Subcutaneous low-molecular-weight heparin compared with continuous intravenous heparin in the treatment of proximal-vein thrombosis

New method to predict patients' intravenous heparin dose requirements

OBJECTIVE

To predict intravenous heparin dose requirements of patients treated for thromboembolic disorders.

DESIGN

A retrospective cohort study in which we used simple linear regression to predict patients' effective maintenance dose (EMD) of heparin (units/kg/hour needed to achieve and maintain APTT therapeutic range) from patients' "heparin responsiveness" (the APTT increase after the initial 6 hours of heparin treatment per units/kg/hour received).

SETTING/PATIENTS

The model was derived from 46 patients treated at one hospital (Hospital A) and then tested in 42 patients treated at another hospital (Hospital B).

MEASUREMENTS AND MAIN RESULTS

Among Hospital A patients, there was a strong linear correlation (r = -.880; p < .001) between EMD (mean 16.02 units/kg/hour; 95% CI 14.9, 17.15) and "heparin responsiveness" (HR): EMD = 25.651 - [95.118 x HR]. This model accurately predicted Hospital B patients' EMD: 97% (37/38) fell within the model's 95% prediction interval; the mean absolute difference between predicted and actual EMD was 1.73 units/kg/hour (95% CI 1.39, 2.08); and only 16% of patients had EMD's more than 3 units/kg/hour different from that predicted by the regression model. The model's accuracy was comparable to that of our gold standard, the weight-based heparin dosing nomogram.

CONCLUSION

The infusion dose of intravenous heparin effective for an individual patient can be predicted accurately from the patient's body weight and APTT response to the initial 6 hours of treatment. Especially in hospitals where validated heparin dosing nomograms are not used, clinicians may find this simple technique useful in achieving timely therapeutic anticoagulation.

[Classical anticoagulant treatment of venous thromboembolic disease in cancer patients. Apropos of a retrospective study of 71 patients]

In order to evaluate the efficiency of classical anticoagulant therapy for venous thromboembolic disease in cancer patients, we retrospectively analysed 71 patients treated with intravenous heparin first and then with antivitamin K. After a mean follow-up of 185 +/- 25 days, 23 patients (33%) were dead; nine patients (12%) had suffered from major haemorrhagic complications, which were not fatal, four of which were due to heparin overdosage; 17 patients (24%) showed recurrent venous thromboembolic disease. According to univariate statistical analysis, risk of major bleeding was not associated with the presence of either thrombocytopenia, abnormal blood coagulation, metastases and/or any other hemorrhagic risk factors; recurrence of venous thromboembolic disease was not associated with the presence of other risk factors for venous thromboembolic disease, nor with the presence or absence of metastases and/or of ongoing chemotherapy. Such results suggest that classical anticoagulant therapy for venous thromboembolic disease in cancer patients is neither effective nor safe. The present retrospective study underlines needs for further prospective analyses in order to evaluate potential benefit from other therapeutic strategies, such as use of low molecular weight heparins and/or vena cava filter placement.

Low-molecular-weight heparins and unfractionated heparin in the treatment of patients with acute venous thromboembolism: results of a meta-analysis

PURPOSE

To obtain reliable estimates of the relative efficacy and safety of low-molecular-weight heparins (LMWHs) and unfractionated heparin (UFH) in the treatment of patients with venous thromboembolism.

METHODS

A literature search of randomized trials evaluating LMWH and UFH for the period from 1980 to 1994 was conducted to obtain data for a meta-analysis. Studies were classified as level 1 if they were double-blind or if there was blinded assessment of outcome measures, and level 2 if they did not provide assurance of blinded outcome assessment.

