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

BACKGROUND

Oral anticoagulants, such as dabigatran etexilate, an oral, direct thrombin inhibitor, that do not require monitoring or dose adjustment offer potential for prophylaxis against venous thromboembolism (VTE) after total knee replacement surgery.

METHODS

In this randomized, double-blind study, 2076 patients undergoing total knee replacement received dabigatran etexilate, 150 mg or 220 mg once-daily, starting with a half-dose 1-4 hours after surgery, or subcutaneous enoxaparin 40 mg once-daily, starting the evening before surgery, for 6-10 days. Patients were followed-up for 3 months. The primary efficacy outcome was a composite of total VTE (venographic or symptomatic) and mortality during treatment, and the primary safety outcome was the incidence of bleeding events.

RESULTS

The primary efficacy outcome occurred in 37.7% (193 of 512) of the enoxaparin group versus 36.4% (183 of 503) of the dabigatran etexilate 220 mg group (absolute difference, -1.3%; 95% CI, -7.3 to 4.6) and 40.5% (213 of 526) of the 150 mg group (2.8%; 95% CI, -3.1 to 8.7). Both doses were noninferior to enoxaparin based on the pre-specified noninferiority criterion. The incidence of major bleeding did not differ significantly between the three groups (1.3% versus 1.5% and 1.3% respectively). No significant differences in the incidences of liver enzyme elevation and acute coronary events were observed during treatment or follow-up.

CONCLUSIONS

Dabigatran etexilate (220 mg or 150 mg) was at least as effective and with a similar safety profile as enoxaparin for prevention of VTE after total knee-replacement surgery.

A new oral direct thrombin inhibitor, dabigatran etexilate, compared with enoxaparin for prevention of thromboembolic events following total hip or knee replacement: the BISTRO II randomized trial

BACKGROUND

Dabigatran etexilate is an oral direct thrombin inhibitor undergoing evaluation for the prevention of venous thromboembolism (VTE) following orthopedic surgery.

METHODS

In a multicenter, parallel-group, double-blind study, 1973 patients undergoing total hip or knee replacement were randomized to 6-10 days of oral dabigatran etexilate (50, 150 mg twice daily, 300 mg once daily, 225 mg twice daily), starting 1-4 h after surgery, or subcutaneous enoxaparin (40 mg once daily) starting 12 h prior to surgery. The primary efficacy outcome was the incidence of VTE (detected by bilateral venography or symptomatic events) during treatment.

RESULTS

Of the 1949 treated patients, 1464 (75%) patients were evaluable for the efficacy analysis. VTE occurred in 28.5%, 17.4%, 16.6%, 13.1% and 24% of patients assigned to dabigatran etexilate 50, 150 mg twice daily, 300 mg once daily, 225 mg twice daily and enoxaparin, respectively. A significant dose-dependent decrease in VTE occurred with increasing doses of dabigatran etexilate (P < 0.0001). Compared with enoxaparin, VTE was significantly lower in patients receiving 150 mg twice daily [odds ratio (OR) 0.65, P = 0.04], 300 mg once daily (OR 0.61, P = 0.02) and 225 mg twice daily (OR 0.47, P = 0.0007). Compared with enoxaparin, major bleeding was significantly lower with 50 mg twice daily (0.3% vs. 2.0%, P = 0.047) but elevated with higher doses, nearly reaching statistical significance with the 300 mg once-daily dose (4.7%, P = 0.051).

CONCLUSIONS

Oral administration of dabigatran etexilate, commenced early in the postoperative period, was effective and safe across a range of doses. Further optimization of the efficacy/safety balance will be addressed in future studies.

Oral, direct Factor Xa inhibition with BAY 59-7939 for the prevention of venous thromboembolism after total hip replacement

BACKGROUND

Joint replacement surgery is an appropriate model for dose-ranging studies investigating new anticoagulants.

OBJECTIVES

To assess the efficacy and safety of a novel, oral, direct factor Xa (FXa) inhibitor--BAY 59-7939--relative to enoxaparin in patients undergoing elective total hip replacement.

METHODS

In this double-blind, double-dummy, dose-ranging study, patients were randomized to oral BAY 59-7939 (2.5, 5, 10, 20, or 30 mg b.i.d.), starting 6-8 h after surgery, or s.c. enoxaparin 40 mg once daily, starting on the evening before surgery. Treatment was continued until mandatory bilateral venography was performed 5-9 days after surgery.

