Patterns of Glaucoma Medication Adherence over Four Years of Follow-Up

Abstract

Purpose: To assess longer-term patterns of glaucoma medication adherence and identify whether patterns established during the first year of medication use persist during 3 subsequent years of follow-up.

Design: Retrospective, longitudinal cohort analysis.

Participants: Beneficiaries aged ≥40 years who were enrolled in a United States (US)-managed care plan for ≥7 years between 2001 and 2012 and newly diagnosed and treated for open-angle glaucoma.

Methods: For each enrollee, we quantified medication adherence using the medication possession ratio. Group-based trajectory modeling (GBTM) was applied to identify patterns of adherence for 1 and 4 years of follow-up. The percent of beneficiaries who remained in the same trajectory group in the 1- and 4-year models was tabulated to evaluate group stability. Factors impacting adherence at 1 and 4 years were identified using regression analyses.

Main outcome measures: Patterns of glaucoma medication adherence.

Results: Of the 1234 eligible beneficiaries, GBTM identified 5 distinct glaucoma medication adherence patterns in both the 1-year and 4-year follow-up periods. These groups were as follows: (1) never adherent after their index prescription fill (7.5% and 15.6% of persons in the 1- and 4-year models, respectively); (2) persistently very poor adherence (14.9% and 23.4% of persons in the 1- and 4-year models, respectively); (3) declining adherence (9.5% and 9.1% of persons in the 1- and 4-year models, respectively); (4) persistently moderate adherence (48.1% and 37.0% of persons in the 1- and 4-year models, respectively); and (5) persistently good adherence (20.0% and 15.0% of persons in the 1- and 4-year models, respectively). More than 90% of beneficiaries in the 4 groups with the worst and best adherence patterns (groups 1, 2, 3, 5) maintained their patterns from their first year throughout their 4 years of follow-up. Those with persistently moderate adherence (group 4), the largest group, were most likely to change groups from 1 to 4 years of follow-up. Persons with the best adherence over 4 years were more likely to be white, to be older, to earn >$60 000/year, and to have more eye care visits (P < 0.05 for all comparisons). Those with a higher initial copayment cost had lower adherence rates (β = -0.06/dollar, P = 0.03).

Conclusions: For most patients who were newly prescribed glaucoma medications, adherence patterns observed in the first year of treatment reflect adherence patterns over the subsequent 3 years. Investing resources in both identifying and helping patients with suboptimal adherence patterns over the first year may have a large impact on longer-term adherence.

Figure 1

Selection of beneficiaries for analysis. Abbreviations: OAG, Open-Angle Glaucoma

Figure 2

a. Group Based Trajectory Models^a Demonstrating Patterns of Glaucoma Medication Adherence Over One Year of Follow-up b. Group Based Trajectory Models^a Demonstrating Patterns of Glaucoma Medication Adherence Over Four Years of Follow-up The Medication Possession Ratio is the number of days the patient had the correct amount of medication in-hand divided by the total number of days of follow-up.

Figure 3

Trajectory Group Stability Over Four Years of Follow-Up This graph describes the movement of participants between trajectory groups from one year of follow-up to four years of follow-up. The numbers noted on the y axis (and specified above each bar) denote the total number of persons in each trajectory group during the first year. The shaded portions of each bar identify the percent of participants who changed to any of the five different trajectory groups when analyzed over four years of follow-up.