To analyse the healthcare resource consumption and related costs for the Italian National Health System of patients estimated to be affected by treatment-resistant depression (TRD) in Italy. Patients and Methods: This was an observational retrospective study based on administrative databases, including those related to residential/semiresidential structures, of Veneto Region and the Local Health Unit of Bergamo in Italy (for a total of around 6 million healthassisted subjects). Between July 2011 and December 2017, all adult patients with a third antidepressant (AD) after ≥2 AD (each one with at least ≥4 weeks duration, ≥1 prescription at maximum dosage reported in datasheets, a grace period ≤30 days when switching AD and treatment maintained ≥9 months) were included. Overall and psychiatry-related healthcare resources consumption and related costs were estimated on a 12-months based analysis. Data were re-proportioned to the Italian population. Results: We have previously estimated a total of 101,455 patients with TRD in Italy (130,049 considering the mean maximum dosage of AD). Of them, 44.2% had at least a psychiatric hospitalization/visit or accessed a residential/semiresidential structure, and 31% added another AD or a mood stabilizer/antipsychotic drug. Patients with at least one psychiatryrelated hospitalization increased over the number of antidepressant lines from 12.0% during first line up to 24.5% during fourth line. Direct healthcare costs increased from €4,405 for first line to €9,251 from fifth line onwards. Psychiatry-related costs went from €1,817 (first line) to €4,606 (fifth line onwards) and were mainly driven by residential/semiresidential structures and hospitalizations. Conclusion:An upward trend with number of AD lines was observed for all healthcare resource utilization and consequently for all direct costs, thus indicating an increasing burden for patients as they move forward AD lines.

The study aims to estimate the number of patients affected by treatment-resistant depression (TRD) in Italy, and to analyse the therapeutic pathways and drug utilization in real-world settings. This retrospective study is based on administrative databases of Italian Entities. Data were re-proportioned on the Italian population. Adult patients were included from July 2011 to December 2017 if they underwent ≥2 antidepressant (AD) cycles matching the following criteria: i) duration of ≥4 weeks for each cycle; ii) presence of ≥1 prescription for each AD at the maximum dosage