Fondaparinux Compared with Enoxaparin for the Prevention of Venous Thromboembolism after Elective Major Knee Surgery
Kenneth A. Bauer, M.D., Bengt I. Eriksson, M.D., Michael R. Lassen, M.D., Alexander G.G. Turpie, F.R.C.P., for the Steering Committee of the Pentasaccharide in Major Knee Surgery Study
Background Despite thromboprophylaxis, major knee surgery carriesa high risk of venous thromboembolism. Fondaparinux, the firstof a new class of synthetic antithrombotic agents, may reducethis risk.
Methods In a double-blind study, we randomly assigned 1049 consecutivepatients undergoing elective major knee surgery to receive subcutaneousdoses of either 2.5 mg of fondaparinux once daily or 30 mg ofenoxaparin twice daily, with both treatments initiated postoperatively.The primary efficacy outcome was venous thromboembolism up topostoperative day 11, defined as deep-vein thrombosis detectedby mandatory bilateral venography, documented symptomatic deep-veinthrombosis, or documented symptomatic pulmonary embolism. Theprimary safety outcome was major bleeding.
Results The primary efficacy outcome was assessed in 724 patients.The fondaparinux group had a significantly lower incidence ofvenous thromboembolism by day 11 (12.5 percent [45 of 361 patients])than the enoxaparin group (27.8 percent [101 of 363 patients];reduction in risk, 55.2 percent; 95 percent confidence interval,36.2 to 70.2; P<0.001). Major bleeding (including overt bleedingwith a bleeding index of 2 or more) occurred more frequentlyin the fondaparinux group (P=0.006), but there were no significantdifferences between the two groups in the incidence of bleedingleading to death or reoperation or occurring in a critical organ.
Conclusions In patients undergoing elective major knee surgery,postoperative treatment with 2.5 mg of fondaparinux once dailywas significantly more effective in preventing deep-vein thrombosisthan 30 mg of enoxaparin twice daily.
Venous thromboembolism is a frequent, life-threatening postoperativecomplication of total-knee-replacement surgery.1,2 Without thromboprophylaxis,the prevalence rate is 40 to 84 percent for venographicallyverified postoperative deep-vein thrombosis and 2 to 7 percentfor pulmonary embolism.1 Thromboprophylaxis that is effectivein hip-replacement surgery, such as low-dose heparin, low-molecular-weightheparin, or warfarin, is less successful in knee-replacementsurgery and reduces the prevalence of deep-vein thrombosis onlyto 31 to 47 percent.1 For this reason, more effective antithromboticprophylaxis is needed in knee-replacement surgery.
Fondaparinux is one of a new class of antithrombotic agents,the selective inhibitors of activated factor X (factor Xa).3,4,5,6Fondaparinux is an entirely synthetic pentasaccharide that isstructurally related to the antithrombin-binding site of heparin.In contrast to heparin, which interacts with many plasma components,the pentasaccharide selectively binds to antithrombin, causingit to rapidly inhibit factor Xa, a key enzyme in the coagulationpathway. Recent dose-ranging studies suggested that a once-dailysubcutaneous injection of 2.5 mg of fondaparinux can preventvenous thromboembolism after hip-replacement7 or knee-replacementsurgery (unpublished data).
This multicenter, randomized, double-blind trial was part ofa program that also evaluated fondaparinux as prophylaxis againstvenous thromboembolism in patients undergoing surgery for hipfracture8 and elective hip replacement.9,10 The aim of the studywas to compare the efficacy and safety of a once-daily subcutaneousinjection of 2.5 mg of pentasaccharide with twice-daily subcutaneousinjections of 30 mg of enoxaparin for the prevention of venousthromboembolism after elective major knee surgery.
Methods
Patients
Patients were considered for inclusion if they were at least18 years of age and were undergoing elective major knee surgery that is, surgery requiring resection of the distal endof the femur or proximal end of the tibia or revision of atleast one component of a previously implanted total-knee prosthesis.
Patients were excluded if surgery in the contralateral kneewas performed at the same time or within two weeks after enrollment.Women were excluded if they were pregnant or not using effectivecontraception. Other main reasons for exclusion were activebleeding; a documented congenital or acquired bleeding disorder;current ulcerative or angiodysplastic gastrointestinal disease;hemorrhagic stroke or brain, spinal, or ophthalmologic surgerywithin the previous three months; insertion of an indwellingintrathecal or epidural catheter during the treatment period;unusual difficulty in administering epidural or spinal anesthesia(e.g., more than two attempts); hypersensitivity to heparin,low-molecular-weight heparins, porcine products, or iodinatedcontrast medium; a contraindication to anticoagulant therapy;a current addictive disorder; a serum creatinine concentrationabove 2 mg per deciliter (177 µmol per liter) in a well-hydratedpatient; and a platelet count below 100,000 per cubic millimeter.Finally, patients who required anticoagulant therapy were alsoexcluded. The use within one week before randomization of dextranor any type of anticoagulant, fibrinolytic, or antiplateletagent was discouraged.
