Warfarin Protocol Research Articles

Tiempo en rango terapéutico e incidencia de complicaciones por warfarina en una cohorte retrospectiva de 20 años

ObjectiveTo characterize the time in therapeutic range (TTR) and estimate the incidence rate of complications (PTIRc) in adults with warfarin protocol. DesignRetrospective cohort based on medical records of patients older than 18years, between 1996 and 2016 and followed for at least three months. SiteHematology unit of a Venezuelan specialized cardiovascular center. ParticipantsElectronic health record. Main measurementsTTR and PTIRc. The variables were sex, functional illiteracy, occupation, International Normalized Ratio (INR) and follow-up time, which were analyzed with TTR and PTIRc using binomial logistic and Poisson regression models, respectively. Results2,770 patients were followed up for a total of 1,201,380 days, 42.3% had a TTR<65% and 3.5% had INR 2.5-3.5. 61.8% had complications. PTIRc was 6.84/100 person-months (95%CI: 6.56-7.15). TTR<65% showed significant adjusted OR with functional illiteracy and INR 2.5-3.5, while for higher PTIRc a significant RR was found in the two factors mentioned, shorter follow-up time, TTR<65% and in women. ConclusionsDespite new anticoagulant treatments, warfarin is useful. As follow-up time increased, control was better and the rate of occurrence of complications decreased; however, the conditions that showed lower TTR and higher rate of occurrence of complications require a thorough review of follow-up especially in patients with functional illiteracy.

Peri-Operative Warfarin Protocol to Decrease Length of Stay After Left Ventricular Assist Device Implantation

<h3>Purpose</h3> A limitation to left ventricular assist device (LVAD) implantation is cost with fixed reimbursement rates for the LVAD implantation hospitalization regardless of hospital length of stay and costs. Patients must have a therapeutic INR on warfarin prior to discharge which can take days and delay discharge. The purpose of this study is to evaluate the impact of a peri-operative warfarin protocol on decreasing length of stay during index LVAD implantation. <h3>Methods</h3> This is a retrospective single center study of adult patients undergoing LVAD implantation between January 1, 2019 and December 31, 2020. Patients who died during the admission were excluded. Patients in the intervention group (INT) underwent LVAD between January 1-December 31, 2020. The peri-operative warfarin protocol included pre-operative vitamin K dosing according to INR, initiation of warfarin by post-operative day (POD) 3, and warfarin titration scheme. The historical control group (CON) included patients receiving LVADs between January 1-December 31, 2019. Warfarin start date was at the discretion of providers. All patients had a goal INR of 2-3. Endpoints included length of stay, post-operative warfarin start date, time to therapeutic INR, warfarin dosing requirements, pre-operative vitamin K dosing and bleeding complications. <h3>Results</h3> Seventy-seven patients were included; n=41 (53.2%) CON and n=36 (46.8%) INT. Total hospital length of stay was 35 [26,43] days in the CON group compared to 27.5 [24,35] days in the INT group (p=0.095). Warfarin was started earlier in the INT group (POD 5.5 [2.8,7.0]) compared to the CON group (POD 8 [6,14]) (p=0.004). Time to therapeutic INR remained the same between the two groups with a median of 6 days. Pre-operative vitamin K decreased from 15 [10,15] mg in the CON group to 5 [0.0,11.3] mg in the INT group (p=<0.001). There was no increase in bleeding with the peri-operative warfarin interventions: 8 bleeds in the CON group and 4 bleeds in the INT group. <h3>Conclusion</h3> Initiating warfarin earlier post-operatively may help decrease hospital length of stay after LVAD implantation without increasing bleeding events.