RESULTS

Of 706 patients treated, 548 were eligible for the primary efficacy analysis. The primary efficacy endpoint was the incidence of any deep vein thrombosis, non-fatal pulmonary embolism, and all-cause mortality; rates were 15%, 14%, 12%, 18%, and 7% for BAY 59-7939 2.5, 5, 10, 20, and 30 mg b.i.d., respectively, compared with 17% for enoxaparin. The primary efficacy analysis did not demonstrate any significant trend in dose-response relationship for BAY 59-7939. The primary safety endpoint was major, postoperative bleeding; there was a significant increase in the frequency of events with increasing doses of BAY 59-7939 (P = 0.045), but no significant differences between individual BAY 59-7939 doses and enoxaparin.

CONCLUSIONS

When efficacy and safety were considered together, the oral, direct FXa inhibitor BAY 59-7939, at 2.5-10 mg b.i.d., compared favorably with enoxaparin for the prevention of venous thromboembolism in patients undergoing elective total hip replacement.

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.

Dose escalating safety study of a new oral direct thrombin inhibitor, dabigatran etexilate, in patients undergoing total hip replacement: BISTRO I

BACKGROUND

Dabigatran etexilate (BIBR 1048) is an oral direct thrombin inhibitor undergoing evaluation for the prevention of venous thromboembolism (VTE) following total hip replacement. Following oral administration, dabigatran etexilate is rapidly converted to its active form dabigatran (BIBR 953 ZW).

OBJECTIVES

To determine the safe therapeutic range of dabigatran etexilate following total hip replacement.

METHODS

In a multicenter, open-label, dose-escalating study, 314 patients received oral doses of dabigatran etexilate (12.5, 25, 50, 100, 150, 200 and 300 mg twice daily or 150 and 300 mg once daily) administered 4-8 h after surgery, for 6-10 days. Dose escalation was based on clinical and pharmacokinetic data. The primary safety outcome was major bleeding. The primary efficacy outcome included venographic deep vein thrombosis (DVT), symptomatic DVT and pulmonary embolism, during the treatment period.

RESULTS

No major bleeding event was observed in any group, but two patients at the highest dose (300 mg twice daily) suffered bleeding from multiple sites associated with reduced renal clearance and prolonged pharmacodynamic (PD) parameters. A dose-response was demonstrated for minor bleeding events. Of the 289 treated patients, 225 patients had evaluable venograms. The overall incidence of DVT was 12.4% (28/225 patients). There was no consistent relationship between the dose and incidence of DVT, the highest incidence in any group being 20.8% (5/24 patients). The lowest dose (12.5 mg twice daily) showed a high rate of proximal DVT [12.5% (3/24)] and no increase in PD parameters. Peak and trough plasma concentrations, area under the dabigatran plasma concentration-time curve and PD parameters also increased in proportion with the dose. Higher dabigatran plasma concentrations were associated with lower DVT rates. Approximately 20% of the patients had low plasma concentrations after the first dose suggesting further optimization of the preliminary tablet formulation is required.

CONCLUSIONS

Dabigatran etexilate demonstrates an acceptable safety profile, with a therapeutic window above 12.5 mg and below 300 mg twice daily. The low number of VTE events within each treatment group indicates a satisfactory antithrombotic potential, although the study was not powered for an efficacy analysis. Additional studies are ongoing to optimize oral absorption and the efficacy/safety balance.

Frequency and timing of clinical venous thromboembolism after major joint surgery

Over a 13-year period we studied all patients who underwent major hip and knee surgery and were diagnosed with objectively confirmed symptomatic venous thromboembolism, either deep venous thrombosis or non-fatal pulmonary embolism, within six months after surgery. Low-molecular-weight heparin had been given while the patients were in hospital. There were 5607 patients. The cumulative incidence of symptomatic venous thromboembolism was 2.7% (150 of 5607), of which 1.1% had developed pulmonary embolism, 1.5% had deep venous thrombosis and 0.6% had both. Patients presented with deep venous thrombosis at a median of 24 days and pulmonary embolism at 17 days after surgery for hip fracture. After total hip replacement, deep venous thrombosis and pulmonary embolism occurred at a median of 21 and 34 days respectively. After total knee replacement, the median time to the presentation of deep venous thrombosis and pulmonary embolism was 20 and 12 days respectively. The cumulative risk of venous thromboembolism lasted for up to three months after hip surgery and for one month after total knee replacement. Venous thromboembolism was diagnosed after discharge from hospital in 70% of patients who developed this complication. Despite hospital-based thromboprophylaxis, most cases of clinical venous thromboembolism occur after discharge and at different times according to the operation performed.

