Switching From SSRI to Desvenlafaxine on Cognitive Functioning

BACKGROUND Depression is a significant contributor to the global burden of disease and affects people in all communities across the world. Today, depression is estimated to affect 350 million people. The World Mental Health Survey conducted in 17 countries found that, on average, about 1 in 20 people reported having an episode of depression in the previous year. Depressive disorders often start at a young age; drastically reduce people's functioning and often are recurring. For all these reasons, depression is the leading cause of disability worldwide in terms of total years lost due to disability. Commonly the diagnosis and treatment of major depressive disorder is based on mood symptoms. However, cognitive impairments are often present in this disorder. In this respect, the recent Diagnostic and Statistical Manual 5 (DSM-5) highlight impairment in cognitive function as a criterion in the diagnosis of a major depressive episode (MDE) (American Psychiatric Association. At clinical level, patients frequently present subjective complaints during and after resolution of an MDE. Moreover, objective deficits measured by neuropsychological tests are also reported in different cognitive domains in cold cognitive function - executive function, processing speed, attention, learning or memory- (Hammar \&Ardal, 2009) or also in hot cognitive function -negative biases in perception, attention and memory, and aberrant reward/punishment processing-. Different meta-analyses have demonstrated that these deficits may emerge from the first depressive episode with relevant intensification during each acute MDE persisting in some depressive patients even during the resolution of the acute episode. These deficits, both in an acute episode and in remission, have a relevant impact on clinical and functional outcomes, in the first case by reducing the chance to fully recover and in the second by increasing the risk of relapse. Moreover, cognitive deficits have shown to have a negative influence in functional performance in academic, social and working life (Lee et al., 2013,). In this context, recent studies have shown that a larger number of MDD episodes, a longer duration of illness and a poor response to antidepressant treatments might explain the maintenance of cognitive dysfunction, even in patients with some clinical response. Persistent cognitive deficits in depression play a crucial role in some patients׳ ability to achieve a functional recovery. With this respect, cognitive function in depression is significantly also related to employment status. A preliminary study suggests that deficits in executive functioning have a mediating effect on the relationship between depression and impaired activities of daily living. Moreover, mood disorder patients with neuropsychological deficits tend to be less compliant with antidepressant treatment (Martinez-Aran et al., 2009) and show an increased risk for suicide. In this context, the identification and treatment of specific cognitive deficits may be a cardinal aspect in the achievement of depression recovery and, even more important, in the functional normalization of patients to their pre-morbid levels. At present there is a growing interest on the role of antidepressant treatment in the modulation of cognitive deficits associated with depression. Despite the wide array of effective antidepressant agents, the knowledge on the impact of available drugs on cognitive function constitutes a relevant unmet need. Indeed, the number of studies focusing on this issue is relatively scarce and the outcome of cognitive symptoms is widely variable. Potential pro-cognitive effect of a particular antidepressant mostly relay on its specific mechanisms of action, anf in the last years the evidence accumulated have support that drug involving more targets such as dual (duloxetine) or multimodal (vortioxetine) antidepressants show more pro-cognitive properties than those with one major mechanism (SSRI). However, the clinical studies putting cognitive dysfunction as the primary outcome in depression trials are scarce and further support of these initial promising findings of the effects of dual/multimodal antidepressants on cognition are required. OBJECTIVES This open-label clinical study will evaluate the clinical outcome of switching to desvenlafaxine on cognitive function of patients with major depressive disorder with inadequate response to selective serotonin reuptake inhibitor (SSRI) \* Primary Objective To study differences in cognitive function in moderate to severe MDD patients with inadequate response to SSRI and healthy controls at baseline and after 12 weeks of treatment with desvenlafaxine. \* Secondary Objective To study differences in subjective cognitive function (cognitive complains), measured by PDQ-5 at baseline and after 12 weeks of treatment with Desvenlafaxine. To study differences in cognitive function, measured by neuropsychological tests battery (including cold and hot cognitive function) at baseline and after 12 weeks of treatment with desvenlafaxine. To study differences in depression severity, measured HDRS-17 and CGI at baseline and after 12 weeks of treatment with desvenlafaxine. To study changes in subjective remission and functional status measured with Remission Depression Questionnaire (RDQ) and the Short Assessement Functioning Test (FAST), respectively.