Multiplicity of medication safety terms, definitions and functional meanings: when is enough enough?

OBJECTIVES: To identify the terms and definitions used by organisations involved in medication safety and to examine differences in functional meaning using a novel scenario assignment method.
METHODS: Medication safety related terms and definitions were sought from websites of organisations associated with medication safety. The functional meanings of terms and definitions were analysed and compared using a scenario assignment method where each definition found was assessed against four scenarios with a central theme. MAIN OUTCOME MEASURES: Medication safety related terms and definitions currently in use, similarities and differences in their functional meanings, and practical implications of the use of these terms and definitions.
RESULTS: Thirty three of 160 websites searched were found to have one or more definitions for medication safety related terms. Twenty five different terms with 119 definitions were found. The most frequently defined groups of terms were "adverse event" (8 different definitions), "error" (n = 9), "near miss" (n = 12), "adverse reaction" (n = 8), and "incident" (n = 4). Substantial diversity of functional meanings of definitions was demonstrated using the scenario-assignment method. Of the five groups of frequently defined terms, definitions within the "adverse event", "near miss", and "incident" groups resulted in three functional meanings each, while two functional meanings resulted for "error" and "adverse reaction".
CONCLUSION: The multiplicity of terms, definitions and, most importantly, functional meanings demonstrates the urgent need for agreement on standardisation of nomenclature describing medication related occurrences. This is an essential prerequisite to enable meaningful analysis of incidence data and development of medication safety improvement strategies.