A pharmacoepidemiologic analysis of the impact of calendar packaging on adherence to self-administered medications for long-term use

Background: Calendar blister packaging (CBP) that incorporates a day or date feature is a simple medication packaging technology that is designed to improve medication adherence and persistence.

Objective: This study was conducted to assess the effect of a new calendar packaging technology on prescription refill adherence and persistence for daily, self-administered, long-term medication use.

Methods: Anonymized pharmacy dispensing data from a large US mass merchandiser were analyzed. This retrospective cohort study included people aged 18 to 75 years who filled prescriptions for oral lisinopril or enalapril (control group) at a study pharmacy during 1 year before and after the switch of lisinopril packaging from vials to CBP. Cohorts were stratified into new and prevalent medication users. We used linear and logistic regression modeling and propensity score matching to assess the impact of CBP on refill adherence, using medication possession ratio (MPR) and proportion of days covered (PDC), and persistence using length of therapy (LOT).

Results: Our sample comprised 76,321 new users and 249,040 prevalent users. Across all user, medication, and packaging groups, the mean unadjusted LOT decreased in the follow-up year, possibly due to economic recession. The LOT decline was attenuated in the CBP cohort. After adjustment for covariates, CBP use in new and prevalent medication users was associated with significantly higher LOT and PDC but not MPR. The odds of achieving PDC ≥80% were higher by 15% in new users (odds ratio [OR] = 1.15; 95% CI, 1.09-1.21) and 12% in prevalent users (OR = 1.12; 95% CI, 1.09-1.15) who switched to CBP, compared with continued vial use.

Conclusions: CBP of medication prescribed for daily, self-administered, long-term use was associated with modest improvement in prescription refill adherence and persistence. An adherence strategy of even small effect size that is broadly implemented on a population level could significantly leverage therapeutic effect and provide substantial cumulative public health benefit. Clinical benefit, or harm, associated with use of CBP should be investigated. Usability assessments of CBP in patient subgroups may provide insight about differential impact on adherence and persistence.