Antiplatelet agents in patients undergoing percutaneous coronary intervention: how many and how much?

Management of patients with high gastrointestinal risk on antiplatelet therapy

Increasing use of antiplatelet therapies is associated with increasing GI complications, such as ulceration and GI bleeding. Identification of high-risk patients and, in such patients, incorporation of strategies to reduce their GI risk would be clinically prudent. After assessment and treatment of H pylori in patients with prior ulcer or GI bleeding histories, further reduction in GI risk in other high-risk patients who require antiplatelet agents is primarily accomplished by prescribing drugs that when coadministered with antiplatelet agents protect against mucosal ulceration, primarily proton pump inhibitors (PPIs). However, observational studies indicate a higher cardiovascular event rate in patients taking PPIs along with clopidogrel and aspirin compared with that of patients undergoing dual antiplatelet therapy without PPIs. Whether concurrent use of a PPI with clopidogrel represents a safety concern or not is currently being evaluated by the US Food and Drug Administration. Until more specific regulatory guidance is available, current recommendations are that patients taking both PPIs and clopidogrel concurrently should probably continue to do so until more data become available.

Current antiplatelet therapies: benefits and limitations

Antiplatelet therapy is the current criterion standard for the treatment of patients undergoing percutaneous coronary intervention and patients who have acute coronary syndromes. Clopidogrel in combination with aspirin is the current standard of care for reducing cardiovascular events in these patients. However, patients who receive currently available antiplatelet therapy may still develop atherothrombotic events. In addition, despite the clinical benefits achieved with clopidogrel, significant clinical limitations are associated with its use. This article summarizes the current understanding of the benefits and limitations of the commonly used antiplatelet therapies.

ADP receptor antagonism: what's in the pipeline?

ADP is one of the most important mediators of both physiologic hemostasis and thrombosis. Development and utilization of agents that block ADP receptors on the platelet membrane, namely thienopyridines, has represented a major advancement for treatment of patients undergoing percutaneous coronary interventions and those with acute coronary syndromes. Currently, clopidogrel, a second-generation thienopyridine that inhibits the ADP P2Y(12) receptor, represents the treatment of choice, in addition to aspirin, for the prevention of stent thrombosis. Further, long-term adjunctive use of this ADP P2Y(12) receptor antagonist is also associated with improved clinical outcomes in high-risk patients, and represents the standard of care for these patients. Despite the unambiguous clinical benefit associated with clopidogrel, accumulating experience with this drug has also led to identification of some of its drawbacks, which are related to inadequate platelet inhibition with standard dosage regimens as well as to its irreversible antiplatelet effects. This has led to the questioning of currently recommended clopidogrel dosage regimens as well as to the development of novel and more potent ADP P2Y(12) receptor antagonists, some of which are also reversible agents. Numerous studies are currently ongoing with the objective of demonstrating how more potent platelet inhibition using higher loading and maintenance dose regimens of clopidogrel or novel ADP P2Y(12) receptor antagonists - such as prasugrel, ticagrelor (AZD 6140) and cangrelor - will affect clinical outcomes. This article reviews the current knowledge of platelet ADP P2Y(12) receptor antagonism and the projected developments in this field.

Effects of glycoprotein IIb/IIIa inhibitors in patients undergoing percutaneous coronary intervention after pretreatment with clopidogrel: a meta-analysis of randomized trials

Glycoprotein (Gp) IIb/IIIa inhibitors reduce morbidity and mortality in patients undergoing percutaneous coronary intervention (PCI) when added to aspirin and heparin. However, the benefits of Gp IIb/IIIa inhibition in patients pretreated with clopidogrel are less clear. We conducted a meta-analysis to determine the efficacy and safety of adding a Gp IIb/IIIa inhibitor to clopidogrel, aspirin, and heparin before PCI. Five trials were identified via electronic searches of the MEDLINE and Cochrane Central Register of Controlled Trials databases. The studies randomized a total of 5303 patients; 2654 received a Gp IIb/IIIa inhibitor. Two trials examined patients with acute coronary syndromes and 3 examined patients undergoing elective PCI. Loading doses of clopidogrel ranged from 375 to 600 mg. Follow-up ranged from 30 days to 1 year.Gp IIb/IIIa inhibition did not reduce the endpoints of death, myocardial infarction (MI), or target vessel revascularization (odds ratio [OR] = 0.84; 95% confidence interval [CI] = 0.58-1.22, P = 0.35 for death; OR = 0.86; 95% CI = 0.69-1.08, P = 0.19 for MI; and OR = 0.96; 95% CI = 0.81-1.15, P = 0.68 for target vessel revascularization). Analyses restricted to acute coronary syndromes trials yielded similar results (OR = 0.70; 95% CI = 0.33-1.48, P = 0.35 for death; OR = 0.78; 95% CI = 0.59-1.03, P = 0.08 for MI). Gp IIb/IIIa inhibition increased major and minor bleeding (OR = 1.35; 95% CI = 1.04-1.75, P = 0.02) driven by use of abciximab. There was no evidence of heterogeneity in the analyses.

