Instruments assessing medication literacy in adult recipients of care: A systematic review of measurement properties

The assessment of medication literacy in patients is an important step in assisting clinicians to plan for education, prescription simplification, assistance and/or medication aids. There have been several attempts to develop a standardised, objective measure of medication literacy. The objectives of this systematic review were to critically appraise, compare and summarise the measurement properties of existing instruments that assess medication literacy in adult recipients of care. A systematic review was performed. Search methods: Structured searches were conducted in Embase, MEDLINE PubMed, CINAHL, APA PsycINFO and Web of Science Core Collection in March 2020. Additional searches were performed in ProQuest Dissertations and Theses, DART Europe, and Google Scholar, followed by citation tracking of included studies. Two researchers independently identified eligible studies. Two researchers then assessed the methodological quality of the studies and quality of measurement properties, using the Consensus-based Standards for selection of health Measurement Instruments (COSMIN) guidelines. A best-evidence synthesis for each instrument was performed. From the 5035 citations, 17 studies were included that concerned 13 instruments using different administration methods (i.e., performancebased or self-report), medication type (i.e., prescribed or nonprescribed) and context of use (i.e., clinical or community settings). Very low- to moderate-quality evidence supported satisfactory content validity regarding relevance and comprehensibility, while comprehensiveness remained inconsistent. Other measurement properties were less frequently examined and were supported by moderate-quality evidence (i.e., structural validity) to low- or very low-quality evidence (i.e., internal consistency, reliability, construct validity). The bestvalidated instrument is the unidimensional 14-item Medication Literacy in Spanish and English assessment tool (MedLitRxSE), based on direct testing of participant performance regarding four hypothetical scenarios on medication use. Nine instruments have the potential to be recommended but require additional research, while for others, their psychometric soundness is too limited and they require content revisions. This is the first systematic review to identify instruments for medication literacy. None of the identified instruments had all measurement properties properly assessed and none reported measurement invariance, measurement error and responsiveness of the instrument. Further research is necessary for a better theoretical understanding of medication literacy in order to assist health professionals in identifying patient needs for education, regimen simplification, assistance and/or medication aids. Such research will help conceptualise new instruments that not only cover relevant domains dedicated to specific populations (e.g., polymorbid and/or older individuals), but also exhibit satisfactory measurement properties.