David Anderson

Dalhousie University, Halifax, Nova Scotia, Canada

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Publications (11)171.46 Total impact

  • Philip Wells, David Anderson
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    ABSTRACT: Venous thromboembolism (VTE) is a common condition that can lead to complications such as postphlebitic syndrome, chronic pulmonary artery hypertension, and death. The approach to the diagnosis of has evolved over the years and an algorithm strategy combining pretest probability, D-dimer testing, and diagnostic imaging now allows for safe, convenient, and cost-effective investigation of patients. Patients with low pretest probability and a negative D-dimer can have VTE excluded without the need for imaging. The mainstay of treatment of VTE is anticoagulation, whereas interventions such as thrombolysis and inferior vena cava filters are reserved for special situations. Low-molecular-weight heparin has allowed for outpatient management of most patients with deep vein thrombosis at a considerable cost savings to the health care system. Patients with malignancy-associated VTE benefit from decreased recurrent rates if treated with long-term low-molecular-weight heparin. The development of new oral anticoagulants further simplifies treatment. The duration of anticoagulation is primarily influenced by underlying cause of the VTE (whether provoked or not) and consideration of the risk for major hemorrhage. Testing for genetic and acquired thrombophilia may provide insight as to the cause of a first idiopathic deep vein thrombosis, but the evidence linking most thrombophilias to an increased risk of recurrent thrombosis is limited.
    Hematology 12/2013; 2013:457-63. DOI:10.1182/asheducation-2013.1.457 · 2.86 Impact Factor
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    ABSTRACT: The benefit of adding rituximab to standard treatment in nonsplenectomized patients with primary immune thrombocytopenia (ITP) is uncertain. We performed a pilot randomized trial to determine the feasibility of recruitment, protocol adherence, and blinding of a larger trial of rituximab versus placebo; and to evaluate the potential efficacy of adjuvant rituximab in ITP. Nonsplenectomized adults with newly diagnosed or relapsed ITP who were receiving standard ITP therapy for a platelet count below 30 × 10(9)/L were randomly allocated to receive 4 weekly infusions of 375 mg/m(2) rituximab or saline placebo. Sixty patients were recruited over 46 months, which was slower than anticipated. Protocol adherence and follow-up targets were achieved, and blinding was successful for research staff but not for patients. After 6 months, there was no difference between rituximab and placebo groups for the composite outcome of any platelet count below 50 × 10(9)/L, significant bleeding or rescue treatment once standard treatment was stopped (21/32 [65.6%] vs 21/26 [80.8%]; relative risk = 0.81, 95% confidence intervals, 0.59%-1.11%). Timely accrual poses a challenge to the conduct of a large randomized trial of rituximab for presplenectomy ITP. No difference in the frequency of the composite outcome was observed in this pilot trial (registered at www.clinicaltrials.gov NCT00372892).
    Blood 02/2012; 119(6):1356-62. DOI:10.1182/blood-2011-08-374777 · 9.78 Impact Factor
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    ABSTRACT: Unanticipated elevation of the INR is common in patients receiving warfarin. We performed a prospective cohort study of 107 warfarin-treated patients with INR values of more than 10 who received a single 2.5 mg dose of oral vitamin K. During the first week, one patient experienced major bleeding, and one died. In the first 90 days after enrolment four patients had major bleeding (3.7%, 1.0% to 9.3%), eight patients (7.5%, 3.3% to 14.2%) died and two had objectively confirmed thromboembolism. Based on our low rate of observed major bleeding we conclude that 2.5 mg of oral vitamin K is a reasonable treatment for patients with INR values of more than 10 who are not actively bleeding.
