In patients at risk of myocardial infarction or stroke, two antiplatelet drugs are not always better than one. In a large recent trial,1,2 adding clopidogrel (Plavix) to aspirin therapy did not offer much benefit to a cohort of patients at risk of cardiovascular events, although a subgroup did appear to benefit: those at even higher risk because they already had a history of myocardial infarction, ischemic stroke, or peripheral arterial disease.
These were the principal findings in the Clopidogrel for High Atherothrombotic Risk and Ischemic Stabilization, Management, and Avoidance (CHARISMA) study,1,2 in which one of us (D.L.B.) was principal investigator.
These findings further our understanding of who should receive dual antiplatelet therapy, and who would be better served with aspirin therapy alone. In this article, we discuss important studies that led up to the CHARISMA trial, review CHARISMA’s purpose and study design, and interpret its results.
PREVENTING ATHEROTHROMBOSIS BY BLOCKING PLATELETS
Platelets are key players in the atherothrom-botic process.3–5 The Antiplatelet Trialists’ Collaboration,6 in a meta-analysis of trials performed up to 1997, calculated that antiplatelet therapy (mostly with aspirin) reduced the vascular mortality rate by 15% in patients with acute or previous vascular disease or some other predisposing condition. Thus, aspirin has already been shown to be effective as primary prevention (ie, in patients at risk but without established vascular disease) and as secondary prevention (ie, in those with established disease).7,8
Yet many patients have significant vascular events in spite of taking aspirin.6 Aspirin failure is thought to be multifactorial, with causes that include weak platelet inhibition, noncompliance, discontinuation due to adverse effects (including severe bleeding), and drug interactions. In addition, aspirin resistance has been linked to worse prognosis and may prove to be another cause of aspirin failure.9–11
Clopidogrel, an adenosine diphosphate (ADP) receptor antagonist, has also been studied extensively as an antiplatelet agent.5,12 Several studies have indicated that clopidogrel and ticlopidine (Ticlid, a related drug) may be more potent than aspirin, both in the test tube and in real patients.13–15
KEY TRIALS LEADING TO CHARISMA
- Clopidogrel is more effective and slightly safer than aspirin as secondary prevention, as shown in the Clopidogrel Versus Aspirin in Patients at Risk of Ischemic Events (CAPRIE) trial.16–21
- The combination of clopidogrel plus aspirin is more beneficial than placebo plus aspirin in patients with acute coronary syndromes, as shown in the Clopidogrel in Unstable Angina to Prevent Recurrent Ischemic Events (CURE) trial,22–24 the Clopidogrel as Adjunctive Reperfusion Therapy-Thrombolysis in Myo-car-dial Infarction (CLARITY-TIMI 28) trial,25 and the Clopidogrel and Metoprolol in Myocardial Infarction Trial (COMMIT).26
- The combination of clopidogrel plus aspirin is beneficial in patients undergoing percutaneous coronary interventions, with or without drug-eluting stent placement,27–30 as shown in the Clopidogrel for the Reduction of Events During Observation (CREDO) trial,28 the Effect of Clopidogrel Pretreatment Before Percutaneous Coronary Intervention in Patients With ST-Elevation Myocardial Infarction With Fibrinolytics (PCI-CLARITY) study,29 and the Effects of Pre-treatment With Clopidogrel and Aspirin Followed by Long-term Therapy in Patients Undergoing Percutaneous Coronary Intervention (PCI-CURE) study.30 In fact, most patients undergoing percutaneous interventions now receive a loading dose of clopidogrel before the procedure and continue to take it for up to 1 year afterward. However, the ideal long-term duration of clopidogrel treatment is still under debate.
In view of these previous studies, we wanted to test dual antiplatelet therapy in a broader population at high risk of atherothrombosis, ie, in patients with either established vascular disease or with multiple risk factors for it.
CHARISMA STUDY DESIGN
CHARISMA was a prospective, randomized, double-blind, placebo-controlled study of the efficacy and safety of clopidogrel plus aspirin vs placebo plus aspirin in patients at high risk of cardiovascular events.
A total of 15,603 patients, all older than 45 years, were randomly assigned to receive clopidogrel 75 mg/day plus aspirin 75 to 162 mg/day or placebo plus aspirin, in addition to standard therapy as directed by individual clinicians (eg, statins, beta-blockers). Patients were followed up at 1, 3, and 6 months and every 6 months thereafter until study completion, which occurred after 1,040 primary efficacy end points. The median duration of follow-up was 28 months.1
Patients had to have one of the following to be included: multiple atherothrombotic risk factors, documented coronary disease, documented cerebrovascular disease, or documented peripheral arterial disease (Table 2). Specific exclusion criteria included the use of oral antithrombotic or chronic nonsteroidal anti-inflammatory medications.1
The primary end point was the combined incidence of the first episode of myocardial infarction or stroke, or death from cardiovascular causes.
The secondary end point was the combined incidence of myocardial infarction, stroke, death from cardiovascular causes, or hospitalization for unstable angina, a transient ischemic attack, or revascularization procedure.
The primary safety end point was severe bleeding, as defined in the Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries (GUSTO) study31 as intracranial hemorrhage, fatal bleeding, or bleeding leading to hemody-namic compromise. Moderate bleeding was defined as bleeding that required transfusion but did not meet the GUSTO definition of severe bleeding.