Applications of trajectory methods in medication adherence research: A decade in review and a look ahead

Background: Poor adherence to medication significantly impacts health outcomes. Adherence has historically been measured using proportion of days covered (PDC) or medication possession ratio (MPR) metrics. However, these composite metrics can oversimplify adherence, failing to capture its dynamic nature. Longitudinal methods, such as group-based trajectory modeling (GBTM), offer nuanced analysis by identifying medication use patterns over time, which is thought to improve upon traditional composite measures. Despite its growing popularity and application within the adherence community at ISPE, considerations for measurement and application warrant further discussion and consensus. This approach was first applied about ten years ago to improve the detection of adherence and offered some advantages over composite adherence measures.

Objectives: To review the use and challenges of trajectory methods in pharmacoepidemiologic studies of adherence, with example applications.

Description: In the past decade, GBTM has increased in popularity and is now commonly used in the pharmacoepidemiology adherence community. Even though calculating adherence via longitudinal methods is an area of increasing interest and importance, consensus on the most optional approaches for its application and potential use cases have not been fully achieved. There may also be important differences across conditions or settings that are worthy of consideration.

As a research community, it will be helpful to facilitate a discussion around methods of measuring adherence to medication using longitudinal approaches. This symposium will focus on concepts behind GBTM, applications of the method across different disease states, and how they might compare with other approaches. The target audience is adherence and drug utilization researchers, and other researchers who wish to gain an insight into using different analytic methods for adherence and utilization research, especially GBTM.

Description of symposium:
1. Welcome and background of the session – Julie Lauffenburger
2. Overview of GBTM and its strengths and limitations – Jessica Franklin
3. GBTM case example 1: Using trajectories to study oral isotretinoin adherence – Cécile Payet
4. GBTM case example 2: Using trajectories to study substance use disorder medication use – Marissa Seamans
5. GBTM case example 3: Applying adherence trajectories to studies of outcomes – Julie Lauffenburger
6. Example of an alternative approach to trajectory modeling (latent variable framework) – Chao Cai
7. Panel discussion/audience feedback, including questions from the audience – Moderators (Ellen Loh and Julie Lauffenburger)