A Less Than 81mg of Aspirin in Heart Mate 3 is Safe Irrespective of Amount of Platelet Inhibition

Purpose Optimal dose of aspirin for Heartmate 3 (HM 3) LVAD patients is still not known. Recently low dose aspirin (81mg compared to 325mg) has shown to be efficacious. Randomized control trial with no dose aspirin is underway. However, platelet inhibition can be still achieved with less than low dose aspirin. So we looked into safety and efficacy of a very low dose aspirin ( Methods We did retrospective analysis of HM3 patients implanted in our institution (2015- 2020). Patients who were on less than 81mg of aspirin/day were identified. Thromboelastogram (TEG) was used to assess response to aspirin. We compared the number of thromboembolic events, bleeding events, LDH, and hematocrit before and after the dose change, with the patients being their own controls, using paired t test. Results In our program, we follow 35 patients on HM3. Most of them 24(68.6%) receive > 81 mg of aspirin daily. We Identified 11 patients on less than 81mg of aspirin. The mean age of this cohort was 51.18 years, 7 were Male. Out of the 11, 3 patients were on aspirin 40.5 mg every other day, 3 on 40.5 mg every day, 4 on 81mg every other day and one patient was not on any aspirin. Reason for dose alteration was adequate inhibition noted on TEG in 5 patients and bleeding in 6 patients (4 out of 6 for gastrointestinal bleed). Mean duration of follow up was 22.57±18months. Six patients in this cohort were on standard warfarin protocol with the INR goal 2-3 and one patient was not on any warfarin. The follow-up on a very low ASA dose was 13.7±8.6 months. There were no pump thrombosis or other thromboembolic events either before or after the dose change. There was no significant difference in LDH levels before (225.2±24.3) or after (220.1±27.8) p=0.7, hematocrit before 33.6+/-9.9 or after 35.0+/-8.1, P=0.08, aspirin dose change. Arachidonic Acid inhibition on thromboelastogram was less than 80% in 7 patients and 5 of them had inhibition less than 50%. Conclusion A very low dose of aspirin (

Early versus delayed removal of the pericardial drain in patients with cardiac tamponade complicating radiofrequency ablation of atrial fibrillation

Cardiac tamponade is a common life-threatening complication during radiofrequency ablation of atrial fibrillation (RAAF) and is mostly managed by pericardiocentesis. Thus far, the optimal timing for drain removal has not been established. We retrospectively enrolled patients with cardiac tamponade complicating RAAF. The ablation was performed with interrupted novel oral anticoagulants, interrupted warfarin or uninterrupted warfarin protocols. An observation period of at least 30 minutes after the last aspiration via the drain was used to monitor the reaccumulation of pericardial fluid, and then, the patients were divided into an early removal (ER) group in the electrophysiology (EP) laboratory and a delayed removal (DR) group in the ward. A total of 51 patients were included: 25 patients in the ER group and 26 patients in the DR group. There were no significant differences in baseline demographics between the two groups, and no cardiac tamponade reoccurred in either group in the ward. Unlike the DR group, the ER group showed an association with a decreased rate of chest pain (P = .000), fever (P = .001), nausea (P = .000), in-hospital recurrent AF (P = .010), and antibiotic use (P = .012). Anticoagulation was earlier (P = .009), and the median in-hospital stay was shorter (P = .001) in the ER group than in the DR group. ER of the pericardial drain after no evidence of pericardial bleeding for at least 30 minutes in the EP laboratory is safe and associated with a better early hospital course.

Instruments for the assessment of patient adherence to oral anticoagulation with warfarin protocol for a systematic review.

