Apixaban after hip or knee arthroplasty versus enoxaparin: efficacy and safety in key clinical subgroups

BACKGROUND

New oral anticoagulants for thromboprophylaxis after hip or knee arthroplasty have been given as fixed-dose regimens.

OBJECTIVE

To evaluate the consistency of the antithrombotic efficacy and bleeding risk of apixaban 2.5 mg twice daily compared with enoxaparin 40 mg once daily after knee or hip arthroplasty across the clinical characteristics of age, gender, body weight, body mass index (BMI) and creatinine clearance.

METHODS

The pooled results of the ADVANCE-2 (knee arthroplasty) and -3 (hip arthroplasty) randomized trials were used to evaluate if treatment had a statistically significantly different effect (P < 0.10) on major venous thromboembolism (VTE) and bleeding for the characteristics of age, gender, body weight, BMI and creatinine clearance. Both univariate analysis and multivariate logistic regression were used.

RESULTS

Univariate analyses identified statistically significant interactions for age and major VTE (P = 0.09); for both age (P = 0.07) and body weight (P = 0.07) and the outcome of major bleeding; and for creatinine clearance (P = 0.03) and the composite outcome of major and clinically relevant non-major bleeding. Estimates of these possible differences were not precise, with wide 95% confidence intervals (CIs) that included a zero difference for several subgroups. Multivariate logistic regression analysis did not detect a statistically significant interaction for any outcomes.

CONCLUSIONS

This analysis found no convincing evidence that age, weight, gender, BMI or creatinine clearance influenced the balance of benefit to risk for apixaban compared with enoxaparin. Because only 5% of patients had a creatinine clearance between 30 and 50 mL min(-1), further data are needed in such patients.

Apixaban versus enoxaparin for thromboprophylaxis after hip or knee replacement: pooled analysis of major venous thromboembolism and bleeding in 8464 patients from the ADVANCE-2 and ADVANCE-3 trials

In order to compare the effect of oral apixaban (a factor Xa inhibitor) with subcutaneous enoxaparin on major venous thromboembolism and major and non-major clinically relevant bleeding after total knee and hip replacement, we conducted a pooled analysis of two previously reported double-blind randomised studies involving 8464 patients. One group received apixaban 2.5 mg twice daily (plus placebo injection) starting 12 to 24 hours after operation, and the other received enoxaparin subcutaneously once daily (and placebo tablets) starting 12 hours (± 3) pre-operatively. Each regimen was continued for 12 days (± 2) after knee and 35 days (± 3) after hip arthroplasty. All outcomes were centrally adjudicated. Major venous thromboembolism occurred in 23 of 3394 (0.7%) evaluable apixaban patients and in 51 of 3394 (1.5%) evaluable enoxaparin patients (risk difference, apixaban minus enoxaparin, -0.8% (95% confidence interval (CI) -1.2 to -0.3); two-sided p = 0.001 for superiority). Major bleeding occurred in 31 of 4174 (0.7%) apixaban patients and 32 of 4167 (0.8%) enoxaparin patients (risk difference -0.02% (95% CI -0.4 to 0.4)). Combined major and clinically relevant non-major bleeding occurred in 182 (4.4%) apixaban patients and 206 (4.9%) enoxaparin patients (risk difference -0.6% (95% CI -1.5 to 0.3)). Apixaban 2.5 mg twice daily is more effective than enoxaparin 40 mg once daily without increased bleeding.

Individual patient data meta-analysis of enoxaparin vs. unfractionated heparin for venous thromboembolism prevention in medical patients

BACKGROUND

Unfractionated heparin (UFH) and low-molecular-weight heparin (LMWH) are both recommended for venous thromboembolism (VTE) prophylaxis in hospitalized medical patients.

OBJECTIVE

To perform an individual patient data meta-analysis to evaluate the relative efficacy and safety of the LMWH enoxaparin and UFH in preventing VTE in hospitalized medical patients.

METHODS

Randomized clinical trials comparing subcutaneous enoxaparin (4000 IU once-daily) and UFH (5000 IU subcutaneous two- or three-times daily) for VTE prevention were identified by a systematic search. Individual patient data were obtained from each eligible trial.

RESULTS

Overall, four trials were eligible, including 3600 patients randomized to receive enoxaparin (n = 1799) or UFH (n = 1801). Median patient age was 71 years, and 49.3% were female. Compared with UFH, enoxaparin was associated with risk reductions of 37% for total VTE [relative risk (RR) 0.63, 95% confidence interval (CI) 0.51-0.77] and 62% for symptomatic VTE (RR 0.38, 95% CI 0.17-0.85) at day 15. RR for total VTE in stroke and non-stroke patients was 0.59 (95% CI 0.47-0.74) and 0.87 (95% CI 0.51-1.50), respectively. Major bleeding rates were consistently low and similar between treatment groups at day 15 (RR 1.13, 95% CI 0.53-2.44). There was a trend towards reduced risk for mortality in patients receiving enoxaparin (RR 0.83, 95% CI 0.64-1.08), compared with UFH.

CONCLUSIONS

Enoxaparin significantly reduces VTE in hospitalized medical patients, compared with UFH, without increasing the risk for major bleeding, and was associated with a trend towards reduced all-cause mortality.

Extended out-of-hospital low-molecular-weight heparin prophylaxis against deep venous thrombosis in patients after elective hip arthroplasty: a systematic review

PURPOSE

Evidence-based medicine guidelines based on venographic end points recommend in-hospital prophylaxis with low-molecular-weight heparin (LMWH) in patients having elective hip surgery. Emerging data suggest that out-of-hospital use may offer additional protection; however, uncertainty remains about the risk-benefit ratio. To provide clinicians with a practical pathway for translating clinical research into practice, we systematically reviewed trials comparing extended out-of-hospital LMWH prophylaxis versus placebo.

DATA SOURCES

Studies were identified by 1) searching PubMed, MEDLINE, and the Cochrane Library Database for reports published from January 1976 to May 2001; 2) reviewing references from retrieved articles; 3) scanning abstracts from conference proceedings; and 4) contacting pharmaceutical companies and investigators of the original reports.

STUDY SELECTION

Randomized, controlled trials comparing extended out-of-hospital prophylaxis with LMWH versus placebo in patients having elective hip arthroplasty.

DATA EXTRACTION

Two reviewers extracted data independently. Reviewers evaluated study quality by using a validated four-item instrument.

DATA SYNTHESIS

Six of seven original articles met the defined inclusion criteria. The included studies were double-blind trials that used proper randomization procedures. Compared with placebo, extended out-of-hospital prophylaxis decreased the frequency of all episodes of deep venous thrombosis (placebo rate, 150 of 666 patients [22.5%]; relative risk, 0.41 [95% CI, 0.32 to 0.54; P < 0.001]), proximal venous thrombosis (placebo rate, 76 of 678 patients [11.2%]; relative risk, 0.31 [CI, 0.20 to 0.47; P < 0.001]), and symptomatic venous thromboembolism (placebo rate, 36 of 862 patients [4.2%]; relative risk, 0.36 [CI, 0.20 to 0.67; P = 0.001]). Major bleeding was rare, occurring in only one patient in the placebo group.

