CASE STUDY: Assessing poolability in a large randomized study on dual-antiplatelet therapy
*Joe Massaro, Boston University School of Public health 


A recently completed study assessed the effect of long-term dual-antiplatelet therapy (DAPT) on incident cardiovascular events in patients receiving drug-eluting stents. Over 9000 patients were given open-label DAPT for 12 months, after which they were randomized to one of two study treatment groups: an additional 18 months of DAPT or 18 months of Placebo. Primary endpoints were stent thrombosis and a composite endpoint of major adverse cardiovascular and cerebrovascular events (MACCE; composite of death, stroke, myocardial infarction). The study was designed in response to a request from the United States Food and Drug Administration (US FDA) to manufacturers of coronary stents, and was conducted through a public-private collaboration involving the US FDA, eight funding major stent and pharmaceutical manufacturers, and Harvard Clinical Research Institute (HCRI). Subjects were enrolled into the trial by HCRI and from four post-marketing stent surveillance studies sponsored by stent manufacturers. Within each of these five studies, patients were enrolled from up to four regions (North America, Europe, Australia, New Zealand). Thus, both poolability of regions and poolability across the studies were of interest. Here we define poolability as consistency of treatment effect across regions and across studies. We will discuss our assessments of whether poolability existed, and how and why we adjusted for potential differences in baseline characteristics across studies and across regions in our poolability assessments, through the use of propensity scores.