Background:Non-adherence can be highlighted as one of the main contributors to the occurrence of adverse events in patients treated with warfarin. The usefulness of self-reporting measures of drug adherence could be improved by following psychometric properties in the development of the measurement scales. Thus, we aimed to describe the protocol of a systematic literature review designed to investigate and describe validated instruments used to assess adherence to warfarin therapy.Methods:We will perform a systematic review will include observational and experimental studies involving the use of validated instruments to assess adherence to warfarin therapy. Dimensions of adherence raised by the selected studies will be extracted to be compared. We will systematically search electronic databases including MEDLINE, LILACS, EMBASE, and Cochrane Library using a comprehensive strategy from inception to June 31, 2019. Two reviewers will revise the literature independently using a standardized form and assess the potential bias. After the comparison of results, discrepancies will be solved after the analysis of a third reviewer.Result:The development of the present systematic will help to summarize and evaluate the validated instruments that have been previously published to assess adherence to warfarin therapy.Conclusion:This review will substantiate the discussion of relevant topics that should be assessed while providing care to patients taking warfarin. This knowledge will enable a comprehensive approach for healthcare professionals to improve treatment outcomes and the design of future investigations.Registration:The systematic review is registered in the PROSPERO international prospective register of systematic review (PROSPERO# CRD42019128324).

Factors associated with availability of anticoagulation reversal agents in rural and community emergency departments.

Results of a study of anticoagulation reversal agent availability in rural and community hospital emergency departments (EDs) are reported. A cross-sectional telephone survey was conducted to test the hypothesis that anticoagulation reversal agents are not commonly stocked in low-volume EDs. In phase 1 of the study, a physician, pharmacist, or nurse manager at a sample of EDs in 1 state was surveyed to characterize anticoagulation reversal agent availability and the presence or absence of reversal protocols; in phase 2, follow-up qualitative interviews were conducted with hospital pharmacists selected by purposive sampling to identify barriers to availability. Among the 103 EDs represented in the survey, 87 (84%) stocked fresh frozen plasma, 14 (14%) stocked 4-factor prothrombin complex concentrate (4F-PCC), and 2 (2%) stocked activated 4F-PCC. Forty-one EDs (40%) had a warfarin reversal protocol, but only 2 (2%) EDs had a protocol for direct oral anticoagulant reversal. ED volume and neurology coverage were significantly associated with reversal agent availability (p = 0.014) and warfarin protocol availability (p < 0.001). Identified factors contributing to reversal agent nonavailability were product cost, lack of knowledge of drug availability, and concerns about shelf life. An investigation of rural and community hospitals in 1 state revealed that the institutions rarely have specialized anticoagulation reversal drugs available. Cost and infrequency of utilization were 2 commonly cited reasons for reversal agent nonavailability.

Personalized Anticoagulation: Optimizing Warfarin Management Using Genetics and Simulated Clinical Trials.

Clinical trials testing pharmacogenomic-guided warfarin dosing for patients with atrial fibrillation have demonstrated conflicting results. Non-vitamin K antagonist oral anticoagulants are expensive and contraindicated for several conditions. A strategy optimizing anticoagulant selection remains an unmet clinical need. Characteristics from 14 206 patients with atrial fibrillation were integrated into a validated warfarin clinical trial simulation framework using iterative Bayesian network modeling and a pharmacokinetic-pharmacodynamic model. Individual dose-response for patients was simulated for 5 warfarin protocols-a fixed-dose protocol, a clinically guided protocol, and 3 increasingly complex pharmacogenomic-guided protocols. For each protocol, a complexity score was calculated using the variables predicting warfarin dose and the number of predefined international normalized ratio (INR) thresholds for each adjusted dose. Study outcomes included optimal time in therapeutic range ≥65% and clinical events. A combination of age and genotype identified different optimal protocols for various subpopulations. A fixed-dose protocol provided well-controlled INR only in normal responders ≥65, whereas for normal responders <65 years old, a clinically guided protocol was necessary to achieve well-controlled INR. Sensitive responders ≥65 and <65 and highly sensitive responders ≥65 years old required pharmacogenomic-guided protocols to achieve well-controlled INR. However, highly sensitive responders <65 years old did not achieve well-controlled INR and had higher associated clinical events rates than other subpopulations. Under the assumptions of this simulation, patients with atrial fibrillation can be triaged to an optimal warfarin therapy protocol by age and genotype. Clinicians should consider alternative anticoagulation therapy for patients with suboptimal outcomes under any warfarin protocol.

