Aspirin administered to women at 100 mg every other day produces less platelet inhibition than aspirin administered at 81 mg per day: implications for interpreting the women’s health study

Influence of Sex on Platelet Reactivity in Response to Aspirin

Background There are sex differences in the efficacy and safety of aspirin for the prevention of myocardial infarction and stroke. Whether this is explained by underlying differences in platelet reactivity and aspirin response remains poorly understood. Methods and Results Healthy volunteers (n=378 208 women) and patients with coronary artery disease or coronary artery disease risk factors (n=217 112 women) took aspirin for 4 weeks. Light transmittance aggregometry using platelet-rich plasma was used to measure platelet reactivity in response to epinephrine, collagen, and ADP at baseline, 3 hours after the first aspirin dose, and after 4 weeks of daily aspirin therapy. A subset of patients underwent pharmacokinetic and pharmacodynamic assessment with levels of salicylate and cyclooxygenase-1-derived prostaglandin metabolites and light transmittance aggregometry in response to arachidonic acid and after ex vivo exposure to aspirin. At baseline, women had increased platelet aggregation in response to ADP and collagen. Innate platelet response to aspirin, assessed with ex vivo aspirin exposure of baseline platelets, did not differ by sex. Three hours after the first oral aspirin dose, platelet aggregation was inhibited in women to a greater degree in response to epinephrine and to a lesser degree with collagen. After 4 weeks of daily therapy, despite higher salicylate concentrations and greater cyclooxygenase-1 inhibition, women exhibited an attenuation of platelet inhibition in response to epinephrine and ADP. Conclusions We observed agonist-dependent sex differences in platelet responses to aspirin. Despite higher cyclooxygenase-1 inhibition, daily aspirin exposure resulted in a paradoxical attenuation of platelet inhibition in response to epinephrine and ADP over time in women but not in men.

Why we should not skip aspirin in cardiovascular prevention

Since more than 20 years, aspirin is an approved and established first-line antiplatelet medication in cardiovascular prevention. This is partially due to ist unique mode of action which is not shared with any other antiplatelet agent as well by the reliability of its pharmacological efficacy: inhibition of platelet COX-1 and subsequent thromboxane formation in almost every patient. Aspirin acts synergistic with ADP-antagonists in dual antiplatelet therapy of acute coronary syndroms (ACS) and percutaneous coronary interventions (PCI) and is also approved for long-term secondary prevention. Patients with atrial fibrillation are an exception and benefit more from anticoagulants. After the introduction of the new oral anticoagulants (NOACs), i.e. direct inhibitors of factor Xa or thrombin formation, there is a renewed discussion about the role of antiplatelet agents, specifically if additional dual antiplatelet treatment is still necessary for an optimum clinical effect or whether one component, such as aspirin might be skipped in favor of other classes of oral antiplatelet agents, such as ADP-antagonists. The available data are insufficient to recommend this because of a low number of studies and a still uncertain benefit/ risk (bleeding) ratio. More research on aspirin as a chemopreventive appears also to be necessary and is going on, in particular in individuals at high-risk for vascular thrombotic diseases (diabetics, preeclampsia, venous thrombembolism).

Mechanisms of nonsteroidal anti-inflammatory drugs in cancer prevention

Various clinical and epidemiologic studies show that nonsteroidal anti-inflammatory drugs (NSAIDs), including aspirin and cyclooxygenase inhibitors (COXIBs) help prevent cancer. Since eicosanoid metabolism is the main inhibitory targets of these drugs the resulting molecular and biological impact is generally accepted. As our knowledge base and technology progress we are learning that additional targets may be involved. This review attempts to summarize these new developments in the field.

The aspirin controversy in primary prevention

PURPOSE OF REVIEW

Apparently conflicting meta-analysis results have led to renewed debate about the role of aspirin for the primary prevention of cardiovascular disease. We review the results of meta-analyses comparing aspirin with placebo or no aspirin for the primary prevention of cardiovascular disease and critically evaluate whether aspirin provides a net benefit.

RECENT FINDINGS

The results of four independently conducted meta-analyses between 2009 and 2012 involving between 95 000 and 102 621 individuals at low risk of cardiovascular disease are consistent with the results of the 2002 Antithrombotic Trialists' Collaboration meta-analysis, which found that aspirin reduces cardiovascular events primarily by reducing nonfatal myocardial infarction (MI). There is no convincing evidence that aspirin reduces cardiovascular mortality, but estimates from all of the meta-analyses suggest a modest reduction in all-cause mortality. Aspirin reduces ischaemic stroke but increases haemorrhagic stroke and major bleeding.

SUMMARY

The meta-analysis results consistently indicate that, in individuals at low risk for cardiovascular disease, aspirin reduces the risk of MI at the cost of an increase in major bleeding and produces a modest nominally significant reduction in total mortality. These results suggest that recommendations for primary prevention with aspirin should be individualized, taking into account the balance between benefits and risks and individual values and preferences.

Aspirin resistance: current status and role of tailored therapy

Aspirin is integral in the primary and secondary prevention of coronary artery disease and acute coronary syndrome. Given the high clinical importance of aspirin in the management of coronary artery disease, much attention has been directed towards the concept of "aspirin resistance." Unfortunately, the term aspirin resistance is ill-defined in the literature, leading to a large variance in the reported prevalence of this phenomenon. In this review, the current understanding of aspirin resistance is discussed. Commonly used functional and diagnostic tests of platelet function, including their strengths and weakness, are reviewed. We next discuss several proposed mechanisms of aspirin resistance and special high-risk groups at risk for aspirin treatment failure. We then discuss optimal dosing and diagnostic strategies for those populations at risk for aspirin resistance with a focus on tailored aspirin therapy for high-risk groups. Finally, future topics of interest in the field of aspirin resistance are considered.

Variability in the response to antiplatelet treatment in diabetes mellitus

Atherothrombosis is a leading cause of death in patients with diabetes mellitus. Among factors contributing to the diabetic prothrombotic state, platelet activation plays a pivotal role. Numerous studies have investigated the benefits of antiplatelet therapy for primary and secondary cardiovascular prevention in diabetic patients. However, there are limited evidences that low-dose aspirin may be effective in this clinical setting. Several disease-specific factors have been identified as potential determinants of aspirin treatment failure. In this review, the main determinants of interindividual variability in response to antiplatelet agents are discussed, with particular emphasis on the pharmacokinetic and pharmacodynamic mechanisms of clinical efficacy and safety of antiplatelet drugs in patients with diabetes mellitus.

Gender Differences in the Primary Prevention of Stroke with Aspirin

Aspirin is used to prevent ischemic stroke and other types of cardiovascular disease. Seven trials of aspirin focusing on the effectiveness of primary prevention of stroke and other cardiovascular events have been performed, but three of these did not include women. Data from these trials, and one meta-analysis, suggest that aspirin prevents myocardial infarction in men and stroke in women, although the findings in women were driven by the results of a single large study, and a subsequent meta-analysis did not find a gender difference. The reasons for the possible gender differences in aspirin's effectiveness are not entirely clear.