Medication (re)fill adherence measures derived from pharmacy claims data in older Americans: a review of the literature.

Medication nonadherence is a significant public health problem that affects the health and well-being of older Americans while burdening the US healthcare system. Pharmacy claims data have gained importance in deriving objective medication (re)fill adherence measures; however, little is known about application of such measures in older Americans. The objective of this study was to assess the types and characteristics of pharmacy claims-derived medication (re)fill adherence measures used in older Americans. A comprehensive literature search strategy was employed to identify all articles using pharmacy claims data to measure (re)fill adherence to prescription medications in older Americans aged 65+ years. Included were articles reporting original research studies conducted and published in the USA in English between 1 January 2000 and 1 November 2012. The basic search used multiple key terms indicating adherence, combined with the term "medication" and the term "pharmacy claims or administrative claims." Due to the variety of measure names used in the literature, a more specific search was added to repeat the basic search for 29 previously used medication (re)fill adherence measure names. Articles identified through the database search were manually reviewed to select only articles meeting the inclusion criteria. The search resulted in a total of 36 articles. Information on medication (re)fill measurements were extracted and summarized. The 36 articles used 20 differently named measures under the three main concepts: medication adherence, persistence, and discontinuation. Measures of medication adherence cumulatively assessed the proportion of time at which medications were (not) filled over a predefined observation period (e.g., medication possession ratio). Measures of medication persistence assessed the continuity of medication filling over a specified time period, while medication discontinuation measures focused on termination of medication (re)fills. Overall, almost two thirds of all identified articles used a single medication (re)fill adherence measure. Among them, 77 % used a medication possession measure. The term "medication possession ratio" (MPR) was used most frequently (65 %), followed by the "proportion of days covered" (PDC; 30 %). No single measure can be generally recommended for the use in older Americans. The challenges in using pharmacy claims-based medication (re)fill adherence measures in older Americans include a lack of consensus terminology and algorithms among measures of the same concepts, insufficient transparency of individual measure operationalization, and inadequate consideration of unique characteristics of the older population, such as temporary nursing home care. Although medication (re)fill adherence measures may be well suited for measuring medication adherence in older Americans, little guidance is available on how to use them in this population. Further efforts need to be given to the development and standardization of pharmacy claims-based medication (re)fill measures that are specifically tailored toward use in older Americans.