Going Beyond Administrative Data: Retrospective Evaluation of an Algorithm Using the Electronic Health Record to Help Identify Bleeding Events Among Hospitalized Medical Patients on Warfarin.

To reliably assess quality, a standardized electronic approach is needed to identify bleeding events. The study aims were the following: (1) clinically validate an electronic health record-based algorithm for bleeding and (2) assess interrater results to determine validity and reliability. Data were analyzed before and after implementation of a pharmacist-managed warfarin protocol. Bleeding was based on ≥2 of 3 criteria: (1) diagnosis indicating bleeding, (2) lab value decrease suggesting bleeding, and (3) blood product use. All suspected bleeds (234) and a sample (58) not meeting criteria were compared with clinical review. There were 234 bleeding cases identified electronically. Reviewer agreement was 78.2% (κ = 0.565). Algorithm sensitivity was 93.9% and positive predictive value 46.2%. Algorithm identification was least accurate for those with only 2 criteria but good for those with all criteria. This study supports using multiple electronic criteria to identify bleeding events. However, cases having exactly 2 criteria may require manual review for validation.

The June Issue of the CGJ.

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Advantages of a Warfarin Protocol for Long-term Care Pharmacists: a Retrospective Cohort Study.

BackgroundWarfarin is an anticoagulant prescribed to 12% of long-term care residents to reduce the risk of thrombo-embolism. This study used indicators to compare warfarin management by pharmacists to usual care.MethodsThis was a retrospective cohort study comparing a pharmacist-managed warfarin protocol with usual care of qualified warfarin recipients at long-term care facilities (two protocol, one control) in Calgary, Alberta. We compared the proportion of international normalized ratio (INR) tests in the range 2.0 to 3.0, time in range, number of tests, and frequency of bleeding at protocol and control sites. Our primary outcome, time in INR therapeutic range, is an indicator for assuring care quality. A cross-sectional survey at these sites compared health professionals’ perceptions of workload and effectiveness of warfarin management.ResultsOf the 197 residents’ charts reviewed in the study period, those on protocol had 45.0 INR tests while those on usual care had 52.7 tests (p = .034, 95% CI for the difference: 0.6 to 14.6 INR tests). No significant difference was found for time in therapeutic range, number of tests in range, or major bleeding events. Of 178 health professionals surveyed, those from protocol facilities were more satisfied with warfarin management (p = .013). Workload and safety were perceived similarly at all sites.InterpretationOur results suggest that a pharmacist-managed warfarin protocol is as effective as usual care and has advantages pertaining to work satisfaction, knowledge of drug interactions, consistent documentation, and fewer INR tests. Further research on teamwork and coagulation management in long-term care facilities is recommended.

An evidence-based warfarin management protocol reduces surgical delay in hip fracture patients

BackgroundUp to 4 % of patients presenting with a hip fracture may be on warfarin at admission. There is little consensus on the timing, dosage or route of vitamin K administration. We aimed to evaluate the impact of a locally developed, evidence-based protocol for perioperative warfarin management on the admission-to-operation time (AOT) in hip fracture patients.Materials and methodsClinical and demographic data were collected prospectively for hip fracture patients who were on warfarin at the time of admission (post-protocol group) and compared to a historical control group of patients who were on warfarin before implementation of the protocol (pre-protocol group). Univariate analysis was undertaken to identify any significant differences between the two groups.ResultsTwenty-seven patients in the pre-protocol group (27/616, 4.4 %) and 40 patients in the post-protocol group (4.7 %, 40/855) were on warfarin at admission. There was a significant reduction in the median AOT from 73 h (IQR 46–105) to 37.7 h (IQR 28–45) after implementation of the warfarin protocol (p < 0.001). The proportion of patients operated on within 48 h of admission increased from 30 % (8/27) in the pre-protocol group to 80 % (32/40) in the post-protocol group (p < 0.001). No significant differences in hospital length of stay (p = 0.77) or the postoperative warfarin recommencement time (p = 0.90) were noted between the two groups.ConclusionImplementation of a perioperative warfarin management protocol can expedite surgery in hip fracture patients, but did not reduce hospital stay in our cohort, possibly because of a delay in recommencing warfarin in these patients postoperatively.Level of evidenceLevel III.