The direct thrombin inhibitor melagatran followed by oral ximelagatran compared with enoxaparin for the prevention of venous thromboembolism after total hip or knee replacement: the EXPRESS study

BACKGROUND

Ximelagatran and its subcutaneous (s.c.) form melagatran are novel direct thrombin inhibitors for the prevention and treatment of thromboembolic disease.

METHODS

In a double-blind study, 2835 consecutive patients undergoing total hip or knee replacement were randomized to either melagatran/ximelagatran or enoxaparin. Melagatran 2 mg was started immediately before surgery; 3 mg was then administered postoperatively, followed by 24 mg of oral ximelagatran b.i.d. beginning the next day. Enoxaparin 40 mg, administered subcutaneously o.d., was started 12 h before surgery. Both treatments were continued for 8-11 days. The main efficacy outcome measures were major venous thromboembolism (VTE); [proximal deep vein thrombosis (DVT), non-fatal and/or fatal pulmonary embolism (PE), death where PE could not be ruled out], and total VTE (proximal and distal DVT; PE; death from all causes). DVT was detected by mandatory bilateral ascending venography at the end of the treatment period or earlier if clinically suspected. The main safety outcome was bleeding.

RESULTS

The rates of major and total VTE were significantly lower in the melagatran/ximelagatran group compared with the enoxaparin group (2.3% vs. 6.3%, P = 0.0000018; and 20.3% vs. 26.6%, P < 0.0004, respectively). Fatal bleeding, critical site bleeding and bleeding requiring reoperation did not differ between the two groups. 'Excessive bleeding as judged by the investigator' was more frequent with melagatran/ximelagatran than with enoxaparin.

CONCLUSIONS

In patients undergoing total hip or knee replacement, preoperatively initiated s.c. melagatran followed by oral ximelagatran was significantly more effective in preventing VTE than preoperatively initiated s.c. enoxaparin.

Prolonged Thromboprophylaxis Following Hip Replacement Surgery – Results of a Double-blind, Prospective, Randomised, Placebo-controlled Study with Dalteparin (Fragmin®)

Discontinuation of thromboprophylaxis a few days after surgery may unmask delayed hypercoagulability and contribute to late formation of deep venous thrombosis (DVT). To investigate whether thromboprophylaxis should be prolonged beyond the hospital stay, a prospective, double-blind randomised study was conducted in 308 patients. All patients received initial thromboprophylaxis with dalteparin, dextran and graded elastic stockings. On day 7, patients were randomised to receive dalteparin (Fragmin®) 5000IU once daily, or placebo, for 4 weeks. All patients were subjected to bilateral venography, perfusion ventilation scintigraphy and chest X-ray on days 7 and 35. Patients with venographically verified proximal DVT on day 7 were withdrawn from the randomised study to receive anticoagulant treatment. The overall prevalence of DVT on day 7 was 15.9%. On day 35, the prevalence of DVT was 31.7% in placebo-treated patients compared with 19.3% in dalteparin-treated patients (p = 0.034). The incidence of DVT from day 7 to day 35 was 25.8% in the placebo-treated group versus 11.8% in the dalteparin-treated group (p = 0.017). The incidence of symptomatic pulmonary embolism (PE) from day 7 to day 35 was 2.8% in the placebo-treated group compared with zero in the dalteparin-treated group. This included one patient who died from PE. No patients experienced serious complications related to the injections of dalteparin or placebo. This study shows that prolonged thromboprophylaxis with dalteparin, 5000 IU, once daily for 35 days significantly reduces the frequency of DVT and should be recommended for 5 weeks after hip replacement 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.

Late occurring clinical deep vein thrombosis in joint-operated patients

In a prospective study of 4,840 patients, we determined the annual incidence of clinical deep vein thrombosis (DVT) in mobilized, discharged orthopedic-operated "high-risk" patients (hip replacement surgery, knee replacement surgery, nailed hip fracture) and assumed "low-risk" patients (diagnostic knee arthroscopy). In addition, the time from the operation to the time when the patients were readmitted with clinically suspected DVT and the distribution of radiologically-confirmed DVT were recorded. Thromboprophylaxis was routinely given for about 10 days to the high-risk groups during the hospital stay but not to patients undergoing knee arthroscopy. During 9 years, the annual incidence of DVT following major procedures was 2.1% (95% CI 1.6-2.6) vs. 0.6% (95% CI 0.2-1.1) after diagnostic knee arthroscopy. Symptoms appeared, on average, 27 (3-150) days after total hip replacement surgery, 36 (3-150) days after nailed hip fracture, 17 (6-30) days after total knee replacement and 1 (1-6) day after knee arthroscopy. In hip-operated patients, 50% of the DVTs were found in the proximal veins vs. 40% following knee arthroplasty.

