A study published in The Lancet reports that low doses of aspirin (75–100mg) were effective in preventing vascular events only in patients weighing less than 70kg whereas higher doses of 325mg or more were effective only in patients who weighed ≥70kg.
The results suggest that aspirin dosing should be tailored to body weight for optimal cardiovascular prevention, say the authors.
The team, led by Professor Peter Rothwell from the Centre for Prevention of Stroke and Dementia at the University of Oxford, used individual patient data from 10 randomised controlled trials involving 117,279 patients to examine the effects of bodyweight and height on low (≤100mg) and higher doses (300–325mg or ≥500mg) of aspirin in primary cardiovascular prevention.
They found that low-dose aspirin reduced the risk of cardiovascular events in patients weighing 50–69kg (hazard ratio [HR] 0.75; p<0.0001) but not in those who weighed 70kg or more (HR 0.95; p=0.24). In patients weighing 70kg or more, low-dose aspirin was actually associated with an increased case fatality of first cardiovascular events (odds ratio [OR] 1.33; p=0.0082). The loss of effect of aspirin in patients weighing 70kg or more was particularly evident in those who smoked or were treated with enteric-coated or delayed-release formulations.
Higher doses of aspirin were associated with reduced cardiovascular events in patients weighing 70kg or more (HR 0.79; p=0.0005).
Notably, patients weighing 70kg or more accounted for 80% of men and nearly 50% of women in the study.
The authors argue that a 'one-dose-fits-all' strategy for daily aspirin use is 'unlikely to be optimal', and suggest that weight-adjusted dosing might substantially improve the effectiveness of aspirin. They also note that sex differences in bodyweight might explain aspirin's long recognised lack of efficacy in preventing stroke in men.
In a linked commentary, Katherine Theken and Tilo Grosser hail the findings as 'provocative results with the potential to substantially affect public health' and call for more research to establish whether weight-adjusted aspirin dosing should be incorporated into clinical care.