073 ATRIAL FIBRILLATION ABLATION UNDER THERAPEUTIC WARFARIN IS SAFE WITH IMPROVED PATIENTS' EXPERIENCE AND POTENTIALLY COST-SAVING COMPARED TO BRIDGING LOW MOLECULAR WEIGHT HEPARIN

Introduction Atrial fibrillation (AF) ablation under therapeutic warfarin reduces periprocedural risk of complications, compared to periprocedural bridging with low molecular weight heparin (LMWH). The aim of study was to compare the safety of an uninterrupted warfarin protocol in patients undergoing AF ablation without intracardiac echocardiography and to assess the experience of patients who had previous ablation with bridging protocol on the change of anticoagulation protocol. Method Two anticoagulation regimes for patients undergoing AF ablation were evaluated—uninterrupted warfarin group (120 in Group 1) and bridging LMWH group (100 in Group 2). Bleeding complications were compared between the two groups. Patients in Group 1 who had had previous ablation on bridging LMWH were asked to comment on their experience with the change of protocol at 4 weeks post discharge. Drug cost comparison in two groups was performed. Results Preprocedural INR in Group 1 was 2.48±0.42 compared to 1.08±0.16 in Group 2 (95% CI 1.38 to 1.41, p Conclusions AF ablation under therapeutic warfarin is safe without echocardiography guidance, associated with improved patients9 experience and potentially cost saving in long term.

Standardization: Novant’s secret for improving medication safety

Medication safety touches every action, initiative, and decision across a hospital system, from the clinical floors to operations and leadership. Elizabeth McGowan, PharmD, believes that the door is wide open with unlimited possibilities for health-system pharmacists to be involved with medication safety on every level, from the pharmacy to the patient bedside.

Aortic thrombosis in dogs: Presentation, therapy, and outcome in 26 cases

ObjectivesThe pathogenesis and presentation of aortic thrombosis (AT) in dogs is not well characterized and an effective antithrombotic therapy for AT in dogs has not been identified. Our goal is to report the clinical presentation and results of therapies in dogs with AT. AnimalsTwenty-six client-owned dogs. MethodsRetrospective review of medical records of dogs diagnosed with AT between 2003 and 2010. ResultsTwenty-six dogs had an apparent primary mural aortic thrombus. None had structural heart disease at diagnosis. Twenty dogs were ambulatory with varying degrees of pelvic limb dysfunction. Duration of ambulatory dysfunction was 7.8 weeks (range 1 day–52 weeks). A majority of dogs (58%) had no concurrent conditions at diagnosis.Fourteen dogs were treated with a standard warfarin protocol for a median period of 22.9 months (range 0.5–53 months). Ambulatory function improved in all dogs treated with warfarin. Time until clinical improvement was 13.9 days (range 2–49 days). Dogs treated with warfarin did not become non-ambulatory, die or undergo euthanasia related to AT, or have a known serious hemorrhagic event. ConclusionsThe pathogenesis of AT in dogs is distinct from that of aortic thromboembolism (ATE) in cats. Aortic thrombosis in dogs is more likely to involve local thrombosis in the distal aorta with embolization to the arteries of the pelvic limb resulting in chronic progressive ambulatory dysfunction. Chronic warfarin administration is well-tolerated and appears to be an effective short-term and long-term therapy for dogs with AT.

The impact of pre-injury anticoagulation therapy in the older adult patient experiencing a traumatic brain injury: A systematic review.

