Brexpiprazole Treatment for Bipolar I Depression

The estimated lifetime prevalence of bipolar disorders is 0.55% for bipolar type I and 1.65% for bipolar type II. In the long term, patients with a bipolar disorder spend on average 60% of their time in depressive states, with intermittent hypomanic or manic phases. Moreover, the depressive episodes tend to become more frequent and difficult to treat as they grow in number and/or frequency. Many studies have demonstrated that even so-called stabilized bipolar patients will go through frequent subsyndromal depressive symptoms during a significant portion of any given year.

Bipolar depression is heavily loaded with general symptoms of psychomotor retardation, anergia, hypersomnolence, hyperphagia, decreased motivation, anhedonia and cognitive difficulties. All these functions are modulated by dopamine, and strategies aimed at improving dopaminergic function are frequently used to resolve residual symptoms of bipolar depression. Brexpiprazole is a new serotonin-dopamine antagonist which possesses unique capabilities with partial dopaminergic (D2) agonistic activities. Moreover, like other atypical agents, Brexpiprazole is a potent antagonist of the 5-HT2a receptor, as well as the adrenergic α1b and α2c receptors, and is a 5-HT1a post-synaptic agonist. These properties enable the molecule to provide antidepressant potentiating capabilities. While Brexpiprazole is currently recognized for its capacity to potentiate antidepressant effects in unipolar depression, there is still a need to evaluate the molecule's effect in bipolar depression.

Depressive symptoms and cognitive deficits are major determinants of functionality and quality of life in individuals with bipolar disorders. Cognitive problems tend to increase with the number of mood episodes, psychotic symptoms, and anxiety. Further, certain medications (and especially polypharmacy) can increase cognitive decline in the long term. As the average age of the patient population increases, risk for cognitive decline due to aging and prolonged medication use is of importance. From a neuroanatomical perspective, current neuroscience literature has related treatment with Aripiprazole to improved memory performance and structural changes in the hippocampus in patients at an early stage of psychosis. The chemically and pharmacologically related compound Brexpiprazole is thus a promising candidate for targeting both depressive symptoms and cognitive deficits observed in bipolar depression given its partial agonistic activity at the D2 receptor and, possibly, because of its 5-HT7 antagonistic activity.

Treatment of bipolar depression is further complicated by the knowledge that, in the long-term, use of antidepressants may be associated with manic/hypomanic switches, rapid cycling, and mixed features. These further increase the risk of cognitive decline and suicidality. In fact, the suicide rate in bipolar disorders is relatively high compared with other disorders, with certain studies reporting that up to 50% of bipolar patients will attempt suicide. Further, mortality is considerably higher among patients with bipolar disorders as compared to the general population given patients' high risk for diabetes and cardiovascular disorders (considerably increased by valproate and antipsychotic treatment). In the prevention of excess mortality, selection of first-line medications with a smaller effect on weight is essential.

Further, an interesting new phenotype for the personalized treatment of bipolar disorders is dysregulated biological rhythms (i.e., sleeping and eating patterns). This is a core etiopathological feature of bipolar disorders, and has been associated with obesity, cancer, and accelerated mortality in the general population. It has been previously shown that a majority of patients with bipolar disorders show a specific pattern of disorganized activity rhythm that is associated with treatment resistance, mood lability and obesity. It was recently reported that Aripiprazole can correct this type of disorganized rhythm. Based on an animal model, this effect is linked to dopaminergic activity. It is expected that Brexpiprazole will have a similar effect. This is supported by a recent sleep study of Brexpiprazole in treatment-resistant major depressive disorder that found an improvement of most sleep parameters in addition to decreasing daytime sleepiness and improving mood symptoms.

In addition, insulin resistance is shown to be one of the most robust predictors of a more chronic course of bipolar disorder. C-reactive protein (CRP) was shown to be two times greater in patients with insulin resistance compared to those without. Higher CRP is thus considered to be a predictor of treatment-resistance and cardiovascular risk in this clinical population. Most importantly, treatment response has been associated with decreasing CRP, decreasing insulin resistance, and decreasing depressive symptoms. As such, treatment-resistant bipolar depression can be viewed as a metabolic mood syndrome that is associated with a cognitive decline.

Taken together, there is a need to improve the repertoire of treatments for bipolar depression. One would favor strategies that procure a rapid onset of action as well as a low risk of switching to hypomania and weight gain. Finally, one would favor strategies that would procure relief for the most frequent and persistent symptoms of bipolar depression, such as psychomotor retardation, cognitive deficits, and reversed neurovegetative symptoms. Thus, the current study will evaluate the efficacy and tolerability of an adjunctive, variable dose of Brexpiprazole treatment in bipolar depression.