There is evidence to support use of aspirin in combination with clopidogrel for patients presenting with all ACS types, as well as for patients presenting with PCI for any indication. The treatment duration varies, but patients who have received stenting should receive at least 1 year of combination therapy. There is no evidence to support this combination for primary prevention of CAD or atherosclerotic ischemic events, secondary prevention of stable CAD, or prevention of cardioembolic stroke in patients with atrial fibrillation. The possible benefits of dual antiplatelet therapy also must be weighed against the risk of bleeding.

The temporary decline in statin persistence appeared to be associated with the withdrawal of cerivastatin, while persistence with the other study medications remained constant. Clinicians need to understand the potential effect of factors such as media attention surrounding a drug's withdrawal on patients' medication-taking behavior.

Prospective, randomized clinical trials are the gold standard for establishing cause-and-effect relationships between therapeutic interventions and specific outcomes. Unfortunately, these types of studies are not always available to evaluate important clinical end points such as mortality. Meta-analyses and observational studies are often used in an attempt to fill the gap in the literature when no prospective, randomized trials exist to answer a research question. A rapid increase in the number of published meta-analyses and observational studies has occurred in recent years. In the absence of prospective, randomized studies, it is essential for the clinician to understand the important issues involved in interpreting these other types of studies. When evaluating a meta-analysis, the clinician should assess for several different forms of bias, clinical heterogeneity, and use of appropriate methodology. When evaluating an observational study, sources of bias and confounding should be identified. If the potential for confounding is present, the methods used to minimize the impact of confounders should be evaluated for appropriateness. Mortality associated with nesiritide in the treatment of acute decompensated heart failure is a contemporary example of the use of nonrandomized research to address a research question that is unanswered by prospective, randomized studies. We review the details of a recent meta-analysis and observational evaluation of mortality associated with nesiritide and discuss the issues that are important in critical evaluation of nonrandomized study designs.