CONCLUSIONS

Extended LMWH prophylaxis showed consistent effectiveness and safety in the trials (regardless of study variations in clinical practice and length of hospital stay) for venographic deep venous thrombosis and symptomatic venous thromboembolism. The aggregate findings support the need for extended out-of-hospital prophylaxis in patients undergoing hip arthroplasty surgery.

Timing of initial administration of low-molecular-weight heparin prophylaxis against deep vein thrombosis in patients following elective hip arthroplasty: a systematic review

BACKGROUND

Perioperative and postoperative venous thrombosis are common in patients undergoing elective hip surgery. Prophylactic regimens include subcutaneous low-molecular-weight heparin 12 hours or more before or after surgery and oral anticoagulants. Recent clinical trials suggest that low-molecular-weight heparin initiated in closer proximity to surgery is more effective than the present clinical practice. We performed a systematic review of the literature to assess the efficacy and safety of low-molecular-weight heparin administered at different times in relation to surgery vs oral anticoagulant prophylaxis.

METHODS

Reviewers (A.F.M. and S.M.M.) identified studies by searching MEDLINE, reviewing references from retrieved articles, scanning abstracts from conference proceedings, and contacting investigators and pharmaceutical companies. Randomized trials comparing low-molecular-weight heparin administered at different times relative to surgery with oral anticoagulants in patients undergoing elective hip arthroplasty, evaluated using contrast phlebography, were selected. Two reviewers (A.F.M. and S.M.M.) extracted data independently.

RESULTS

The literature review identified 4 randomized trials meeting predefined inclusion criteria. The results indicate that low-molecular-weight heparin initiated in close proximity to surgery resulted in absolute risk reductions of 11% to 13% for deep vein thrombosis, corresponding to relative risk reductions of 43% to 55% compared with oral anticoagulants. Low-molecular-weight heparin initiated 12 hours before surgery or 12 to 24 hours postoperatively was not more effective than oral anticoagulants. Low-molecular-weight heparin initiated postoperatively in close proximity to surgery at half the usual dose was not associated with a clinically or statistically significant increase in major bleeding rates (P =.16).

CONCLUSIONS

The timing of initiating low-molecular-weight heparin significantly influences antithrombotic effectiveness. The practice of delayed initiation of low-molecular-weight heparin prophylaxis results in suboptimal antithrombotic effectiveness without a substantive safety advantage.

Orally active heparin and low-molecular-weight heparin

The heparins, (unfractionated heparin (UFH) and low-molecular-weight heparins (LMWH)) given by subcutaneous or intravenous injection have been used extensively in the prevention and treatment of both venous and arterial thromboembolic disorders. The increasing use of the heparins, LMWHs in particular, in the out of hospital setting has stimulated interest in the development of orally absorbable antithrombotic agents that require little or no monitoring, and this includes the heparins. UFH or LMWH delivered orally has been shown to have an antithrombotic effect in animal thrombosis models although there is little change in plasma coagulation tests. The addition of a simple organic chemical N -(8-(2-hydroxybenzoyl)amino)caprylate (SNAC) to UFH markedly enhances its absorption. A phase II study in patients undergoing total hip replacement indicated that SNAC heparin in two different doses was as effective and safe as UFH given subcutaneously. A phase III clinical trial comparing two doses of SNAC heparin given orally with LMWH by subcutaneous injection for the prevention of venous thromboembolism in patients undergoing total hip replacement is currently underway.

Dalteparin sodium

Dalteparin sodium (Fragmin, Pharmacia Corporation) is a low molecular weight heparin (LMWH) with a mean molecular weight of approximately 5000 Da. As with the other LMWHs, dalteparin sodium has certain advantages over unfractionated heparin (UFH), most important of which are improved bio-availability by sc. injection, a prolonged antithrombotic activity which is highly correlated with body weight permitting the o.d. administration of the drug. Dalteparin sodium has been subjected to a large number of well-designed randomised clinical trials for the prevention and treatment of thrombotic disorders. Based on data from the randomised clinical trials, dalteparin sodium has been approved internationally for a wide spectrum of clinical indications (e.g., prevention of thromboembolic events after surgery). Dalteparin sodium has also been studied in randomised controlled trials in the maintenance of graft patentcy following peripheral vascular surgery, in place of warfarin for the long-term treatment of patients presenting with deep vein thrombosis (DVT), in the prevention of upper extremity thrombosis in patients with indwelling portacath devices and in pregnant patients with a history of previous venous thromboembolism with or without thrombophilia. Dalteparin sodium has been compared with heparin for the prevention of thrombotic complications during haemodyalisis and haemofiltration. These studies have shown promising results but further work is required before dalteparin sodium can be recommended for these indications.

Cost-effectiveness of currently accepted strategies for pulmonary embolism diagnosis

Improvements in the methods of clinical trials combined with the use of objective tests to detect venous thrombosis have enhanced the clinician's ability to diagnose pulmonary embolism and venous thrombosis (venous thromboembolism). The authors updated a previous cost-effectiveness analysis of the commonly recommended strategies for pulmonary embolism diagnosis and management to reflect current clinical practice. Two criteria of effectiveness were used: correct identification of venous thromboembolism and correct identification of venous thromboembolism and correct identification of patients for whom treatment was unnecessary. The cost of each diagnostic alternative was defined as the direct cost of administering the diagnostic tests plus the treatment costs associated with a positive test result. A strategy based on the combined use ofventilation-perfusion lung scanning, serial ultrasonography, cardiorespiratory evaluation, and pulmonary angiography was the most cost-effective. This strategy also necessitated pulmonary angiography in the fewest number of patients. The safety of this strategy relates to two important biologic concepts: 1) local extension of submassive pulmonary embolism in the lung is not an important cause of morbidity or mortality in patients with adequate cardiorespiratory reserve, and 2) in most patients, proximal vein thrombi of the lower extremities are the source of recurrent pulmonary embolism.

New developments in the prevention and treatment of venous thromboembolism

Although unfractionated heparin has been widely used for preventing and treating venous thromboembolism, low-molecular-weight heparins (LMWHs) have been extensively studied. In particular, LMWHs have been valuable in the prevention of venous thromboembolism in high-risk surgical patients, such as those undergoing total joint replacement, and in high-risk medical patients. Recent studies indicated that the extended use of LMWHs after discharge in patients undergoing total hip replacement significantly decreases the frequency of venous thrombosis compared with placebo. Furthermore, LMWHs have been shown to be as effective and safe as unfractionated heparin for the initial treatment of both deep vein thrombosis and pulmonary embolism and have extended the treatment of these conditions into the outpatient setting. New recommendations from the sixth American College of Chest Physicians Consensus Conference on Antithrombotic Therapy and the rationale for change are discussed.

Low-molecular-weight heparin in the treatment of venous thromboembolism

The low-molecular-weight heparins (LMWHs) have been evaluated in the prevention and treatment of deep-vein thrombosis and pulmonary embolism. LMWHs have been found to be safe and effective in this clinical setting and have advantages over unfractionated heparin. These advantages include less serious and less frequent therapeutic complications. The favorable pharmacokinetic profile of LMWHs compared with heparin has allowed for safe, effective, and convenient treatment of patients with venous thromboembolism. Use of LMWHs ultimately results in considerable cost savings for the health care system.

