Heparin

Recombinant hirudin: a specific thrombin inhibiting anticoagulant for hemodialysis

The first experience with hirudin as an alternative anticoagulant for heparin in hemodialysis is reported. Recombinant hirudin (HBW 023) was administered in 20 patients as a bolus before dialysis with low flux polysulfone dialyzers (PS400), the dosage being adapted stepwise from patient to patient by 0.02 mg/kg to the occurrence of clotting or bleeding. Four different administration schedules were studied. The first three schedules (0.02 mg/kg, N = 1; 0.04 mg/kg, N = 1; 0.06 mg/kg, N = 4) were discontinued because of clotting. The 0.08 mg/kg schedule was maintained without clotting event in 14 patients. Bleeding was not observed. Plasma hirudin averaged 503.9 +/- 214.0 and 527.7 +/- 217.1 ng/ml after two and four hours of dialysis, and decreased during an interdialytic interval of 44 hours to 223.2 +/- 86.2 ng/ml. Modified antithrombin III (P < 0.05) and activated partial thromboplastin times were lower (P < 0.01) under hirudin compared to heparin; these coagulation parameters were closer to normal during hirudin treatment. The patients developing clotting could be distinguished from those without clotting by the registration of the activated clotting times (9.2 +/- 3.0 vs. 18.7 +/- 3.2 min after 2 hr, P < 0.01; 8.1 +/- 3.0 vs. 16.2 +/- 3.8 min after 4 hr of dialysis, P < 0.05); cut-off value below which clotting is to be expected was 12 min). It is concluded that administration of hirudin as a bolus before the start of dialysis, at a dosage of 0.08 mg/kg, is not complicated by clotting or by bleeding. Coagulation tendency can optimally be monitored by the registration of the activated clotting time.(ABSTRACT TRUNCATED AT 250 WORDS)

A pilot trial of recombinant desulfatohirudin compared with heparin in conjunction with tissue-type plasminogen activator and aspirin for acute myocardial infarction: results of the Thrombolysis in Myocardial Infarction (TIMI) 5 trial

OBJECTIVES

The purpose of this study was to assess the value of recombinant desulfatohirudin (hirudin) as adjunctive therapy to thrombolysis in acute myocardial infarction.

BACKGROUND

Failure to achieve initial reperfusion and reocclusion of the infarct-related artery remain major limitations of thrombolytic therapy despite aggressive regimens of heparin and aspirin. Hirudin, a direct thrombin inhibitor, has been shown in experimental models to enhance thrombolysis and reduce reocclusion.

METHODS

The Thrombolysis in Myocardial Infarction (TIMI) 5 trial was a randomized, dose-ranging, pilot trial of hirudin versus heparin, given with front-loaded tissue-type plasminogen activator and aspirin to 246 patients with acute myocardial infarction. Patients received either intravenous heparin or hirudin at one of four ascending doses for 5 days. Patients underwent coronary angiography at 90 min and at 18 to 36 h, unless rescue angioplasty was performed.

RESULTS

The primary end point, TIMI grade 3 flow in the infarct-related artery at 90 min and 18 to 36 h without death or reinfarction before the 18- to 36-h catheterization was achieved in 97 (61.8%) of 157 evaluable hirudin-treated patients compared with 39 (49.4%) of 79 evaluable heparin-treated patients (p = 0.07). All four doses of hirudin led to similar findings in the angiographic and clinical end points. At 90 min, TIMI grade 3 flow was present in 105 (64.8%) of 162 hirudin-treated patients compared with 48 (57.1%) of 84 heparin-treated patients (p = NS). Infarct-related artery patency (TIMI grade 2 or 3 flow) was similar in the two groups (82.1% and 78.6%, respectively). At 18 to 36 h, 129 (97.8%) of 132 hirudin-treated patients had a patent infarct-related artery compared with 58 (89.2%) of 65 heparin-treated patients (p = 0.01). Reocclusion by 18 to 36 h occurred in 2 (1.6%) of 123 hirudin-treated patients versus 4 (6.7%) of 60 heparin-treated patients (p = 0.07). Death or reinfarction occurred during the hospital period in 11 (6.8%) of 162 hirudin-treated patients compared with 14 (16.7%) of 84 heparin-treated patients (p = 0.02). Major spontaneous hemorrhage occurred in 1.2% of hirudin-treated patients versus 4.7% of heparin-treated patients (p = 0.09), and major hemorrhage at an instrumented site occurred in 16.3% and 18.6%, respectively (p = NS).

CONCLUSIONS

Hirudin is a promising agent compared with heparin as adjunctive therapy with thrombolysis for acute myocardial infarction, and its evaluation in larger trials is warranted.

Hirudin: clinical potential of a thrombin inhibitor

Hirudin is the most potent and specific known inhibitor of thrombin, the enzyme that plays a key regulatory function in hemostasis and blood coagulation. The importance of thrombosis in cardiovascular disease has recently highlighted the limitations of existing antithrombotic drugs and the potential value of direct thrombin inhibition as an effective approach to antithrombotic therapy. Hirudin and a small peptidomimetic analog--hirulog--are being developed as alternatives to heparin for the treatment of unstable angina, for prevention of abrupt closure and restenosis following coronary angioplasty, for prevention of deep vein thrombosis after major orthopedic surgery, and as an adjunct to fibrinolytic therapy. Direct thrombin inhibitors have several potential advantages over heparin: They can inhibit thrombin bound to clots or extracellular matrices, which are relatively resistant to heparin; they do not require antithrombin III as a cofactor, which may lead to a more predictable dose response; and they are not inhibited by activated platelets, which release platelet factor 4 and other molecules that neutralize heparin. The results of early clinical studies suggest that hirudin and hirulog may be more efficacious and more predictable and may have fewer bleeding complications than heparin for several clinical indications.