Antiplatelet therapy in type 2 diabetes mellitus

PURPOSE OF REVIEW

Patients with diabetes mellitus are characterized by a prothrombotic status. Since platelet reactivity is key to the development of atherothrombotic complications, antiplatelet therapy has a pivotal role in reducing ischemic risk, especially in diabetes mellitus patients. This review summarizes the current knowledge on how antiplatelet therapy affects this high-risk patient population.

RECENT FINDINGS

Numerous studies have shown the clinical benefit of antiplatelet agents in reducing ischemic events in diabetes mellitus patients. Despite the clinical benefit achieved with antiplatelet agents, however, patients with diabetes mellitus continue to have an increased risk of ischemic events compared to non-diabetes mellitus. Recent observations suggest that this may be in part due to inadequate platelet inhibition achieved in diabetes mellitus patients compared to non-diabetics, exposing these subjects to an enhanced ischemic risk.

SUMMARY

Whilst antiplatelet therapy has been clearly shown to reduce morbidity and mortality in patients with diabetes mellitus, there are accruing data demonstrating that in these patients the degree of platelet inhibition achieved with standard treatment regimens may be inadequate. This supports the need for specific antiplatelet drug regimens, with either different dosages of current medication or development of novel antiplatelet drugs, which are more specific to tackle the hyperreactive diabetic platelet.

Consistent platelet inhibition during long-term maintenance-dose clopidogrel therapy among 359 compliant outpatients with documented vascular disease

BACKGROUND

Numerous reports have dichotomized responses after clopidogrel therapy using varying definitions and platelet tests in patients immediately after acute vascular events; however, no large study has assessed platelet characteristics in outpatients receiving long-term treatment for more than 30 days with the maintenance dose (75 mg/d) of clopidogrel. The aim of this study was to describe the responses of ex vivo measures of platelet aggregation and activation to long-term clopidogrel therapy in a large population of outpatients after coronary stenting or ischemic stroke.

METHODS

We conducted a secondary post hoc analysis of a data set represented by presumably compliant patients after coronary stenting (n = 237) or a documented ischemic stroke (n = 122) treated with clopidogrel-and-aspirin combination antiplatelet therapy.

RESULTS

The mean duration of treatment was 5.8 months (range 1-21 months). Every patient exhibited a significant inhibition of adenosine diphosphate-induced platelet aggregation (mean 52.9%, range 36%-70%) as compared with the preclopidogrel measures. Inhibition of aggregation strongly correlated with a diminished expression of PECAM-1 (platelet/endothelial cell adhesion molecule 1, r = 0.75), glycoprotein IIb/IIIa (r = 0.62), and PAR-1 (protease-activated receptor 1, r = 0.71). None of the patients developed hyporesponsiveness (reduction from the baseline <15%) or profound inhibition (residual platelet activity <10%).

CONCLUSIONS

In contrast to the wide variability of responses that exists in the acute setting, long-term therapy with clopidogrel leads to consistent and much less variable platelet inhibition. Lack of nonresponse and profound inhibition with clopidogrel allow for the maintenance of a delicate balance between proven efficacy and acceptable bleeding risks for long-term secondary prevention in outpatients after acute vascular events.

Management of symptomatic intracranial arterial stenosis: endovascular therapy

Patients with symptomatic intracranial stenosis are at high risk of subsequent stroke despite the use of antithrombotic agents or surgical management. Although endovascular therapy appears to promise therapeutic solutions, the reported high peri-procedural adverse event rate limits the widespread use of this technique. In the past few years, the morbidity and mortality associated with intracranial angioplasty and stenting have decreased with the development of new intracranial specific devices. The most recent prospective studies on intracranial stenting have been nothing more than registries of patients with symptomatic intracranial stenosis of 50% or greater who have failed medical therapy. However, no randomized controlled data exist on the comparison between endovascular therapy and medical treatment. There are new data identifying factors associated with a higher risk of stroke in medically treated patients. These findings will help to define a high-risk patient population on whom the initial controlled trials will be conducted.