Background: Clopidogrel, aspirin (ASA), and the fixed-dose combination of extended-release dipyridamole and ASA (ER-DP+ASA) are widely used in post-stroke regimens.
Objective: This study compared serial changes in multiple biomarkers of platelet activation with ER-DP+ASA and clopidogrel with or without ASA in patients with type 2 diabetes mellitus and a history of transient ischemic attack (TIA).
Methods: This was a randomized, single-blind pilot study conducted at an outpatient center in the United States. Eligible patients were aged 40 years and had a diagnosis of type 2 diabetes and a history of TIA. Patients were allocated to receive ER-DP+ASA 200/25 mg BID, clopidogrel 75 mg/d, or clopidogrel 75 mg/d plus ASA 81 mg/d. Multiple platelet bio-markers were assessed at baseline, day 15, and day 30 using aggregometry, cartridge-based platelet function analyzers, and flow cytometry. The primary end point was the change in platelet receptor expression after 30 days of therapy. Compliance and tolerability were monitored by measuring plasma dipyridamole levels and recording all episodes of headache and vomiting.
Results: The study enrolled 60 consecutive patients (20 per treatment arm), all of whom completed the study. There were no significant differences between treatment arms, although the ER-DP+ASA group had a numerically greater mean age, higher proportion of men, and a greater prevalence of vascular disease and smoking compared with the other groups. There were no deaths or serious adverse events during the study, including symptoms attributable to cerebral ischemia, worsening of diabetes, or cerebral or systemic bleeding. Three patients in the ER-DP+ASA group and 1 in the clopidogrel plus ASA group reported headache during the first several days of therapy; 1 patient in the clopidogrel monotherapy group experienced transitory nausea and vomiting. ER-DP+ASA was associated with a significantly delayed (day 30) reduction in expression of glyco-protein (GP) Ilb/IIIa activity (P = 0.02), platelet-endothelial cell adhesion molecule 1 (PECAM-1) (P = 0.03), GP Ib (P = 0.001), vitronectin (P = 0.001), P-selectin (P = 0.001), lysosome-associated membrane protein 1 (P = 0.001), and cluster of differentiation 40 ligand (P = 0.01), as well as significant inhibition of the intact (P = 0.01) and cleaved (P = 0.01) epitopes of protease-activated receptor 1. Clopidogrel monotherapy, on the other hand, was associated with significant inhibition of adenosine diphosphate-induced platelet aggregation (P = 0.001), closure-time prolongation (P = 0.01), and reduction in measurements on the rapid platelet function assay-ASA at day 15 (P = 0.001). Expression of PECAM-1 (P = 0.03) and GP IIb/IIIa activity (P = 0.01) was reduced at day 15 in clopidogrel-treated patients. The addition of ASA to clopidogrel was associated with significant inhibition of collagen-induced platelet aggregation (P = 0.001) and diminished formation of platelet-monocyte microparticles at days 15 (P = 0.02) and 30 (P = 0.03).
Conclusions: In these patients with type 2 diabetes and a history of TIA, patterns of platelet inhibition differed significantly according to whether treatment was with ER-DP+ASA or clopidogrel with or without ASA. The antiplatelet activity of clopidogrel was more potent and occurred earlier (15 days), whereas ER-DP+ASA was associated with moderate downregulation of multiple activation-dependent platelet receptors that occurred later (30 days).