Cerebrovascular lesions in infants and children dying after extracorporeal membrane oxygenation

The neuropathologic autopsy findings of a group of infants and children at Children's Hospital of Pittsburgh who died after treatment with extracorporeal membrane oxygenation (ECMO) were reviewed and tabulated. The study surveyed an 11-year period (February, 1980 to May, 1991); of 268 children receiving ECMO therapy for severe cardiopulmonary failure, 94 patients died, 70 of whom were autopsied and permission for brain examination was granted in only 44. The frequency of ischemic neuronal necrosis (50%), focal cerebral infarcts (50%), intracerebral hemorrhages (52%), and periventricular leukomalacia (41%) was higher in this group of ECMO-treated patients than that observed in the general autopsy population from which the study patients were selected. The frequency of ischemic and hemorrhagic brain lesions was similar among neonates and older infants and children. This documentation of cerebrovascular lesions in children dying after ECMO may provide a better understanding of potential brain damage in the larger population of infants and children who survive this invasive procedure.

Treatment of thromboembolic complications in patients with brain tumors

Thromboembolic disease is common in patients with malignant brain tumors and represents a major cause of morbidity and mortality in these patients. The presenting signs and symptoms of deep venous thrombosis and pulmonary emboli can be subtle; thus, a high index of suspicion is required to ensure a timely diagnosis. The accuracy of non-invasive studies of the lower extremities and lungs have significant limitations. Venography and pulmonary angiography remain the best diagnostic techniques when difficult decisions arise regarding the need for anticoagulants in these patients. Patients with malignant brain tumors can be safely anticoagulated with heparin and warfarin, if these agents are monitored carefully. Continuous intravenous infusions of heparin are associated with lower risks of bleeding than intermittent boluses. Clinicians may wish to modify the recommended initial bolus dose of heparin in patients without life-threatening thromboembolic disease. Warfarin reduces the incidence of recurrent thromboembolic events. The incidence of warfarin-related bleeding can be lowered without compromising efficacy by maintaining the PT ratio at 1.3. Potential warfarin drug interactions must be considered, aspirin containing medications and NSAIDS should be avoided, and the platelet count should be kept above 50,000 using transfusions if required to prevent potentially life-threatening bleeding in anticoagulated patients. Thrombolytics are contraindicated in this patient population. Vena caval filters and thrombectomy are rarely required. Additional research is needed to determine the best techniques to prevent deep venous thrombosis and pulmonary embolism in patients with brain tumors.

Effects of thermal exposure on binding of heparin in vitro to the arterial wall and to clot and on the chronic angiographic luminal response to local application of a heparin film during angioplasty in an in vivo rabbit model

Experimentally, heparin inhibits mechanisms that promote fibrosis, neointimal cellular proliferation, and thrombin bound to fibrin at the surface of intraluminal thrombus, but only in relatively high concentrations. A preliminary hypothesis was tested and confirmed in vitro that initial binding of 3H-heparin to mechanically injured porcine aorta is concentration-dependent over a 1,000-50,000 units/ml range (r = 0.9). The hypothesis was then tested in vitro that thermal exposure during contact of heparin to arterial tissue and to clot would enhance binding of the drug. 3H-heparin binding to clot, whole blood particulates, and washed erythrocytes was markedly enhanced by exposure to temperatures > 70 degrees C. Thermal exposure (80 degrees C x 40 s) also enhanced tissue persistence of the drug within porcine aorta subjected to a shear rate of 1,100(-1) in an annular Baumgartner chamber perfused with normal saline at 37 degrees C for 48 h. Heparin in vitro anticoagulant activity persisted after thermal exposure and binding to tissues. A new method was developed for local application of a heparin film that provides a maximum concentration with a tolerable systemic dose during an angioplasty procedure. In an in vivo rabbit model of mural fibrosis after iliac artery angioplasty, the 1-month mean angiographic luminal diameter loss (23% compared to the acute postangioplasty result by computer image analysis) in response to conventional balloon angioplasty (BA) and laser balloon angioplasty (LBA) was the same (P > 0.05). Local application of a heparin film (3,000 units at a concentration > 100,000 units/g), however, reduced the mean % loss in diameter 1 month after LBA (12%), but not after BA (29%), compared to arteries subjected to angioplasty without local heparin (P < .05). The results are consistent with the hypothesis that thermal energy enhances heparin binding to tissues and that local application of a heparin film favorably modulates arterial luminal responses to LBA, but not to BA, in this animal model.

History of drugs for thrombotic disease. Discovery, development, and directions for the future

The history of the antithrombotic agents--aspirin, heparin, warfarin, and the thrombolytics--is a rich and lively odyssey of serendipity, perseverance, vision, and conflict involving a number of striking personalities. The history of aspirin spans ages and continents from Hippocrates' analgesic for women in labor to the rediscovery of the white willow bark by English country scholar Reverend Edward Stone. Bayer chemist Felix Hoffmann reinvented aspirin for his ailing father; suburban physician L.L. Craven pioneered the prophylactic antithrombotic uses of aspirin; and Sir John Vane elucidated aspirin's mechanism of action as the inhibition of prostaglandin synthetase. Heparin was discovered by McLean, working as a medical student in 1915 in search of a pure procoagulant in dog liver. His original impure material differed somewhat from today's heparin, but purified heparin was rapidly accepted for a myriad of clinical uses; to this day, diverse new properties of this complex glycosaminoglycan continue to be elucidated. The oral anticoagulants emerged from veterinary research in the 1920s on a hemorrhagic disorder afflicting cattle that consumed spoiled sweet clover hay. Several chance encounters led Karl Link and his University of Wisconsin team to the identification of dicumarol as the offending agent in 1939 and its widespread therapeutic use by Wright and others in the 1940s. Link later developed warfarin as a rodenticide, but its use in humans soon followed in the 1950s. Vitamin K was discovered in the 1930s; its involvement in the mechanism of the anticoagulant agents was not delineated until the 1970s. The intrinsic ability of clotted blood to liquify and the fibrinolytic properties of normal urine were noted in the 1800s. Tillett and Sherry's group stumbled on the fibrinolytic properties of streptokinase in the 1930s and pioneered the therapeutic use of streptokinase in the 1940s and of urokinase in the 1960s. Several teams found tissue-type plasminogen activator in various body sites beginning in the 1940s, leading to its cloning and widespread use in the 1980s; anisoylated plasminogen-streptokinase activator complex is an example of rational drug design. The discoverers of these diverse agents have not only provided physicians with a potent armamentarium of antithrombotic drugs but also helped elucidate much basic science and vividly demonstrated the merits of perseverance, independent thought, and adherance to the scientific method.