    Thrombosis and Haemostasis 05/2010; 104(1):118-21. DOI:10.1160/TH09-12-0822 · 5.76 Impact Factor
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    ABSTRACT: Low-dose oral vitamin K decreases the international normalized ratio (INR) in overanticoagulated patients who receive warfarin therapy. Its effects on bleeding events are uncertain. To see whether low-dose oral vitamin K reduces bleeding events over 90 days in patients with warfarin-associated coagulopathy. Multicenter, randomized, placebo-controlled trial. Randomization was computer-generated, and participants were allocated to trial groups by using sequentially numbered study drug containers. Patients, caregivers, and those who assessed outcomes were blinded to treatment assignment. 14 anticoagulant therapy clinics in Canada, the United States, and Italy. Nonbleeding patients with INR values of 4.5 to 10.0. Oral vitamin K, 1.25 mg (355 patients randomly assigned; 347 analyzed), or matching placebo (369 patients randomly assigned; 365 analyzed). Bleeding events (primary outcome), thromboembolism, and death (secondary outcomes). 56 patients (15.8%) in the vitamin K group and 60 patients (16.3%) in the placebo group had at least 1 bleeding complication (absolute difference, -0.5 percentage point [95% CI, -6.1 to 5.1 percentage points]); major bleeding events occurred in 9 patients (2.5%) in the vitamin K group and 4 patients (1.1%) in the placebo group (absolute difference, 1.5 percentage points [CI, -0.8 to 3.7 percentage points]). Thromboembolism occurred in 4 patients (1.1%) in the vitamin K group and 3 patients (0.8%) in the placebo group (absolute difference, 0.3 percentage point [CI, -1.4 to 2.0 percentage points]). Other adverse effects were not assessed. The day after treatment, the INR had decreased by a mean of 1.4 in the placebo group and 2.8 in the vitamin K group (P < 0.001). Limitation: Patients who were actively bleeding were not included, and warfarin dosing after enrollment was not mandated or followed. Low-dose oral vitamin K did not reduce bleeding in warfarin recipients with INRs of 4.5 to 10.0. Funding: Canadian Institutes of Health Research and Italian Ministry of Universities and Research.
    Annals of internal medicine 03/2009; 150(5):293-300. · 16.10 Impact Factor
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    ABSTRACT: Use of low-molecular-weight heparins is avoided in patients with renal insufficiency because of concerns about an excessive anticoagulant effect and increased bleeding risk. To challenge this premise, we evaluated if deep vein thrombosis (DVT) prophylaxis with dalteparin sodium confers an excessive anticoagulant effect in critically ill patients with severe renal insufficiency. We conducted a multicenter, single-arm clinical trial of DVT prophylaxis with dalteparin sodium, 5000 IU once daily in critically ill patients with a creatinine clearance lower than 30 mL/min (to convert to milliliters per second, multiply by 0.0167). Bioaccumulation was defined by a trough anti-Xa level higher than 0.40 IU/mL, measured twice weekly. The pharmacodynamic properties of dalteparin were assessed by serial anti-Xa levels measured on days 3, 10, and 17. We enrolled 156 patients with a mean (SD) creatinine clearance of 18.9 (6.5) mL/min; 18 were excluded because they died or were discharged before testing (n = 3) or had prevalent DVT (n = 15). Of 138 patients included, the median (interquartile range [IQR]) duration of dalteparin exposure was 7 (4-12) days. In 120 patients who had at least 1 trough anti-Xa level (427 total measurements), no patient had bioaccumulation (0%; 95% confidence interval [CI]: 0%-3.0%); the median (IQR) trough anti-Xa level was undetectable (<0.10 IU/mL [<0.10 to <0.10 IU/mL]). Based on serial measurements, peak anti-Xa levels were 0.29 to 0.34 IU/mL and trough levels were lower than 0.06 IU/mL. Deep vein thrombosis occurred in 7 of 138 patients (5.1%; 95% CI, 2.5%-10.1%); major bleeding occurred in 10 patients (7.2%; 95% CI, 4.0%-12.8%), all with trough anti-Xa levels of 0.18 IU/mL or lower. In critically ill patients with severe renal insufficiency, DVT prophylaxis with dalteparin sodium, 5000 IU once daily, is not associated with an excessive anticoagulant effect due to drug bioaccumulation and is unlikely to contribute to bleeding. clinicaltrials.gov Identifier: NCT00138099.
