MI is an early complication of pneumonia and is associated with in vivo platelet activation and serum TxB2 overproduction; aspirin 100 mg/day seems insufficient to inhibit thromboxane biosynthesis. (MACCE in Hospitalized Patients With Community-acquired Pneumonia; NCT01773863).

These data indicate that flavonoids inhibit platelet function by blunting hydrogen peroxide production and, in turn, phospholipase C activation and suggest that the synergism among flavonoids could contribute to an understanding of the relation between the moderate consumption of red wine and the decreased risk of cardiovascular disease.

The study demonstrates that a long-term treatment with aspirin is associated with a progressive reduction in platelet sensitivity to this drug.

No abstract

Summary.  Background: Patients treated with aspirin may have a reduced sensitivity to its antiplatelet effect. The mechanism accounting for such a reduced sensitivity might involve an impaired interaction of aspirin with cyclooxygenase‐1 (COX)‐1. Objective: We sought to investigate whether platelets from patients under chronic treatment with aspirin still produce TxA2 and whether there is any relationship between the eventual persistent TxA2 formation and platelet aggregation. Finally, whether platelet‐derived TxA2 can be inhibited by in vitro addition of aspirin. Methods: Collagen‐induced platelet aggregation and thromboxane‐A2 (TxA2) were measured in 196 patients treated with aspirin (100–330 mg day−1) because of previous vascular events or presence of risk factors of atherosclerosis. Results: Collagen‐induced TxA2 production of the entire cohort was 128.7 ± 21.6 pg 10−8 cells, and was significantly correlated with platelet aggregation (Spearman's correlation coefficient = 0.44; P < 0.0001). Patients in the highest quartile of TxA2 showed higher platelet response to collagen (P < 0.0001) when compared with those in the lowest quartile. In a subgroup of 96 patients, platelets were treated in vitro with a TxA2 receptor antagonist (13‐azaprostanoic acid) or aspirin before stimulation with collagen. 13‐APA acid significantly inhibited platelet aggregation. Aspirin reduced (−72.9%) TxA2 production in patients with TxA2 values above the median but it was ineffective in those with TxA2 values below the median. Conclusion: In some patients chronically treated with aspirin platelet production of TxA2 may persist and account for enhanced platelet aggregation. Incomplete inhibition of COX‐1 seems to be implicated in persistent TxA2 production.