Adherence to antidepressants among women and men described with trajectory models: a Swedish longitudinal study

The purpose of this study are to analyse adherence to antidepressant treatment over 2 years in Sweden among women and men who initiated treatment with citalopram and to identify groups at risk of non-adherence using trajectory models.

The study population, including individuals 18-85 years who initiated citalopram use between 1 July 2006 and 30 June 2007, was identified in the Swedish Prescribed Drug Register and followed for 2 years. Adherence was estimated with continuous measure of medication acquisition (CMA) and group-based trajectory modelling, a method which describes adherence patterns over time by estimating trajectories of adherence and the individual's probability of belonging to a specific trajectory.

The study population included 54,248 individuals, 64 % women. Mean CMA was 52 % among women and 50 % among men (p < 0.001). Five different adherence patterns (Trajectories) were identified. Similar proportion of women and men belonged to each Trajectory. Around 29 % of the women and 27 % of the men belonged to the Trajectory which showed full adherence throughout the 2-year study period. The other four Trajectories showed adherence that declined to different degrees and at different stages in time. Having low socioeconomic status was more common among individuals in Trajectories showing declining adherence than in the adherent Trajectory.

Using trajectory modelling, five Trajectories describing different patterns of adherence to citalopram treatment over time were identified. A large proportion discontinued treatment early and having low socioeconomic status increased the risk of being non-adherent.