Review Question/Objective The objective of this systematic review is to synthesize the best available evidence on the impact of pre-injury anticoagulation therapy in the older adult patient who experiences a traumatic brain injury. Inclusion Criteria Types of Participants This systematic review will consider studies which include patients age 65 years or older, regardless of gender or ethnicity, who have experienced a traumatic brain injury. Types of Intervention The intervention of interest is the use of anticoagulants and/or antiplatelet prescription medication prior to the traumatic brain injury. Types of Comparator The intervention of interest will be compared to non-use of prescription anticoagulants and/or antiplatelet medication therapy. Types of Outcome Measures This review will consider studies that include the following outcome measure: death before discharge from the acute care setting.

Catheter Ablation for Atrial Fibrillation on Uninterrupted Warfarin: Can It Be Done Without Echo Guidance?

Catheter ablation for atrial fibrillation is an effective treatment for symptomatic patients who have failed drug therapy. Recent studies using intracardiac echocardiography have demonstrated that ablation can be performed safely on uninterrupted warfarin and may be superior to bridging low molecular weight heparin (LMWH). We sought to assess the safety of an uninterrupted warfarin protocol using a simplified ablation protocol in a prospective controlled study. Two anticoagulation regimes for patients undergoing catheter ablation for atrial fibrillation were evaluated--a bridging LMWH group and an uninterrupted warfarin group. Bleeding complications were compared between the 2 groups. In total 198 patients were evaluated (109 bridging LMWH, 89 uninterrupted warfarin). The preprocedure INR in the LMWH group (mean age 60.6 years, 72% male) was 1.2 ± 0.3 compared to 2.3 ± 0.5 in the uninterrupted warfarin group (mean age 60.9 years, 69% male). The primary outcome (a composite of major and minor bleeding complications) was observed in 78% in the LMWH group compared to 56% in the warfarin group (P = 0.001), mainly due to increased pain at the venous access site (41% vs 16%, P = 0.001). Two patients undergoing ablation on warfarin required pericardiocentesis for cardiac tamponade. Drug costs were lower in the warfarin group ($64.77 ± 31.86 vs $20.76 ± 15.60, P = 0.005), but the overall cost of treatment per patient (including bed occupancy costs) was similar in the LMWH group compared to the warfarin group ($883.96 ± 278.78 vs $816.59 ± 182.72, P = 0.06). Catheter ablation for atrial fibrillation can be performed safely on uninterrupted warfarin without intracardiac echocardiography, with a reduced risk of bleeding complications.

Relationship between chromogenic factor X and international normalized ratio differs during early warfarin initiation compared with chronic warfarin administration

Chromogenic factor X (CFX) monitoring is necessary in patients with potential international normalized ratio (INR) artifacts during warfarin therapy. The relationship of CFX with the INR needs to be quantitated to have warfarin protocols that are equivalent with either test as a monitoring parameter. This study investigated whether the CFX/INR relationship is different during warfarin initiation compared with that during chronic warfarin therapy. Outpatients (N = 164) taking chronic doses of warfarin and inpatients (N = 137) initiating warfarin therapy had plasma samples tested for CFX and INR. The best fit mathematical relationship of CFX and INR was determined for both groups. A six hundred and twenty-five bed, adult-only, private, tertiary care teaching hospital was the setting of the study. The best fit equation for chronic warfarin patients was quadratic using a reciprocal transformation of the INR. The best fit equation for the warfarin initiation patients was linear using logarithmic transformation of CFX and INR. The predicted CFX from INRs over the range of 1.4-2.2 was 7-18% higher in the warfarin initiation patients than in the chronic warfarin patients. Translation of CFX values into equivalent INRs for use in warfarin initiation and maintenance protocols is improved when using equations specific to the patient situation.