von Willebrand factor, endothelial cell damage and atherosclerosis

von Willebrand factor (vWf) is an interesting and potentially important molecule whose biology in health and disease warrants attention. A growing body of knowledge now suggests that plasma levels of this specific product of the endothelial cell may have potential as a marker for the assessment of endothelial injury in vivo. As its functions include platelet aggregation and mediation of platelet adhesion to the subendothelium, it may also have a role in the pathogenesis of progression of atherosclerosis. In comparison to asymptomatic controls, increased levels of vWf are found in atherosclerotic vascular disease and in the presence of several of its major risk factors (smoking, hypercholesterolaemia, hypertension, obesity and diabetes). High plasma levels of vWf are also associated with the prediction of adverse clinical events such as myocardial infarction and poor outcome following arterial surgery, possibly by the promotion of thrombus formation. These and other studies indicate that research directed towards determining whether therapy to reduce levels of vWf also influences the progression of arterial disease should prove to be profitable.

Heparin: a review of its pharmacology and therapeutic use in horses

Heparin is used clinically in horses to treat hemostatic abnormalities associated with severe gastrointestinal disease, septicemia, and endotoxemia. The primary anticoagulant effect of heparin is through the suppression of thrombin-dependent amplification of the coagulation cascade, and inhibition of thrombin-mediated conversion of fibrinogen to fibrin. Heparin may be of benefit in preventing the complications associated with hypercoagulable states such as jugular vein thrombosis, laminitis, and organ failure. Heparin may also be beneficial in the prevention of intraabdominal adhesions after gastrointestinal surgery, and in amelioration of hemodynamic abnormalities associated with endotoxic shock. Because a sequential rise in serum heparin concentration occurs during a uniform dosage regimen, a decreasing dosage regimen is recommended. The initial dose recommended is 150 U heparin/kg body weight subcutaneously, followed by 125 U heparin/kg body weight subcutaneously, every 12 hours for six doses. The dose should be decreased to 100 U heparin/kg body weight subcutaneously, every 12 hours, after the seventh dose. Anemia, hemorrhage, thrombocytopenia, and painful swelling at injection sites are complications of heparin administration in horses.

Maximizing benefits of therapies in acute myocardial infarction

Major advances in the management of acute myocardial infarction have been achieved by a combination of careful experimental work and development of effective pharmacologic and interventional strategies in conjunction with the conduct of large, reliable randomized trials. Current trials indicate that a combination of thrombolytic therapy, aspirin, and intravenous followed by oral beta blockers reduces mortality. There are a number of additional promising interventions, such as intravenous magnesium, nitrates, and the newer antithrombin agents. However, before these agents are used widely in clinical practice, clear proof of benefit and adequate safety should be available from the ongoing randomized trials. Following discharge from the hospital, long-term therapy with aspirin and beta blockers should be considered in all patients. In patients with heart failure and low ejection fraction, angiotensin-converting enzyme (ACE) inhibitors have been shown to reduce mortality, reinfarction, and the need for further hospitalizations for heart failure. Therefore, these therapies, in conjunction with risk factor modification (cessation of cigarette smoking, treatment of hypercholesterolemia, treatment of hypertension), should be considered in all appropriate patients. A number of new strategies for the prevention of atherosclerosis and its complications are currently being evaluated in prospective randomized trials. These include the natural antioxidant vitamins, estrogen replacement therapy, tamoxifen therapy, and ACE inhibitors in patients without evidence of heart failure or left ventricular dysfunction.

Suppression by intradermal administration of heparin of eosinophil accumulation but not oedema formation in inflammatory reactions in guinea-pig skin

1. Heparin is widely used in the treatment of thrombotic disorders and as an aid in surgery. Anti-inflammatory effects of heparin have also been described. In this study, we have investigated the effects of locally-injected heparin on the oedema formation and eosinophil accumulation induced by various inflammatory stimuli in guinea-pig skin. 2. Heparin dose-dependently suppressed the accumulation of 111In-labelled eosinophils induced by i.d. injection of zymosan-activated plasma (ZAP). The 111In-eosinophil accumulation induced by other inflammatory stimuli (compound 48/80, platelet activating factor, interleukin-8 and in a passive cutaneous anaphylaxis reaction) was also suppressed by locally-injected heparin. 3. Oedema formation in response to these same stimuli was not altered by the local injection of heparin. 4. Fucoidin, a negatively-charged sulphated algal polymer, had no effect on the 111In-eosinophil accumulation or oedema formation induced by ZAP. Nevertheless, fucoidin significantly suppressed the oedema formation induced by i.d. injection of cationic protein-containing extracts of Schistosoma mansoni larvae. Heparin also inhibited oedema induced by the extracts, suggesting that both fucoidin and heparin were effectively neutralizing the cationic protein of the extracts to inhibit their oedema-inducing activity. 5. Thus, heparin significantly inhibited the accumulation of 111In-eosinophils, but not oedema formation, induced by various inflammatory stimuli. This, taken together with the lack of effect of fucoidin, suggests that heparin interferes with the process of eosinophil trafficking by a mechanism that does not depend on neutralisation of the charge of the stimulatory molecules.

