Background and purpose: Aspirin for primary prevention reduces the risk of vascular events; however it remains unclear for which subgroups of individuals low dose aspirin is beneficial. The authors' objective was to estimate the potential benefits, risks, and cost-effectiveness of aspirin prophylaxis compared with no prophylaxis separately for men and women of different ages with varying levels of vascular risk.

Methods: Decision and cost-effectiveness analyses were performed with a Markov model. The study population consisted of hypothetical cohorts of 10,000 initially healthy men or women aged 45, 55 or 65 years with either a low, moderate or high risk of developing vascular disease. Event rates of myocardial infarction, ischemic stroke, hemorrhagic stroke, and gastrointestinal bleeding were taken from observational studies and relative risk reductions were taken from a sex-specific meta-analysis. Outcomes included number of vascular events prevented and incremental cost-effectiveness in euros per quality-adjusted life year saved. Costs were estimated from a societal perspective. Sensitivity analyses and Monte Carlo simulation evaluated the robustness of the results.

Results: In men aspirin prophylaxis yielded the greatest health effects in terms of a reduction of myocardial infarctions (127 events/100,000 person-years), whereas in women a small reduction of ischemic strokes was predicted (17 events/100,000 person-years). In men aspirin implies a net investment and QALY gain, i.e., the incremental cost-effectiveness ratio in 55-year old men with a low vascular risk was approximately € 111,000/QALY (€1=$1.27; April 2007). When prescribed to 55-year old men with a moderate vascular risk the incremental cost-effectiveness ratio approached € 20,000/QALY. Conversely, for women aspirin treatment implies additional costs as well a QALY loss. Results were sensitive to drug treatment costs, effectiveness of aspirin treatment, and utility of taking aspirin.

Conclusions: Aspirin for the primary prevention of vascular disease in women is detrimental. Aspirin is (cost-) effective in men aged 55 or older with a moderate to high vascular risk.