Systematic review: aspirin for prevention of cardiovascular disease
A systematic review published in the Journal of the American Medical Association looks at the evidence for aspirin in the prevention of cardiovascular disease. The authors note that more than 50 million US adults [about 1 in 6 of the total population] take aspirin daily for prevention of cardiovascular disease, however there is still controversy over the most appropriate dose for long-term use. Doses most commonly used in the US are 81mg or 325mg daily; outside the US, 75mg and 300mg daily are also common. In an attempt to clarify the issue, they have reviewed the literature to investigate the mechanism of action of aspirin, and any relationships among aspirin dosage, efficacy, and safety.
The review included data from clinical trials using various doses of aspirin for cardiovascular disease, ranging from 81mg/day to 325 mg/day. Most were for secondary prevention. Pharmacodynamic studies indicate that doses around 30mg daily are sufficient to inhibit platelet thromboxane production. Clinical trials indicate that 75 to 81mg daily is effective, and that higher doses do not increase efficacy but are associated with a higher incidence of adverse effects - mainly gastro-intestinal.
The authors conclude that long-term aspirin therapy at doses greater than 75 to 81 mg/day does not enhance the prevention of cardiovascular events but does increase the risk of gastrointestinal bleeding. They therefore conclude that currently available evidence does not support the routine, long-term use of aspirin dosages greater than 75 to 81mg/day for cardiovascular disease prevention.
JAMA 2007; 297: 2018-24 (link to abstract).