Low-molecular-weight heparin prophylaxis: preoperative versus postoperative initiation in patients undergoing elective hip surgery

Administration of low-molecular-weight heparin prophylaxis in elective hip implant patients commonly begins 12 h preoperatively in European practices to optimize effectiveness, and 12 to 24 h postoperatively in North American practices to optimize safety. A meta-analysis comparing these two treatment regimes revealed that preoperative initiation demonstrated greater efficacy and superior safety for patients (10.0% rate of total deep-vein thrombosis vs. 15.3%, P = .023). In addition to the pre/postsurgical debate, proximity of initiation of low-molecular-weight heparin in relation to surgery is an issue of critical importance. Recent studies revealed that beginning therapy immediately within 2 h preoperatively or 6 h postoperatively dramatically decreased the risk of venous thrombosis. An investigation of low-molecular-weight heparin prophylaxis initiated 2 h before elective hip surgery or approximately 6 h after surgery compared with warfarin sodium revealed that total and proximal deep-vein thrombosis rates were reduced in patients receiving low-molecular-weight heparin compared with warfarin. The frequencies of deep-vein thrombosis for patients receiving preoperative and postoperative dalteparin vs. warfarin for all deep-vein thrombosis were 36 of 337 (10.7%, P < .001) and 44 of 336 (13.1%, P < .001) vs. 81 of 338 (24.0%); and for proximal deep-vein thrombosis were 3 of 354 (0.8%, P = .035) and 3 of 358 (0.8%, P = .033) vs. 11 of 363 (3.0%). Relative risk reductions for the dalteparin groups vs. warfarin ranged from 45% to 72%. In this case, low-molecular-weight heparin administered in close proximity to surgery provided superior efficacy over warfarin. Major bleeding was significantly increased with the preoperative regimen but not the postoperative regimen.

The economic impact of treating deep vein thrombosis with low-molecular-weight heparin: outcome of therapy and health economy aspects

Subcutaneous low-molecular-weight heparin (LMWH) is at least as safe and effective as classical intravenous heparin therapy for the treatment of proximal vein thrombosis. Anticoagulant monitoring and intravenous administration are not required with LMWH treatment, therefore this therapy may offer economic advantages. An economic evaluation of these therapeutic approaches was performed comparing the costs and effectiveness. The evaluation was aimed at helping decision-makers to maximize the health of the population served, subject to available resources. The American-Canadian Thrombosis Study was a multicentre, randomized, double-blind clinical trial that compared treatment by initial continuous intravenous infusion of heparin (followed by 3 months of warfarin therapy) with a once-daily dose of subcutaneous LMWH, tinzaparin sodium (followed by 3 months of warfarin treatment) in patients with acute proximal deep vein thrombosis. In the LMWH-treated group, the cost incurred for 100 patients was $399,403 (Canadian) or $335,687 (US) with a frequency of objectively documented recurrent venous thromboembolism of 2.8%. In the intravenous heparin-treated group, the cost incurred for 100 patients was $ 414,655 (Canadian) or $ 375,836 (US), with a frequency of objectively documented recurrent venous thromboembolism of 6.9%. These results show a cost saving of $ 15,252 (Canadian) or $ 40,149 (US) with the use of LMWH. Multiple sensitivity analyses did not alter the findings of the study which indicated that LMWH therapy is at least as safe and effective but less costly than intravenous heparin treatment. The potential for outpatient therapy in up to 37% of patients who are receiving LMWH would substantially augment the cost-saving. The cost-effectiveness findings presented in this paper are based on the assumption that all costs are covered by a single payer. Outpatient management in many countries will shift the healthcare costs from the healthcare payer to the patient, increasing the economic burden to the patient.

Low-molecular-weight heparin prophylaxis using dalteparin in close proximity to surgery vs warfarin in hip arthroplasty patients: a double-blind, randomized comparison. The North American Fragmin Trial Investigators

BACKGROUND

Based on the current understanding that venous thrombosis starts perioperatively, administration of just-in-time low-molecular-weight heparin immediately before or in close proximity after hip arthroplasty may be more effective than usual clinical practice.

METHODS

We performed a randomized, double-blind trial comparing subcutaneous dalteparin sodium given once daily immediately before or early after surgery with the use of postoperative warfarin sodium in 1472 patients undergoing elective hip arthroplasties. The primary end point was deep vein thrombosis detected using contrast venography performed after surgery (mean, 5. 7 days) in each group.

RESULTS

The frequencies of deep vein thrombosis for patients with interpretable venograms receiving preoperative and postoperative dalteparin for all deep vein thrombosis were 36 (10.7%) of 337 (P<.001) and 44 (13.1%) of 336 (P<.001), respectively, vs 81 (24.0%) of 338 for warfarin; for proximal deep vein thrombosis, 3 (0.8%) of 354 (P =.04) and 3 (0.8%) of 358 (P =.03), respectively, vs 11 (3.0%) of 363. Relative risk reductions for the dalteparin groups ranged from 45% to 72%. Symptomatic thrombi were less frequent in the preoperative dalteparin group (5/337 patients [1.5%]) vs the warfarin group (15/338 patients [4.4%]) (P =.02). Serious bleeding was similar among groups. Increased major bleeding at the surgical site was observed for patients receiving preoperative dalteparin vs warfarin (P =.01).

CONCLUSIONS

A modified dalteparin regimen in close proximity to surgery resulted in substantive risk reductions for all and proximal deep vein thrombosis, compared with warfarin therapy. Such findings have not been observed with low-molecular-weight heparin therapy commenced 12 hours preoperatively or 12 to 24 hours postoperatively vs oral anticoagulants. Increased major but not serious bleeding occurred in patients receiving preoperative dalteparin. Dalteparin therapy initiated postoperatively provided superior efficacy vs warfarin without significantly increased overt bleeding.

Low-molecular-weight heparin prophylaxis using dalteparin extended out-of-hospital vs in-hospital warfarin/out-of-hospital placebo in hip arthroplasty patients: a double-blind, randomized comparison. North American Fragmin Trial Investigators

BACKGROUND

No randomized trials have directly evaluated the need for extended out-of-hospital thromboprophylaxis for patients who have hip arthroplasty in the United States or Canada. The uncertainty as to the need for extended prophylaxis in North American patients is complicated by early hospital discharge, resulting in a short thromboprophylaxis interval.

METHODS

To resolve this uncertainty, we performed a randomized double-blind trial in 569 patients who underwent hip arthroplasty comparing the use of dalteparin sodium started immediately before surgery or early after surgery and extended out-of-hospital to an overall interval of 35 days with the use of warfarin sodium in-hospital and placebo out-of-hospital.

