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Systematic Review ARTICLE Provisionally accepted The full-text will be published soon. Notify me

Front. Pharmacol. | doi: 10.3389/fphar.2018.01290

A systematic review of medication adherence thresholds dependent of clinical outcome

  • 1Pharmaceutical Care Research Group, Universität Basel, Switzerland
  • 2Department of Health Research Methods, Evidence and Impact, McMaster University, Canada

Background: In pharmacotherapy, the achievement of a target clinical outcome requires a certain level of medication intake or adherence. Based on Haynes’s early empirical definition of sufficient adherence to antihypertensive medications as taking ≥80% of medication, many researchers used this threshold to distinguish adherent from non-adherent patients. However, we propose that different diseases, medications and patient’s characteristics influence the threshold of the adherence rate above which the clinical outcome is satisfactory. Moreover, the assessment of adherence and clinical outcomes may differ greatly and should be taken into consideration. We aimed at investigating medication adherence thresholds in relation to clinical outcomes. 
Method: We searched for studies that determined the relationship between adherence rates and clinical outcomes in the databases PubMed, Embase® and Web of Science™ until December 2017, limited to English-language. Our outcome measure was any threshold value of adherence. Inclusion criteria were 1) any measurement of medication adherence; 2) any assessment of clinical outcomes 3) any method to define medication adherence thresholds in relation to clinical outcomes. Two authors independently screened titles and abstracts for relevance, reviewed full-texts, and extracted items. The results of the included studies are presented qualitatively.
Result: We analyzed six articles that assessed clinical outcomes linked to adherence rates in seven chronic disease states. Medication adherence was measured with Medication Possession Ratio (MPR, n = 3), Proportion of Days Covered (PDC, n = 1), both (n = 1), or Medication Event Monitoring System (MEMS). Clinical outcomes were event free episodes, hospitalization, cortisone use, reported symptoms and reduction of lipid levels. To find the relationship between the targeted clinical outcome and adherence rates, three studies applied logistic regression and three used survival analysis. Five studies defined adherence thresholds between 46% and 92%. One study confirmed the 80% threshold as valid to distinguish adherent from non-adherent patients.
Conclusion: The analyzed studies were highly heterogeneous, predominantly concerning methods of calculating adherence. We could not compare studies quantitatively, mostly because adherence rates could not be standardized. Therefore, we cannot reject or confirm the validity of the historical 80% threshold. Nevertheless, the 80% threshold was clearly questioned as a general standard.

Keywords: Medication adherence (MeSH), Patient Compliance, threshold, Systematic (Literature) Review, clinical outcome, Adherence measurement method, Adherence metric, Adherence methodologies, Medication Possession Ratio (MPR), Proportion of days covered (PDC)

Received: 30 Jul 2018; Accepted: 22 Oct 2018.

Edited by:

Brian Godman, Karolinska Institutet (KI), Sweden

Reviewed by:

Joseph O. Fadare, Ekiti State University, Nigeria
Dan Kibuule, University of Namibia, Namibia  

Copyright: © 2018 Baumgartner, Haynes, Hersberger and Arnet. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Mr. Pascal C. Baumgartner, Universität Basel, Pharmaceutical Care Research Group, Basel, Switzerland, pascal.baumgartner@unibas.ch