RESULTS

In level 1 studies, the relative risk (RR) of recurrent venous thromboembolism during the first 15 days and over the entire period of anticoagulant therapy was 0.24 (95% confidence intervals [CI] 0.06 to 0.80, P = 0.02) and 0.39 (95% CI 0.30 to 0.80, P = 0.006), respectively, in favor of LMWH treatment. The RR for major bleeding was 0.42 (95% CI 0.2 to 0.9, P = 0.01), in favor of LMWH. In level 2 studies, no significant differences in the rates of recurrent venous thromboembolism or major bleeding were observed. Pooling level 1 and level 2 studies, the RR for overall mortality and mortality in cancer patients was 0.51 (95% CI 0.2 to 0.9, P = 0.01), and 0.33 (95% CI 0.1 to 0.8, P = 0.01), respectively in favor of LMWH.

CONCLUSIONS

LMWH are likely to be more effective than UFH in preventing recurrent venous thromboembolism, to produce less major bleeding, and to be associated with a lower mortality rate, particularly in the subgroup of patients with cancer.

Low-molecular-weight heparin in pediatric patients with thrombotic disease: a dose finding study

OBJECTIVE

To compare low-molecular-weight preparations of heparin (LMWH) with standard heparin in children requiring anticoagulant treatment for thromboembolic disease.

METHODS

We treated 25 children who required heparin, but were at significant risk of bleeding, with LMWH (enoxaparin, Rhone-Poulenc Rorer). The median age was 4 years (range, newborn to 17 years), with nine infants less than 2 months of age. Fourteen children had a deep vein thrombosis or pulmonary embolism, nine had thrombotic complications in the central nervous system, and two had complex congenital heart disease, for which they received prophylaxis at a lower dosage (0.5 mg/kg given subcutaneously twice a day). The remaining 23 children received an initial dose of 1 mg/kg, every 12 hours subcutaneously, with subsequent doses adjusted to achieve a 4-hour anti-factor Xa level between 0.5 and 1.0 unit/ml.

RESULTS

Newborn infants had increased dose requirements; an average of 1.60 units/kg was required to achieve therapeutic heparin levels. For the remaining children, the initial dose of 1.0 mg/kg was sufficient. After the initial dose adjustment, LMWH was administered with twice-weekly monitoring. The median duration of therapy with LMWH was 14 days. Two children with previously documented gastrointestinal ulcers bled and required transfusion therapy. Therapy with LMWH was continued without further events. There were no new thrombotic events during the treatment with LMWH. The cost of administering LMWH compared with heparin was reduced by 30% because of decreased laboratory monitoring, blood sampling times, intravenous starts, and nursing time. Needle punctures were reduced with LMWH therapy by the placement of a subcutaneous catheter.

CONCLUSION

These results provide the basis for a randomized, controlled trial comparing LMWH with standard heparin in pediatric patients.

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.

Indications and drugs for anticoagulation therapy in children

The indications for using anticoagulants in children are reviewed. These include venous thromboembolic disease, thrombosis associated with central venous lines, inherited conditions, arterial thromboembolic disease and umbilical catheterization. The anticoagulants presently available for paediatric use consist of heparin and oral agents including low molecular weight heparin (LMWH). The problems associated with their use in children are examined and potential advantages described. Increasing numbers of children are now requiring anticoagulant therapy and the potential advantages of LMWHs makes it imperative that randomized, controlled trials be carried out in children in prophylactic as well as therapeutic situations.

Low-molecular-weight heparin for the treatment of acute ischemic stroke

BACKGROUND

Despite doubts about their efficacy and concern about their safety, antithrombotic agents are often used to treat acute ischemic stroke. Recent experience in patients with other thromboembolic disorders suggests that low-molecular-weight heparin, which requires only subcutaneous administration once or twice daily, may be more effective and safer than standard (unfractionated) heparin.

METHODS

We conducted a randomized, double-blind, placebo-controlled trial comparing two dosages of low-molecular-weight heparin with placebo in the treatment of ischemic stroke. Patients were randomly assigned within 48 hours of the onset of symptoms to receive high-dose nadroparin (4100 anti-factor Xa IU twice daily), low-dose nadroparin (4100 IU once daily), or placebo subcutaneously for 10 days. The primary measure of outcome was death or dependency regarding activities of daily living six months after randomization. Secondary outcomes were death, hemorrhagic transformation of the infarction, and other complications at 10 days, and death or dependency at 3 months.

