In search of a standard when analyzing medication adherence in patients with heart failure using claims data: a systematic review.

To determine and address medication non-adherence is important and may improve patient outcomes. Our aim was to perform a systematic review on the operationalization of adherence measures in patients with heart failure using claims data. We searched the MEDLINE, EMBASE, and Cochrane databases. A quality check of the full-text articles was performed using the Quality in Prognosis Studies tool. We included 28 studies. Eleven studies used the medication possession ratio, 15 the proportion of days covered, and six studies used own methods to calculate medication adherence. Almost all studies used an observation period of 1 year. Twenty-one studies considered angiotensin converting enzyme inhibitors or angiotensin receptor antagonists, 17 beta-blockers, 11 diuretics, eight mineralocorticoid receptor antagonists, six digitalis-glycosides, and six statins. Eight studies looked at single substance classes; 18 studies analyzed more than one drug class. Different assumptions for the dosage were used. In seven studies, switching within therapeutic classes was allowed. Three studies allowed stockpiling, nine studies censored hospital stays, and four studies censored death. Seventeen studies dichotomized the results, applying the cutoff ≥ 0.8 to define a patient as adherent. Eight studies analyzed adherence as a continuous value. The reporting quality of the methodology applied varied widely between studies. A gold standard is currently not available for the quantification of medication adherence in patients with chronic heart failure via claims data. To assess the methodology, the following parameters should be described: method of measurements, observation period, substances, dosing, switches, stockpiling, truncations, statistical analysis, and cutoff for adherence.