    Archives of internal medicine 09/2008; 168(16):1805-12. DOI:10.1001/archinte.168.16.1805 · 13.25 Impact Factor
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    ABSTRACT: There is no randomized trial comparing low-molecular weight heparin (LMWH) and unfractionated heparin (UFH) for thromboprophylaxis in medical-surgical ICU patients. The primary objective of this randomized pilot study on LMWH vs UFH was to assess the feasibility of conducting a large randomized trial with respect to timely enrollment and blinded study drug administration, practicality of twice-weekly lower limb ultrasounds to screen for deep venous thrombosis, LMWH bioaccumulation and dose adjustment in renal insufficiency, and recruitment rates for a future trial in medical-surgical intensive care unit (ICU) patients. Its additional goals were to evaluate the suitability of the exclusion criteria and to document the range of research activities that precede accrual of patients into a trial to plan multisite management. By computerized telephone randomization, we allocated 129 medical-surgical ICU patients to treatment with dalteparin 5,000 IU QD SC or that with UFH 5,000 IU BID SC. Within each clinical center, only the study pharmacist was not blinded. We performed bilateral lower limb compression ultrasounds within 48 hours of ICU admission, twice weekly, on suspicion of deep venous thrombosis, and 7 days after ICU discharge. Research coordinators and investigators at 7 centers reported the time they engaged in all research activities before the first patient was randomized. Timely complete study drug administration occurred after enrollment. More than 99% of scheduled doses were administered in a blinded fashion. Scheduled ultrasounds were performed without exception. No bioaccumulation of dalteparin was observed when creatinine clearance decreased to lower than 30 mL/min. Average recruitment was 2 patients/center per month before the study exclusion criteria were modified. Study startup activities required, on average, 65.5 hours of combined investigator and research coordinator time at each center. Careful examination of the accrual in the pilot study led to a reexamination of the Prophylaxis of Thromboembolism in Critical Care Trial (PROTECT) study exclusion criteria. This pilot study suggests that a multicenter randomized clinical trial comparing LMWH with UFH in critically ill medical-surgical patients is feasible. Pilot studies can improve the design of larger trials and may enhance successful timely completion.
    Journal of Critical Care 01/2006; 20(4):364-72. DOI:10.1016/j.jcrc.2005.09.010 · 2.19 Impact Factor
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    ABSTRACT: Many patients with the antiphospholipid antibody syndrome and recurrent thrombosis receive doses of warfarin adjusted to achieve an international normalized ratio (INR) of more than 3.0. However, there are no prospective data to support this approach to thromboprophylaxis. We performed a randomized, double-blind trial in which patients with antiphospholipid antibodies and previous thrombosis were assigned to receive enough warfarin to achieve an INR of 2.0 to 3.0 (moderate intensity) or 3.1 to 4.0 (high intensity). Our objective was to show that high-intensity warfarin was more effective in preventing thrombosis than moderate-intensity warfarin. A total of 114 patients were enrolled in the study and followed for a mean of 2.7 years. Recurrent thrombosis occurred in 6 of 56 patients (10.7 percent) assigned to receive high-intensity warfarin and in 2 of 58 patients (3.4 percent) assigned to receive moderate-intensity warfarin (hazard ratio for the high-intensity group, 3.1; 95 percent confidence interval, 0.6 to 15.0). Major bleeding occurred in three patients assigned to receive high-intensity warfarin and four patients assigned to receive moderate-intensity warfarin (hazard ratio, 1.0; 95 percent confidence interval, 0.2 to 4.8). High-intensity warfarin was not superior to moderate-intensity warfarin for thromboprophylaxis in patients with antiphospholipid antibodies and previous thrombosis. The low rate of recurrent thrombosis among patients in whom the target INR was 2.0 to 3.0 suggests that moderate-intensity warfarin is appropriate for patients with the antiphospholipid antibody syndrome.
    New England Journal of Medicine 10/2003; 349(12):1133-8. DOI:10.1056/NEJMoa035241 · 54.42 Impact Factor
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    ABSTRACT: Public concerns about the increase in health care expenditure have prompted investigators to analyze the costs and benefits of health care interventions. We conducted a systematic review of economic analyses of venous thromboembolism treatment focusing on studies evaluating low-molecular-weight heparin. We identified studies by a MEDLINE search and a review of bibliographies of retrieved articles. From each eligible study, we extracted data on the study characteristics, the effectiveness, and the cost of managing the venous thromboembolism with respect to treatment. We critically appraised the studies according to the framework from the Users' Guides to the Medical Literature XIII: How to Use an Article on Economic Analysis of Clinical Practice. Six of these eight economic analyses of venous thromboembolism treatment that met the inclusion criteria for this review showed that low-molecular-weight heparin is associated with less recurrent venous thromboembolism and is less costly than treatment with unfractionated heparin. Although discrete recurrent venous thromboembolism event rates were not included in the seventh study, these investigators concluded that the cost of low-molecular-weight heparin for the treatment of venous thromboembolism treatment was offset by the savings associated with fewer hospital admissions when low-molecular-weight heparin was used. In the eighth study, although the cost of treatment with low-molecular-weight heparin was higher than treatment with unfractionated heparin, the investigators concluded that low-molecular-weight heparin is cost-effective for inpatient management. Low-molecular-weight heparin treatment may confer economic advantages over unfractionated heparin therapy because it does not require anticoagulant monitoring and it facilitates outpatient therapy.