Toxic effects of methylmethacrylate monomer on leukocytes and endothelial cells in vitro

The influence of methylmethacrylate monomer (MMA) on the cellular integrity of monocytes, granulocytes and endothelial cells in vitro was investigated. Clinically relevant blood concentrations of MMA (i.e., 5-10 micrograms/mL) were clearly cytotoxic to all cell types studied, as evidenced by the release of lactic dehydrogenase (LD) and 51Cr, and increased uptake of trypan blue (vital staining). Scanning electron microscopic examination of cells treated with 10 micrograms/mL MMA showed marked signs of cytotoxicity after 1 min incubation, and after 30 min the majority of the cells were totally disintegrated. These findings may have clinical bearing on intraoperative cardiorespiratory dysfunction and deep vein thrombosis in MMA-fixed joint replacement surgery.

Dabigatran versus enoxaparin for prevention of venous thromboembolism after hip or knee arthroplasty: a pooled analysis of three trials

BACKGROUND

Three randomized, double-blind trials compared dabigatran, an oral direct thrombin inhibitor, with enoxaparin for the primary prevention of venous thromboembolism (VTE) in patients undergoing elective total hip and knee arthroplasty.

OBJECTIVES AND METHODS

We conducted a pre-specified pooled analysis of these trials. 8,210 patients were randomized, of whom 8,135 were treated (evaluable for safety) with dabigatran 220 mg or 150 mg once-daily, or subcutaneous enoxaparin (40 mg once-daily or 30 mg twice-daily). Efficacy analyses were based on the modified intention-to-treat population of 6,200 patients with an evaluable outcome. The common risk difference (RD) of treatment effect between each dabigatran dose and enoxaparin was estimated using fixed-effects models, and statistical heterogeneity was estimated using the I2 statistic.

RESULTS

The composite outcome of major VTE (proximal deep vein thrombosis and/or pulmonary embolism) and VTE-related mortality occurred in 3.3% of the enoxaparin group versus 3.0% of the dabigatran 220 mg group (RD vs. enoxaparin -0.2%, 95% CI -1.3% to 0.9%, I2=37%) and 3.8% of the 150 mg group (RD vs. enoxaparin 0.5%, -0.6% to 1.6%, I2=0%). Major bleeding occurred in 1.4% of the enoxaparin group versus 1.4% of the dabigatran 220 mg group (RD vs. enoxaparin -0.2%, -0.8% to 0.5%, I2=40%) and 1.1% of the 150 mg group (RD vs. enoxaparin -0.4%, -1.0% to 0.2%, I2=0%).

CONCLUSIONS

Oral dabigatran was as effective as subcutaneous enoxaparin in reducing the risk of major VTE and VTE-related mortality after hip or knee arthroplasty and has a similar bleeding profile.

Association between asymptomatic deep vein thrombosis detected by venography and symptomatic venous thromboembolism in patients undergoing elective hip or knee surgery

BACKGROUND

Venography is commonly used to compare the efficacy of different thromboprophylaxis strategies for preventing deep vein thrombosis (DVT) in patients undergoing total hip replacement (THR) or total knee replacement (TKR).

METHODS

We explored the relation between asymptomatic DVT and symptomatic venous thromboembolism (VTE) in patients undergoing THR or TKR treated with standard doses of enoxaparin (30 mg b.i.d. or 40 mg o.d.) by comparing the incidence of asymptomatic DVT in venographic studies with the incidence of symptomatic VTE in studies where venography was not performed.

RESULTS

In 10 venographic studies involving 5796 patients, the incidence of asymptomatic DVT after THR was 13.2% [95% CI, 12.2-14.2%] and after TKR was 38.1% (95% CI, 35.5-40.8%). In two studies involving 3500 patients who did not undergo venography, the 90-day incidence of symptomatic VTE after THR was 2.7% (95% CI, 2.1-3.4%) and after TKR was 1.8% (95% CI, 0.9-2.7%). For every symptomatic VTE in THR studies where venography was not performed there were five asymptomatic DVTs in the venographic studies; for TKR, the ratio was 1:21. The incidence of asymptomatic DVT and the symptomatic VTE/asymptomatic DVT ratio was influenced by the venogram reading committee (Gothenburg vs. Hamilton: total DVT after THR, 19.5% vs. 8.7%, P < 0.0001; for TKR, 42.7% vs. 27.2%, P < 0.0001).

