Effectiveness of aspirin in primary prevention appears to vary by patient weight

Reference

Rothwell PM, Cook NR, Gaziano JM, et al. Effects of aspirin on risks of vascular events and cancer according to bodyweight and dose: analysis of individual patient data from randomised trials. Lancet 2018;392(10145):387-399.

Synopsis

These authors searched previous systematic reviews and obtained data from a collaboration of researchers who conducted clinical trials of antithrombotic agents. The chosen trials had to include more than 1000 patients, last longer than 90 days, and have authors who were willing to share individual patient data. Although this is not your typical systematic review search strategy it likely identified most of the important studies. The primary purpose of this paper was to address the potential association between aspirin dose and body weight. The authors included 10 trials for primary prevention of cardiovascular events (more than 117,000 patients) and 5 for cancer prevention (more than 73,000 patients). They didn't assess the risk of bias for the included studies, didn't formally assess the potential for publication bias, and didn't adjust for conducting multiple analyses. After slicing and dicing the data, they determined that for preventing cardiovascular outcomes and cancer, the effectiveness of aspirin varied by dose and patient sex and weight. The effectiveness of low-dose aspirin (< 100 mg daily) to prevent cancer or a first cardiac event was diminished in patients who weigh more than 70 kg, and was even less effective in men than women. For patients who weigh less than 70kg the hazard ratio was 0.77 (95% CI 0.68 - 0.87) and for those who weigh 70 kg or more the hazard ratio was 0.95 (0.86 - 1.04). Additionally, among patients who weigh less than 50 kg, low-dose aspirin was associated with an increased risk of death from any cause.