Cost of medication adherence and persistence in type 2 diabetes mellitus: a literature review

Abstract

Purpose: To explore published evidence on health care costs associated with adherence or persistence to antidiabetes medications in adults with type 2 diabetes mellitus (T2DM).

Methods: Primary research studies published between January 2006 and December 2015 on compliance, adherence, or persistence and treatment in patients with T2DM that document a link with health care costs were identified through literature searches in bibliographic databases and 2015 abstract books for relevant DM congresses. Results were assessed for relevance by two reviewers. The review was part of a larger overview evaluating the impact of adherence and persistence on a range of clinical and economic outcomes; only findings from the cost element are reported herein.

Results: A total of 4,662 de-duplicated abstracts were identified and 110 studies included in the wider review. Of these, 19 reported an association between adherence (n=13), persistence (n=5), or adherence and persistence (n=1), and health care costs. All studies were retrospective, with sample sizes ranging from 301 to 740,195. Medication possession ratio was the most commonly employed adherence measure (n=11). The majority of adherence studies (n=9) reported that medication adherence was associated with lower total health care costs. Pharmacy costs were often increased in adherent patients but this was offset by beneficial effects on other costs. Findings were more variable in persistence studies; three reported that higher pharmacy costs in persistent patients were not sufficiently offset by savings in other areas to result in a reduction in total health care costs.

Conclusions: Few studies have evaluated the relationship between adherence, persistence, and health care costs in T2DM. However, it has been consistently shown that medication nonadherence increases health care costs, suggesting that cost savings from better adherence could be substantial. Available data support the economic case for identification of strategies that facilitate improved medication adherence in patients with T2DM.

Keywords: adherence; costs; persistence; review; type 2 diabetes mellitus.

Figure 1

Flow chart of search results. Abbreviations: ADA, American Diabetes Association; CDSR, Cochrane Database of Systematic Reviews; CENTRAL, Cochrane Central Register of Controlled Trials; DARE, Database of Abstracts of Reviews of Effects; EASD, European Association for the Study of Diabetes; HTA, Health Technology Assessment Database; ISPOR, International Society for Pharmacoeconomics and Outcomes Research; EED, Economic Evaluation Database; T2DM, type 2 diabetes mellitus.

Figure 2

Mean postindex annual health care expenditures in insulin pen users with T2DM according to level of medication adherence. Notes: Data from Chandran et al. Postindex pharmacy costs were higher in most versus least adherent patients (P<0.001), representing 43% of total costs versus 21%, respectively. Total all-cause per-patient expenditure (inpatient, outpatient, ER, and pharmacy) was 9.4% lower in most versus least adherent group (P=0.007). Abbreviations: ER, emergency room; MPR, medication possession ratio; T2DM, type 2 diabetes mellitus.

Figure 3

Impact of treatment persistence on health care costs in patients initiating basal insulin. Notes: (A) Health care costs in previously insulin naïve patients with T2DM initiating basal insulin (retrospective cohort study using US claims data); continuers were patients having no gap between insulin prescriptions, interrupters had one or more prescriptions after a gap (≥30 days), and discontinuers had no prescription after a ≥30-day gap; *P=0.022 versus discontinuers, **P<0.001 versus interrupters, ***P<0.001 versus interrupters and discontinuers. Data from Perez-Nieves et al. (B) Health care costs in previously insulin-naïve patients with T2DM initiating basal insulin (retrospective longitudinal analysis of Japanese claims data); continuers were patients having no gap between insulin prescriptions, interrupters had one or more prescriptions after a gap (≥30 days), and discontinuers had no prescription after a ≥30-day gap; *P<0.04 versus continuers; **P=0.02 versus continuers. Data from Hadjiyianni et al. Abbreviation: T2DM, type 2 diabetes mellitus.