Heparins modulate extracellular matrix and protein synthesis of cultured rat mesangial cells

Heparins blunt the development of glomerulosclerosis in several disease models in the rat and this protective effect may be related to suppression of glomerular cell proliferation. In this study the direct effect of heparins on another key event in glomerulosclerosis, extracellular matrix (ECM) deposition, was examined. Standard heparin (hep) and non-anticoagulant N-desulfated acetylated heparin (DSA-hep) significantly reduced the fibronectin content in the conditioned media of subconfluent, confluent, and supraconfluent rat glomerular mesangial cells (MCs) in culture, as assessed by a sandwich ELISA technique. Both heparins significantly increased the amount of cell-associated fibronectin in sparse and subconfluent MCs. DSA-hep, but not hep, increased the fibronectin content of ECM formed by confluent and supraconfluent MCs. Using 3H-proline pulse-labeling, Hep and DSA-hep were found to significantly decrease cell-associated collagen in subconfluent but not in confluent MCs. No effects were seen on newly synthesized collagen secreted into the culture medium. Neither hep nor DSA-hep affected total protein synthesis, studied by metabolic labeling with 35S-methionine. High resolution 2-D electrophoresis (molecular weight range, 120 to 10 Kd; isoelectric interval, 5.0 to 7.0) revealed one particular intracellular protein (molecular weight 54 Kd, pI 5.91) which was consistently overexpressed in hep. Both heparins affected an identical set of another 19 different intracellular MC proteins (over-/underexpression or shift to higher molecular weights). In conclusion, the present data demonstrate the profound direct metabolic effects of hep and DSA-hep.(ABSTRACT TRUNCATED AT 250 WORDS)

Complications from heparin-induced thrombocytopenia in patients undergoing cardiopulmonary bypass

The purpose of this study was to evaluate retrospectively the incidence and severity of heparin-induced thrombocytopenia (HIT)-related complications in patients undergoing cardiopulmonary bypass. We reviewed the records of 1,500 consecutive patients who underwent cardiopulmonary bypass between August 1987 and December 1991 at Thomas Jefferson University Hospital. During this period of time, there were 1,155 coronary artery bypass graft operations (77 percent); 225 valve replacements and repairs, or both (15 percent); 60 combination coronary artery bypass graft or valve operations, or both (4 percent); and 60 miscellaneous procedures (4 percent). Although not all patients with postoperative complications were tested for the HIT antibody, 11 patients (0.75 percent) were diagnosed with HIT. There were 17 complications in these 5 men and 6 women including 6 cases of ischemic limbs which required amputation, 4 strokes, 2 instances of saphenous vein graft occlusion with resulting myocardial infarction, 2 cases of pulmonary emboli, 1 case of phlegmasia cerulea dolens, and 2 deaths. The complications occurred an average of 3.6 days postoperatively, with a range of occurrence of 1 to 11 days postoperatively. The mean nadir platelet count at the time of recognition was 123,000/mm3 (range 32,000 to 193,000/mm3) with 9 of 11 patients (81.8 percent) having counts greater than 100,000/mm3. There was, however, a mean percent decrease in the platelet count of 50 percent (range, 31 to 75 percent) from the time of first exposure to heparin to the time of recognition of HIT. In our patients, HIT was not related to the type, duration of treatment with or amount of heparin, or to pretreatment with aspirin.

Different effects of two methods of low-density lipoprotein apheresis on the coagulation and fibrinolytic systems

OBJECTIVE

Immunoadsorption (IMA) and dextran sulfate adsorption (DSA) are two methods for selective extracorporeal elimination of low-density lipoproteins which are known as LDL apheresis. Their influence on haemostasis until now is widely unknown.

DESIGN

The effects of both LDL apheresis procedures on the coagulation and fibrinolytic systems were compared amongst five patients treated with IMA and four patients who received a DSA therapy.

SUBJECTS

All patients with severe heterozygous familial hypercholesterolaemia were participants in a long-term LDL apheresis programme with treatments every 1-2 weeks.

INTERVENTION

Combined anticoagulation with heparin and citrate in IMA, and also heparin exclusively in DSA were used for the extracorporeal circulation.

MEASURES

Blood samples were taken immediately before and after a single LDL apheresis and five times during the weekly interval until the next therapy.

RESULTS

DSA had a significantly greater effect on standard clotting tests than IMA at the end of plasma therapy despite identical dosages of heparin. DSA caused a considerable reduction of the coagulation factors V, VIII:C, vWF:Ag, XI, XII, and prekallikrein by 48-99% at the end of apheresis treatment whereas only factor VIII:C showed a marked decrease of 72% after IMA. All abnormalities of the global coagulation tests and of most clotting factors were restored 1 day after treatment in both procedures followed by a moderate rebound phenomenon of single coagulation factors during the next few days in IMA-treated patients.

CONCLUSION

DSA exerts a more profound effect on the coagulation system than IMA by a substantial co-elimination of various clotting factors in addition to the desired removal of atherogenic lipoproteins.

Aspirin versus heparin to prevent myocardial infarction during the acute phase of unstable angina

BACKGROUND

Antiplatelet therapy with aspirin and antithrombotic therapy with heparin both prevent the complications of unstable angina; however, no definitive data exist on the relative clinical efficacy of the two drugs.

METHODS AND RESULTS

Aspirin (325 mg bid) or heparin (5000-U intravenous bolus followed by a perfusion titrated to the APTT) were compared in a double-blind randomized trial of 484 patients in two cohorts enrolled sequentially. The study was initiated at admission to hospital at a mean of 8.3 +/- 7.8 hours after the last episode of pain. End points were assessed 5.7 +/- 3.3 days later, when the decision for long-term management was made. Myocardial infarction occurred in 2 (0.8%) of the 240 patients randomized to heparin and in 9 (3.7%) of the 244 randomized to aspirin (P = .035), an odds ratio of 0.22 and a risk difference of 2.9% (95% confidence limits, 0.3% to 5.6%) with heparin. The only death resulted from a myocardial infarction in an aspirin patient. Survival curves with Cox logistic regression analysis showed that the improvement in survival without myocardial infarction with heparin (P = .035) was independent of other baseline characteristics.

CONCLUSIONS

This study documents that heparin prevents myocardial infarction better than aspirin during the acute phase of unstable angina.

