Pooled analysis of trials may, in the presence of heterogeneity inadvertently lead to fragile conclusions due to the importance of clinically relevant variables being either hidden or lost when the findings are pooled

Efficacy and Safety of Enoxaparin versus New Oral Anticoagulants to Prevent Venous Thromboembolism after Total Hip Replacement: A Systematic Review and Meta-Analysis

Prophylactic anticoagulant therapy is recommended for reducing the risk of venous thromboembolism (VTE) after a total hip replacement (THR). However, it is not clear which anticoagulant is preferable. Hence, a systematic review and meta-analysis of randomized double-blind controlled trials (RDBCTs) were conducted to investigate the clinical efficacy and safety of enoxaparin in comparison with newer oral anticoagulants for the prevention of VTE after THR. The Cochrane Library, Scopus, Web of Science, Embase, and PubMed/Medline databases were used for PICO search strategy. Relative risks (RR) of symptomatic VTE, clinically relevant bleeding, mortality, and a net clinical endpoint were estimated employing a random effect meta-analysis. ITC and RevMan software were used for indirect and direct comparisons, respectively. Nine RDBCTs comprising 24,584 patients were included. As compared to enoxaparin, a reduced risk for symptomatic VTE was observed with rivaroxaban (confidence interval [CI]: 0.32–0.77; RR: 0.46%) and comparable with apixaban (0.12–1.26; 0.42%) and dabigatran (0.22–2.20; 0.70%). Contrarily to enoxaparin, a greater risk for clinically relevant bleeding was observed with rivaroxaban (1.03–1.48; 1.23%), comparable with dabigatran (0.96–1.33; 1.10%) and reduced with apixaban (0.19–5.66; 0.96%). In indirect or direct comparisons, the interventions did not differ on the net clinical endpoint. In conclusion, the findings of this meta-analysis revealed no significant difference in the efficacy and safety of new oral anticoagulants as compared to enoxaparin for the prevention of VTE after total hip replacement surgery.

Benefit-to-harm ratio of thromboprophylaxis for patients undergoing major orthopaedic surgery

Surgeons consider the benefit-to-harm ratio when making decisions regarding the use of anticoagulant venous thromboembolism (VTE) prophylaxis. We evaluated the benefit-to-harm ratio of the use of newer anticoagulants as thromboprophylaxis in patients undergoing major orthopaedic surgery using the likelihood of being helped or harmed (LHH), and assessed the effects of variation in the definition of major bleeding on the results. A systematic literature search was performed to identify phase II and phase III studies that compared regulatory authority-approved newer anticoagulants to the low-molecularweight heparin enoxaparin in patients undergoing major orthopaedic surgery. Analysis of outcomes data estimated the clinical benefit (number-needed-to-treat [NNT] to prevent one symptomatic VTE) and clinical harm (number-needed-to-harm [NNH] or the NNT to cause one major bleeding event) of therapies. We estimated each trial’s benefitto-harm ratio from NNT and NNH values, and expressed this as LHH = (1/NNT)/(1/NNH) = NNH/NNT. Based on reporting of efficacy and safety outcomes, most studies favoured enoxaparin over fondaparinux, and rivaroxaban over enoxaparin. However, when using the LHH metric, most trials favoured enoxaparin over both fondaparinux and rivaroxaban when they included surgical-site bleeding that did not require reoperation in the definition of major bleeding. The exclusion of bleeding at surgical site which did not require reoperation shifted the benefit-to-harm ratio in favour of the newer agents. Variations in the definitions of major bleeding may change the benefit-to-harm ratio and subsequently affect its interpretation. Clinical trials should attempt to improve the consistency of major bleeding reporting.

Systematic review of randomized controlled trials of new anticoagulants for venous thromboembolism prophylaxis in major orthopedic surgeries, compared with enoxaparin

BACKGROUND

In the past 10 years, new anticoagulants (NACs) have been studied for venous thromboembolism (VTE) prophylaxis.

OBJECTIVE

To evaluate the risk/benefit profile of NACs versus enoxaparin for VTE prophylaxis in major orthopedic surgery.

METHODS

A systematic review of double-blind randomized phase III studies was performed. The search strategy was run from 2000 to 2011 in the main medical electronic databases in any language. Independent extraction of articles was performed by 2 authors using predefined data fields, including study quality indicators.

RESULTS

Fifteen published clinical trials evaluating fondaparinux, rivaroxaban, dabigatran, and apixaban were included. Primary efficacy (any deep vein thrombosis [DVT], nonfatal pulmonary embolism, or all-cause mortality) favored fondaparinux (relative risk [RR] 0.50; 95% CI, 0.39, 0.63) and rivaroxaban (RR, 0.50; 95% CI, 0.34, 0.73) over enoxaparin, although significant heterogeneity was observed in both series. The primary efficacy of dabigatran at 220 mg, apixaban, and bemiparin were similar, with RRs of 1.02 (95% CI, 0.86, 1.20), 0.63 (95% CI, 0.39, 1.01), and 0.87 (95% CI, 0.65, 1.17), respectively. The primary efficacy of dabigatran at 150 mg (RR, 1.20; 95% CI, 1.03, 1.41), was inferior to enoxaparin. The incidence of proximal DVT favored apixaban (RR, 0.45; 95% CI, 0.27, 0.75) only. Rivaroxaban (RR, 0.45; 95% CI, 0.27, 0,77) and apixaban (RR, 0.38; 95% CI, 0.16, 0.90) produced significantly lower frequencies of symptomatic DVT. The incidence of major VTE favored rivaroxaban (RR, 0.44; 95% CI, 0.25, 0.81), only. Bleeding risk was similar for all NACs, except fondaparinux (RR, 1.27; 95% CI, 1.04, 1.55), which exhibited a significantly higher any-bleeding risk compared with enoxaparin, and apixaban (RR, 0.88; 95% CI, 0.79, 0.99), which was associated with a reduced risk of any bleeding. Alanine amino transferase was significantly lower with 220 mg of dabigatran, (RR, 0.67; 95% CI, 0.79, 0.99) than with enoxaparin.