CONCLUSIONS

Comparisons across trials show a consistent relation between asymptomatic venographic DVT in patients undergoing elective THR or TKR surgery and symptomatic VTE in patients not undergoing venography. Differences exist in the strength of the relation depending on the type of surgery and the venogram reading committee.

Sequential intrapulmonary and systemic activation of coagulation and fibrinolysis during and after total hip replacement surgery

Hip joint replacement surgery, using acrylic cement for prosthesis fixation, is associated with intraoperative cardiorespiratory dysfunction, and a high frequency of postoperative proximal deep vein thrombosis (DVT). Levels of prothrombin fragments 1+2 (F1+2), tissue plasminogen activator antigen (t-PA), plasminogen activator inhibitor 1 activity (PAI-1), D-dimer and interleukin 6 (IL-6) were measured in arterial (AB) and mixed venous blood (MVB) in five patients during and after total hip replacement operation with acrylic cement prosthesis fixation. Sequential peaks of F1+2, t-PA, PAI-1 and IL-6 appeared, starting with activation of coagulation during preparation of bone, closely followed by activation of fibrinolysis. Later, this was counteracted by an antifibrinolytic response and increase of IL-6. After a fibrinolytic shutdown on the third postoperative day as evidenced by a drop in t-PA and D-dimer concentrations, a second wave of coagulation was seen at the end of the first week. The present model, with frequent sampling of blood entering and leaving the lungs, confirms our earlier findings of the lung as a key organ in promoting coagulation following traumatic activation.

Increased activation of coagulation and formation of late deep venous thrombosis following discontinuation of thromboprophylaxis after hip replacement surgery

Hip replacement surgery (HRS) is associated with a high frequency of deep vein thrombosis (DVT). At the same time there is a substantial systemic and local activation of coagulation. This study indicates that discontinuation of thromboprophylaxis one week after surgery may allow a second wave of coagulation and fibrinolysis activation to occur. An almost parallel increase in plasma TAT and D-dimer levels between the 6th and the 35th postoperative day may indicate late DVT formation. Repeated bilateral ascending venography is though to be necessary to evaluate the suitability of using selected activation markers of the coagulation and fibrinolytic systems as indices of DVT formation.

A critical appraisal of bleeding events reported in venous thromboembolism prevention trials of patients undergoing hip and knee arthroplasty

BACKGROUND

Anticoagulants are effective for the prevention of venous thromboembolism (VTE) but cause bleeding. Interpretation of the risks and benefits of new anticoagulant regimens for VTE prevention is complicated by a lack of standardized definitions and reporting of bleeding. We reviewed the reporting of bleeding in randomized controlled trials of new anticoagulants compared with standard doses of enoxaparin in hip and knee arthroplasty, and examined the possible impact of differences in the definition of major bleeding on interpretation of the trial results.

METHODS

Electronic searches identified 16 phase III trials published between 2001 and 2010 involving 41,265 patients comparing one of five new anticoagulants with a common comparator, enoxaparin.

RESULTS

Major bleeding rates in patients treated with enoxaparin ranged from 0.1% to 3.1% in hip arthroplasty trials and from 0.2% to 1.4% in knee arthroplasty trials. In studies that excluded surgical-site bleeding from the definition, major bleeding rates were about 10-fold lower than in those which included surgical-site bleeding. Within the individual trials, the choice of bleeding definition and the methods of assessment of bleeding influenced the conclusions regarding the risk of bleeding with new anticoagulant regimens relative to enoxaparin. Eight of the 16 studies demonstrated a ≥ 40% relative risk differences in major bleeding between treatment groups but the difference was statistically significant in only two of these trials.

CONCLUSION

Randomized VTE prevention trials report markedly different rates of major bleeding despite similar patient populations and doses and durations of anticoagulant prophylaxis and were underpowered to detect modest differences in patient-important bleeding events. Standardization of bleeding definitions and reporting seems desirable.

Partial factor IXa inhibition with TTP889 for prevention of venous thromboembolism: an exploratory study

BACKGROUND

Inhibitors of factor (F) IXa show potent antithrombotic activity with a low risk of bleeding in preclinical models. We investigated the anticoagulant potential of oral TTP889, a small molecule that inhibits up to 90% of FIXa activity at therapeutic doses, using a clinical model of extended prophylaxis in hip fracture surgery (HFS).

METHODS

In this multicenter, randomized, double-blind study, 261 patients received oral TTP889 (300 mg once daily) or placebo starting 6-10 days after HFS, and standard thromboprophylaxis for 5-9 days. Treatment was continued for 3 weeks and all patients then underwent mandatory bilateral venography. The primary efficacy outcome was venous thromboembolism (VTE; venographic or symptomatic deep vein thrombosis or pulmonary embolism) during treatment, and it was evaluated centrally by an independent adjudication panel. The main safety outcome was bleeding (major, clinically relevant non-major, and minor events).