    Thrombosis Research 02/2003; 112(4):193-201. DOI:10.1016/j.thromres.2003.12.001 · 2.43 Impact Factor
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    ABSTRACT: We compared three rapid D-dimer methods for the diagnosis of venous thromboembolism. Patients presenting to four teaching hospitals with the possible diagnosis of deep vein thrombosis or pulmonary embolism were investigated with a combination of clinical likelihood, D-dimer (SimpliRED) and initial non-invasive testing. Patients were assigned as being positive or negative for deep vein thrombosis or pulmonary embolism based on their three-month outcome and initial test results. The three D-dimer methods compared were: (a) Accuclot D-dimer (b) IL-Test D-dimer (c) SimpliRED D-dimer. Of 993 patients, 141 had objectively confirmed deep vein thrombosis or pulmonary embolism. The sensitivity of SimpliRED, Accuclot and IL-Test were 79, 90 and 87% respectively. All three D-dimer tests gave similar negative predictive values. The SimpliRED D-dimer was found to be less sensitive than the Accuclot or IL-Test. When combined with pre-test probability all three methods are probably acceptable for use in the diagnosis of venous thromboembolism.
    British Journal of Haematology 11/2001; 115(1):140-4. DOI:10.1046/j.1365-2141.2001.03060.x · 4.96 Impact Factor
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    ABSTRACT: The optimal management of patients who have recurrent thromboembolism while being treated with oral anticoagulation therapy is unknown. This study reports managing such patients with extended duration low molecular weight heparin therapy. This study was a retrospective review of the prospective databases of three tertiary care teaching hospitals over a 27-month period. All patients who had recurrent symptomatic thromboembolism while being treated with warfarin were identified. All patients were treated with low molecular weight heparin (dalteparin), 200 U/kg daily. Data were collected for recurrent venous thromboembolism, bleeding, and survival. Eight hundred eighty-seven patients were managed for acute thromboembolism. In 32 patients, symptomatic, objectively documented thromboembolism recurred while they were taking warfarin; 63% of the patients with recurrence had cancer, compared with 30% of patients without recurrence. All recurrences were treated with dalteparin. In 3 patients (9% [95% confidence interval: 2% to 25%]), symptomatic recurrence developed while they were being treated with low molecular weight heparin. Nineteen patients (59%) died while receiving anticoagulation therapy; all deaths but 1 were due to malignancy, and none was due to pulmonary embolism or bleeding. These results suggest that recurrent venous thromboembolism is more likely to develop in cancer patients while being treated with warfarin and that long-term therapy with low molecular weight heparin may be effective in managing warfarin-failure thromboembolic disease.
    The American Journal of Medicine 10/2001; 111(4):270-3. DOI:10.1016/S0002-9343(01)00840-3 · 5.30 Impact Factor
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    ABSTRACT: Patients with acute proximal deep-vein thrombosis are usually treated first in the hospital with intravenous standard (unfractionated) heparin. However, the longer plasma half-life, better bioavailability after subcutaneous administration, and more predictable anticoagulant response of low-molecular-weight heparins make them attractive for possible home use. We compared these two approaches. Patients with acute proximal deep-vein thrombosis were randomly assigned to receive either intravenous standard heparin in the hospital (253 patients) or low-molecular-weight heparin (1 mg of enoxaparin per kilogram of body weight subcutaneously twice daily) administered primarily at home (247 patients). The study design allowed outpatients taking low-molecular-weight heparin to go home immediately and hospitalized patients taking low-molecular-weight heparin to be discharged early. All the patients received warfarin starting on the second day. Thirteen of the 247 patients receiving low-molecular-weight heparin (5.3 percent) had recurrent thromboembolism, as compared with 17 of the 253 patients receiving standard heparin (6.7 percent; P=0.57; absolute difference, 1.4 percentage points; 95 percent confidence interval, -3.0 to 5.7). Five patients receiving low-molecular-weight heparin had major bleeding, as compared with three patients receiving standard heparin. After randomization, the patients who received low-molecular-weight heparin spent a mean of 1.1 days in the hospital, as compared with 6.5 days for the standard-heparin group; 120 patients in the low-molecular-weight- heparin group did not need to be hospitalized at all. Low-molecular-weight heparin can be used safely and effectively to treat patients with proximal deep-vein thrombosis at home.
    New England Journal of Medicine 04/1996; 334(11):677-81. DOI:10.1056/NEJM199603143341101 · 54.42 Impact Factor