RESULTS

For patients with interpretable venograms in the preoperative, postoperative, and combined dalteparin groups, new proximal vein thrombosis out-of-hospital was observed in 1.3%, 0. 7% (P =.04), and 1.0% (P =.02) of patients, respectively, compared with 4.8% in the in-hospital warfarin/out-of-hospital placebo group. The respective overall cumulative frequencies of all deep vein thrombosis were 30 (17.2%) of 174 patients (P<.001), 38 (22.2%) of 171 (P =.003), and 68 (19.7%) of 345 (P<.001) in the dalteparin groups compared with 69 (36.7%) of 188 for the in-hospital warfarin/out-of-hospital placebo group. For proximal deep vein thrombosis, the respective frequencies were 5 (3.1%) of 162 (P =.02), 3 (2.0%) of 151 (P =.007), and 8 (2.6%) of 313 (P =.002) compared with 14 (9.2%) of 153. No major bleeding occurred during the extended prophylaxis interval.

CONCLUSIONS

Extended dalteparin prophylaxis resulted in significantly lower frequencies of deep vein thrombosis compared with in-hospital warfarin therapy. Despite in-hospital thromboprophylaxis, patients having hip arthroplasty in the United States and Canada remain at moderate risk out-of-hospital. The number needed to treat provides a public health focus; only 24 to 28 patients require extended prophylaxis to prevent 1 new out-of-hospital proximal vein thrombosis. Recent studies demonstrate that asymptomatic deep vein thrombi cause the postphlebitic syndrome; thus, extended out-of-hospital prophylaxis will lessen the burden to both the patient and society.

Low-molecular-weight heparin vs heparin in the treatment of patients with pulmonary embolism. American-Canadian Thrombosis Study Group

BACKGROUND

Pulmonary embolism (PE) occurs in 50% or more of patients with proximal deep-vein thrombosis. Low-molecular-weight heparin treatment is effective and safe in patients with deep vein thrombosis and may also be so in patients with PE. Recent rigorous clinical trials have established objective criteria for determining a high probability of PE by perfusion lung scanning.

OBJECTIVE

To compare low-molecular-weight heparin with intravenous heparin for the treatment of patients with objectively documented PE and underlying proximal deep vein thrombosis.

METHODS

In a multicenter, double-blind, randomized trial, we compared fixed-dose subcutaneous low-molecular-weight heparin (tinzaparin sodium) given once daily with dose-adjusted intravenous heparin given by continuous infusion using objective documentation of clinical outcomes. Pulmonary embolism at study entry was documented by the presence of high-probability lung scan findings.

RESULTS

Of 200 patients with high-probability lung scan findings at study entry, none of the 97 who received low-molecular-weight heparin had new episodes of venous thromboembolism compared with 7 (6.8%) of 103 patients who received intravenous heparin (95% confidence interval for the difference, 1.9%-11.7%; P = .01). Major bleeding associated with initial therapy occurred in 1 patient (1.0%) who was given low-molecular-weight heparin and in 2 patients (1.9%) given intravenous heparin (95% confidence interval for the difference, -2.4% to 4.3%).

CONCLUSIONS

Low-molecular-weight heparin administered once daily subcutaneously was no less effective and probably more effective than use of dose-adjusted intravenous unfractionated heparin for preventing recurrent venous thromboembolism in patients with PE and associated proximal deep vein thrombosis. Our findings extend the use of low-molecular-weight heparin without anticoagulant monitoring to patients with submassive PE.

Treatment of Venous Thromboembolism with Low-Molecular-Weight Heparin

There is now ample evidence to indicate that certain low-molecular-weight heparins given subcutaneously can replace continuous intravenous unfractionated heparin for the initial treatment of venous thromboembolism. The low-molecular-weight heparins have a predictably high absorption rate when given subcutaneously and a prolonged duration of action, permitting them to be given by a once or twice daily injection for the prevention or treatment of venous thrombosis. Furthermore, treatment does not require laboratory monitoring, thus eliminating the need for continuous IV infusion and permitting the early discharge of patients with venous thromboembolism. This should eventually lead to the outpatient treatment of venous thromboembolism. Studies to date indicate that low-molecular-weight heparin is more cost-effective than unfractionated heparin in the treatment of venous thromboembolism and the cost effectiveness will be increased by out-of-hospital treatment. At the present time, the findings associated with any individual low-molecular-weight heparin preparation cannot be extrapolated to different low-molecular-weight heparins, and therefore each must be evaluated in separate clinical trials. The information to date is that low-molecular-weight heparin is safer and more effective than continuous intravenous unfractionated heparin in the treatment of proximal venous thrombosis. The decreased mortality rate seen in two clinical trials, particularly in patients with metastatic cancer, was quite unexpected. This requires further confirmation in larger prospective randomized trials.

A Noninvasive Approach for the Treatment of Patients with Suspected Pulmonary Embolism

The diagnosis of pulmonary embolism is challenging because the signs and symptoms are nonspecific, the findings on ventilation-perfusion lung scans are often nondiagnostic, and pulmonary angiography, although definitive, is not always available. We previously reported that serial noninvasive leg testing provided a practical, noninvasive alternative to pulmonary angiography in patients who had nondiagnostic lung scans and adequate cardiorespiratory reserve. In this prospective cohort study of 1564 patients with suspected pulmonary embolism, ventilation-perfusion lung scanning and serial impedance plethysmography were used to objectively assess prognosis. Only 12 of 627 patients (1.9%) with nondiagnostic lung scans but normal serial leg testing results who were not given anticoagulants had venous thromboembolism during long-term follow-up. Noninvasive serial leg testing can avoid the need for pulmonary angiography for the majority of patients, identify those with proximal vein thrombosis who require anticoagulant treatment, and avert treatment and further investigation of patients who have adequate cardiorespiratory reserve.

Extended prophylaxis against venous thromboembolism following total hip and knee replacement

The recently reported reductions in the incidence of post-operative venous thromboembolism (VTE) are related to the widespread use of prophylactic anticoagulants. Many uncertainties remain with regard to the most effective ways to use thromboprophylaxis, however. The trend towards shorter hospital stays means that patients may receive less than the recommended 7-10 days of prophylaxis. Prolonged periods of thromboprophylaxis may be beneficial for patients at high risk of post-operative VTE, such as those undergoing major orthopaedic surgery. The relative rarity of symptomatic deep vein thrombosis and pulmonary embolism means that very large patient populations are required for studies that rely on clinical endpoints, but studies using venographic endpoints have shown 28-35 days of prophylaxis with low-molecular-weight heparin to be more effective than 10-14 days. Other factors that may influence the efficacy of thromboprophylaxis include the timing of the first injection and the choice of agent.

Long term outpatient prophylaxis for venous thromboembolism

Recent reductions in the incidence of postoperative venous thromboembolism are related to the widespread use of prophylactic anticoagulants, but many uncertainties about the most effective ways to use thromboprophylaxis remain. Orthopedic patients are at high risk of thromboembolism, and the trend towards shorter hospital stays means that they may receive less than the recommended 7 to 10 days of prophylaxis. Longer periods of thromboprophylaxis may be beneficial for high risk patients. The relative rarity of symptomatic deep-vein thrombosis and pulmonary embolism means that very large patient populations are required for studies that rely on clinical endpoints, but studies using venographic endpoints have shown 30 days of prophylaxis with low molecular weight heparin (LMWH) to be more effective than 7 days. Other factors that may influence the efficacy of thromboprophylaxis include the timing of the first injection and the choice of agent.

