Aspirin, chemically acetylsalicylic acid or ASA, is called a wonder drug and has been in use since antiquity. Aspirin is a pain reliever, fever reducer, is used as a blood clot preventer, and is recommended for primary and secondary prevention of cardiovascular disease (CVD). One of its drawbacks, however, is that it can cause bleeding in the gastrointestinal system (GI bleeding). A common misconception is that aspirin causes stomach or intestinal bleeding by directly irritating or eroding the lining of the stomach or intestines. Actually aspirin inhibits the production of prostaglandins. Prostaglandins enhance the inner lining of the stomach and intestines and protect those organs from damage from stomach acids and digestive enzymes. The reduction of prostaglandin production makes the stomach and intestinal lining more susceptible to erosion and bleeding from these acids and enzymes.
Aspirin is used in prevention of CVD due to its anti-blood clotting or blood-thinning effects. Aspirin poisons platelets making them unable to stick to each other and form a clot. One of the problems in this use is aspirin’s short half-life, or the amount of time it takes the blood level to reach 50 percent of the maximum level. The bone marrow constantly makes platelets but the half-life of aspirin is only about 20 minutes. While aspirin is rapidly absorbed – peak blood levels occur about 40 minutes after ingestion of uncoated aspirin and five hours after ingestion of enteric-coated aspirin – it is also rapidly removed from the bloodstream so the anti-platelet activity may only last one hour after ingestion while the marrow continues to make platelets for the remaining 23 hours. It is for this reason that some experts are now recommending dosing aspirin two or three times daily at lower doses. There is also a new medication available called Durlaza which is a slow-release aspirin product that releases aspirin slowly, over many hours, making its anti-platelet function much better.
Aspirin does not work for everyone though. Some people with inflammatory states such as diabetes, smoking, metabolic syndrome, and post-coronary artery bypass grafting have large, more active platelets that are less susceptible to aspirin. Platelet size is measured by an automated complete blood count, or CBC. The MPV (mean platelet volume) is a measurement of platelet size. Normal values are usually 7.5 to 11.5. Someone with an MPV over 12 will have larger, more active platelets that are more likely to form a clot and less likely to be susceptible to aspirin.
While low-dose aspirin has been proven to reduce the risk of repeat cardiovascular events and death in those who have CVD, its use in primary prevention of CVD in those at risk to develop it is still being studied. In addition the use of enteric-coated aspirin is being questioned for two reasons. Firstly, coated aspirin still has the risk of bleeding because it also reduces prostaglandin production plus coated aspirin has less aspirin available for absorption because the coating reduces the amount of available aspirin. More aspirin products are in production as modern medicine continues to tweak an ancient drug.
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