A<unk>  is a set of medications and other compounds that have a similar chemical structures, the same mechanism of action (i.e. binding to the same biological target), a related mode of action, and/or are used to treat the same disease. In several dominant<unk> ification systems, these four types of<unk> ifications form a hierarchy. For example, the fibrates are a chemical<unk>  of<unk> s (amphipathic carboxylic acids) that share the same mechanism of action (PPAR agonist) and mode of action (reducing blood triglycerides), and that are used to prevent and treat the same disease (atherosclerosis). Conversely, not all PPAR agonists are fibrates, not all triglyceride lowering agents are PPAR agonists, and not all<unk> s used to treat atherosclerosis are triglyceride-lowering agents. A<unk>  is typically defined by a prototype<unk> , the most important, and typically the first developed<unk>  within the<unk> , used as a reference for comparison.
Drug class
Strain 
Subspecialty
Dose 
Regimen
Risk factor
Serotype
Isotype 