RESULTS

Two hundred and twelve patients with an evaluable venogram were included in the efficacy analysis. The primary efficacy outcome occurred in 32.1% (35/109) of patients who had been allocated TTP889, and 28.2% (29/103) of patients on placebo (P = 0.58). There were no major bleeding events, and only two clinically relevant non-major bleeding events with TTP889.

CONCLUSION

Partial FIXa inhibition with TTP889 300 mg daily was not effective for extended prevention of VTE after standard prophylaxis for up to 9 days. Coupled with the low incidence of bleeding episodes, this suggests a lack of antithrombotic potential. Further investigation of TTP889 in different clinical settings is needed. (Clinical trial registration information URL: http://www.clinicaltrials.gov. Unique identifier: NCT00119457).

Orthopaedic thromboprophylaxis

Thromboprophylaxis remains a controversial subject. A vast amount of epidemiological and trial data about venous thromboembolism has been published over the past 40 years. These data have been distilled and synthesised into guidelines designed to help the practitioner translate this extensive research into ‘evidence-based’ advice.

Guidelines should, in theory, benefit patient care by ensuring that every patient routinely receives the best prophylaxis; without guidelines, it is argued, patients may fail to receive treatment or be exposed to protocols which are ineffective, dangerous or expensive.

Guidelines, however, have not been welcomed or applied universally. In the United States, orthopaedic surgeons have published their concerns about the thromboprophylaxis guidelines prepared by the American College of Chest Physicians. In Britain, controversy persists with many surgeons unconvinced of the risk/benefit, cost/benefit or practicality of thromboprophylaxis. The extended remit of the recent National Institute of Clinical Excellence thromboprophylaxis guidelines has been challenged.

The reasons for this disquiet are addressed in this paper and particular emphasis is placed on how clinically-acceptable guidelines could be developed and applied.

No difference in mortality between cemented and uncemented hemiprosthesis for elderly patients with cervical hip fracture. A prospective randomized study on 334 patients over 75 years

INTRODUCTION

Laboratory and human mechanical studies indicated that chemical substances in bone cement had toxic and prothrombotic effects. Impaction of cement added a mechanical trauma to the reaming and broaching procedure and contributed to a substantial local and systemic thrombin generation. Case reports and materials have indicated bone cement as the immediate trigger of cardiorespiratory and vascular dysfunction, occasionally fatal, and described as the bone cement implantation syndrome. In spite of this knowledge, bone cement has gained popularity and is widely used for prosthesis fixation, possibly due to a lack of clinical evidence supporting the basic science indicating bone cement as a mortality risk factor.

METHOD

This is a prospective, randomized study comparing cemented and non cemented hemiprosthesis on patients suffering a dislocated cervical hip fracture. Perioperative characteristics and 1 year mortality differences between the groups were estimated.

PATIENTS

Hundred and thirty-four patients over 75 years were enrolled from two hospitals in Norway. Average age was 84 years, 75 % were female and 60 % had symptomatic comorbidities.

RESULTS

We find no difference in mortality between cemented and uncemented hemiprosthesis up to 1 year (HR 0.77, 95 % CI 0.51-1.18, p = 0.233). However, statistically significant reduced operation time and blood loss were found in the non-cemented group. (mean difference of 13 min, 95 % CI 4-22, p = 0.004 and 92 ml 95 % CI 3-181, p = 0.043, respectively).

CONCLUSION

Installation of non-cemented hemiprostheses in elderly with hip fracture may have benefits perioperatively regarding operation time and bleeding, and do not seem to influence 1 year mortality relative to cemented implants.

Intrapulmonary thrombin generation and its relation to monomethylmethacrylate plasma levels during hip arthroplasty

Frequent peroperative sampling of arterial and mixed venous blood was undertaken in eight consecutive patients during cemented hip arthroplasty to obtain a sequential picture of thrombin-antithrombin (TAT) and methylmethacrylate monomer (MMA) concentrations. TAT, detected neo-antigenically, reached its maximum levels after bone preparation, prior to introduction of cement and prosthesis. Furthermore, TAT values were higher in arterial than in mixed venous blood, indicating generation and inactivation of thrombin when blood is passing the lung. MMA concentration, measured by high pressure liquid chromatography, increased very rapidly and declined within 1 min following socket as well as shaft implantation, reaching the highest mean value of 3599 ng/ml only 30 s after femoral impaction of cement. MMA concentration was higher in mixed venous than in arterial blood, indicating elimination of the monomer during lung passage. This study confirms our previous observation that coagulation is activated prior to the implantation of bone cement and prosthesis into the femoral shaft; in addition, it provides further evidence of the thrombin-generating potential of the pulmonary capillary bed. Very frequent sampling was necessary to reveal the sharp rise in MMA levels following impaction of cement. Further investigations are needed to establish whether interaction between activated coagulation and MMA may predispose to cardiovascular complications.

