapy during coronary thrombolysis with streptokinase is controversial, in part because the efficacy of different conjunctive heparin regimens in inhibiting early increases of thrombin activity is not known.

METHODS

Twenty-eight patients treated with 1.5 million U of streptokinase and 165 mg of aspirin for acute myocardial infarction were randomly assigned to receive fixed dose subcutaneous heparin therapy (12,500 U every 12 h delayed until 4 h after the end of streptokinase therapy [n = 14]) or fixed dose intravenous heparin (5,000-U bolus followed by 1,000-U/h infusion [n = 14]). Anticoagulation was assessed with serial measurements of activated partial thromboplastin time, and thrombin activity by measuring fibrinopeptide A and thrombin-antithrombin III complex levels. Plasma concentrations of creatine kinase (CK) MM isoforms were measured for 3 h to determine recanalization (increase in activity > 0.18%/min).

RESULTS

Recanalization occurred in 27%, 64% and 79% of patients given subcutaneous heparin versus 43%, 76% and 86% of those given intravenous heparin at 1, 2 and 3 h, respectively (p = 0.6). Concentrations of fibrinopeptide A (mean +/- SEM) at 1 h were higher in patients without (n = 5) than in those with (n = 23) CK-MM isoform criteria for recanalization (76.4 +/- 25.7 vs. 25.2 +/- 5.2 nmol/liter, p = 0.02), and at 1, 2 and 3 h were significantly lower with fixed dose intravenous heparin (18.4 +/- 4.8 vs. 46.7 +/- 10.2 nmol/liter at 1 h, p = 0.004) than without heparin. After fixed dose subcutaneous heparin at 4 h, fibrinopeptide A levels were similar in both groups despite lower activated partial thromboplastin times in patients who received fixed dose subcutaneous heparin. However, fibrinopeptide A was not consistently suppressed in either group (fixed dose subcutaneous heparin 8.7 +/- 1.8 nmol/liter vs. fixed dose intravenous heparin 11.8 +/- 5.2 nmol/liter) at 48 h (p = 0.4). No significant changes in the concentration of thrombin-antithrombin III complexes were found between the two groups.

CONCLUSIONS

Fixed dose intravenous heparin attenuates increases in fibrinopeptide A early after streptokinase. Subsequent fixed dose intravenous and subcutaneous heparin have similar effects but are relatively ineffective in suppressing thrombin activity, suggesting a role for more potent antithrombin agents during coronary thrombolysis with streptokinase.