Many adults who experience major depressive disorder (MDD) late in life do not respond well to treatment with antidepressants, a new study has found.

Investigators tracked the incidence of treatment resistance in more than 27,000 patients using the Taiwan National Health Insurance Research Database. Patients, aged 65 years and older, and were followed during the first year after an MDD diagnosis. 

The researchers also looked at the potential effects of physical and psychiatric comorbidities on treatment for depression. Fully 17% of the patients studied had a diagnosis of an anxiety disorder, 1.5% had alcohol use disorders, and 1.6% had a substance use disorder. Most patients had at least some physical comorbidities based on measures from the Charlson Comorbidity Index.

About one fifth of the patients did not respond to the first antidepressant treatment during the study period. This treatment-resistant tendency was associated with anxiety disorders and higher comorbidity scores, the investigators reported. In addition, 1.6% of the patients developed treatment-resistant depression. This outcome was linked to anxiety, substance use disorders and high comorbidity scores. 

The results could serve as a reminder to clinicians to be aware of possible psychiatric comorbidities among seniors — particularly anxiety and substance use disorders — when reporting poor treatment response to antidepressants in such cases, the authors concluded.

There are varied estimates of how many nursing home residents have a diagnosis of depression, ranging from under 10% according to the Minimum Data Set to nearly 50% in other analyses. 

The study was published in the Journal of Clinical Psychiatry.

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