Overcoming aspirin treatment failure in diabetes

People with diabetes have an increased risk of life-threatening cardiovascular disease compared to the general population. Furthermore, people with diabetes are at greatly increased risk of not responding to standard anti-platelet therapy, such as aspirin, for the prevention of atherothrombotic events. This phenomenon is often referred to as treatment failure. Those who are at increased risk of such events despite aspirin therapy can be prospectively identified by a variety of laboratory measures of residual on-treatment platelet function, known as aspirin resistance. However, there is little agreement among laboratories on the approaches to these measurements, and insufficient data to guide the clinical management of people with diabetes-associated aspirin resistance if it is prospectively identified. This review provides a critical appraisal of the different approaches to the detection and evidence of mechanisms which contribute to this phenomenon, as well evidence for the potential effectiveness of different clinical approaches to overcoming aspirin treatment failure in diabetes. Potential mechanisms of aspirin resistance in diabetes include elevated platelet turnover that results in an immature platelet fraction able to synthesise the uninhibited therapeutic target of aspirin, cyclooxygenase-1 (COX-1); residual thromboxane production by both COX-1-dependent and COX-1-independent pathways; up-regulation of aspirin-insensitive pathways of platelet function, such as adenosine diphosphate signalling; and increased underlying atherosclerotic disease burden that results in elevated underlying platelet hyper-reactivity. High on-aspirin platelet reactivity in diabetes may be related to glycemic control. Potential approaches to treatment include controlling modifiable risk factors to achieve effective glycemic control, guided increases in aspirin dose or frequency of administration, or the use of additional antiplatelet therapies. While evidence suggests that altering antiplatelet therapy, particularly by increasing frequency of aspirin administration, can overcome incomplete inhibition of thromboxane synthesis, no clinical studies to date have assessed the effectiveness of these in preventing breakthrough atherothrombosis. While some clinicians currently alter therapy on the basis of theoretical potential benefit of these strategies following identification of aspirin resistance in the laboratory, this is not yet supported by clinical evidence of a benefit, and clear clinical guidelines for the management of aspirin resistance are lacking.