Thrombin inhibitors as anticoagulant agents

Hirudin and its analogues and the synthetic antithrombin agents are interesting new antithrombotic agents that have been studied in a number of well-designed randomized clinical trials and further studies are underway. These agents offer certain advantages over heparin and low-molecular-weight heparin, and at least one agent is orally bioavailable. Studies have shown that the specific thrombin inhibitors can significantly decrease the incidence of composite cardiac endpoints in acute ischemic syndromes (following thrombolysis for myocardial infarction, unstable angina, and non-Q wave myocardial infarction and coronary angioplasty), but it is disappointing that the benefits obtained during short-term treatment are not sustained in the long term. Recent data are reviewed here from clinical trials supporting the use of the specific antithrombin agents in the treatment of acute cardiac ischemic syndromes, the prevention and treatment of venous thromboembolism, and the management of heparin-induced thrombocytopenia.

The role of newer diagnostic techniques in the diagnosis of pulmonary embolism

Among the evolving techniques for the diagnosis of acute pulmonary embolism, contrast enhanced spiral CT takes a particularly prominent role because it is available at most centers, it images the pulmonary embolism directly, and it is minimally invasive. It has not yet been fully evaluated, however. Magnetic resonance angiography also has appeal for similar reasons. Few patients have been studied, however. Magnetic resonance angiography for pulmonary embolism is still in the early testing phase. Transesophageal echocardiography can image pulmonary embolism in central pulmonary arteries, but preliminary tests suggest that it has a low negative predictive value and cannot be used to exclude pulmonary embolism. Finally, it seems that a rapid and sensitive technique for measuring d-dimer may now be available, which may assist in eliminating the diagnosis of acute pulmonary embolism in a significant percentage of patients in whom the diagnosis is suspected.

Preoperative vs postoperative initiation of low-molecular-weight heparin prophylaxis against venous thromboembolism in patients undergoing elective hip replacement

BACKGROUND

Although preoperative and postoperative initiation of prophylaxis for deep vein thrombosis (DVT) with low-molecular-weight heparin (LMWH) are effective, the relative effectiveness and safety of these approaches is unknown. In the absence of a published definitive level 1 trial addressing this question, a meta-analysis is appropriate.

OBJECTIVE

To report a meta-analysis comparing preoperative with postoperative initiation of prophylaxis of DVT in patients undergoing elective hip replacement.

METHODS

Relevant trials were identified, and potential biases in the meta-analysis were minimized by analyzing all rigorously performed randomized trials that met all of the following criteria for conduct of the trial: (1) double-blind design, (2) objective documentation of the frequencies of DVT by ascending contrast venography, (3) venography performed before or at the time of discharge from the hospital, (4) initiation of the same LMWH preoperatively or postoperatively in dosages shown to be effective, (5) compliance with the criteria for a level 1 trial, and (6) objective documentation of major and minor bleeding according to strict criteria.

RESULTS

Treatment with LMWH initiated preoperatively was associated with a DVT frequency of 10.0% compared with a frequency of 15.3% when the LMWH was initiated postoperatively (P = .02, Fisher exact test). Major bleeding was less frequent in patients receiving preoperatively initiated LMWH than in patients receiving postoperatively initiated LMWH (0.9%, vs. 3.5%; P = .01, Fisher exact test).

CONCLUSIONS

Our findings support the need for a randomized comparison of preoperative and postoperative initiation of pharmacological prophylaxis of DVT. Such a trial would resolve the divergent practices for DVT prophylaxis between Europe and the North American countries, the United States and Canada, and would affect the treatment for thousands of patients on both continents.

Treatment and prevention of venous thromboembolism

Where available, low-molecular-weight heparin (LMWH) is the recommended approach for initial management of venous thromboembolism. When unfractionated heparin is administered, one of the cited heparin nomograms should be used to ensure that the heparin dose is sufficient to rapidly produce heparin levels in the therapeutic range for all patients. Because of the varying sensitivities of thromboplastins, each laboratory should correlate the activated partial thromboplastin time results with heparin's therapeutic range, which will correspond to 0.35 to 0.70 U of heparin/ml blood when using the antifactor Xa assay. Constant vigilance and a high level of suspicion are necessary to establish the clinical diagnosis of heparin-induced thrombocytopenia, and to institute appropriate therapy. When administering warfarin therapy, physicians should be aware of the sensitivity of the thromboplastin being used to provide the international normalized ratio (INR). To ensure that the patients are maintained within the target therapeutic range for INR (in most cases 2.0 to 3.0), the INR should be determined frequently, and the warfarin dosage should then be adjusted appropriately. Patients with an acute episode of venous thromboembolism should receive warfarin therapy for at least 3 months. At the present time, it is reasonable to treat the first recurrence with oral anticoagulants for 12 months and to indefinitely treat more than one recurrence. All patients at moderate to high risk for developing venous thromboembolism should receive prophylaxis. The approaches of proven value include low-dose heparin, LMWH, oral anticoagulants, and intermittent pneumatic compression.

Heparin and low-molecular-weight heparin therapy for venous thromboembolism. The twilight of anticoagulant monitoring

Recent improvements in the methods of clinical trials and the use of accurate objective tests to detect venous thromboembolism have made possible a series of randomized trials to evaluate various treatments for venous thromboembolism. The results of these trials have resolved many of the uncertainties a clinician confronts in selecting an appropriate course of anticoagulant therapy. These trials have shown that the intensity of both initial heparin treatment and long-term anticoagulant therapy must be sufficient to prevent unacceptable rates of recurrence of venous thromboembolism. Patients with proximal deep vein thrombosis who receive inadequate anticoagulant therapy have a risk of clinically evident, objectively documented recurrent venous thromboembolism that approaches 20% to 25%. The need for therapy with heparin and the importance of monitoring blood levels of the effect of heparin have been established. The importance of achieving adequate heparinization was suggested by a nonrandomized trial in 1972 and randomized trials in the 1980s have confirmed this finding. Furthermore, randomized trials have demonstrated the importance of achieving adequate heparinization early in the course of therapy. Unfractionated intravenous heparin has provided an effective therapy for more than half a century, but the need to monitor therapy and establish therapeutic levels is a fundamental problem. It is evident that validated heparin protocols are more successful in establishing adequate heparinization than intuitive ordering by the clinician. However, even with the best of care using a heparin protocol, some patients treated with intravenous heparin will receive subtherapy. In this context, subtherapy reflects a practical limitation of the use of unfractionated heparin, rather than a poor standard of care. Furthermore, it is recognized that the practical difficulties associated with heparin administration are compounded by the substantive practical difficulties of standardizing APTT testing and the therapeutic range. Our findings emphasize the confounding effect that initial heparin treatment has on long-term outcome. In future trials of longterm therapy, it is imperative that the initial therapy is of adequate intensity and duration; failure to administer adequate initial treatment may lead to a poor outcome that is falsely attributed to the long-term therapy under evaluation. Therapy with low-molecular-weight heparin, which does not require monitoring and dose finding, is the likely practical solution to these dilemmas. Based on the experience of difficulties achieving adequate therapy with subcutaneous unfractionated heparin dosing, we administered a low-molecular-weight heparin formulation in a single daily dose, rather than splitting the treatment into 2 equal doses. The initial intensity of therapy was thereby maximized. Therapy with low-molecular-weight heparin proved to be better than therapy with unfractionated heparin.

