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Aspirin for the primary prevention of cardiovascular disease in women |
Pignone M, Earnshaw S, Pletcher M J, Tice J A |
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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 The study examined low-dose aspirin (100 mg every other day) for the primary prevention of cardiovascular disease in women. The comparator was no aspirin.
Study population The study population comprised a hypothetical cohort of women at "moderate risk" of cardiovascular disease. Specifically, 65-year-old women with the following risk factor profile: a systolic blood pressure of 120 mmHg, total cholesterol level of 184 mg/dL, and no smoking, diabetes, or atrial fibrillation. Such a patient would have an estimated 10-year total risk of coronary heart disease events of 7.5% and a stroke risk of 2.8%.
Setting The setting was not described, but it can be assumed that the setting for prophylaxis with aspirin was outpatient care. The setting for treatment of complications and cardiovascular events was inpatient care. The economic study was carried out in the USA.
Dates to which data relate The effectiveness data used to populate the model came from studies published between 2005 and 2006. The resource use data came from papers published between 2003 and 2006. The price year was 2005.
Source of effectiveness data The clinical and epidemiological data used in the economic evaluation included the background non-cardiovascular and cardiovascular mortality rates for women, the estimated effect of aspirin on cardiovascular events (haemorrhagic stroke and ischaemic stroke), and the excess risk of gastrointestinal bleeding with aspirin.
Modelling A Markov model with a lifetime horizon was developed. The health state and time-dependent transition probabilities were not reported, but it was stated that the 10-year risks were translated into annual, event-related, transition probabilities based on an assumed exponential distribution. The protection against cardiovascular events afforded by aspirin and the adverse effects of aspirin were built into the model.
Sources searched to identify primary studies The age dependent non-cardiovascular mortality rates for women were estimated from National Vital Statistics life tables. The cardiovascular event rates were taken from published papers. The excess risk of gastrointestinal bleeding with aspirin was estimated from a systematic review; the data on strokes were derived from published systematic reviews and meta-analyses conducted mainly on men. Data on treatment efficacy were derived from a large study of primary prevention with aspirin in women older than 45 years.
Methods used to judge relevance and validity, and for extracting data Although the data were derived from published sources, the authors did not state that a systematic review was performed. No inclusion criteria were reported and the sources searched were not described.
Measure of benefits used in the economic analysis The measure of benefit used was the quality-adjusted life-years (QALYs) gained. The utilities were obtained from published values that had been derived from men or mixed populations. Time trade-off techniques were most commonly employed in the studies that derived these values. The QALYs were discounted at a rate of 3% per year.
Direct costs The authors reported that the costing methods were detailed elsewhere (Pignone et al. 2006, see 'Other Publications of Related Interest' below for bibliographic details). It appears that the health service costs have been included in the analysis. The costs were obtained from published literature and national databases. The annual costs of different treatments were reported. The events that incurred these costs were determined in the model. The costs were discounted at a rate of 3% per year.
Statistical analysis of costs No statistical analyses of the costs were conducted as the objective of the study was to produce a cost-utility measure.
Indirect Costs No productivity losses were considered.
Sensitivity analysis Sensitivity analyses were performed on the starting age and cardiovascular risk factors. Further one-way sensitivity analyses were performed on the main efficacy estimates, adverse events, cost and utility estimates. Such analyses used plausible ranges of values from the literature with their 95% confidence intervals, or varied the estimates by 20% in each direction. A probabilistic sensitivity analysis was also performed. The parameters given probability distributions were the relative risk of various cardiovascular events and complications of drug therapy, mortality after the initial cardiovascular event, and utilities for all health states. The distributions were not reported in the paper.
Estimated benefits used in the economic analysis Aspirin produced 10.963 QALYs in the base-case analysis of moderate-risk women, while no treatment produced 10.957 QALYs.
Cost results The mean cost in the aspirin group was $3,145, while no treatment cost $3,069.
Synthesis of costs and benefits The authors calculated an incremental cost-effectiveness ratio. The cost per additional QALY gained with aspirin was $13,300 in the base-case scenario.
For 55-year-old women with a 10-year stroke risk of 1.4%, the use of aspirin was less effective and more costly than no treatment. For 75-year-old women with a 10-year stroke risk of 5.5%, the use of aspirin was more effective than no treatment with an incremental cost-effectiveness ratio of $2,532. For 65-year-old women with an increased stroke risk of 5.2%, aspirin dominated no treatment (i.e. it was more effective and less costly). If the risk of gastrointestinal bleeding was as high as 1% per year, or if the risk of haemorrhagic stroke was more than 28 per 100,000 per year, aspirin would be less effective than no treatment.
The probabilistic sensitivity analyses suggested that there was a moderately high probability (27%) that aspirin would be less effective than no treatment for these moderate-risk women.
Authors' conclusions Aspirin is likely to be beneficial for women at higher risk of ischaemic stroke. Women at low risk should probably not use aspirin prophylaxis because the risk of harm exceeds potential benefits.
CRD COMMENTARY - Selection of comparators The comparator of "no aspirin" is a natural comparator to the use of aspirin. Validity of estimate of measure of effectiveness The authors used data from published studies and systematic reviews. Some of the data related to data from studies on males. The methods used in the review of the literature were not reported. Validity of estimate of measure of benefit The estimation of health benefits (QALYs) was modelled using a Markov model. The utilities were taken from published literature and no details of the valuation method were reported.
Validity of estimate of costs The analysis of the costs was performed from the perspective of the third-party payer. Given that perspective, it appears that all the relevant categories of costs and relevant costs have been included in the analysis. The costs were obtained from published sources and national databases. It was not stated if charges were used to proxy costs. Annual costs were reported for various treatments, which was appropriate for the model. The cost methods were adequately reported. The costs were discounted appropriately.
Other issues The authors compared their findings with those from other studies and found the results, in general, to be in agreement. The impact of varying the effectiveness data and risks of complication was evaluated through sensitivity analysis. The authors did not present their results selectively and their conclusions reflected the scope of the analysis. The authors reported a number of limitations to their study, especially those arising from the absence of gender-specific complication rates for aspirin.
Implications of the study The authors suggest that further studies to investigate the disutility of taking pills daily or on alternate days are required. They suggest that there are limited data on the adverse effects of aspirin in women.
Source of funding Supported by a grant from Bayer Inc.
Bibliographic details Pignone M, Earnshaw S, Pletcher M J, Tice J A. Aspirin for the primary prevention of cardiovascular disease in women. Archives of Internal Medicine 2007; 167(3): 290-295 Other publications of related interest Because readers are likely to encounter and assess individual publications, NHS EED abstracts reflect the original publication as it is written, as a stand-alone paper. Where NHS EED abstractors are able to identify positively that a publication is significantly linked to or informed by other publications, these will be referenced in the text of the abstract and their bibliographic details recorded here for information.
Pignone M, Earnshaw T, Tice JA, Pletcher MJ. Aspirin, statins, or both drugs for the primary prevention of coronary heart disease events in men: cost-utility analysis. Ann Intern Med 2006;144:326-36.
Indexing Status Subject indexing assigned by NLM MeSH Aged; Aspirin /economics /therapeutic use; Cardiovascular Diseases /economics /etiology /prevention & Cost-Benefit Analysis; Drug Costs; Female; Fibrinolytic Agents /economics /therapeutic use; Humans; Markov Chains; Middle Aged; Quality-Adjusted Life Years; Risk Assessment; control AccessionNumber 22007008040 Date bibliographic record published 31/07/2007 Date abstract record published 31/07/2007 |
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