Clopidogrel: How good is it and how does it work?

Bleeding tendency in dual antiplatelet therapy with aspirin/clopidogrel: rescue of the template bleeding time in a single-center prospective study

Background

Patients with heightened platelet reactivity in response to antiplatelet agents are at an increased risk of recurrent ischemic events. However, there is a lack of diagnostic criteria for increased response to combined aspirin/clopidogrel therapy. The challenge is to identify patients at risk of bleeding. This study sought to characterize bleeding tendency in patients treated with aspirin and clopidogrel.

Patients/methods

In a single-center prospective study, 100 patients under long-term aspirin/clopidogrel treatment, the effect of therapy was assayed by template bleeding time (BT) and the inhibition of platelet aggregation (IPA) by light transmission aggregometry (LTA). Arachidonic acid (0.625 mmol/L) and adenosine diphosphate (ADP; 2, 4, and 8 μmol/L) were used as platelet agonists.

Results

Bleeding episodes (28 nuisance, 2 hematuria [1 severe], 1 severe proctorrhagia, 1 severe epistaxis) were significantly more frequent in patients with longer BT. Template BT ≥ 24 min was associated with bleeding episodes (28 of 32). Risk of bleeding increased 17.4% for each 1 min increase in BT. Correlation was found between BT and IPAmax in response to ADP 2 μmol/L but not to ADP 4 or 8 μmol/L.

Conclusion

In patients treated with dual aspirin/clopidogrel therapy, nuisance and internal bleeding were significantly associated with template BT and with IPAmax in response to ADP 2 μmol/L but not in response to ADP 4 μmol/L or 8 μmol/L.

Combination of clopidogrel and everolimus dramatically reduced the development of transplant arteriosclerosis in murine aortic allografts

Our group has shown that platelet inhibition with clopidogrel, an antagonist of the P2Y12 adenosine diphosphate receptor on platelets, reduced the formation of transplant arteriosclerosis. The aim of this study was to investigate whether a combination of cyclosporin or everolimus with clopidogrel has a beneficial effect on the development of transplant arteriosclerosis. Fully MHC mismatched C57Bl/6 (H2(b)) donor aortas were transplanted into CBA.J (H2(k)) recipients and mice received either clopidogrel alone (1 mg/kg/day) or in combination with cyclosporin (2 mg/kg/day) or everolimus (0.05 mg/kg/day). Grafts were analysed by histology and morphometry on day 30 after transplantation. In mice treated with clopidogrel alone, transplant arteriosclerosis was significantly reduced [intima proliferation 56 +/- 11% vs. 81 +/- 7% (control)/n = 7]. Daily application of everolimus reduced the development of transplant arteriosclerosis compared with untreated controls [intima proliferation of 29 +/- 9% vs. 81 +/- 7% (control)/n = 7]. Strikingly, combination of clopidogrel and everolimus almost abolished the formation of transplant arteriosclerosis [intima proliferation: 11 +/- 8% vs. 81 +/- 7% (control)/n = 7]. By contrast, combination of cyclosporin and clopidogrel compared with clopidogrel alone showed no additive effect. These results demonstrate that combination of platelet- and mammalian target of Rapamycin-inhibition can dramatically reduce the development of transplant arteriosclerosis.

Does platelet administration affect mortality in elderly head-injured patients taking antiplatelet medications?

A significant portion of patients sustaining traumatic brain injury (TBI) take antiplatelet medications (aspirin or clopidogrel), which have been associated with increased morbidity and mortality. In an attempt to alleviate the risk of increased bleeding, platelet transfusion has become standard practice in some institutions. This study was designed to determine if platelet transfusion reduces mortality in patients with TBI on antiplatelet medications. Databases from two Level I trauma centers were reviewed. Patients with TBI 50 years of age or older with documented preinjury use of clopidogrel or aspirin were included in our cohort. Patients who received platelet transfusions were compared with those who did not to assess outcome differences between them. Demographics and other patient characteristics abstracted included Injury Severity Score, Glasgow Coma Scale, hospital length of stay, and warfarin use. Three hundred twenty-eight patients comprised the study group. Of these patients, 166 received platelet transfusion and 162 patients did not. Patients who received platelets had a mortality rate of 17.5 per cent (29 of 166), whereas those who did not receive platelets had a mortality rate of 16.7 per cent (27 of 162) (P = 0.85). Transfusion of platelets in patients with TBI using antiplatelet therapy did not reduce mortality.

