The Development of an In Vitro Assay for the Prospective Determination of Aspirin Sensitivity.

Aspirin remains the standard for stroke prophylaxis. However, as many as 20%-25% of patients may fail to show a full response to aspirin. Ideally, patients who are resistant to aspirin could be identified, then receive an increased dose of aspirin or be changed to an alternative therapy more efficiently. We have developed an in vitro assay that may make this possible. Healthy volunteers (n = 13) between 18 and 50 years of age were tested for both ex vivo and in vivo responses to aspirin. Dimethyl sulfoxide (DMSO) was selected as the solvent for aspirin in the assay. DMSO can exhibit antiplatelet effects, necessitating the use of a concentration low enough to avoid such antiplatelet effects. Blood samples were tested against DMSO 0%, 0.05%, 0.5%, and 1% w/v with and without aspirin 0, 50, and 100 µM. The effects of both agents were measured via whole-blood aggregometry. A 3-dimensional response model described the data well, quantifying the combinatorial effect of DMSO and aspirin on platelet aggregation. Across all participants, baseline aggregation stimulated with collagen 1 µM or arachidonate 0.5 mM was approximately 18 and 13 Ω, respectively. The response model showed that 0.05% DMSO with 100 µM aspirin would provide platelet aggregation of 3.4 Ω. A DMSO concentration of 0.05% in the absence of aspirin would result in no discernable effects on platelet aggregation (17.7 Ω). Overall, the use of 100 µM of aspirin in 0.05% DMSO provides a robust method to test for ex vivo inhibition of platelet aggregation.