Study Design
Immediately after surgery, patients were randomly assigned (ina ratio of 1:1 in blocks of four, stratified according to center),through a central computer-derived randomization scheme to receivesubcutaneous doses of either 2.5 mg of fondaparinux (Arixtra,NV Organon, Oss, the Netherlands, and SanofiSynthelabo,Paris) once daily and a placebo once daily or 30 mg of enoxaparin(Clexane/Lovenox, Aventis Pharmaceuticals, Bridgewater, N.J.)twice daily. In the enoxaparin group, the first dose was givenbetween 12 and 24 hours after surgery, according to the recommendationof the manufacturer. Since fondaparinux is a new compound, whichdiffers from enoxaparin in its mechanism of action and pharmacokineticproperties, the starting time after surgery and the dose weredetermined during the early development of the drug7; the firstpostoperative injection was administered 6±2 hours aftersurgery and the second injection 12 hours or more after thefirst.
The day of surgery was defined as day 1. Treatment was scheduledto continue until day 5 to day 9, and the primary efficacy outcomewas assessed between day 5 and day 11. Patients were then followedup in person, by mail, or by telephone between day 35 and day49. During follow-up, patients were instructed to report anysymptoms or signs of venous thromboembolism or bleeding andany other clinical event occurring since the completion of treatment.Investigators could extend prophylaxis during follow-up withany currently available therapy, but only after venography hadbeen performed. If venous thromboembolism occurred during thestudy, treatment was left to the discretion of the investigator.
The study was conducted according to the ethical principlesstated in the Declaration of Helsinki and local regulations.The protocol was approved by independent local institutionalreview boards, and written informed consent was obtained fromall patients before randomization.
Medications
Study medications were packaged in boxes of identical appearance,each containing 19 prefilled, single-dose syringes: 10 syringesof fondaparinux and 9 syringes of placebo for each patient assignedto fondaparinux, or 18 syringes of enoxaparin and 1 syringeof placebo for each patient assigned to enoxaparin. Each syringecontained 2.5 mg of fondaparinux sodium in 0.25 ml of waterfor injectable preparations (a concentration of 10 mg per milliliter),30 mg of enoxaparin sodium in 0.3 ml of water for injectablepreparations (a concentration of 100 mg per milliliter), orplacebo (0.25 or 0.3 ml of isotonic saline). Each syringe wasloaded inside an opaque autoinjector (Autoject, Owen Mumford,Woodstock, United Kingdom) to maintain blinding.
Throughout the treatment period, the use of intermittent pneumaticcompression, dextran, and any other anticoagulant, thrombolytic,or antiplatelet agent was prohibited. Centers were advised toavoid giving patients aspirin or nonsteroidal antiinflammatorydrugs whenever possible. The use of graduated-compression stockingsand physiotherapy was recommended.
Outcome Measures
The primary efficacy outcome was assessed by the rate of venousthromboembolism (defined as deep-vein thrombosis, pulmonaryembolism, or both) up to day 11. Secondary efficacy outcomeswere total, proximal, or distal deep-vein thrombosis or symptomaticvenous thromboembolism up to day 11 and symptomatic venous thromboembolismup to day 49. Patients were examined for deep-vein thrombosisby systematic bilateral ascending venography of the legs11 betweenday 5 and day 11, but no more than two days after the last injectionof study drug, or earlier if thrombosis was clinically suspected.Symptomatic pulmonary embolism was confirmed by a lung scanindicating a high probability of pulmonary embolism, pulmonaryangiography,12 or helical computed tomography or at autopsy.
The primary safety outcome was the incidence of major bleeding,which included fatal bleeding; bleeding that was retroperitoneal,intracranial, or intraspinal or that involved any other criticalorgan; bleeding leading to reoperation; and overt bleeding witha bleeding index of 2 or more. The bleeding index was calculatedas the number of units of packed red cells or whole blood transfusedplus the hemoglobin values before the bleeding episode minusthe hemoglobin values after the episode (in grams per deciliter).Secondary safety outcomes were death, other bleeding, a needfor transfusion, thrombocytopenia, and any other adverse event.