RESULTS

A total of 2750 patients were screened for the study. Among 312 patients randomized, 306 had outcomes that were analyzed at six months. Forty-five patients (45 percent) in the high-dose group, 53 patients (52 percent) in the low-dose group, and 68 patients (65 percent) in the placebo group died or became dependent. There was a significant dose-dependent effect among the three study groups in favor of low-molecular-weight heparin (P = 0.005 by the chi-square test for trend). No significant differences among the groups in the occurrence of secondary outcomes were observed at 10 days.

CONCLUSIONS

For patients with ischemic stroke treated within 48 hours of the onset of symptoms, low-molecular-weight heparin was effective in improving outcomes at six months.

Heparin levels to guide thromboembolism prophylaxis during pregnancy

OBJECTIVE

Our purpose was to determine the dose of heparin required in pregnant women to achieve the same heparin levels as standard doses of 5000 units given subcutaneously every 12 hours in the nonpregnant population.

STUDY DESIGN

Fourteen pregnant women placed on heparin prophylaxis for a history of thromboembolism had blood drawn for 64 anti-Xa level determinations in the second and third trimesters. Heparin doses were adjusted in an attempt to achieve a midinterval or peak level of 0.05 to 0.25 U/ml, which corresponds to the range seen in nonpregnant patients given standard doses of 5000 units subcutaneously every 12 hours.

RESULTS

A standard heparin dose of 5000 units given subcutaneously every 12 hours was inadequate to achieve the desired range in this pregnant population. In five of nine second-trimester pregnancies 7500 units given subcutaneously every 12 hours was inadequate to attain this range. In six of 13 third-trimester pregnancies, > 10,000 units subcutaneously every 12 hours was needed.

CONCLUSIONS

Heparin requirements may increase and are highly variable in patients during pregnancy. Until appropriate clinical outcomes trials can determine optimal dosing, measuring anti-Xa activity may be useful to guide therapy.

Uses of low-molecular-weight heparin

Low-molecular-weight-heparin fractions are prepared from standard unfractionated heparin and are thus similar to unfractionated heparin in many aspects. The main advantages of this new class of antithrombotic agents as compared with unfractionated heparin are: (1) an improved bioavailability and a prolonged half-life, which alleviate cumbersome laboratory monitoring and may permit one single daily subcutaneous injection; (2) an improved efficacy-to-safety ratio, with less bleeding despite similar or improved efficacy. While low-molecular-weight heparin should replace unfractionated heparin for preventing postoperative thromboembolism, some unresolved issues remain to be addressed in specific trials before low-molecular-weight heparin can generally replace unfractionated heparin for all indications. These issues include the use of low-molecular-weight heparin in patients with arterial thrombosis, unstable angina, or myocardial infarction (usually in conjunction with thrombolytic treatment), and in patients with symptomatic pulmonary embolism, as well as formal cost-effectiveness analyses substantiating the advantages of the new agents. The potential of using low-molecular-weight-heparin outpatient treatment of established deep-vein thrombosis should be scrutinized from an economic and logistic point of view because two large-scale controlled trials have suggested both efficacy and safety.

Prolonged antithrombin activity of low-molecular-weight heparins. Clinical implications for the treatment of thromboembolic diseases

BACKGROUND

The mechanism for the efficacy of once- or twice-daily subcutaneous injections of low-molecular-weight heparins (LMWHs) for the treatment of venous thromboembolism has been difficult to explain. The confusion exists because the observation from experimental studies that the antithrombin activity of LMWHs is necessary for their antithrombotic effect is inconsistent with the reported short half-life of the antithrombin activity of LMWHs. Previous pharmacokinetic studies were performed with lower doses of LMWHs than have been used in contemporary trials, and antithrombin activity was assessed with the barely sensitive chromogenic assay.