Heparin and low-molecular-weight heparin in the treatment of venous thromboembolism

Venous thromboembolism (deep vein thrombosis and pulmonary embolism) continues to constitute a major clinical challenge. Effective and safe prophylactic measures against venous thromboembolism are now available for most high risk patients. In spite of this, pulmonary embolism is responsible for approximately 150,000 to 200,000 deaths per year in the United States alone. Over the past 20 years, based on a number of high quality (Level I) clinical trials, patterns of practice with respect to the treatment of venous thromboembolism have changed dramatically. The standard treatment of venous thromboembolism has been the use of unfractionated heparin by continuous intravenous infusion, with laboratory monitoring using the activated partial thromboplastin time (APTT), with warfarin starting on day 1 or 2 and continued for 3 months. Unfractionated heparin has withstood the test of time and has been shown to be safe and effective in preventing recurrent venous thromboembolism and death in numerous clinical trials. The response of individual patients to heparin is highly variable, requiring frequent laboratory monitoring. Heparin has a number of other troublesome side effects including bleeding, heparin-induced thrombocytopenia and osteoporosis. The low-molecular-weight heparins have a number of advantages over unfractionated heparin. In particular, their increased bio-availability and prolonged half-life permit once daily subcutaneous injections and their predictable antithrombotic response based on body weight permits treatment without laboratory monitoring. Low-molecular-weight heparin in therapeutic doses causes less bleeding than unfractionated heparin and evidence is accumulating that the incidence of heparin-induced thrombocytopenia and osteoporosis are decreased as well. In individual clinical trials and meta-analyses, low-molecular-weight heparin treatment results in decreased recurrent thromboembolism, major bleeding and death when compared with unfractionated heparin in the treatment of deep vein thrombosis and pulmonary embolism. These agents have also been shown to be both effective and safe for the out-of-hospital treatment of venous thrombosis. Therefore, in many countries, low-molecular-weight heparin has replaced unfractionated heparin for the treatment of venous thromboembolism.

Venous thromboembolism and cancer

The association of thrombosis with malignant disease has been recognized for well over 100 years. Evidence from experimental and clinical studies indicates that the haemostatic system is involved in the growth, invasion and metastasis of tumours. Laboratory parameters of haemostasis are frequently deranged in patients with cancer and overt thrombosis is common spontaneously where it may be the first sign of malignancy or secondary to therapy. The mechanisms by which coagulation activation facilitates the malignant process remain to be completely elucidated, but it is clear that cells and proteins of the coagulation and fibrinolytic systems are involved at many steps in the processes of tumour growth and dissemination. The low-molecular-weight heparins with their well-proven safety and efficacy profiles offer unique modalities for the prevention and treatment of cancer-associated thrombosis. They may also play a role in overall mortality reduction in patients with malignant disease.

Thrombophilia: disorders predisposing to venous thromboembolism

Venous thromboembolism continues to present a challenge to clinicians. Over the years, a number of risk factors which predispose to venous thromboembolism have been identified, and these risk factors are taken into account in the formulation of recommendations for the prevention and treatment of these disorders. In more recent years, there have been major advances in our understanding of congenital or acquired defects that predispose to thrombosis leading to these so-called acquired or inherited forms of thrombophilia. The list of acquired forms of thrombophilia now includes anti-thrombin, protein C, protein S, activated protein C resistance, the prothrombin 20210A mutant, homocysteinemia and a number of rare defects which either enhance coagulation or interfere with fibrinolysis. In spite of these advances, there are numerous families with thrombophilia in whom none of the known defects can be demonstrated. The challenge for the future is to discover some of these as yet unknown factors and to determine the most appropriate methods for the prevention and treatment of venous thromboembolism in susceptible individuals with thrombophilia.

Prophylaxis of deep venous thrombosis and pulmonary embolism. Current recommendations

Pulmonary embolism is responsible for approximately 150,000 to 200,000 deaths per year in the United States. Venous thromboembolism usually occurs as a complication in patients who are sick and hospitalized, but it may also affect ambulant and otherwise healthy individuals. Many patients who die from pulmonary embolism succumb suddenly or within 2 hours after the acute event (i.e., before therapy can be initiated or take effect). Therefore, prevention is the key to reducing death and morbidity from venous thromboembolism. Effective and safe prophylactic measures against venous thromboembolism are now available for most high-risk patients. This article highlights practical approaches to the prevention of venous thromboembolism.

Unfractionated and low-molecular-weight heparin. Comparisons and current recommendations

Intravenous heparin followed by warfarin has been the classical anticoagulant therapy of acute venous thromboembolism for the past 30 years. In recent years a number of low-molecular-weight heparins have become available for clinical trials. These agents have a number of advantages over unfractionated heparin and are now being used internationally for the prevention and treatment of venous thromboembolism. Low-molecular-weight heparin will undoubtedly replace intravenous unfractionated heparin not only in the treatment of venous thromboembolism but in other conditions where heparin therapy is indicated. Whether or not the low-molecular-weight heparins can decrease or eliminate some of the complications of unfractionated heparin will depend on the outcome of future clinical trials.

Different effects of heparin in males and females

OBJECTIVE

To determine whether women have a Pharmacological predisposition to bleeding and a worse outcome than men during heparin therapy, in light of recent studies showing that women have a higher risk of bleeding complications following anticoagulant therapy for thrombotic disorders than men.

DESIGN

Prospectively planned subgroup analysis of a double-blind randomized study.

SETTING

Academic tertiary care hospitals in Hamilton, Ont.

PATIENTS

A total of 199 consecutive patients (105 women, 93 men) presenting with proximal deep vein thrombosis. (One patient was not included due to incomplete data).

OUTCOME MEASURES

Activated partial thromboplastin time (APTT) values and heparin levels were assessed every 4 to 6 hours after a standard heparin bolus and infusion. The effect of sex on heparin doses and levels was also assessed after stable therapeutic heparin infusions were achieved.

RESULTS

The women had higher heparin levels than the men (0.560 [standard error of the mean, SEM 0.056] units/mL v. 0.347 [SEM 0.062] units/mL, p < 0.0001) and higher APTT values (94.9 [SEM 0.50] seconds v. 81.2 [SEM 0.53] seconds, p = 0.0002) 4 to 6 hours after being given the same heparin bolus and infusion doses. After achieving therapeutic APTT values, the women received lower heparin doses than the men (27.9 [SEM 0.24] 1000 units/24 hours v. 34.5 [SEM 0.24] 1000 units/24 hours, p < 0.0001) but had higher heparin levels (0.349 [SEM 0.035] units/mL v. 0.292 [SEM 0.036] units/mL, p = 0.034). The effect of sex was also determined after correcting for the known effects of weight and age on heparin therapy. After adjusting for patient weight, among the women, older women had higher heparin levels but, among the men, there was little effect of age. There were no sex differences with respect to bleeding complications or recurrent thromboembolic disease.

