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infarction—the drugs actually increased the frequency of sudden cardiac death. Thus, the ultimate test of a drug's efficacy must arise from actual clinical outcomes rather than surrogate markers.

The sample of patients selected for a clinical trial may not be representative of the entire population of patients with that disease. Patients entered into a trial usually are selected according to the severity of their disease and other characteristics (inclusion criteria) or are excluded because of coexisting disease, concurrent therapy, or specific features of the disease itself (exclusion criteria). It always is important to ascertain that the clinical characteristics of an individual patient correspond with those of patients in the trial. For example, the Randomized Aldactone Evaluation Study (RALES) showed that treatment with the mineralocorticoid-receptor antagonist spironolactone was associated with a 30% reduction in death in patients with severe congestive heart failure. Hyper-kalemia, a potential adverse effect, was seen only rarely in this study, which excluded patients with serum creatinine levels >2.5 mg/dL. With the expanded use of spironolactone after RALES was published, numerous patients, many of whom did not meet the RALES inclusion criteria, developed severe hyperkalemia. Therefore, knowledge of the criteria for selecting the patients in a trial must inform the application of study results to a given patient.

Determination of efficacy and safety is an ongoing process usually based on results from multiple randomized, double-blind, controlled trials. A meta-analysis of similarly designed studies that measured the same endpoint can be used to better assess possible significance of drug treatment; by narrowing confidence limits; they can strengthen the likelihood that an apparent effect is (or is not) due to the drug rather than chance.

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