Attenuation of transplant arteriosclerosis with clopidogrel is associated with a reduction of infiltrating dendritic cells and macrophages in murine aortic allografts

BACKGROUND

Monotherapy with clopidogrel reduced the formation of transplant arteriosclerosis in a murine aortic allograft model. However, the underlying immunologic mechanisms are still unknown.

METHODS

Fully major histocompatibility complex-mismatched C57BL/6 (H2b) donor aortas were transplanted into CBA.J (H2k) recipients and mice received different doses (1, 10, and 20 mg/kg) of clopidogrel, an antagonist of the P2Y12 ADP receptor on platelets, or control saline for 30 days. Blood was analyzed for changes in adhesion molecule and sCD40L concentrations by ELISA. Grafts were analyzed by histology, morphometry, and immunofluorescence on day 30 after transplantation. Intragraft cytokine mRNA production was analyzed by reverse-transcriptase polymerase chain reaction on day 14 after transplantation.

RESULTS

Treatment with clopidogrel resulted in significantly decreased blood concentrations of sCD40L and P-selectin after transplantation. Cellular analysis of the aortic transplant revealed fewer numbers of infiltrating dendritic cells (CD205+) and macrophages (F4/80+) after application of clopidogrel, whereas T-cells within the graft were unaltered. In addition cellular P-/E-selectin, ICAM-1, and platelet-derived-growth-factor (PDGF)-beta surface expression were significantly reduced as compared with untreated controls. Intragraft mRNA expression confirmed these results and showed significant lower production of P-/E-selectin, ICAM-1, and PDGF-beta after treatment with clopidogrel. Antiglycoprotein-Ib and antiglycoprotein VI had no beneficial effect on the development of transplant arteriosclerosis.

CONCLUSION

This report shows that application of clopidogrel after transplantation results in a reduction in adhesion molecule expression within the blood and transplant tissue and is associated with reduced transendothelial migration of dendritic cells and macrophages within the vascular wall.

Vascular protection in brain ischemia

Vascular damage occurring after cerebral ischemia may lead to a worse outcome in patients with ischemic stroke, as it facilitates edema formation and hemorrhagic transformation. There are several phases in the development of vascular injury (acute, subacute and chronic) and different mediators act in each one. Therapeutic options to avoid vascular injury must be focused on acting in each phase. However, even though experimental studies have demonstrated the benefit of therapeutic interventions both in the acute and chronic phases of cerebral ischemia, only the chronic phase offers a therapeutic window sufficiently wide enough to provide vascular protection in clinical practice. Several drugs including erythropoietin and HMG-CoA reductase inhibitors (statins), antihypertensive (angiotensin modulators), antibiotics (minocycline) and antihyperglycemic drugs (thiazolidinediones) have been proved to provide vascular protection in patients with ischemic stroke. Anti-inflammatory, antioxidant, and antiapoptotic actions are responsible for the vascular protective effect related to these drugs.

Clopidogrel reduces the development of transplant arteriosclerosis

BACKGROUND

Transplant arteriosclerosis, the hallmark feature of chronic rejection, is still the major limiting factor for the long-term success of heart transplantation. Platelets have been implicated to play a role in the pathogenesis of this disease. Therefore the aim of this study was to investigate whether platelet inhibition alone has a positive effect on the development of transplant arteriosclerosis.

METHODS

Fully major histocompatibility complex-mismatched C57BL/6 (H2(b)) donor aortas were transplanted into CBA (H2(k)) recipients, and mice received different doses (1, 10, and 20 mg/kg) of clopidogrel or control saline as a daily intraperitoneal injection for 30 days. Blood was analyzed on days 2, 7, 14, and 30 by using a platelet aggregation test (adenosine diphosphate) for effectiveness of the treatment. Grafts were analyzed by means of histology and morphometry on day 30 after transplantation.