Subcutaneous heparin in postangioplasty management: comparative trial with intravenous heparin

Abrupt closure of a coronary artery after successful angioplasty remains a problem for the interventionalist. Many laboratories continue to administer heparin intravenously for 12 to 24 hours in an attempt to alleviate this problem. But prolonged heparin therapy delays sheath removal and may lead to groin and vascular complications, and so prolong the hospital stay. To test the hypothesis that subcutaneous heparin was as efficacious as intravenous heparin in preventing acute closure while reducing the vascular complications associated with extended sheath placement, we prospectively randomized 151 patients to two groups. The intravenous group, 77 patients, received continuous intravenous heparin at 1000 units/hour for 12 to 18 hours; the subcutaneous group, 74 patients, received 12,500 units subcutaneously every 12 hours for three doses after sheath removal 2 to 3 hours after the angioplasty. The activated clotting time immediately after the angioplasty was 401 +/- 108 seconds in subcutaneous group, as compared with 368 +/- 67 seconds in the intravenous group (p = 0.028). Patients receiving subcutaneous heparin continued to show adequate anticoagulation, with a PTT of 85 +/- 21 seconds obtained approximately 12 hours after the procedure. The PTT at discharge was statistically greater in the subcutaneous group, at 49.2 +/- 21 seconds, versus 35.6 +/- 13 seconds in the intravenous group (p < 0.001). Abrupt occlusion was similar in both groups, but the hematomas and bleeding/oozing in the intravenous group was significantly higher when compared with that of the subcutaneous group, 16 versus 6 (p = 0.026) and 26 versus 7 (p < or = 0.002), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Phase I--study with aprosulate, a new synthetic anticoagulant

This paper describes the first human study with aprosulate, a new chemically synthesized anticoagulant with a defined molecular structure and a molecular weight of 2388. Twelve healthy male volunteers received subcutaneous injections of placebo on the first day followed by ascending doses of aprosulate in the range of 0.25 mg/kg to 2.0 mg/kg body weight on alternate days. Anticoagulant, pharmacokinetic and safety parameters were assessed for 48 hours after each injection. The activated partial thromboplastin time and the Heptest showed a dose-dependent increase for up to ten hours after each application. A trend towards prolongation of the bleeding time was indicated with higher doses. In general, the tolerance was good. Plasma transaminase concentrations were raised in some volunteers but returned spontaneously to normal during or after the study.

Antithrombin-III plasma activity during and after prolonged use of heparin in unstable angina

Heparin effectively prevents the complications of unstable angina but disease reactivation has been documented following its discontinuation. To investigate whether this could be related to antithrombin-III depletion, 50 patients with unstable angina had serial determinations of activated partial thromboplastin time and of the plasma levels of heparin, antithrombin-III activity and of the thrombin-antithrombin-III complex before, during and, in a subgroup of 8 patients, 4 hours after heparin discontinuation. Heparin was administered intravenously at therapeutic doses for a mean of 7.6 +/- 4.1 days. Plasma antithrombin-III activity decreased rapidly from 1.05 +/- 0.03 to 1.0 +/- 0.03 U/ml (p < 0.03) following heparin initiation with no further significant subsequent decrease. Antithrombin-III activity returned to the control values 4 hours after the discontinuation of heparin. Thus, heparin treatment is associated with small, non-cumulative and rapidly reversible decrease in antithrombin-III activity. Reactivation of unstable angina after discontinuation of heparin must be explained by a mechanism other than antithrombin-III deficiency.

Intravenous heparin dosing: patterns and variations in internists' practices

OBJECTIVE

To characterize internists' dosing practices when administering and adjusting intravenous heparin regimens.

DESIGN

A survey administered by physician-investigators.

SETTING

Two community teaching hospitals and one Veterans Affairs Medical Center.

SUBJECTS

Sixty-one attending physicians in internal medicine.

MEASUREMENTS

Physicians' choices of therapeutic activated partial thromboplastin time (APTT) range, initial heparin bolus, initial infusion dose, and dose/infusion adjustments when APTT levels are < 1.2 x control (< 35 seconds), 1.2-1.5 x control (35-45 seconds), 1.5-2.3 x control (46-70 seconds), 2.3-3.0 x control (71-90 seconds), and > 3.0 x control (> 90 seconds).

RESULTS

Physicians' dosing decisions and therapeutic ranges during heparin treatment varied widely. Responses to nontherapeutic APTT levels had especially high coefficients of variation (0.67-0.81). Two groups of physicians, together comprising a majority of all respondents, use mutually exclusive therapeutic ranges (mean 44-56 seconds and 60-83 seconds). These two groups differ significantly in several types of dosing decisions.

CONCLUSION

In the absence of generalizable standard guidelines for intravenous heparin therapy, internists' dosing practices vary widely. Because such practices may impede timely, effective anticoagulation, experimental studies comparing standardized dosing protocols are needed.

Initial experience with a direct antithrombin, Hirulog, in unstable angina. Anticoagulant, antithrombotic, and clinical effects

BACKGROUND

Currently available antithrombotic therapy for unstable angina is unwieldy and occasionally ineffective. This study was designed to investigate the potential of Hirulog, a new synthetic specific antithrombin agent, for the management of this condition.

METHODS AND RESULTS

A total of 55 patients in the acute phase of unstable angina received intravenous Hirulog according to one of two protocols. In an acute dose-escalating study, 0.02, 0.05, 0.1, 0.25, and 0.5 mg.kg-1 x h-1, each for 30 minutes, were infused in 15 patients. Prolongation of activated partial thromboplastin time (aPTT) (r = .95), fibrinopeptide A inhibition (r = .96), and Hirulog plasma levels (r = .91) correlated closely with the dose infused, with significant changes compared with baseline appearing at doses of 0.25 mg.kg-1 x h-1 and higher. The purposes of the second protocol were to determine whether the anticoagulant and antithrombotic effects of the drug were sustained during a 72-hour infusion and to assess whether such treatment prevented the complications of unstable angina. Based on the initial study, we planned to give a dose of 0.25 mg.kg-1 x h-1 to each patient until 2 patients failed therapy, then successively higher doses until a 95% success rate was achieved or adverse effects intervened, increasing the dose after two failures had occurred at each level. Five patients received the 0.25-mg.kg-1 x h-1 dose and 14 the 0.5-mg.kg-1 x h-1 dose before two failures occurred. Failure was observed in only one of 21 patients at the dose of 1 mg.kg-1 x h-1. aPTT (+/- SEM) levels increased to 62 +/- 5, 76 +/- 2, and 98 +/- 3 seconds at the three doses, with minimal intraindividual variation, and Hirulog plasma levels to 1050, 2100, and 4200 mg/mL, respectively. Fibrinopeptide A plasma levels decreased at all doses but more consistently at the dose of 1 mg.kg-1 x h-1. The overall clinical success rate was 87.5%: 60% (3/5) at the low dose, 86% (12/14) at the intermediate dose, and 95% (20/21) at the high dose. No deaths, myocardial infarctions, or bleeding complications occurred.

