A subgroup analysis eventually may offer answers in a trial that assessed once-daily, low-dose aspirin to prevent atherosclerotic cardiovascular disease in Japan, according to a study published online Nov. 17 in JAMA. The trial was terminated early due to futility.

Researchers found that between two randomized groups, one given low-dose aspirin and one not, outcomes were not significantly different. Yasuo Ikeda, MD, of Waseda University in Tokyo, and colleagues intended to follow 14,464 patients with hypertension, dyslipidemia or diabetes mellitus between the ages of 60 and 85 years for a total of 6.5 years. The follow-up ended a median of nearly a year and a half earlier than intended.

The rate of a composite of death from cardiovascular causes, nonfatal stroke, or nonfatal MI was similar between the two groups: 2.77 percent for patients taking aspirin and 2.96 percent in patients who were not. Over a median follow-up of 5.02 years, 58 patients taking aspirin and 57 patients in the no aspirin group died from cardiovascular disease. Little difference was also seen between patients taking aspirin or not in occurrence of nonfatal stroke: 114 vs. 108, respectively.

Differences were noted between the two groups when reducing nonfatal MI or transit ischemic attack, favoring aspirin in a reduction of more than half. However, aspirin increased patients’ risk for extracranial hemorrhage significantly (hazard ratio, 1.85).

Later review of the research determined a 28 percent probability of finding significant difference in favor of aspirin had the study continued. Ikeda et al determined it was likely the study was underpowered to fully observe a positive effect with aspirin.

The team planned to conduct a subgroup analysis in the future to determine if one group or another derives more benefit from aspirin use.