efficacy drug treatment efficacy drugTreatmentEfficacy Matthew Diller The efficacy measured for some instance(s) of drug treatment for preventing or ameliorating some disease outcome. The efficacy measured for some instance(s) of drug treatment for preventing or ameliorating some disease outcome. While we understand that 'drug efficacy' can have multiple interpretations, this class is specifically referring to drug efficacy in the context of clinical outcomes. As such, our definition excludes any mention of efficacy as it relates to pharmacodynamics. William R. Hogan