CONCLUSION

Women showed alterations in the pharmacokinetics of heparin, which could explain a predisposition to bleeding complications. Under the heparin protocol used in this study, heparin doses were rapidly adjusted, which may explain why rates of bleeding complications and recurrent thromboembolism were similar in men and women. We do not recommend changes in heparin therapy based on these results, but suggest the use of protocols that assess coagulation parameters frequently and then adjust heparin doses rapidly, in order to individualize therapy. Further study is required to determine whether there are sex differences in bleeding complications associated with anticoagulant therapy, and to confirm the altered pharmacokinetics of heparin in women.

Relation between the time to achieve the lower limit of the APTT therapeutic range and recurrent venous thromboembolism during heparin treatment for deep vein thrombosis

BACKGROUND

Randomized trials have demonstrated the importance of achieving adequate heparinization early in the course of therapy. Recently, some authors reported a pooled analysis of selected studies in the literature that suggested that there is no convincing evidence that the risk of recurrent venous thromboembolism is critically dependent on achieving a therapeutic activated partial thromboplastin time result at 24 to 48 hours.

METHODS

We provide the analyses of patient groups entered into our series of 3 consecutive double-blind randomized trials evaluating initial heparin therapy for proximal deep venous thrombosis.

RESULTS

Logistic regression analysis of the patient groups receiving the less intense initial intravenous heparin dose of 30,000 U/24 h demonstrated that subtherapy for 24 hours predicted the onset of venous thromboembolic events. Failure to achieve a therapeutic activated partial thromboplastin time by 24 hours was associated with a 23.3% frequency of venous thromboembolism vs 4% to 6% for those whose activated partial thromboplastin time exceeded the therapeutic threshold by 24 hours (P=.02). Time-to-event analysis shows the increased frequency of recurrent venous thromboembolic events during the period of study in patients who were subtherapeutic for 24 hours compared with those who were therapeutic (P=.001).

CONCLUSIONS

Our findings reaffirm the clinical importance of rapidly achieving therapeutic levels of heparin. Patients who failed to achieve the therapeutic threshold by 24 hours were at an increased risk of subsequent recurrent venous thromboembolism. These findings are independently supported by the results of a randomized trial comparing different intensities of initial heparin treatment by continuous infusion.

The importance of initial heparin treatment on long-term clinical outcomes of antithrombotic therapy. The emerging theme of delayed recurrence

BACKGROUND

Recent clinical trials of venous thromboembolism treatment suggest inadequate initial heparin therapy predisposes patients to late recurrence of thromboembolism. However, a recent review article was unable to demonstrate a relationship between initial heparin therapy and late recurrence.

OBJECTIVE

To evaluate the relationship between initial heparin treatment and long-term clinical outcome in 3 consecutive, randomized, double-blind trials that used similar study designs and patient populations and objective documentation of recurrent venous thromboembolism.

METHODS

The trials were performed sequentially and compared the use of continuous intravenous with subcutaneous heparin, continuous intravenous heparin for 10 or 5 days, and continuous intravenous heparin with once-daily subcutaneous low-molecular-weight heparin. All patients were followed up for 3 months to assess the a priori hypothesis that inadequate initial heparin therapy could lead to recurrent venous thromboembolism during long-term therapy with warfarin sodium.

RESULTS

The following were the observed rates of recurrent venous thromboembolism: continuous intravenous heparin, 3 (5.2%) of 58 patients vs subcutaneous heparin, 11 (19.3%) of 57 patients; continuous intravenous heparin for 10 days, 7 (7.0%) of 100 patients or for 5 days, 7 (7.1%) of 99 patients; and continuous intravenous heparin, 15 (6.9%) of 219 patients vs low-molecular-weight heparin, 6 (2.8%) of 213 patients. Pooled analysis of the patients treated with continuous intravenous heparin showed that of the total 32 patients with recurrent venous thromboembolism, in 6 patients thromboembolism occurred early (< 10 days) and 26 patients thromboembolism occurred late. Of these patients, the majority (20/32 [62.5%]) had therapeutic prothrombin time or international normalized ratio values before or at the time of the recurrent thromboembolic event.

CONCLUSION

Our findings demonstrate that the initial heparin treatment affects the long-term outcome. This conclusion applies when these data are analyzed for each individual study by treatment group, observed difference in outcome, and pooled analysis.

Treatment of proximal vein thrombosis with subcutaneous low-molecular-weight heparin vs intravenous heparin. An economic perspective

BACKGROUND

Subcutaneous low-molecular-weight heparin is at least as effective and safe as classic intravenous heparin therapy for the treatment of proximal vein thrombosis. Anticoagulant monitoring is not required with low-molecular-weight heparin.

OBJECTIVE

To perform an economic evaluation of these therapeutic approaches by comparing cost and effectiveness.

PATIENTS AND METHODS

A randomized trial in 432 patients with proximal vein thrombosis that compared intravenous heparin and low-molecular-weight heparin with objective documentation of clinical outcomes provided the opportunity to perform an analysis of cost-effectiveness to rank these alternative therapies in terms of both their cost and effectiveness. The economic viewpoint of this analysis was that of a third-party payer (ie, a ministry of health in Canada or an insurance company in the United States).

RESULTS

In the intravenous heparin-treated group, the cost incurred for 100 patients was $414,655 (Canadian dollars) or $375,836 (US dollars), with a frequency of objectively documented venous thromboembolism of 6.9%. In the low-molecular-weight heparin-treated group, the cost incurred for 100 patients was $399,403 (Canadian dollars) or $335,687 (US dollars), with a frequency of objectively documented venous thromboembolism of 2.8%, thus providing a cost saving of $15,252 (Canadian dollars) or $40,149 (US dollars). Multiple sensitivity analyses were performed, and these procedures did not alter the findings of the study.

CONCLUSIONS

The findings indicate that low-molecular-weight heparin therapy is at least as effective and safe but less costly than intravenous heparin treatment. The potential for outpatient therapy in up to 37% of patients who are receiving low-molecular-weight heparin would substantially augment the cost saving.

Subcutaneous low-molecular-weight heparin vs warfarin for prophylaxis of deep vein thrombosis after hip or knee implantation. An economic perspective

BACKGROUND

Postoperative venous thrombosis and pulmonary embolism present a major clinical threat to patients undergoing total hip or knee arthroplasty. We performed an economic evaluation of warfarin sodium and subcutaneous low-molecular-weight heparin sodium prophylaxis comparing cost and effectiveness.

METHODS

A consecutive series of 1436 patients who underwent hip or knee arthroplasty comparing these 2 regimens in a randomized trial with objective documentation of outcomes provided the opportunity to perform economic evaluations for Canada and the United States.