Efficacy and safety outcomes were adjudicated by a central independentcommittee whose members were unaware of the treatment assignmentsand included reviews of all venograms and reports of bleedingand death.
Statistical Analysis
Assuming an incidence of venous thromboembolism by day 11 of34 percent in the enoxaparin group and a risk reduction of about30 percent (i.e., an incidence of 24 percent in the fondaparinuxgroup), 319 patients were needed in each group (for a totalof 638 patients) to provide the study with a power of 85 percent.The target number of recruited patients was 912, a number thatallowed for failure to obtain primary efficacy data in up to30 percent of patients.
The analysis of the primary efficacy outcome included data onall patients who had received at least one dose of study medication,had undergone the appropriate surgery, and had had an adequateassessment for venous thromboembolism by day 11. The analysisof safety included data on patients who had received at leastone dose of study medication.
A two-tailed P value of less than 0.05 was considered to indicatestatistical significance. The analysis of the primary efficacyoutcome was performed with the use of a two-sided Fisher's exacttest. Exact 95 percent confidence intervals for the absolutedifference between fondaparinux and enoxaparin and the riskratio were calculated. The treatment effect was also analyzedaccording to predefined categorical covariates with the useof a logistic-regression model.
The study was supervised by a steering committee of 11 people,which included 7 representatives of the sponsors (NV Organonand SanofiSynthelabo). The committee designed the study,interpreted the data, and wrote the article. The final statisticalanalysis was performed by the sponsor. The central adjudicationcommittee and the data monitoring committee operated independentlyof the sponsor. One planned interim analysis was conducted byan independent statistical center when half the projected patientpopulation had been enrolled, for reestimation of the samplesize, since the rate of venous thromboembolism in patients undergoingknee surgery was uncertain. Simulations demonstrated that thepredefined procedure did not inflate the type I error. No changein the sample size was found to be necessary, and the studycontinued as planned.
Results
Study Populations
Between December 1998 and January 2000, 1049 patients were enrolledin 64 centers in North America. Fifteen patients did not receiveany study drug, leaving 1034 available for the safety analysis(Table 1); primary efficacy had not been assessed by day 11in 310 patients. Thus, 724 patients (69.0 percent) were includedin the primary efficacy analysis, a percentage in line withother large multicenter trials that used venography after orthopedicsurgery.13,14,15,16 The characteristics of patients excludedfrom the primary efficacy analysis did not differ from thoseof patients included in the analysis (data not shown).
Table 1. Patients Included in the Analyses and Reasons for Exclusion.
Base-line characteristics did not differ significantly betweenthe two groups of patients included in the analysis of safety(Table 2) or primary efficacy (data not shown). Among patientsanalyzed for primary efficacy, the median time between surgeryand the qualifying examination for venous thromboembolism wasseven days in both groups; most patients underwent this examinationbetween day 5 and day 11, as planned. The two groups did notdiffer with regard to the last day of active treatment or theuse of concomitant treatments up to day 11 (Table 3).
Table 3. Treatments Received during the Study Period by Patients Assessed for the Primary Efficacy Outcome.
Overall, 514 patients treated with fondaparinux and 511 patientstreated with enoxaparin returned for the follow-up visit onday 49. The duration of follow-up was similar in the two groups.During follow-up of patients who were not treated for an acutethromboembolic event, 19.1 percent of patients assigned to fondaparinux(86 of 450) and 20.2 percent of patients assigned to enoxaparin(82 of 406) received prolonged thromboprophylaxis, primarilywith a preparation of heparin or a vitamin K antagonist.
Incidence of Venous Thromboembolism
The incidence of venous thromboembolism by day 11 was 27.8 percent(101 of 363 patients) in the enoxaparin group and 12.5 percent(45 of 361 patients) in the fondaparinux group (reduction inrisk, 55.2 percent; 95 percent confidence interval, 36.2 to70.2 percent; P<0.001) (Table 4). A similar result was foundin sensitivity analyses when patients who had had no primaryefficacy assessment by day 11 were included in the primary efficacyanalysis (data not shown). As compared with enoxaparin, fondaparinuxreduced the incidence of proximal deep-vein thrombosis by 54.5percent (P=0.06) and distal deep-vein thrombosis by 55.9 percent(P<0.001). The incidence of symptomatic venous thromboembolismwas low and did not differ significantly between the two groups(Table 4). Overall, the superiority of fondaparinux over enoxaparinwith respect to primary efficacy was consistent according toage, sex, body-mass index (the weight in kilograms divided bythe square of the height in meters [<30 vs. 30]), type ofanesthesia (general, regional, or both), type of surgery (primaryor revision), use or nonuse of cement, and whether or not patientshad had previous venous thromboembolism (data not shown). Thenumber of patients treated by participating physicians for avenous thromboembolic event by day 11 was significantly lowerin the fondaparinux group (15.1 percent [67 of 443]) than inthe enoxaparin group (25.1 percent [111 of 442], P<0.001).
