Measuring adherence to multiple medications: A scoping review

Measuring medication adherence in patients can be challenging, both in clinical practice and in research studies. In an effort to define and standardise medication adherence terminology for clinical and research use, the European Ascertaining Barriers for Compliance (ABC) project developed a Taxonomy of Adherence including three essential components; (1) initiation (taking the first dose of the prescribed medication); (2) implementation (taking medication as prescribed); and (3) discontinuation (stopping treatment). While there are several methods available to measure medication adherence e.g. pill counts, self-report measures, administrative databases (pharmacy and insurance claim databases, registries) and electronic monitoring systems there is no established standardised method of measuring adherence. When patients’ medication regimens involve taking multiple medications (polypharmacy), accurately measuring adherence becomes even more challenging given the complexity of managing multiple medications for a range of acute and chronic conditions, with varying dosage and timing schedules. In recent years, polypharmacy and multimorbidity has become increasingly more prevalent and more than 30% of the global population has more than five acute or chronic conditions requiring multiple medications. A previous review of methods for measuring multiple medication adherence between the years 1973 and 2015 by the ISPOR Medication Adherence and Persistence Special Interest Group found no standardised method and a lack of consistency in the application of multiple medications adherence measures across studies. The aim of this review is to build on this previous review, by reviewing the more recent literature, to identify and evaluate measures of multiple medication adherence, in patients with polypharmacy.