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Cost-effectiveness of enoxaparin versus low-dose heparin for prophylaxis against venous thrombosis after major trauma |
Devlin J W, Petitta A, Shepard A D, Obeid F N |
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Record Status This is a critical abstract of an economic evaluation that meets the criteria for inclusion on NHS EED. Each abstract contains a brief summary of the methods, the results and conclusions followed by a detailed critical assessment on the reliability of the study and the conclusions drawn. Health technology Use of enoxaparin 30 mg/twice daily for prophylaxis against venous thrombosis after major trauma.
Economic study type Cost-effectiveness analysis.
Study population Patients admitted to hospital with major trauma, with an Injury Severity score of more than 9, and no evidence of intracranial bleeding.
Setting A simulated cohort was used, the setting being a hospital. The economic study was conducted in the United States.
Dates to which data relate Effectiveness data were extracted from a retrospective study performed in the authors' setting between Jan 1995 and June 1996, and from studies published between 1980 and 1995. Cost data related to 1996. 1996 prices were used.
Source of effectiveness data Effectiveness data were derived from institutional data, a synthesis of previously completed studies and expert advice.
Modelling A decision-analytic model was developed from best literature practice, institutional data and expert advice, outlining prophylaxis, diagnosis and treatment of DVT and pulmonary embolism (PE) in patents admitted with trauma.
Outcomes assessed in the review The main health outcomes derived from literature review for use in the model were:
overall DVT frequency for heparin and enoxaparin,
percentage of proximal DVT frequency for heparin and enoxaparin,
percentage of proximal DVT clinically diagnosed,
percentage of distal DVT clinically diagnosed,
percentage of undiagnosed proximal DVT leading to readmission for DVT,
percentage of undiagnosed proximal DVT leading to PE,
percentage of patients with no DVT falsely diagnosed with DVT,
percentage of patients with no DVT falsely diagnosed with PE,
mortality for diagnosed PE, mortality for undiagnosed PE and life expectancy.
Study designs and other criteria for inclusion in the review Randomised controlled trials were used for extracting the bulk of the effectiveness data.
Sources searched to identify primary studies Studies were identified by searching MEDLINE for the years 1980-1995 using the following key words: deep vein thrombosis, pulmonary embolus, prophylaxis, trauma, heparin, low-molecular-weight heparin, randomised controlled trial and cost-effectiveness analysis. Also, life expectancy was based on a 1995 published study on the African-American male population in urban Detroit.
Criteria used to ensure the validity of primary studies Randomised controlled trials were the source of the effectiveness data.
Methods used to judge relevance and validity, and for extracting data Number of primary studies included Twelve studies were referenced.
Methods of combining primary studies Investigation of differences between primary studies Results of the review The best, low and high values used in the model derived from literature review were:
overall DVT frequency for heparin and enoxaparin, 0.44/0.40/0.48 versus 0.31/0.27/0.41;
percentage of proximal DVT frequency for heparin and enoxaparin, 0.33/0.28/0.40 versus 0.20/0.07/0.26;
percentage of proximal DVT clinically diagnosed, 0.40/0.32/0.48;
percentage of distal DVT clinically diagnosed, 0.05/0.04/0.07;
percentage of undiagnosed proximal DVT leading to readmission for DVT, 0.02/0.01/0.04;
percentage of undiagnosed proximal DVT leading to PE, 0.5/0.4/0.6;
percentage of patients with no DVT falsely diagnosed with DVT, 0.1/0.08/0.13;
percentage of patients with no DVT falsely diagnosed with PE, 0.02/0.01/0.03;
mortality for diagnosed PE, 0.08/0.03/0.1;
mortality for undiagnosed PE, 0.3/0.15/0.4; and
life expectancy, 30/20/40 years.
Methods used to derive estimates of effectiveness Expert advice was used for some of the estimates of effectiveness.
Estimates of effectiveness and key assumptions Estimates of effectiveness based on expert opinion (as well as literature and institutional data) used in the model overlapped with those from the review. The authors did not describe how they were combined.
Measure of benefits used in the economic analysis Life-years saved, and DVTs and PEs avoided were used as the measures of benefit.
Direct costs Direct health service costs were used, namely the cost of drug prophylaxis, hospital stay, duplex scan, venogram, chest radiograph, VQ scan, electrocardiogram, pulmonary angiogram, anticoagulation therapy for DVT and PE respectively and cost of DVT and PE readmissions. Length of stay data and 1996 institutional drug use and acquisition costs at the Henry Ford Hospital were used to estimate the cost of enoxaparin and heparin therapy, whilst diagnosis and treatment costs for DVT and PE were derived from institutional charge data using cost:charge ratios. Quantities (dosages and length of stay) and costs were detailed separately. Costs were not discounted since they were assumed to occur within a year. 1996 prices were used.
