mental studies of the efficacy of a pharmacogenomic intervention based on accumulated data (e.g., a randomized controlled trial).

An advantage of randomized controlled trials (RCTs) over cohort studies is that they provide controlled exposure to treatment. In addition, randomization helps avoid the type of confounding that can occur in an observational study, in which treatment may be selected based on patient characteristics.

A retrospective trial of a pharmacogenomic marker is carried out after a RCT of a drug has been completed, with researchers testing patient samples to identify which patients were positive or negative for a particular marker and then comparing that information with the patients’ responses to the drugs being tested (Figure 3-1). Retrospective trials can provide useful data when a marker is unknown at trial initiation. They are also ideal for

FIGURE 3-1 Pharmacogenomic trial designs, including retrospective, prospective stratified, and prospective screened.

SOURCE: Lerman, IOM workshop presentation on November 17, 2010.