Background: There is evidence that blockade of 5-HT 6 receptors can improve cognitive dysfunction in schizophrenic patients. A number of antagonists of 5-HT6 receptors are in development as cognitive enhancers. One of the agents with relatively strong 5-HT6 activity is dimebon. We tested the hypothesis that this 5-HT6 antagonist administered in the early stage of stabilization after an acute episode can improve both neurocognitive and clinical symptoms in schizophrenia. A phase II study of dimebon as add-on to risperidone therapy was conducted.
Subjects and methods: 56 male subjects with paranoid schizophrenia were included in the study. All the patients demonstrated therapeutic response to risperidone as treatment of the acute psychotic episode. After 4 weeks of stability patients were randomized into two groups with placebo or dimebon add-on treatment in a 1 to 1 ratio for 8 weeks. PANSS, CGI-S, CSDS and NSA-16 were used as clinical measures of symptom severity. Different aspects of memory, psycho-motor coordination and executive functioning were assessed with a battery of cognitive tests. Clinical and cognitive assessment was performed twice: after a patient was randomized and 2 months later.
Results: Severity of negative symptoms (by NSA-16) were significantly lower in the dimebon group then in the placebo group (p=0.036). Patients in the dimebon group demonstrated improvement in more cognitive dimensions than patients in the placebo group, including working memory, attention, psycho-motor coordination and planning.
Conclusion: Dimebon as add-on therapy to antipsychotic treatment in the period of stabilization after an acute episode can improve some aspects of clinical and cognitive status in schizophrenic patients.