METHODS AND RESULTS

We performed a pharmacokinetic study to compare the relative half-lives of prophylactic and therapeutic doses of LMWHs assessing antithrombin activity with both the chromogenic and a more sensitive assay (plasma thrombin neutralization assay). An eight-way cross-over randomized study in healthy volunteers was performed. Enoxaparin (20 and 40 mg and 1 and 2 mg/kg) and nadroparin (7500 and 10,000 ICU and 225 and 450 ICU/kg) were administered subcutaneously. The maximal peak activity for aPTT ratio was 1.7. A dose-dependent peak activity was found for both antifactor Xa and antithrombin activities. Disappearance time of these activities after the highest dose of both LMWHs was longer than 16 hours. Overall mean antifactor Xa activity half-life was 4.6 hours. Overall mean antithrombin activity half-life was longer than 4 hours.

CONCLUSIONS

Our results provide an explanation for the effectiveness of LMWHs administered either once or twice daily. High and sustained plasma antithrombin activity is achieved when LMWHs are administered in therapeutic doses used in contemporary trials with only a moderate prolongation of the aPTT.

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.

Magnetic bead protamine-linked microtiter assay for detection of heparin using iodinated low-molecular-mass heparin-tyramine

We have developed a competitive heparin binding assay employing protamine-coated magnetic beads for detection and measurement of heparin. The assay utilizes 125-iodine specifically bound to newly synthesized low-molecular-mass (LMM) heparin-tyramine. The tracer was stable over a period of 3 weeks, as demonstrated by gel filtration chromatography. The protamine-coated beads were found to be stable over at least two months. The heparin-tyramine bead assay had in buffer a lower detection limit of 0.04 microgram/ml and in plasma of 0.23 microgram heparin/ml. 50% binding was obtained at 0.7 microgram/ml and 20% binding at 4 micrograms/ml in plasma. The within assay coefficient of variation ranged from 9 to 28% for unfractionated, high molecular mass (HMM) heparin and from 12 to 15% for LMM-heparins in buffer system and in plasma. Various heparin fractions displaced the tracer from the protamine-coated magnetic beads to different extents. The validity of the assay was proven after intravenous administration of unfractionated and LMM-heparin in man. The elimination rate was similar using the heparin-tyramine bead assay compared with the anti-factor Xa coagulation assay. After intravenous dosing of LMM-heparin the maximal concentration was lower using the heparin-tyramine bead assay compared with the anti-factor Xa coagulation assay. The bead assay was found to be reproducible, valid, and rapid for measurement of the concentration of heparin preparations in purified systems and for HMM-heparin in plasma. Measurement of the concentration of LMM-heparin in plasma has a high coefficient of variation using the binding assay.

Effects of recombinant hirudin (r-hirudin, HBW 023) on coagulation and platelet activation in vivo. Comparison with unfractionated heparin and a low-molecular-weight heparin preparation (fragmin)

In a double-blind, randomized, crossover study, we investigated in 15 healthy male volunteers the effects of recombinant (r-) hirudin (HBW 023, 0.35 mg/kg body wt SC), unfractionated heparin (UFH, HeparinNovo; 150 IU/kg body wt SC), and a low-molecular-weight heparin preparation (LMWH, Fragmin; 75 IU/kg body wt SC) on coagulation and platelet activation in vivo by measuring specific coagulation-activation peptides (prothrombin fragment 1 + 2 [F1 + 2], thrombin-antithrombin-III complex [TAT], and beta-thromboglobulin [beta-TG]) in bleeding-time blood (activated state) and venous blood (basal state). In bleeding-time blood, r-hirudin and the heparin preparations significantly inhibited formation of both TAT and F1 + 2. However, the inhibitory effect of r-hirudin on F1 + 2 generation was short-lived and weaker compared with that of UFH and LMWH, and the TAT-to-F1 + 2 ratio was significantly lower after r-hirudin than after UFH or LMWH. Thus, in vivo, when the coagulation system is in an activated state, r-hirudin exerts its anticoagulant effects predominantly by inhibiting thrombin (factor IIa), whereas UFH and LMWH are directed against both factors Xa and IIa. A different mode of action for UFH and LMWH was not detectable. In venous blood, r-hirudin caused a moderate reduction in TAT formation and an increase (at 1 hour) rather than a decrease in F1 + 2 generation. Formation of TAT and F1 + 2 was suppressed at various time points following both UFH and LMWH. There was no difference in the TAT-to-F1 + 2 ratio after r-hirudin and heparin.(ABSTRACT TRUNCATED AT 250 WORDS)

