Methods: We developed a Markov model using data from published literature, including the newly completed Women's Health Study, to simulate the effect of aspirin for women with no previous history of cardiovascular disease. In the base case, we examined 65 year-old women over a time horizon of 20 years, using a third party payer perspective. The main outcome was cost per quality-adjusted life-year-gained. Discount rate was 3%. The health states of interest included healthy, GI bleeding, hemorrhagic stroke, ischemic stroke, angina, myocardial infarction, and death. Based on meta-analysis of relevant trials, aspirin was assumed in the base case to reduce risk of ischemic stroke (RR = 0.81) but have little effect on angina (RR = 1.0), myocardial infarction (RR = 0.99), or risk of sudden death (RR = 1.0). We performed extensive one-way and probabilistic sensitivity analyses to examine the effect of uncertainty.

Results: For women at 7.5% 10-year risk of CHD events and 2.8% risk of stroke, aspirin had mean costs of $2,778 compared with $2,673 for no therapy; mean net quality-adjusted life-years (QALY) were 10.40 for aspirin and 10.38 for no treatment. The incremental cost per additional QALY gained was $18,100. Aspirin remained relatively cost-effective (cost-utility ratio less than $50,000 per QALY) when the relative risk of ischemic stroke was less than 0.91, the relative risk of myocardial infarction is less than 1.08, relative risk of angina is less than 1.06, the annual risk of death from GI bleeding is less than 6 per 100,000, and the annual risk of hemorrhagic stroke with aspirin is less than 3.3 per 10,000. Reasonable variation is cost and utility inputs had little effect on results. However, changes in age and risk of ischemic stroke have important effects on efficacy: for 55 year old women with a 1.4% 10 year risk of stroke, the incremental cost per QALY-gained was $269,000.

Conclusions: For primary prevention of CHD events, aspirin, compared with no treatment, is cost-effective for older women at moderate or greater risk of cardiovascular events.