Assessing Treatment-Resistant Depression with ECT

Patients were classified as having TRD if at least two subsequent pharmacological treatment trials for depression (a different Anatomic Therapeutic Chemical classification code, or an antidepressant add-on medication) were recorded in the PDR during the 2 years before ECT. To be considered adequate, a treatment trial needed to be at least 28 days long, reflecting a duration commonly required for antidepressants to have effect. The duration of each filled prescription was estimated from package size, dosage and prescription text. Add-on medications were defined as lithium, risperidone, olanzapine, aripiprazole and quetiapine, which are recommended for the treatment of TRD by guidelines.⁵ Patients not meeting criteria for TRD were classified as ‘non-TRD’. A validation study^{21 (link)} has shown that patients identified as TRD with this register-based method have similar characteristics as adaptations of clinical methods. In patients with depression, incidence rates of TRD as identified by register-based methods are similar in Swedish^{2 (link)} and Danish²² studies.
Additionally, we categorised exposure according to the number of pharmacological treatment trials before ECT, ranging from zero to five or more.