CONCLUSIONS

In unstable angina patients, Hirulog infusions quickly and reproducibly yield stable, dose-dependent anticoagulant and antithrombotic effects with a favorable clinical efficacy profile.

Anticoagulant-related bleeding: clinical epidemiology, prediction, and prevention

OBJECTIVE

To review (1) the clinical epidemiology of bleeding during anticoagulant therapy with heparin or warfarin, (2) data useful in estimating the risk for bleeding in individual patients, and (3) the efficacy of methods for its prevention.

METHODS

Relevant literature was identified by a computerized search of the Medline database and by review of the bibliographies of original and review articles. Studies were classified according to their design. Estimates of the risk for bleeding during anticoagulant therapy, compared with the risk without therapy, were obtained from randomized trials. Estimates of the frequency of bleeding during the course of anticoagulant therapy and information about risk factors for bleeding were obtained primarily from longitudinal studies of inception cohorts of patients followed from the start of therapy.

MAIN RESULTS

The average daily frequencies of fatal, major, and major or minor bleeding during heparin therapy were 0.05%, 0.8%, and 2.0%, respectively; these frequencies are approximately twice those expected without heparin therapy. The average annual frequencies of fatal, major, and major or minor bleeding during warfarin therapy were 0.6%, 3.0%, and 9.6%, respectively; these frequencies are approximately five times those expected without warfarin therapy. The risk for anticoagulant-related bleeding is highest at the start of therapy: during warfarin therapy, the risk for major bleeding during the first month of therapy is approximately 10 times the risk after the first year of therapy. An individual patient's risk for major anticoagulant-related bleeding can be estimated on the basis of specific risk factors such as the intensity of the anticoagulant effect achieved and the presence of serious comorbid diseases, especially cerebrovascular, kidney, heart, and liver disease; older age and concurrent medicines may also be independent risk factors. Major bleeding most often affects the gastrointestinal tract, soft tissues, and urinary tract. Diagnostic evaluation of gastrointestinal bleeding and gross hematuria leads to identification of previously unknown lesions in approximately one-third of cases, even when the prothrombin time is elevated. Intracranial bleeding is rare, but it is frequently fatal. The frequency of bleeding during warfarin therapy is reduced by less intense therapy achieving a prothrombin time with an International Normalized Ratio of 2.0 to 3.0, which is efficacious for most indications.

CONCLUSION

Anticoagulant-related bleeding is common and often serious. The risk for bleeding can be estimated in an individual patient, giving the primary physician a quantitative basis for weighing the risks and benefits of therapy and for optimizing patient management. The frequency of anticoagulant-related bleeding is reduced by less intense warfarin therapy. Future studies should evaluate new approaches to management that may further reduce complications while maintaining efficacy.

Anticoagulants in pregnancy

Pregnancy is associated with a prethrombotic state. Pulmonary embolism is the major cause of maternal mortality. Anticoagulant prophylaxis and therapy are therefore commonplace in pregnant women. Those with inherited and acquired thrombophilic conditions are at increased risk and special considerations arise in management. Heparin has recently become the favoured anticoagulant drug in pregnancy. Its use carries risks of osteopaenia and thrombocytopaenia, as well as haemorrhage, in the mother. Warfarin is teratogenic and may also cause haemorrhagic complications in mother and fetus. Few clinical trial data exists for guidance on optimal anticoagulant regimes during pregnancy and the puerperium and details of management will depend upon the personal preferences of patient and clinician, after due consideration of the perceived risks and benefits in the individual clinical situation.

Effect of intravenous nitroglycerin on heparin dosage requirements in coronary artery disease

Patients admitted to the coronary care unit who received both intravenous nitroglycerin and heparin were studied to evaluate heparin dosage requirements. Physicians ordered all nitroglycerin and heparin doses as well as coagulation studies without knowledge of this study. Activated partial thromboplastin time (APTT) values obtained during steady-state heparin administration were considered therapeutic if the ratio of APTT/APTT-baseline was > or = 1.5. Sixty patients with myocardial infarction or unstable angina were included in the study. The initial therapeutic heparin dose of 1,014 +/- 151 units/hour produced an APTT ratio of 2.0 +/- 0.5. At the time of the initial therapeutic dose, the nitroglycerin dose was 110 +/- 108 micrograms/min. There was a significant correlation between the initial therapeutic dose and both total (r = 0.56; p = 0.0001) and lean (r = 0.26; p < 0.05) body weight. Comparison of patients with nitroglycerin doses < and > or = 100 micrograms/min revealed a significant difference in the initial therapeutic dose (971 +/- 147 vs 1,077 +/- 136 U/hour, p < 0.01), but not the initial therapeutic dose standardized to total body weight (14.0 +/- 2.5 vs 13.5 +/- 2.7 U/kg/hour). Similarly, analysis of variance revealed a significant difference in the initial therapeutic dose (p < 0.05), but not the initial therapeutic dose standardized to weight among 5 different nitroglycerin dosage ranges (10 to 533 micrograms/min). Neither aspirin use, thrombolytic therapy nor decreasing or discontinuing the nitroglycerin dose significantly affected heparin requirements. Thus, contrary to prior reports, clinically significant heparin resistance induced by nitroglycerin was not found.