Heparin-induced thrombocytopenia in patients treated with low-molecular-weight heparin or unfractionated heparin

BACKGROUND

Heparin-induced thrombocytopenia, defined by the presence of heparin-dependent IgG antibodies, typically occurs five or more days after the start of heparin therapy and can be complicated by thrombotic events. The frequency of heparin-induced thrombocytopenia and of heparin-dependent IgG antibodies, as well as the relative risk of each in patients given low-molecular-weight heparin, is unknown.

METHODS

We obtained daily platelet counts in 665 patients in a randomized, double-blind clinical trial comparing unfractionated heparin with low-molecular-weight heparin as prophylaxis after hip surgery. Heparin-induced thrombocytopenia was defined as a decrease in the platelet count below 150,000 per cubic millimeter that began five or more days after the start of heparin therapy, and a positive test for heparin-dependent IgG antibodies. We also tested a representative subgroup of 387 patients for heparin-dependent IgG antibodies regardless of their platelet counts.

RESULTS

Heparin-induced thrombocytopenia occurred in 9 of 332 patients who received unfractionated heparin and in none of 333 patients who received low-molecular-weight heparin (2.7 percent vs. 0 percent; P = 0.0018). Eight of the 9 patients with heparin-induced thrombocytopenia also had one or more thrombotic events (venous in 7 and arterial in 1), as compared with 117 of 656 patients without heparin-induced thrombocytopenia (88.9 percent vs. 17.8 percent; odds ratio, 36.9; 95 percent confidence interval, 4.8 to 1638; P < 0.001). In the subgroup of 387 patients, the frequency of heparin-dependent IgG antibodies was higher among patients who received unfractionated heparin (7.8 percent, vs. 2.2 percent among patients who received low-molecular-weight heparin; P = 0.02).

CONCLUSIONS

Heparin-induced thrombocytopenia, associated thrombotic events, and heparin-dependent IgG antibodies are more common in patients treated with unfractionated heparin than in those treated with low-molecular-weight heparin.

Anticoagulation in the prevention and treatment of pulmonary embolism

The anticoagulant agents commonly used in prevention and treatment of pulmonary embolism are unfractionated heparin, and more recently, low molecular weight heparins, and oral anticoagulants. Unfractionated heparin is the drug of choice for prophylaxis and short-term treatment of pulmonary embolism. Oral anticoagulants are used for prophylaxis in high risk patients and in long-term treatment of pulmonary embolism. Independent overview analysis of clinical trials in elective surgery showed a 60 to 70% reduction in the incidence of fatal pulmonary embolism in heparin-treated patients when they were compared with placebo-treated patients. Low dose heparin has also been shown to be effective in reducing venous thromboembolism after myocardial infarction and other serious medical disorders. In high risk patients prophylaxis with low molecular weight heparins or adjusted doses of unfractionated heparin is recommended. The objectives of treating patients with pulmonary embolism are to prevent death, to reduce morbidity from the acute event, and to prevent thromboembolic pulmonary hypertension. These objectives are achieved by the administration of heparin followed by oral anticoagulants. Heparin is generally administered for 7 to 10 days and is followed by oral anticoagulants. Although widely used and effective in the prevention and treatment of pulmonary embolism, unfractionated heparin has some pharmacological limitations. Heparin presents an aspecific "nonfunctional" binding to plasma proteins such as fibrinogen, factor VIII, vitronectin, and fibronectin. This aspecific binding limits the anticoagulant effect of unfractionated heparin and, is responsible for the heparin resistance observed in some patients with pulmonary embolism as well as of the high intersubject variability of the heparin-induced anticoagulant effect. Antithrombotic agents, such as low molecular weight heparins and pure thrombin inhibitors (hirudin and its analogues), do not specifically bind to plasma protein and they will probably improve the efficacy and practicality of the treatment of pulmonary embolism.