AVE5026, a new hemisynthetic ultra-low-molecular-weight heparin for the prevention of venous thromboembolism in patients after total knee replacement surgery--TREK: a dose-ranging study

BACKGROUND

AVE5026 is a new hemisynthetic ultra-low-molecular-weight heparin, with a novel anti-thrombotic profile resulting from high anti-factor (F)Xa activity and residual anti-FIIa activity. AVE5026 is in clinical development for venous thromboembolism (VTE) prevention, a frequent complication after total knee replacement (TKR) surgery.

OBJECTIVES

This study evaluated the dose-response of AVE5026 for the prevention of VTE in patients undergoing TKR surgery.

PATIENTS/METHODS

In this parallel-group, double-blind, double-dummy study, 690 patients were randomized, and 678 treated with once-daily doses of AVE5026 (5, 10, 20, 40, or 60 mg) or enoxaparin 40 mg in the calibrator arm. The primary efficacy end point was VTE until post-operative day 11, defined as deep vein thrombosis (DVT) detected by bilateral venography, symptomatic DVT, non-fatal pulmonary embolism (PE) and VTE-related death. The primary safety outcome was the incidence of major bleeding.

RESULTS

The primary efficacy outcome was assessed in 464 patients. There was a significant dose-response across the five AVE5026 groups for VTE prevention (P<0.0001), with the incidence of VTE ranging from 5.3% to 44.1% compared with 35.8% in the enoxaparin group and for proximal DVT (P=0.0002). Also, a significant dose-response for AVE5026 was seen for major bleeding (P=0.0231) and any bleeding (P=0.0003). Six patients in the AVE5026 groups, four in the 60 mg group, experienced major bleeding; none did in the enoxaparin group.

CONCLUSIONS

The safety and efficacy results of this study suggest that a AVE5026 dose of between 20 and 40 mg presents an adequate benefit-to-risk ratio.

The role of bone traumatization in the initiation of proximal deep vein thrombosis during cemented hip replacement surgery in pigs

Hip arthroplasty is associated with a high frequency of postoperative solitary proximal deep vein thrombosis which seems most frequently observed when bone cement is used for prosthesis fixation. Eighteen pigs underwent hemiarthroplasty, eight with cement-fixed prostheses and eight with non-cement prosthesis installation. Levels of thrombin-antithrombin (TAT) complexes, tissue plasminogen activator (t-PA) activity and plasminogen activator inhibitor 1 (PAI-1) activity were determined in femoral vein blood from both limbs during and after surgery. On the operated side, TAT increased during bone traumatization followed by a substantial rise in t-PA activity and a gradual decline in PAI-1 activity. This indicates a local per- and post-operative sequential activation of coagulation and fibrinolysis followed by a fibrinolytic shutdown, all reflected in femoral vein blood on the operated side. In the animals receiving noncemented hip prostheses, the same pattern of activation of coagulation and fibrinolysis occurred on the operated side. This was, however, less marked than with the cement-fixed prostheses. Postoperative scanning electron microscopic (SEM) examination of the femoral veins showed thrombi on the operated side in 62% of the animals in the cement group and 25% in the non-cement group. In an additional study with eight animals undergoing cement-anchored hip prosthesis operations the levels of TAT, t-PA and PAI-I were analysed in femoral vein blood, mixed venous blood and arterial blood. Significantly higher levels were found in femoral vein blood compared with mixed venous blood while no significant change was found in arterial blood compared with mixed venous blood. The hyperthermia induced by curing bone cement was effectively conducted by the implanted prosthesis and did not seem to exert major influence on the activation of coagulation. Extreme rotation of the limbs during surgery did not in itself induce visible vein wall damage as judged by SEM. These studies indicate that traumatization of bone marrow during hip surgery induce a marked local activation of coagulation and a high incidence of deep vein thrombosis in proximal veins, in particular if bone cement is used for prosthesis fixation.

