A pooled analysis of individual patient data suggested that low doses of aspirin (75–100 mg) were only effective in preventing vascular events in patients weighing less than 70 kg, and higher doses of aspirin were only effective in patients weighing 70 kg or more. The analysis included 117 279 participants in 10 eligible trials of aspirin in primary prevention. Bodyweight varied four-fold and trial median weight ranged from 60·0 kg to 81·2 kg in the trials. The ability of 75–100 mg aspirin to reduce cardiovascular events decreased with increasing weight, with benefit seen in people weighing 50–69 kg (hazard ratio [HR] 0·75) but not in those weighing 70 kg or more. Furthermore, the case fatality of a first cardiovascular event was increased by low-dose aspirin in people weighing 70 kg or more (odds ratio 1·33). Higher doses of aspirin (≥325 mg) had the opposite interaction with bodyweight, reducing cardiovascular events only at higher weight. Findings were similar in men and women, in people with diabetes, in trials of aspirin in secondary prevention, and in relation to height. Aspirin-mediated reductions in long-term risk of colorectal cancer were also weight dependent. Stratification by body size also revealed harms due to excess dosing: risk of sudden death was increased by aspirin in people at low weight for dose and risk of all-cause death was increased in people weighing less than 50 kg who were receiving 75–100 mg aspirin (HR 1·52). In participants aged 70 years or older, the 3-year risk of cancer was also increased by aspirin (1·20), particularly in those weighing less than 70 kg (1·31) and consequently in women (1·44). The study suggests that more tailored weight-based dosing strategy is required for aspirin. Source: https://www.thelancet.com/