Care of patients with deep venous thrombosis in an academic medical center: limitations and lessons

PURPOSE

The primary goal of our study was to review the quality of care in patients with deep vein thrombosis,, with emphasis on identifying recurrent and remedial problems. Secondary goals were (1) to evaluate the use of the vascular laboratory and (2) to characterize our patient population with deep vein thrombosis and to identify a subset of patients with uncomplicated deep vein thrombosis who might be candidates for outpatient therapy in the future.

METHODS

A retrospective review was performed for all patients with deep vein thrombosis diagnosed with duplex scanning who were treated as inpatients from January 1993 through March 1993.

RESULTS

Fifty-four (16%) of 306 duplex scans were positive; 50 patients were treated as inpatients. Forty percent of patients had uncomplicated deep vein thrombosis that was potentially treatable on an outpatient basis. Mean time to obtain a therapeutic partial thromboplastin time was 22 hours (range 4 to 54 hours). Ten (20%) patients had inferior vena cava filters placed. The in-hospital mortality rate was 4%. Management problems occurred in 18 (36%) patients and included difficulty titrating anticoagulation, (10) physician failure to provide treatment after diagnosis, (five) and inappropriate use or complication of inferior vena cava filter placement (three).

CONCLUSIONS

Venous duplex examination is liberally but appropriately used. The primary remediable problem resulting in suboptimal management is difficulty titrating anticoagulation; inappropriate placement of inferior vena cava filters and physician failure to provide treatment also occur. In the future a substantial number of patients may be suitable for outpatient therapy.

Acute thrombosis of a vena cava filter with a clot above the filter. Successful treatment with low-dose urokinase

Inferior vena cava thrombosis is a major complication after filter placement. The thrombus can propagate through the filter leading to a high risk of pulmonary embolism. We report such a case in a patient with a Günther filter, successfully treated with urokinase, and we discuss the efficacy and the safety of thrombolytic therapy in such situations.

Relative risks of anticoagulant treatment of acute pulmonary embolism based on an angiographic diagnosis vs a ventilation/perfusion scan diagnosis

The purpose of this investigation was to assess the relative risks of antithrombotic treatment following pulmonary angiography vs no angiography in patients with acute pulmonary embolism (PE). Comparisons of risks of diagnosis and therapy were made among patients treated on the basis of a pulmonary angiographic diagnosis vs patients treated on the basis of a ventilation/perfusion (V/Q) scan combined with clinical assessment in the presence of a single negative test for deep venous thrombosis. Calculations of risks assumed major complications of pulmonary angiography equal to 1.3 percent, major bleeding with heparin equal to 4.9 percent (1.1 percent among patients with a low risk of bleeding and 10.8 percent among patients with a high risk of bleeding), and major bleeding with warfarin (international normalized ratio 2 to 3) equal to 1.7 percent. Among patients with a risk of major bleeding from heparin followed by warfarin of 6.6 percent, if the estimated probability of PE was greater than about 80 percent, fewer major complications of diagnosis and treatment would occur if treatment was initiated on the basis of the V/Q scan. If the probability of PE in such patients was less than 80 percent, fewer major complications of diagnosis and treatment would occur if the diagnosis was established by pulmonary angiography. Among patients with a high (12.5 percent) risk of major bleeding, it was shown to be safer to treat on the basis of an angiographic diagnosis if the estimated probability of PE was less than 90 percent. If the patients, however, were at low (2.8 percent) risk of major bleeding, fewer major complications would occur if angiography was reserved for patients with an estimated risk of PE less than about 50 percent. Serial studies of the leg veins may eliminate the need for angiography in such patients.

Recurrent pulmonary embolism in patients treated because of acute venous thromboembolism: a prospective study

OBJECTIVE

To evaluate the risk of pulmonary embolism (PE) despite adequate heparin therapy in a large series of patients with acute deep venous thrombosis and/or pulmonary embolism.

