Abstract 3285: A Crossover Trial Assessing the Degree of Platelet Inhibition Among Women Taking Two Different Low-Dose Aspirin Regimens
The recent Women’s Health Study of low-dose aspirin failed to show a significant reduction in major cardiovascular events among women taking aspirin. The dose used, however, 100 mg every other day, is lower than the typical low-dose aspirin used for cardiovascular risk reduction in the United States, 81 mg daily. We hypothesized that aspirin 100 mg every other day does not attain as high a degree of platelet inhibition as aspirin 81 mg daily.
Methods: We enrolled 49 healthy female volunteers and used a crossover design to compare the two regimens. Participants received a 17-day course of each aspirin regimen separated by a 7-day washout period. The degree of platelet inhibition was measured on days 14 – 17 of each dosing regimen using the point-of-care platelet function assay VerifyNow-Aspirin.
Results: Participants attained a significantly greater level of platelet inhibition on days 14 – 17 while taking aspirin 81 mg daily compared to aspirin 100 mg every other day (31.3% vs. 12.7%, p < 0.0001) with mean achieved ARU values of 445 ± 50 vs 570 ± 68, p <0.0001 (see figure⇓). Significantly more daily readings in participants were ≥ 550 ARU (previously correlated to a low response to aspirin, or “aspirin resistance”) with the 100 mg every other day regimen (72.0% versus 6.4% with 81 mg daily, p<0.0001), and this alternate-day regimen also resulted in more day-to-day variability in platelet function (p=0.0036).
Conclusions: We observed that the degree of platelet inhibition was significantly lower with aspirin 100 mg every other day compared with aspirin 81 mg daily, suggesting that 81 mg daily may be a preferred low dose regimen, and doses below this may not be optimal.