Background: Antidepressant nonadherence is a significant threat to clinical outcomes and can be divided into 2 primary domains, persistence and consistency. Although antidepressant persistence has been well described, little is known about consistency patterns.
Objectives: The primary objective of this study was to characterize consistency among persistent antidepressant users. Patients with depression may also exhibit poor adherence to medications for chronic comorbid conditions. Thus, a second objective was to compare their consistency with chronic, nonpsychiatric medications with that of nonantidepressant users.
Methods: Continuously eligible adult patients were selected from the Iowa Medicaid Pharmaceutical Case Management program based on receiving an antidepressant or a selected chronic nonpsychiatric medication for at least the first 4 months after program enrollment. Consistency over the first year of enrollment was determined from prescription refill patterns, using the MED-OUT index.
Results: The mean consistency rate was 86% among the 1122 persistent antidepressant users. Consistency was not significantly different among polyantidepressant users or across the antidepressant classes. Among antidepressant users, consistency with antidepressants was not significantly different from consistency with chronic nonpsychiatric medications. Antidepressant users were not significantly less consistent with chronic nonpsychiatric medications than nonantidepressant users, after controlling for the confounding factors of age, sex, and total number of medications.
Conclusions: Consistency with medications in this population of persistent antidepressant users with medical illnesses was fairly good, and comparable to that of nonantidepressant users. The unique population may have influenced consistency rates. Focusing on persistent antidepressant users may have limited the expected impact of depression on medication consistency.