DESIGN

Prospective study.

SETTING

University Hospital Germans Trias i Pujol, Badalona, Spain.

MATERIALS

348 patients admitted because of deep venous thrombosis in the lower limbs and/or pulmonary embolism. A baseline lung scan was obtained initially in every patient, whether the original diagnosis was PE or deep vein thrombosis (DVT). Repeat chest X-ray and lung scans were obtained routinely at 8 days of heparin onset.

OUTCOME MEASURES

The primary trial endpoint was a finding of confirmed, clinically apparent recurrent PE; in addition, laboratory evidence of subclinical PE at the repeat scan was also considered.

RESULTS

PE recurrences were found in 23/348 patients (7%). No significant differences were found in age and sex distribution, or in the degree of DVT proximity between patients who developed and those who did not develop recurrences. Recurrent PE was more commonly found in patients with scintigraphic evidence of PE on admission, irrespectively of the original diagnosis being DVT or PE (18/151 vs. 3/155; p = 0.0005, Fisher's exact test). Recurrences were also more common in patients in whom thrombosis developed in the absence of any known risk factor (10/70 vs. 13/278; p = 0.007). The logistic regression analysis confirmed the statistical significance of these two clinical variables.

CONCLUSIONS

Pulmonary embolism despite adequate heparin therapy is not an uncommon event. It appears possible to identify a subgroup of patients at a higher risk, and, modify treatment accordingly.

Comparison of efficacy and safety of low molecular weight heparins and unfractionated heparin in initial treatment of deep venous thrombosis: a meta-analysis

OBJECTIVE

To compare the efficacy and safety of low molecular weight heparins and unfractionated heparin in the initial treatment of deep venous thrombosis for the reduction of recurrent thromboembolic events, death, extension of thrombus, and haemorrhages.

DESIGN

Meta-analysis of results from 16 randomised controlled clinical studies.

SUBJECTS

2045 patients with established deep venous thrombosis.

INTERVENTION

Treatment with low molecular weight heparins or unfractionated heparin.

MAIN OUTCOME MEASURES

Incidences of thromboembolic events (deep venous thrombosis or pulmonary embolism, or both); major haemorrhages; total mortality; and extension of thrombus.

RESULTS

A significant reduction in the incidence of thrombus extension (common odds ratio 0.51, 95% confidence interval 0.32 to 0.83; P = 0.006) in favour of low molecular weight heparin was observed. Non-significant trends also in favour of the low molecular weight heparins were observed for the recurrence of thromboembolic events (0.66, 0.41 to 1.07; P = 0.09), major haemorrhages (0.65, 0.36 to 1.16; P = 0.15), and total mortality (0.72, 0.46 to 1.4; P = 0.16).

CONCLUSIONS

Low molecular weight heparins seem to have a higher benefit to risk ratio than unfractionated heparin in the treatment of venous thrombosis. These results, however, remain to be confirmed by using clinical outcomes in suitably powered clinical trials.

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)

Low-molecular-weight heparin

Low molecular weight heparins (LMWHs) are mixtures of heparin molecules in the range of 3000 to 10,000 daltons. As LMWHs of various manufacturers are all produced differently, they are not comparable to each other and are therefore considered to be individual products with different pharmacologic and clinical properties. All these agents have some common characteristics, however, such as a higher availability after subcutaneous administration and a longer biologic half-life. Numerous clinical trials have demonstrated that LMWHs are highly effective and safe for postsurgical prophylaxis of deep vein thrombosis (DVT); therefore, the LMWHs that are commercially available so far, are mainly approved in this indication. LMWHs are also effective in the prophylaxis of DVT in medical indications, as well as for the treatment of established DVT.