Table 4. Incidence of Venous Thromboembolic Events by Day 11.
By day 49, the incidence of symptomatic venous thromboembolismdid not differ significantly between the fondaparinux group(1.0 percent [5 of 517 patients]) and the enoxaparin group (1.9percent [10 of 517 patients]). Fatal pulmonary embolism occurredin one patient in each group; nonfatal pulmonary embolism occurredin two patients in the fondaparinux group and four in the enoxaparingroup.
Safety Outcomes
There were no instances of fatal bleeding or bleeding in a criticalorgan in either treatment group; bleeding requiring reoperationoccurred in two patients in the fondaparinux group and one inthe enoxaparin group. In all three patients, drainage of a kneeeffusion was performed. In the fondaparinux group, nine episodesof overt bleeding were associated with a bleeding index of 2or more; seven occurred at the surgical site, and only threeled to discontinuation of study treatment. The total for theprimary safety outcome was therefore 11 major bleeding episodesin the fondaparinux group and 1 in the enoxaparin group (P=0.006)(Table 5). The incidence of minor bleeding, a need for transfusion,and other adverse events during treatment or follow-up did notdiffer significantly between the two groups. Platelet countslower than 100,000 per cubic millimeter were measured in 14patients (2.7 percent) in the fondaparinux group as comparedwith 19 (3.7 percent) in the enoxaparin group (P=0.27). No episodeof a decreased platelet count was reported as a serious adverseevent in either group. By day 49, two patients in the fondaparinuxgroup (0.4 percent) and three in the enoxaparin group (0.6 percent)had died from causes unrelated to the treatment.
This study demonstrates that fondaparinux is significantly moreeffective than enoxaparin in preventing venous thromboembolismafter elective major knee surgery. Deep-vein thrombosis hasbeen more difficult to prevent with anticoagulation therapyafter knee surgery than after total hip replacement, even withlow-molecular-weight heparin, the most effective thromboprophylactictherapy to date.1 The 27.8 percent incidence of venous thromboembolicevents in the enoxaparin group by day 11 is consistent withthe incidence of 19.0 to 25.0 percent in other trials of enoxaparinafter knee surgery.16,17,18,19 In our study, the reduction to12.5 percent in the fondaparinux group is consistent with theresults of three other large studies in patients undergoingsurgery for hip fracture8 or elective hip replacement.9,10 Thesuperior efficacy of fondaparinux may be related to its abilityto initiate selective inhibition of factor Xa, its predictablelinear pharmacokinetics, the choice of dose, and the startingtime after surgery.
The low incidence of symptomatic events in our study shouldbe interpreted with caution, as it is likely to be lower thanwould be observed in typical clinical situations. As in othertrials of thromboprophylaxis, most of our asymptomatic patientswith positive venograms had been receiving an anticoagulantat a therapeutic dose. Moreover, about 20 percent of our patientswere receiving prophylaxis after the study treatment periodended. Both of these factors may have prevented symptomaticvenous thrombosis.
Major bleeding was significantly more frequent in the fondaparinuxgroup (11 patients, including 9 with a bleeding index of 2 ormore) than in the enoxaparin group (1 patient). Administrationof fondaparinux was continued in six of the nine patients witha bleeding index of 2 or more. Nevertheless, the two groupsdid not differ significantly with respect to fatal bleeding,bleeding in critical organs, or bleeding leading to reoperation.
Supported by NV Organon and SanofiSynthelabo. All authorshave served as consultants to NV Organon and SanofiSynthelabo.
Presented in abstract form at the 42nd Annual Meeting of theAmerican Society of Hematology, San Francisco, December 15,2000 (Blood 2000;9:491A, A2111).
* Participants in the study are listed in the Appendix.