RESULTS

Deep vein thrombosis was documented in 231 (37.4%) of 617 patients given warfarin and in 185 (31.4%) of 590 patients given low-molecular-weight heparin (P = .03). In Canada, warfarin and low-molecular-weight heparin (tinzaparin sodium) incurred costs per 100 patients of $11,598 and $9,197, respectively, providing a cost savings of $2,401 for the low-molecular-weight heparin group. The drug cost of low-molecular-weight heparin (tinzaparin) was $6 per day and for warfarin was $0.32 per day. Sensitivity analysis showed that low-molecular-weight heparin is more costly if drug costs are increased by 1.5-fold (ie, the cost of tinzaparin is increased from $6 per day to $8.82 per day or more). In the United States, the analysis was also not definitive; low-molecular-weight heparin was more costly than warfarin at drug costs of $15 and $2.01 per day, respectively.

CONCLUSIONS

Our findings indicate that the decision to use low-molecular-weight heparin or warfarin prophylaxis in patients undergoing major joint replacement surgery is a finely tuned trade-off. Prophylaxis with low-molecular-weight heparin is equally or more effective than the more complex prophylaxis with warfarin. Major bleeding is uncommon but less frequent with warfarin use. The most significant parameters that influence the comparative cost-effectiveness are the cost of the drug, the cost of international normalized ratio monitoring, and the costs associated with major bleeding. The analysis also demonstrates that the results are health care system dependent (Canada vs US). In Canada, low-molecular-weight heparin (tinzaparin) is less costly because it avoids the need for international normalized ratio monitoring. In the United States, the drug cost for low-molecular-weight heparin will likely be the principal determinant of relative cost-effectiveness.

Low-molecular-weight heparin therapy and mortality

There is ample evidence from clinical trials to justify giving certain low-molecular-weight heparins (LMWHs) subcutaneously rather than administering continuous intravenous unfractionated heparin for the initial treatment of venous thromboembolic disease. The LMWHs given by subcutaneous injection have a predictable anticoagulant response and prolonged duration of action. They can, therefore, be administered once or twice daily to treat venous thrombosis. Furthermore, treatment with these agents does not require laboratory monitoring. Eliminating the need for intravenous therapy and for laboratory monitoring should allow patients to be discharged earlier, and eventually lead to the outpatient treatment of venous thromboembolism. Studies to date indicate that LMWH is safer and as effective as continuous intravenous heparin in the treatment of venous thrombosis. The decreased mortality rates seen in two clinical trials, particularly in patients with metastatic cancer, were an unexpected but intriguing finding. This requires further confirmation, in larger prospective randomized trials.

Low-molecular-weight heparin: prophylaxis and treatment of venous thromboembolism

Intravenous heparin followed by warfarin has been the classical anticoagulant therapy of acute venous thromboembolism for the last 30 years. Furthermore, low-dose unfractionated heparin given two to three times daily has been the most popular form of prophylaxis for venous thrombosis. In recent years, a number of low-molecular-weight heparins have become available for clinical trials. These agents have many advantages over unfractionated heparin and are now being used widely internationally for the prevention and treatment of venous thromboembolism. Indeed, low-molecular-weight heparin will undoubtedly replace intravenous unfractionated heparin not only in the treatment of venous thromboembolism, but in other conditions where heparin therapy is indicated. Whether or not the low-molecular-weight heparins can decrease or eliminate some of the complications of unfractionated heparin will depend on the outcome of future clinical trials.

Prevention and treatment of venous thromboembolism

All patients at moderate to high risk for the development of venous thromboembolism should receive prophylaxis. The approaches of proven value include low dose heparin, low molecular weight heparin, oral anticoagulants and intermittent pneumatic compression. The use of one of the cited heparin nomograms will ensure that all patients are rapidly brought within the therapeutic range. Because of the varying sensitivities of thromboplastins, each laboratory should establish a therapeutic range using the activated partial thromboplastin time (APTT) which will correspond to 0.2 to 0.4 U/ml of heparin. Constant vigilance and a high level of suspicion are necessary to establish the clinical diagnosis of heparin-induced thrombocytopenia, and to institute appropriate therapy. Physicians should be aware of the sensitivity of the thromboplastin being used in the performance of the International Normalised Ratio (INR). Care must be taken to ensure that patients are maintained within the target therapeutic range for INR (in most cases 2 to 3) by frequent determination of the INR and appropriate adjustments of warfarin dosage. Low molecular weight heparin is the recommended approach to the initial management of venous thromboembolism where these agents are available. Patients with an acute episode of venous thromboembolism should receive warfarin therapy for at least 3 months. At the present time it is reasonable to treat the first recurrence with oral anticoagulants for a period of 12 months and indefinitely for more than 1 recurrence. For selected patients with acute massive pulmonary embolism, thrombolytic therapy with one of the available agents is recommended. However, the role of thrombolytic therapy in patients with proximal venous thrombosis remains unclear. In selected patients with acute venous thromboembolism who have contraindications to anticoagulant therapy or who-have objectively documented recurrent disease while on adequate therapy, the insertion of an inferior vena cava filter is recommended.

Aging and heparin-related bleeding

BACKGROUND

Many studies have suggested that elderly patients are at increased risk of bleeding during heparin therapy.

OBJECTIVE

To establish whether the risk of bleeding in the elderly results from concomitant risk factors or is associated with the aging process itself.

METHODS

One hundred ninety-nine patients who presented with proximal deep vein thrombosis were treated with a standard intravenous heparin protocol in a double-blind, randomized, prospective study. Bleeding complications were monitored. Activated partial thromboplastin times and heparin levels were assessed 4 to 6 hours after a standard intravenous heparin bolus and infusion. Heparin doses and heparin levels were also assessed after stable therapeutic heparin infusion rates were established.

RESULTS

There was an increase in total and major bleeding complications with aging (P < .05) that was not accounted for by standard risk factors for bleeding. Aging was associated with an increase in heparin levels (r = .239, P = .003) and a tendency for an increase in activated partial thromboplastin time (r = .134, P = .07) after standard heparin doses. Aging was also associated with lower heparin dose requirements (r = .267, P = .003) after therapeutic activated partial thromboplastin times were achieved.

CONCLUSION

Aging is a risk for heparin-related bleeding that may be explicable by age-related changes in the pharmacologic characteristics of heparin.

Cost-effectiveness of pulmonary embolism diagnosis

BACKGROUND

In recent years, improvements in the methods of clinical trials and the use of objective tests to detect venous thrombosis have enhanced the clinician's ability to diagnose pulmonary embolism.

OBJECTIVE

To perform a cost-effectiveness analysis of the commonly recommended strategies for pulmonary embolism diagnosis and management.

METHODS

Two criteria of effectiveness were used: correct identification of pulmonary embolism and correct identification of patients in whom treatment was unnecessary. The cost of each diagnostic alternative was defined as the direct cost of administering the diagnostic test plus the treatment cost associated with a positive test result. Data derived from a decision analysis published separately on 662 patients were used for this study.

RESULTS

A strategy based on the use of ventilation-perfusion lung scans, serial impedance plethysmography, and pulmonary angiography was the most cost-effective. It remained so under all possible variations within the sensitivity analysis.

CONCLUSIONS

The strategy that requires pulmonary angiography in the fewest patients is a combination of ventilation-perfusion lung scans and serial impedance plethysmography. This strategy also proved to be the most cost-effective.