Comparison of efficacy of low molecular weight heparin (parnaparin) with that of unfractionated heparin in the presence of activated platelets in healthy subjects

Arterial thrombosis is typically platelet-rich. In this study, it is shown that heparin levels resulting in the usual activated partial thromboplastin time therapeutic range provide only a small anticoagulant effect in the presence of activated platelets. Thrombin inhibition is also negligible when heparin is added to platelet-rich plasma. Aspirin improves the anticoagulant effect of heparin in these circumstances, but the degree of anticoagulation is still considerably lower than that observed in platelet-poor plasma. A low molecular weight heparin (parnaparin) is more active in the presence of activated platelets (such as may occur in acute coronary syndromes) regardless of whether aspirin is used concomitantly.

Prevention of fetal loss in experimental antiphospholipid syndrome by low-molecular-weight heparin

OBJECTIVE

The purpose of this study was to compare the effectiveness of low-molecular-weight heparin with regular heparin in the prevention of fetal resorption in mice with the antiphospholipid syndrome.

STUDY DESIGN

Antiphospholipid syndrome was passively induced in ICR mice by injecting them with anticardiolipin antibodies on the first day of pregnancy. Subsequently, these mice were treated with low-molecular-weight heparin in two different doses, with regular heparin, and with a placebo. On gestational day 17 the mice were killed by cervical dislocation, and the pregnancy outcome was evaluated. Statistical analysis was performed by means of a one-way analysis of variance using Bonferroni's t test.

RESULTS

Treatment with low-molecular-weight heparin resulted in a resorption rate of 22.4% as opposed to 41.4% in mice with antiphospholipid syndrome that were given regular heparin and 51.7% in nontreated controls.

CONCLUSION

We conclude that low-molecular-weight heparin can prevent fetal resorptions in mice with antiphospholipid syndrome.

Effects of short-term low-dose heparin administration on biochemical parameters of bone turnover

Heparin therapy may cause osteoporosis. The effects of short-term low-dose heparin are not known. We have studied the effects of short-term heparin administration, twice daily 5000 IU s.c., for 10 days on the biochemical parameters of bone turnover in six healthy male volunteers. No effects were observed on the urinary excretion of hydroxyproline and calcium. Serum levels of cross-linked carboxy-terminal telopeptide of type I collagen (ICTP), a new marker of bone resorption, did not change significantly. A slight but significant decrease in serum alkaline phosphatase was observed. TmP/GFR increased significantly during heparin administration. In all volunteers a uniform increase in serum transaminases appeared which completely reversed after discontinuation of heparin administration. We conclude that short-term low-dose heparin administration does not change biochemical parameters of bone resorption, but has a small significant suppressing effect on serum alkaline phosphatase levels. Heparin administration resulted in a significant but transient increase of serum transaminase levels.

Inhibition of smooth muscle cell proliferation and experimental angioplasty restenosis by beta-cyclodextrin tetradecasulfate

Heparin inhibits smooth muscle cell proliferation in vitro, a property that makes it potentially useful in preventing restenosis after angioplasty. Its utility in this setting is limited by the inability to use high doses (secondary to anticoagulant effects) and the need for subcutaneous administration. We tested the ability of beta-cyclodextrin tetradecasulfate (CDT), a nonanticoagulant synthetic heparin mimic, to inhibit smooth muscle cell proliferation in vitro and tested its efficacy when orally administered for the prevention of angioplasty restenosis in a rabbit atherosclerosis model. Vascular smooth muscle cells were cultured from rabbit aortas by the explant technique. Passaged cells were plated at low density in microtiter plates in the presence or absence of varying concentrations of heparin or CDT in culture medium containing 10% fetal calf serum. Using both 3H-thymidine incorporation and total protein assays, both heparin and CDT caused a similar dose-dependent inhibition of proliferation. We next tested the effect of orally administered CDT in the prevention of restenosis in focal femoral artery arteriosclerotic lesions created in hypercholesterolemic New Zealand White rabbits by air-dessication endothelial injury and subsequent peripheral angioplasty. Animals were followed up for 1 month and were fed normal chow supplemented by tap water with or without CDT. In animals receiving the highest concentration of CDT (2 mg/mL drinking water), the percentage of arterial cross-sectional area with intimal hyperplasia decreased from 50.5 +/- 1.7% (control) to 26.9 +/- 2.2% (p < 0.001), with the intimal/medial ratio being decreased from 1.4 +/- 0.4 to 0.5 +/- 0.2 (p = 0.056).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of hirudin and heparin as adjuncts to streptokinase thrombolysis in a canine model of coronary thrombosis

Recombinant desulfatohirudin (HI), a potent and specific thrombin inhibitor, was compared with heparin (HE) as an adjunct to streptokinase thrombolysis. In pentobarbital-anesthetized dogs, an occlusive thrombus (whole blood+thrombin) was introduced into the left anterior descending coronary artery (LAD) with superimposed endothelial damage and distal high-grade stenosis. Intravenous infusion of saline (vehicle), HI (0.3 mg/kg followed by 0.3 mg/kg per hour, 1 mg/kg followed by 1 mg/kg per hour, or 2 mg/kg followed by 2 mg/kg per hour), or HE (60 units/kg followed by 40 units/kg per hour or 100 units/kg followed by 60 units/kg per hour) was initiated 15 minutes before streptokinase (750,000 units for 60 minutes) administration. Vessel patency was monitored for 180 minutes after streptokinase administration with a volume flow probe on the proximal LAD. In dogs treated with no adjunctive agent (saline control), none of the vessels were recanalized with streptokinase. Both HI and HE promoted reperfusion, inhibited reocclusion, and reduced the residual thrombus mass in a dose-dependent fashion. However, at comparable levels of therapeutic anticoagulation (activated partial thromboplastin time [APTT] = 1.5-2.0 times baseline) HI exhibited a higher incidence of reperfusion (eight of eight dogs [100%] versus one of eight dogs [12%]), a shorter time to reperfusion (33 +/- 6 versus 59 minutes), a longer duration of initial reperfusion (106 +/- 21 versus 10 minutes), and a smaller residual thrombus mass than did HE. Likewise, the slope of the relation between the APTT prolongation and the total reperfusion time ("anticoagulation/antithrombosis profile") was almost five times higher for the combined HI data than for the HE data. Our results indicate that HI is more effective than HE in enhancing and sustaining coronary recanalization with streptokinase at a HI dose that modestly prolongs coagulation time and does not alter bleeding times.

