OBJECTIVE: This study investigated which comorbidities or comedications increased the probability of receiving quetiapine extended release formulation (quetiapine XR) as an add-on treatment.

METHODS: Danish administrative registers were used as data sources. The study period was from January 1, 2011 to July 1, 2017. New users of Selective Serotonin Reuptake Inhibitors (SSRI), Serotonin and Norepinephrine Reuptake Inhibitors (SNRI), Atypical Antidepressants (AAD) and Tricyclic Antidepressants (TCA) aged ≥65 years were included in the study population. A multivariable Cox regression model was used to find predictors for receiving quetiapine XR add-on within the first year of antidepressant therapy.

RESULTS: 123 655 new users of SSRI, SNRI, TCA and AAD were eligible. The study population was composed of 57.7% females and the mean age was 77.2 years (SD 7.9 years). SSRIs users comprised 49.6% of the study population. Among users of antidepressants, 171 (0.14%) patients received quetiapine XR as add-on treatment. In the adjusted analyses, female patients (HR 0.70; 95%CI 0.52-0.95) and glucocorticoid users (HR 0.41; 95%CI 0.21-0.80) had a significantly lower hazard of receiving quetiapine XR. Patients with dementia (HR 2.43; 95%CI 1.52-3.87) had a significantly higher hazard of receiving quetiapine XR than patients without this condition. When compared to SSRI users, AAD (HR 1.80; 95%CI 1.31-2.46) and TCA users (HR 0.18; 95%CI 0.06-0.49) had an increased/reduced hazard of receiving quetiapine XR, respectively.

CONCLUSIONS: This study suggests that the choice of prescribing quetiapine add-on is driven by patient's differences in comorbidities, comedications and the type of antidepressant drug.