Background: Determining the proportion of patients with treatment-resistant depression (TRD) among patients with unipolar depression receiving adequate pharmacological treatment (pharmaceutically treated depression [PTD]) is clinically important and may affect health care utilization. In Taiwan, these issues can be assessed by analyzing population-based data. Methods: The present study included data from the Taiwan National Health Insurance Research Database from 2010 to 2017. Among patients with depression, PTD was defined by the receipt of at least one adequate antidepressant treatment, and TRD was defined as receiving a third adequate antidepressant treatment after failure to respond to two prior treatments. Time of progression from PTD to TRD was estimated via the Kaplan–Meier function. A propensity-matched case–comparison cohort approach was used to compare resource utilization between patients with non-TRD PTD and TRD. Results: TRD was defined in 11.2 % of patients with unipolar depression and 37.1 % of PTD patients. The time of progression from PTD to TRD was approximately 1 year. Most TRD patients were women, middle-aged, and treated in general practice clinics. Antidepressant monotherapy, followed by antidepressant with augmentation, was the most common treatment strategy applied to TRD patients. Medical utilization was significantly higher in patients with TRD than those with non-TRD PTD across most aspects. Limitations: TRD was defined based on pharmacological treatment patterns, as the reasons for changes in antidepressant regimens were not available. Conclusion: Approximately one-third of patients with PTD developed TRD, often soon after receiving adequate pharmacological treatment. Patients with TRD used more medical resources than patients with non-TRD PTD.
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