RESULTS

When mice were treated daily with 1 mg/kg clopidogrel in the absence of any other immunosuppression, transplant arteriosclerosis was significantly reduced compared with that seen in saline-treated control animals (intimal proliferation of 66% +/- 9% [1 mg/kg clopidogrel] vs 77% +/- 5% [control], n = 7, P < or = .03). Daily application of 10 mg/kg and 20 mg/kg clopidogrel also significantly reduced the development of transplant arteriosclerosis compared with that seen in control animals (intimal proliferation of 61% +/- 11% [10 mg/kg clopidogrel] vs 54% +/- 10% [20 mg/kg clopidogrel] vs 77% +/- 5% [control], n = 8, P < or = .003). There was, however, no additional beneficial effect when compared with mice treated with 1 mg/kg clopidogrel (P = .06). Isografts did not show any signs of vascular lesions on day 30 after transplantation.

CONCLUSION

These results demonstrate that monotherapy with clopidogrel can effectively reduce the formation of transplant arteriosclerosis in a murine aortic allograft model.

Models of blood coagulation

Our research aims to provide quantitatively transparent, biologically realistic descriptions of the processes involved in hemostasis which will permit predictions of the behavior of the coagulation system in normal and pathologic states. We use four models of coagulation: (1) numerical approximations of the tissue factor (Tf) pathway of thrombin generation based upon mechanism and dynamics; (2) Tf activation of the "blood coagulation proteome" from isolated cells and proteins; (3) Tf activated contact pathway inhibited whole blood in vitro; and (4) blood shed from standardized microvascular wounds in vivo. The results from these models are integrated in interactive assessments aimed at achieving convergence of biochemical rigor and biological authenticity. Microvascular injury is the most biologically secure but least accessible to mechanistic study. Numerical models while quantitatively transparent are biologically limited. By the integrated analyses of all four models, we establish observations which require inclusion or discovery of new parameters to achieve mechanistically interpretable biological reality. Discoveries made in this fashion have included thrombin's role in the initiation phase, TFPI/ATIII/APC synergy interactions, rfVIIa in fVII deficiency, the roles of fVIII and fIX in the Tf reaction, and the cleavage of fIX by fXa membrane. Ideally, our results will provide descriptions which predict the behavior of the biological blood coagulation system under normal and pathologic conditions.

Pharmacodynamics, pharmacokinetics, and safety of the oral reversible P2Y12 antagonist AZD6140 with aspirin in patients with atherosclerosis: a double-blind comparison to clopidogrel with aspirin

AIMS

This double-blind, parallel-group study was conducted to assess the pharmacodynamics, pharmacokinetics, and safety of AZD6140, the first oral, reversible adenosine diphosphate (ADP) receptor antagonist.

METHODS AND RESULTS

Patients (n = 200) with atherosclerosis were randomized to receive AZD6140 50, 100, or 200 mg twice daily (bid) or 400 mg daily (qd) or clopidogrel 75 mg qd for 28 days. All groups received aspirin 75-100 mg qd. AZD6140 (100 and 200 mg bid, 400 mg qd) rapidly and nearly completely inhibited ADP-induced platelet aggregation after initial dosing (day 1) and at day 28. On day 1, peak final-extent inhibition of platelet aggregation (IPA) was observed 2-4 h post-dose with AZD6140, whereas clopidogrel minimally inhibited platelet aggregation (mean percentage IPA < 20%, all time points). Four hour post-dose at steady state, the three higher doses of AZD6140 produced comparable final-extent mean percentage IPA (approximately 90-95%), which exceeded that with AZD6140 50 mg bid or clopidogrel (approximately 60%). AZD6140 was generally well tolerated. All bleeding events, except one in a patient receiving 400 mg qd, were minor and of mild-to-moderate severity.

CONCLUSION

AZD6140 100 and 200 mg bid were well tolerated and were superior to AZD6140 50 mg bid and clopidogrel 75 mg qd with regard to antiplatelet efficacy.