Challenges in systematic reviews that evaluate drug efficacy or effectiveness.

Increasingly, consumers, clinicians, regulatory bodies, and insurers are using systematic reviews of drug interventions to select treatments and set policies. Although a systematic review cannot provide all the information a clinician needs to make an informed choice for therapy, it can help decision makers distinguish what claims about effectiveness are based on evidence, identify critical information gaps, describe features of the evidence that limit applicability in practice, and address whether drug effectiveness differs for particular subgroups of patients. To improve the relevance and validity of reviews of drug therapies, reviewers need to delineate clinically important subgroups, specific aims of therapy, and most important outcomes. They may need to find unpublished trials, studies other than direct comparator (head-to-head) trials, and additional details of published trials from pharmaceutical manufacturers and regulatory agencies. In this paper, we address ways to formulate questions relevant to specific clinical therapeutic aims; discuss types of studies to include in drug efficacy and effectiveness reviews and how to find them; and describe ways to assess applicability of studies to actual practice.