Statistical analysis of costs No statistical analysis was performed.
Indirect Costs Indirect costs were not considered.
Sensitivity analysis The overall uncertainty of the model was estimated by Monte Carlo multiway sensitivity analysis with spreadsheet forecasting software (Crystal Ball). The Monte Carlo simulation allowed each assumption to vary randomly across its range of values while performing 10,000 iterations. One-way sensitivity analysis was conducted for variables that provided the greatest contribution to overall model variability. These were hospitalisation costs for increased length of stay associated with embolic events during the index admission and the percentage of DVTs that are proximal for patients receiving heparin prophylaxis. 95% certainty ranges were used for the multiway sensitivity analysis.
Estimated benefits used in the economic analysis Projected life-years saved were 67.6 (95% CI: 8 - 130) and discounted at 3% were 46.6 (95% CI: 6 - 84). Total DVTs and PEs avoided were 62.2 (95% CI: -113 to -12) as a result of enoxaparin use.
Cost results The total cost for enoxaparin was $357,418 versus $252,654 for heparin: a net cost increase of $104,764.
Synthesis of costs and benefits For 1000 patients with mixed trauma, enoxaparin versus heparin resulted in a cost of $1,684 for each DVT or PE avoided and a cost/discounted life-year saved of $2,303. For 1000 patients with lower extremity fractures, enoxaparin versus heparin resulted in a cost of $751 for each DVT and PE avoided and a cost/discounted life-year saved of $1,017.
Authors' conclusions Although enoxaparin increases overall health care costs, it is associated with a cost per additional life-year saved of only $2,300, which is lower than the commonly used hurdle rate of $30,000 per life-year saved. The cost-effectiveness ratio is more favourable for patients with lower extremity fractures than for the general mixed trauma patients.
CRD COMMENTARY - Selection of comparators The reason for the choice of the comparator, heparin, is clear, as both enoxaparin and heparin are widely used for prophylaxis against venous thrombosis after major trauma. You, as a database user, should consider if the same applies to your own setting.
Validity of estimate of measure of effectiveness For the estimates of effectiveness derived from the study performed in the authors' institution, the analysis was based on a single centre, retrospective case series, with a study sample representative of the study population. However no groups were defined for heparin and enoxaparin prophylaxis and there was no real statistical analysis to take account of the potential biases and confounding factors. For the estimates based on literature review, the authors conducted a search for relevant literature (MEDLINE search based on relevant key words) although the methods and conduct of the review were not completely reported. The authors did not adopt a weighting scheme in order to reflect differences in sample sizes and did not consider the impact that difference between the primary studies might have on estimates of effectiveness. The estimates of effectiveness derived from expert opinion were based on experts from the Henry Ford Hospital, but the authors did not report on the way in which the expert panel was selected or how estimates were derived from multiple sources. However, all estimates were investigated by one-way and multiway sensitivity analyses, with 95% certainty ranges.
Validity of estimate of measure of benefit Life-years saved, DVTs and PEs avoided were, appropriately, used as measures of benefits. The estimation of benefits was modelled. The instrument used to derive the measure of benefits, a decision-analytic model, was appropriate.
Validity of estimate of costs All categories of costs relevant to the perspective adopted (the health care system) were included in the analysis and quantities and costs were presented separately, thus allowing generalisability to be tested. Costs were not discounted due to the short duration of the study (1 year).
Other issues The authors made appropriate comparisons with the results of other relevant studies and the generalisability of results was addressed by the data used in the final model and the sensitivity analysis.
Implications of the study The authors stated that the cost-effectiveness ratio was more favourable for patients with lower extremity fractures than for the general mixed trauma patients when enoxaparin is used versus heparin. Generally, the method of analysis was appropriate to support this, although more could have been stated on the combination of data to produce the parameter estimates.
Bibliographic details Devlin J W, Petitta A, Shepard A D, Obeid F N. Cost-effectiveness of enoxaparin versus low-dose heparin for prophylaxis against venous thrombosis after major trauma. Pharmacotherapy 1998; 18(6): 1335-1342 Indexing Status Subject indexing assigned by NLM MeSH Anticoagulants /therapeutic use; Cost-Benefit Analysis; Enoxaparin /economics /therapeutic use; Health Care Costs /statistics & Heparin /administration & Humans; Venous Thrombosis /economics /prevention & Wounds and Injuries /drug therapy; control; dosage /therapeutic use; numerical data AccessionNumber 21998001795 Date bibliographic record published 31/01/2002 Date abstract record published 31/01/2002 |
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