CONCLUSIONS

NACs can be considered alternatives to conventional thromboprophylaxis regimens in patients undergoing elective major orthopedic surgery, depending on clinical characteristics and cost-effectiveness. The knowledge of some differences concerning efficacy or safety profile, pointed out in this systematic review, along with the respective limitations, may be useful in clinical practice.

Blood loss in cemented THA is not reduced with postoperative versus preoperative start of thromboprophylaxis

BACKGROUND

Thrombin formation commences perioperatively in orthopaedic surgery and therefore some surgeons prefer preoperative initiation of pharmacologic thromboprophylaxis. However, because of the potential for increased surgical bleeding, the postoperative initiation of thromboprophylaxis has been advocated to reduce blood loss, need for transfusion, and bleeding complications. Trials on timing of thromboprophylaxis have been designed primarily to detect thrombotic events, and it has been difficult to interpret the magnitude of blood loss and bleeding events owing to lack of information for bleeding volume and underpowered bleeding end points.

QUESTIONS/PURPOSES

We therefore asked whether there are differences in blood loss, transfusion requirements, and other postoperative clinical complications with preoperative versus postoperative start of thromboprophylaxis with dalteparin.

METHODS

In a double-blind, randomized controlled trial, 80 patients undergoing primary cemented THA were allocated to dalteparin injections starting 12 hours before or 6 hours after surgery. Blood loss was measured by weighing sponges and drapes, volume in suction drains during surgery, and wound drains until removal 24 hours postoperatively. Hemoglobin and hematocrit were recorded at predefined times during and after surgery.

RESULTS

We found no differences in blood loss (1081 mL ± 424 mL versus 1023 mL ± 238 mL), bleeding-related events (10% versus 17%), or number of patients who had transfusions (12 versus five) with preoperative and postoperative thromboprophylaxis, respectively. Other complications were few in both groups.

CONCLUSIONS

Our data suggest blood loss is similar with preoperative and postoperative initiation of dalteparin thromboprophylaxis, but indicate a trend toward fewer transfusion requirements which might favor postoperative start of thromboprophylaxis.

Dabigatran: a review of clinical and pharmacoeconomic evidence

Dabigatran etexilate is the first commercially available oral direct thrombin inhibitor. A single trial has studied patients at risk for stroke associated with nonvalvular atrial fibrillation; in this trial, dabigatran 150 mg twice a day met the criteria for superiority over warfarin in preventing stroke and systemic embolism while reducing the rate of hemorrhagic stroke with a similar risk of major bleeding. For the treatment of venous thromboembolism, dabigatran 150 mg twice a day had comparable efficacy and safety versus warfarin. In contrast, dabigatran was less effective than enoxaparin 30 mg twice a day in venous thromboembolism prevention in orthopedic surgery. Advantages of dabigatran over warfarin include its lack of need for routine laboratory monitoring, a fixed-dose regimen, and potentially fewer clinically important drug interactions. Concerns include higher incidences of dyspepsia and gastrointestinal bleeding, twice-daily dosing, and lack of effective antidote. Additional drawbacks include higher drug cost versus warfarin, accumulation in case of renal impairment, higher discontinuation rates due to adverse events, and limited long-term safety and trial data. From a payer perspective, overall costs will be higher with dabigatran compared with warfarin, but dabigatran does meet the threshold to be considered a cost-effective therapy. In addition, the lack of need for regular laboratory monitoring is a quality of life advantage for patients on dabigatran. These observations suggest that dabigatran is a valuable addition to the therapeutic armamentarium for stroke prevention in selected patients with atrial fibrillation although caution should be exercised given the limited data on this agent and higher cost.

Safety and efficacy of rivaroxaban for thromboprophylaxis following lower limb surgery: an update

INTRODUCTION

Thromboprophylaxis in orthopedic surgery remains a controversial issue despite recent changes to NICE guidelines, particularly with the addition of oral factor Xa inhibitors. The healthcare burden of venous thromboembolism is substantial and needs frequent academic and clinical appraisal.

AREAS COVERED

The authors review the available relevant literature on the use of rivaroxaban in orthopedic surgery, identified using an EMBASE (1980 - 2010) and Ovid MEDLINE (1950 - 2010) search of published articles up to August 2010. This includes clinical studies, case reports and experimental studies where applicable. Search terms include: 'rivaroxaban', 'safety', 'efficacy', 'bleeding', 'toxicity', 'tolerability' and 'complication'.

EXPERT OPINION

Rivaroxaban is a safe and effective choice of thromboprophylactic agent following lower limb arthroplasty surgery. More research is required to expand the application of this novel agent to other areas of orthopedic surgery.