Changes in symptoms of anhedonia in adults with major depressive or bipolar disorder receiving IV ketamine: Results from the Canadian Rapid Treatment Center of Excellence.

<bold>Background: </bold>Anhedonia is a trans-diagnostic, multidimensional phenotype that mediates patient outcomes and suicidality. Convergent evidence suggests that ketamine may be effective in targeting measures of anhedonia in adults with treatment resistant depression (TRD).<bold>Methods: </bold>This retrospective, post-hoc analysis included 203 (x̄ = 45 ± 14.6 years of age) patients receiving four infusions of intravenous (IV) ketamine at a community-based clinic. The primary outcome measure was change in anhedonia severity, as measured by the Snaith-Hamilton Pleasure Scale (SHAPS). Secondary measures sought to determine if improvement on the SHAPS mediated the effect of repeated IV ketamine infusions on symptoms of depression and suicidal ideations, as measured by the Quick Inventory for Depression Symptomatology-Self Report 16-Item (QIDS-SR16) and anxiety, as measured using the Generalized Anxiety Disorder-7 (GAD-7).<bold>Results: </bold>After adjusting for age, sex, primary diagnosis, concomitant medication, body mass index, and baseline depression severity, there was a statistically significant reduction in symptoms of anhedonia with IV ketamine treatment (F (2, 235.6) = 31.6, p < 0.001). Improvements in depressive symptoms, suicidal ideation, and anxiety symptoms with repeated-dose IV ketamine were significantly partially mediated by reduction in anhedonic severity. Moreover, the combination of number of infusions received and change in anhedonic severity accounted for 26% of the variance in depressive score improvements.<bold>Limitations: </bold>This is a post-hoc analysis of retrospective data and lacks a control group.<bold>Conclusion: </bold>Ketamine was effective in improving measures of anhedonia in this large, well-characterized community-based sample of adults with TRD. Improvements in anhedonia also partially mediated the significant improvement in depressive symptoms, suicidality, and anxiety. [ABSTRACT FROM AUTHOR]