Plasma ratio of clozapine to N-desmethylclozapine can predict cognitive performance in treatment-resistant psychotic patients.

Cognitive symptoms play a central role in schizophrenia and are strongly associated with social functioning. Treatment with clozapine presents controversial results regarding its effects on cognition. The opposite effects of clozapine and n-desmethylclozapine (NDMC) on cholinergic system have been suggested to underlie these inconclusive findings. The aim of this study is to determine whether clozapine/NDMC ratio can predict cognitive performance in patients with treatment-resistant psychosis. Nineteen clinically stable patients with schizophrenia or schizoaffective disorder treated with clozapine monotherapy completed demographic and clinical interviews. For the purpose of the study, patients were assessed with a neuropsychological battery and on the same day a blood sampling was obtained from each patient to measure plasma levels of clozapine and NDMC. Our results showed that clozapine/NDMC ratio, but not clozapine or NDMC plasma levels separately, was a predictive factor of cognitive performance, specifically of executive functioning. Our results showed that lower clozapine/NDMC ratios are associated with better executive functioning in clinically stable patients. These findings could be interpreted by the different pharmacodynamic properties on cholinergic, dopaminergic and serotonergic systems of NDMC compared to clozapine.

Altered amplitude of low frequency fluctuations in schizophrenia patients with persistent auditory verbal hallucinations.

The aim of this study is to analyze the differences in low frequency fluctuation (LFF) values between schizophrenia patients with and without auditory verbal hallucinations (AVH). Nineteen schizophrenia patients with persistent AVH (HP), fourteen non-hallucinating schizophrenia patients (nHP) and twenty healthy controls (HC) underwent R-fMRI. LFF values were calculated in the slow frequency band (0.01-0.08Hz). By means of group level contrasts, we performed direct voxel-wise group comparisons. Both groups of patients showed decreased amplitude LFF (ALFF) values in the occipital pole and lingual gyrus compared to HC, whereas increased ALFF values were found in the temporal pole and fusifom gyrus. Schizophrenia patients exhibited decreased fractional ALFF (fALFF) values in the precuneus, occipital pole and bilateral occipital cortex, and increased fALFF in the insula compared to HC. There were also differences between patients with and without AVH. (Ok to start with lower case?) fALFF values were higher in the putamen and insular cortex and lower in the frontal pole in HP compared to nHP and HC. ALFF increased in HP patients in the bilateral thalamus and bilateral parahippocampal gyrus, compared to nHP patients and HC. Our results suggest that altered dynamics in low-frequency fluctuations may play a key role in the neurophysiology of auditory hallucinations.