Marinko Bilušić, MD, specialist in clinical Pharmacology and Toxicology
Recently there has been extensive writing about how "the myth of aspirin has been destroyed" and that its beneficial effects in the prevention of cardiovascular events in patients with present risk factors that favour the emergence of these events, which include high blood pressure, diabetes and high fat in the blood, are questionable.
Although referring to the results of large and serious clinical research, interpretation of these results in the media creates somehow a doubt that aspirin as a matter of fact is not effective in this indication.
A more detailed analysis of the results of these recent research gives us a somewhat different picture and the effectiveness of aspirin in preventing cardiovascular events is not called into question in any segment, but the question is posed regarding the positive benefit of daily taking a low-dose aspirin in the primary prevention of cardiovascular events in patients with risk factors present. It is important to emphasize that these conclusions apply only to the use of aspirin in primary prevention, while in the secondary prevention a high ratio of benefits and risks in application of a low-dose aspirin has repeatedly been proven and confirmed on the results collected from a number of clinical trials conducted in patients with advanced cardiovascular disease. Since primary prevention means that the drug is taken by all who have persistent risk factors, regardless of whether they have marked signs of cardiovascular disease or not, it is logical that the benefits of aspirin will be experienced by only those with rapidly progressive form of cardiovascular diseases where the probability of occurrence of myocardial infarction and / or stroke is significantly increased, while, on the other hand, the risk of side effects will be present in all patients taking aspirin. When aspirin would not have any serious side effects, the benefit-risk ratio would probably still be significantly positive.
However, continuously taking aspirin increases the risk of bleeding, especially in the digestive tract, the question is what proportion of patients should benefit from taking low-dose aspirin to outweigh the proportion of patients who, due to aspirin develop a serious bleeding. Figuratively, if taking aspirin therapy would prevent one death from myocardial infarction, but on the other hand cause one death due to severe bleeding, it is logical to ask whether such treatment makes sense, since the ratio of benefits and risks of the drug is not positive.
It is this dilemma that represents a key part of a large Japanese study named Japanese Primary Prevention Project (JPPP) conducted on nearly 15,000 patients (JAMA. Published online November 17, 2014), referred to by the most recent comments. The epidemiological experts on the basis of available data estimate that the proportion of patients with risk factors who will develop a more severe form of cardiovascular disease in a given population should be at least 10% for the benefit-risk with low-dose aspirin in the primary prevention of cardiovascular events in these patients to be positive (Am J Cardiol. 2014; 64: 319-327).
However, the results of the Japanese study (JPPP) show that this frequency in the Japanese population is less than this estimate, i.e. although their patients who have developed risk factors, however, do not have such a great risk of subsequent cardiovascular disease. From these results, it follows a logical question, whether this new ratio of benefits and risks obtained in this study can further justify the application of low-dose aspirin in the primary prevention of cardiovascular events.
For the final global conclusions and guidance on the role of low-dose aspirin in the primary prevention of cardiovascular events in patients with risk factors, the results of other studies that are still pending (ARRIVE, ASCEND, ASPREA, ACCEPT-D), which assess the relationship between benefits and risk with low-dose aspirin in the primary prevention of cardiovascular events in patients with risk factors present in other populations should be awaited, since we know that a number of factors, especially those genetical, cultural, including eating habits, and economical can significantly affect the level of risk of developing severe cardiovascular disease in a given population.
However, regardless of guidelines, these or those, we must not forget that they provide only a framework, and that each patient requires an individual approach and that a final decision on the application of aspirin in primary prevention, as well as all other drugs, should be made by a doctor on the basis of medical documentation and examination of each patient individually.