Preprocedural anticoagulation does not reduce angioplasty heparin requirements

To determine whether continuous preprocedural heparin influences the need for anticoagulation during percutaneous transluminal coronary angioplasty (PTCA), we compared heparin requirements in patients therapeutically anticoagulated after continuous heparinization for > or = 12 hours with patients not pretreated with heparin (controls). A Hemochron device was used to monitor the activated clotting time (ACT) values during the procedure. An ACT > or = 300 seconds was used as a measure of optimal anticoagulation. Patients pretreated with heparin had significantly higher preprocedural ACT measurements (163 +/- 31.5 vs 126 +/- 13 seconds, p < 0.001) and partial thromboplastin time (PTT) measurements (46 +/- 15 vs 25 +/- 3 seconds, p < 0.001) than controls. While the amount of heparin needed to achieve an initial ACT > 300 seconds was slightly greater in control patients (10,682 +/- 1,852 vs 9,269 +/- 2,993 units, p < 0.001), the total heparin required to maintain an ACT > 300 seconds throughout the procedure was similar between the two groups (11,551 +/- 3,181 units vs 12,136 +/- 2,575 units, p = NS). Thus preprocedural anticoagulation does not significantly reduce total heparin requirements, and these patients should receive the same initial heparin regimen as patients not pretreated with intravenous heparin.

Anticoagulant effects of hirulog, a novel thrombin inhibitor, in patients with coronary artery disease

Selective thrombin inhibitors are a new class of antithrombotic drugs that, unlike heparin, can effectively inhibit clot-bound thrombin and escape neutralization by activated platelets. Hirulog is a 20 amino acid hirudin-based synthetic peptide that has shown promise in experimental models of thrombosis. Little information is available about the effects of hirulog in patients with coronary artery disease. Forty-five patients undergoing cardiac catheterization, who were taking aspirin, were randomized to receive either (1) hirulog, 0.05 mg/kg intravenous bolus followed by 0.2 mg/kg/hour intravenous infusion until the end of the catheterization; (2) hirulog, 0.15 mg/kg intravenous bolus followed by 0.6 mg/kg/hour intravenous infusion; or (3) heparin; 5,000 U intravenous bolus. Serial activated partial thromboplastin time (APTT), prothrombin time, activated clotting time and fibrinopeptide A were measured. Hirulog produced a dose-dependent prolongation of all coagulation parameters; the 0.6 mg/kg/hour dose prolonged the APTT to 218 +/- 50% of baseline after 2 minutes and 248 +/- 50% of baseline after 15 minutes. The half-life of the effect on APTT was 40 minutes. The hirulog blood level correlated well with the APTT, prothrombin time and activated clotting time (r = 0.77, 0.73, and 0.82 respectively, all p < 0.001). Both doses of hirulog potently suppressed the generation of fibrinopeptide A (p < 0.05). There were no major hemorrhagic, thrombotic or allergic complications in patients treated with hirulog or heparin. Thus, hirulog, a direct thrombin inhibitor, provides a predictable level of anticoagulation and appears to have a potent yet well-tolerated anticoagulant profile in patients with coronary artery disease.

Efficacy of 1.4 percent sodium citrate in maintaining arterial catheter patency in patients in a medical ICU

PURPOSE

The primary purpose of this study was to compare the efficacy of 1.4 percent sodium citrate with heparin, 4 U/ml, for maintaining radial artery catheter patency in patients in the medical ICU.

PATIENTS AND METHODS

Patients in the medical ICU (n = 40) were randomized to either a 1.4 percent sodium citrate or heparin 4 U/ml arterial line flush solution in a double-blind, parallel fashion. The flush solutions were continuously infused at approximately 3 ml/h over a maximum of 96 h. Catheter survival rates were compared using Kaplan-Meier survival curves. The frequency of catheter malfunctions and corrective manipulations were recorded and compared. Coagulation status (APTT, PT) and ionized calcium values were monitored to evaluate the systemic effects of sodium citrate.

RESULTS

Ninety-four percent of catheters flushed with sodium citrate were functional at 48 h compared with 88 percent for heparin (p > 0.05). At 96 h, 80 percent vs 88 percent of the catheters were functional in the citrate and heparin groups, respectively (p > 0.05). Frequency of catheter malfunctions did not differ between the two groups. No systemic effects of sodium citrate were observed.

CONCLUSION

Arterial catheter flush solutions containing sodium citrate (1.4 percent) are an effective and safe alternative to heparin in patients requiring peripheral arterial catheterization.

Prothrombin fragment F1 + 2 concentrations for monitoring anticoagulation therapy with heparin

We have compared the activated partial thromboplastin time with measurement of prothrombin fragment F1 + 2 concentrations (ELISA assay) during a 24-h period in a group of patients (n = 10) who had undergone elective coronary angioplasty and were anticoagulated post-procedure with heparin 1000 U/h. Four hours after the procedure all the patients were adequately anticoagulated according to activated partial thromboplastin time (median ratio 4.7:1) and the prothrombin fragment F1 + 2 concentration was significantly lower than pre-angioplasty values (0.5 vs 1.4 nmol/l, p = 0.04). At 24 h the median activated partial thromboplastin time ratio was still higher than the pre-procedure value (1.35 vs 0.9, p < 0.01), but the prothrombin fragment F1 + 2 concentration had risen to 2.1 nmol/l, with more variability in individual results within the patient group for the prothrombin fragment F1 + 2 concentration than for activated partial thromboplastin time (interquartile ranges (Q1, Q3) prothrombin fragment F1 + 2, 1.2-2.5; activated partial thromboplastin time, 1.2-1.5). The activated partial thromboplastin time is the standard method of monitoring the anticoagulant effect of heparin but may not fully reflect the functional coagulation status and accurately identify individual patients with less than adequate anticoagulation. Prothrombin fragment F1 + 2 concentrations may provide a more reliable indicator in individual patients of functional coagulation status in certain important situations where anticoagulation is critical such as following complicated coronary angioplasty.