The role of the pulmonary circulation in the regulation of coagulation and fibrinolysis in relation to major surgery

Cardiac surgery and hip replacement surgery (HRS) are associated with serious cardiorespiratory and vascular complications. Activation of blood coagulation and fibrinolysis in the lung vasculature seem to play a key role in the pathophysiology of this process. This article reviews the results of several experimental and clinical studies within this field. Animal studies have shown that bone traumatization induces a marked local activation of coagulation and fibrinolysis in femoral vein blood draining from the surgical area as shown by a 2.5-fold increase in plasma levels of thrombin-antithrombin complexes (TAT) and a seven-fold increase in tissue plasminogen activator (tPA) activity. A slight increase in TAT in femoral vein blood on the unoperated side has also been found and indicates increased activation of coagulation in recirculated blood, which had passed the pulmonary microvasculature. In addition, human studies have shown that bone preparation induced a 200-fold increase in systemic circulating fibrinopeptide-A during surgery and a five-fold increase in TAT (when thromboprophylaxis was stopped 1 week after surgery). Both increases are markers of thrombin generation. Furthermore, cellular studies have shown that thrombin and certain cytotoxic chemicals, such as methylmethacrylate monomer (bone cement), separately and together trigger monocytes to tissue factor (TF) expression and cause endothelial cell shape changes and detachment. This may allow pericellular fibrin formation to occur on monocytes and also transforms the nonthrombogenic endothelial coverage into a highly thrombogenic surface that triggers the conversion of fibrinogen to fibrin and releases fibrinopeptide-A. Finally, sequestration of granulocytes caused release of autodigestive proteases, which may have further strengthened this procoagulant process. Synchronous to the massive intrapulmonary activation of coagulation, an increased fibrinolytic activity was found, as evidenced by a marked drop in arterial blood tPA during surgery. This indicated tPA binding to fibrin deposits in the lung capillaries. However, this clearing process, to obtain adequate blood flow and gas exchange, was shut down several hours after surgery by an antifibrinolytic activity (PAI-1). Thus, these studies indicated that bone surgery induces a substantial intraoperative hemostatic activation in the lung capillaries, which is the primary target organ for venous blood-borne bone-marrow debris. Soft-tissue surgery and vascular surgery seem to induce less systemic activation of coagulation and fibrinolysis.

Sustained prothrombotic profile after hip replacement surgery: the influence of prolonged prophylaxis with dalteparin

In a randomized trial on the effect of dalteparin for 5 weeks after HRS we evaluated hemostatic variables in plasma sampled before and 1, 6 and 35 days postoperatively. In 218 patients we found that prothrombin fragment 1 + 2 (F1 + 2), thrombin-antithrombin complexes (TAT), d-dimer and fibrinogen were significantly higher on day 35 as compared with baseline values in the placebo group (P < 0.001 for all). The same pattern was found in the dalteparin group, but with significantly lower values for F1 + 2, TAT and d-dimer. In patients in the placebo group with venographically proven deep vein thrombosis (DVT) on day 35 (33%), significantly higher values were found for F1 + 2, TAT and d-dimer than in patients without DVT. Patients in the highest quartile of d-dimer (>2850 ng mL-1) had an odds ratio for the presence of DVT of 24.0 when compared with patients in the lowest quartile (<1625 ng mL-1). It is concluded that a substantial hypercoagulability is sustained until day 35 after HRS, significantly reduced with prolonged administration of dalteparin.

Cardiorespiratory and vascular dysfunction related to major reconstructive orthopedic surgery

Major orthopedic reconstructive surgery is highly traumatic and may be associated with serious peri-operative cardiorespiratory and vascular complications which occasionally may be fatal. These complications are commonest in patients receiving cemented hip prostheses following femoral neck fractures. The etiology is multifactorial. Bone traumatization induces activation of the hemostatic system, i.e., thrombin generation, in venous blood draining the operation area. When this activated blood passes the lung, more thrombin is generated and the blood becomes hypercoagulable and causes fibrin-formation in the lung vessels, with trapping of cellular debris. Thrombin has many hormone-like effects beyond its function in the coagulation cascade system. It may increase vein wall permeability and cause constriction of vessels, which increases blood pressure in the lung. In addition, impaction of bone cement to fill bone cavities or to fix prostheses causes additional mechanical trauma and further release of procoagulant substances into venous blood. Further, release of the cytotoxic chemical methyl-methacrylate monomer into venous blood is superimposed on the thrombin-primed hemostatic disturbances in the lung microvasculature. All these effects may finally induce hemodynamic insufficiency, which occasionally may be fatal. To prevent these adverse reactions, thrombin activity should be reduced and impaction of bone cement minimized.