Poster 38: Survey of General Dentist and Oral and Maxillofacial Surgeon Warfarin Protocol for Tooth Extractions

Statement of the Problem: Perioperative bleeding risk must be weighed against the risks of thromboembolic events when warfarin anticoagulant therapy discontinuation is considered. Dentists and dental specialists may not be aware of the protocols recommended by current literature that discourage discontinuation of warfarin prior to dental treatment as patients may be placed at unnecessary medical risk.

4 years’ experience with a pharmacy warfarin dosing service for orthopedic rehabilitation inpatients

Rationale Complex, surgical patients are routinely referred to rehabilitation hospitals for subacute and transition care. Before 2003, there was no anticoagulation service at Providence Healthcare (PH). Objectives The goals of the pharmacy warfarin service were: (1) to optimize anticoagulation management; and (2) to improve patient outcomes. Design The key ingredients were a strong interdisciplinary team; certified anticoagulation pharmacists; an evidence-based medicine approach to anticoagulation management; and continuous quality improvement. Retrospective evaluations were completed 2003–2006, comparing two control groups to the anticoagulation service patients. Results The 2003/2004 (5month) pilot project started on an orthopedic rehabilitation unit. The control groups showed less favourable patient outcomes. Without warfarin nomograms, protocols or anticoagulation training, there was delayed time to therapeutic INR (3.03 days); less therapeutic INR results (50.9%); more subtherapeutic INRs (33.2%) and supratherapeutic INRs (14.9%); increased morbidity and mortality (e.g. 1 fatal PE, 2 major bleeds, 5 doses of vitamin K). The results showed that the warfarin dosing service was safer and more effective. Advantages included faster time to therapeutic INR (2.84 days); more INR results (67.9%) within the therapeutic range; less subtherapeutic INR results (22.7%) and supratherapeutic INR (9.4%); no vitamin K or FFP; no new diagnoses of DVT, PE or CVA; and no deaths. Two more 12-month evaluations were completed, also showing favourable results (for 2004/2005 and 2006). Upon demand, the anticoagulation service expanded into stroke and transitional rehabilitation units in 2006. Conclusion This cost-effective anticoagulation service is supported by a strong interdisciplinary team and 4 years of data analysis.

Low-Dose Warfarin for Prevention of Symptomatic Thromboembolism after Orthopedic Surgery

Warfarin dosing with a target international normalized ratio (INR) range of 1.5-2.5 has not been reported as adequate for venous thromboembolism (VTE) prophylaxis after total knee (TKR) and total hip replacement (THR) surgery. To evaluate the rate of symptomatic VTE after TKR and THR surgery using a low-dose (INR 1.5-2.5) warfarin protocol started the evening before surgery compared with a literature cohort treated with enoxaparin. TKR/THR patients treated with a 21-day low-dose warfarin protocol were followed via a consecutive observational design. Main outcome measures were symptomatic VTE and pulmonary embolism (PE), with major bleeds and death as secondary outcomes. Low-dose warfarin was compared with a literature cohort of patients treated with enoxaparin who received enoxaparin for a similar length of time and was evaluated for the same outcomes. Cohort event rates were derived as a weighted average using the DerSimonian model. VTE, PE, bleeds, and deaths in the low-dose warfarin group were 8 (1.04%), 4 (0.52%), 8 (1.04%), and 4 (0.52%), respectively. The cohort weighted average values were 35 (1.33%), 19 (0.72%), 65 (2.46%), and 18 (0.67%), respectively. Odds ratios for low-dose warfarin for VTE, PE, and VTE plus PE were 0.778 (95% CI 0.36 to 1.68), 0.717 (0.24 to 2.11), and 0.754 (0.41 to 1.42), respectively, all nonsignificant. Odds ratios for bleeds and death were 0.420 (0.20 to 0.87; p = 0.02) and 0.756 (0.26 to 2.24; NS), respectively. For this evaluation, low-dose warfarin was comparable to the enoxaparin cohort for development of VTE, PE, and VTE+PE. Incidences of bleeds in the enoxaparin cohort were significantly higher than in patients receiving low-dose warfarin.