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. 2017 Apr 20;17(1):66.
doi: 10.1186/s12874-017-0339-z.

Does the association between adherence to statin medications and mortality depend on measurement approach? A retrospective cohort study

Mhd Wasem Alsabbagh  1 , Dean Eurich  2 , Lisa M Lix  3 , Thomas W Wilson  4 , David F Blackburn  5
Affiliations

Does the association between adherence to statin medications and mortality depend on measurement approach? A retrospective cohort study

Mhd Wasem Alsabbagh et al. BMC Med Res Methodol. .

Abstract

Background: The aim of this study was to examine the relationship between mortality and statin adherence using two different approaches to adherence measurement (summary versus repeated-measures).

Methods: A retrospective cohort study was conducted using administrative data from Saskatchewan, Canada between 1994 and 2008. Eligible individuals received a prescription for a statin following hospitalization for acute coronary syndrome (ACS). Adherence was measured using proportion of days covered (PDC) expressed either as: 1) a fixed summary measure, or 2) as a repeatedly measured covariate. Multivariable Cox-proportional hazards models were used to estimate the association between adherence and mortality.

Results: Among 9,051 individuals, optimal adherence (≥80%) modeled with a fixed summary measure was not associated with mortality benefits (adjusted HR 0.97, 95% CI 0.86 to 1.09, p = 0.60). In contrast, repeated-measures approach resulted in a significant 25% reduction in the risk of death (adjusted HR 0.75, 95% CI 0.67 to 0.85, p < 0.01).

Conclusions: Unlike the summary measure, the repeated measures approach produces a significant reduction of all-cause mortality with optimal adherence. This effect may be a result of the repeated measures approach being more sensitive, or more prone to survival bias. Our findings clearly demonstrate the need to undertake (and report) multiple approaches when assessing the benefits of medication adherence.

Keywords: Compliance/adherence; Lipids and cholesterol; Mortality; Secondary prevention; Treatment.

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Figures

Fig. 1
Fig. 1
Adjustment of the adherence measure (proportion of days covered) to prevent overestimation from early refills or refills extending beyond measurement period represented on days’ time scale (shadowed panels) as original data a and data with adjusted date(s) and quantities b
Fig. 2
Fig. 2
Flow chart for cohort selection
Fig. 3
Fig. 3
Concordance between two measures of statin adherence (summary measure and repeated-measures) among individuals with coronary heart disease
Fig. 4
Fig. 4
Kaplan-Meier estimates of survival among individuals classified using adherence summary measure (a) and adherence repeated-measures (b)
See this image and copyright information in PMC

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