Source Information
From the Department of Medicine, Veterans Affairs Boston Healthcare System and Beth Israel Deaconess Medical Center, Boston (K.A.B.); the Department of Orthopedics, Sahlgrenska University HospitalÖstra, Göteborg, Sweden (B.I.E.); the Department of Orthopedics, Hillerød University, Hillerød, Denmark (M.R.L.); and the Department of Medicine, Hamilton Health Sciences CorporationGeneral Division, Hamilton, Ont., Canada (A.G.G.T).
Address reprint requests to Dr. Bauer at the Beth Israel Deaconess Medical Center, 330 Brookline Ave., Boston, MA 02215, or at kbauer{at}caregroup.harvard.edu.
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Appendix
The members of the Pentasaccharide in Major Knee Surgery StudyGroup were as follows: Steering Committee A.G.G. Turpie(chair), K.A. Bauer, J. Bouthier, R.G. Cariou, J.F.M. Egberts,B.I. Eriksson, J.A. Hoek, M.R. Lassen, A.W.A. Lensing, H. Magnani,L. Snow-Adami; Data Monitoring Committee D. Bergqvist,G.D. Paiement, A. Planes; Central Independent Adjudication Committee M. Gent (chair), J.S. Ginsberg, J. Hirsh, C. Kearon,M.N. Levine, J.G. Thomson, A.G.G. Turpie, J. Weitz; IndependentStatistical Center A. Leizorovicz, Lyons, France; Sponsor,NV Organon, the Netherlands Study Management: L. Snow-Adami,E. Warga; Statistical Analysis: R. Vijayaraghavan, W.F. Sommer;Clinical Documentation: E. Osifchin; Investigators, United States(861 patients) N. Abramson, Jacksonville, Fla.; J. Albrigo,Alexandria, Va.; J. Barnett, Orlando, Fla.; K. Beer, Toledo,Ohio; B. Bierbaum, Boston; W. Bose, West Mobile, Ala.; D. Bramlet,St. Petersburg, Fla.; F. Burke, Lexington, Ky.; D. Butler, Sacramento,Calif.; V. Cabanas and M. Swank, Cincinnati; F. Cannon, Ocala,Fla.; J. Caraveo, Temple, Tex.; C. Chalian, Pomona, Calif.;C. Christensen, J. Muntz, and S. Siff, Houston; P. Comp, OklahomaCity; D. Covall, Decatur, Ga.; R. Ennis, Hollywood, Fla.; G.S.Gill, Lubbock, Tex.; D. Green, Chicago; D. Gremillion, Nashville;N. Halbridge, Fountain Valley, Calif.; W. Hefley, R. Lavender,and R.B. Sorrells, Little Rock, Ark.; M. Hollman, Orlando, Fla.;W. Hopkinson, Maywood, Ill.; C. Hummer, Upland, Pa.; F. Ivey,Galveston, Tex.; A. Jahnke, Fort Gordon, Ga.; G. Johnson, Minneapolis;G. Kantor, Palm Beach Gardens, Fla.; H. Kim, San Francisco;W. Kim, Fountain Valley, Calif.; M. Koren, South Jacksonville,Fla.; W. Lanzer, Seattle; D. Lawlor, Olathe, Kans.; L. Levy,La Mesa, Calif.; A. Lombardi, Columbus, Ohio; P. Lunseth, Tampa,Fla.; D. MacDonald, East Lansing, Mich.; M. Mancao, Pensacola,Fla.; G. Mayfield, Honolulu; J. Ohar, St. Louis; P. Peters,Dallas; K. Plancher, Stamford, Conn.; P. Richin, Decatur, Ga.;D. Riff, Anaheim, Calif.; M. Ritter, Mooresville, Ind.; L. Rocamora,Winston-Salem, N.C.; W. Shelton, Jackson, Miss.; B. Spetzler,Salem, Va.; E. Strauss, Great Neck, N.Y.; J. Tozzi, Neptune,N.J.; C. Walker, Whittier, Calif.; L. Walker, San Bernardino,Calif.; M. Ward, Covina, Calif.; C. Williamson, South Daytona,Fla.; and I. Ziv, Buffalo, N.Y.; Investigators, Canada (188patients) D. Anderson and M. Gross, Halifax, N.S.; R.Bhargava, Oshawa, Ont.; J. Brandwein and J. Gollish, Toronto;L. Desjardins, Ste. Foy, Que.; M. Mant, Edmonton, Alta.; W.Pisesky, Kelowna, B.C.; B. Pressnail, Barrie, Ont.; M. Rodger,Ottawa, Ont.; S. Solymoss, Montreal; T. Sparling, Burnaby, B.C.;and J. Wilson, North York, Ont.
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