Factors associated with initial medication adherence with first-line therapy for depression.

Background: Despite the well-documented efficacy and long-term adherence, little is known about the initial medication adherence (IMA) to antidepressant medications in the acute phase of therapy in Major Depressive Disorder (MDD). This study investigated the factors associated with optimal IMA among patients with MDD.

Methods: This retrospective cohort study used 2017-2019 Merative MarketScan Data, focusing on adults (≥18 years) with MDD initiating selective serotonin reuptake inhibitors or serotonin-norepinephrine reuptake inhibitors. Optimal IMA was defined as the proportion of days covered (PDC) ≥80 % within the first three months after initiation. Multivariable logistic regression was used to examine the factors associated with optimal IMA.

Results: The study cohort consisted of 397,976 MDD patients initiating antidepressant therapy, and 60.71 % of them achieved optimal IMA. Logistic regression found that medications such as patients using escitalopram (adjusted Odds Ratio [aOR]: 1.04), fluoxetine (aOR: 1.11), venlafaxine (aOR: 1.05), and levomilnacipran (aOR: 1.58) had higher odds of optimal IMA, while those on paroxetine (aOR: 0.88) and desvenlafaxine (aOR: 0.96) had lower odds. The other significant patient characteristics were age, sex, region, year, employment status, year, and number of medications. The comorbidities that influenced optimal IMA were hypertension, obesity, hyperlipidemia, Crohn's disease, psoriasis, arthritis, human immunodeficiency virus/acquired immunodeficiency syndrome, backache, and substance use disorder.

Conclusions: About 61 % of the MDD patients had optimal IMA with significant variation in IMA across antidepressant agents, in addition to other patients' characteristics. Findings highlight the importance of IMA and the need for targeted interventions to achieve optimal IMA.