Regression of deep vein thrombosis by i.v.-administration of a low molecular weight heparin--results of a pilot study

Twenty-five patients with phlebographically confirmed deep vein thrombosis of the lower limb were treated with intravenous infusions of low molecular weight heparin for 7 to 29 days. The mean dosage was 15.2 +/- 3.0 Uanti-Xa (equivalent 7.6 +/- 1.5 U-aPTT). Phlebograms were taken before, during and after the treatment with low molecular weight heparin and evaluated using the score system of Marder. Nearly complete recanalization of the occluded veins was found in six (24%) patients, improvement of the Marder score of 60 to 90% was found in four patients and of 30 to 60% in seven patients, while eight patients remained unchanged. With an average dose of 15.2 I.U./kg/h the heptest was prolonged to 70 to 120 seconds while the aPTT-level did not significantly increase. tPA-antigen-levels increased significantly in most of the patients after the third day of treatment, while PAI-activity remained unchanged. A positive conclusion between the decrease of the Marder score and the duration of treatment was found. Thus the low molecular weight heparin used in this investigation proved to be effective and safe in treating deep vein thrombosis.

Anticoagulant therapy in deep venous thrombosis. A randomized controlled study

Ninety patients with venographically proven deep venous thrombosis(DVT) but without clinical signs of pulmonary embolism(PE) were randomized into two different treatment regimens to compare the safety and efficacy of continuous intravenous heparin and oral anticoagulant(AC) treatment versus non-AC treatment. All patients in the two treatment groups were actively mobilized from the day of admission and wore graduated compressing stockings. In the non-AC-group the patients were treated with phenylbutazone for ten days. Treatment with heparin was maintained for 6 days and oral AC treatment was given from the third day and continued for 3 months. Venography was repeated after 30 days. A perfusion-ventilation lung scan was performed on day 1-2, 10 and 60. In fifty-nine patients a revenography was performed, twenty nine in the AC-group and thirty in the non-AC group. For distal veins regression was found in nine and eight respectively (4.4% in favour of AC, 95% confidence limit 27.5% to -18.7%) and in proximal veins regression was found in five and eight, respectively (10.9% in favour of AC, 95% confidence limit 32.0% to -10.1%). No difference in lung scans was found after 10 days (0.8% in favour of AC, 95% confidence limit 21.5% to -19.9%) or after 60 days (3.3% in favour of non-AC treatment, 95% confidence limit 21.8% to -28.5%). In the AC group the incidence of bleeding complications was 8.3%. No side-effects of phenylbutazone was found. The present controlled clinical study demonstrated no effect of AC-treatment on DVT progression in actively mobilized patients wearing graduated compressing stockings when compared to a non-AC treated group receiving analgetic therapy with phenylbutazone. However, the patient population of the study is relatively small with wide confidence intervals for differences between groups. Before more general recommendations can be made, a large scale placebo-controlled study is needed to evaluate the possible effect of AC-treatment in DVT patients, who can be mobilized from the first day.

Venous thromboembolism in neurosurgery and neurology patients: a review

Thromboembolism is a common problem in neurosurgery and neurology patients. Within this diverse population are subpopulations of patients with varying degrees of thromboembolic risk: low, moderate, and high. Patients at substantial risk for deep vein thrombosis and pulmonary embolism include those with spinal cord injury, brain tumor, subarachnoid hemorrhage, head trauma, stroke, and patients undergoing a neurosurgical operation. There are prophylactic strategies that can be applied to these various risk groups that will dramatically reduce the incidence of thromboembolism. The risk of pulmonary embolism or fatal pulmonary embolism typically exceeds the risk of severe or fatal bleeding from adequate prophylaxis, and these techniques should be applied on a routine basis. To adequately care for patients with deep venous thrombosis and pulmonary embolism, the physician requires a thorough understanding of the methods of diagnosis, the pharmacokinetics of heparin and warfarin, and a knowledge of their role in the treatment strategies that have proven efficacy and safety. In addition, an awareness of the low molecular weight heparins and heparinoids is becoming essential. These new agents have a potentially promising role in both the prophylaxis and treatment of patients with neurological disease. The principles concerning the prophylaxis, diagnosis, and clinical management of venous thromboembolic disease in neurosurgery and neurology patients are dealt with in this review.

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.

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.