Barriers to long-acting injectable atypical antipsychotic use in Japan: Insights from a comparative psychiatrist survey.

AIMS: To investigate the negative attitudes of Japanese psychiatrists toward atypical long-acting injectable (LAI) antipsychotics, which are the current mainstream LAIs in Japan. METHODS: We surveyed 69 Japanese psychiatrists using a 5-point Likert scale to assess their attitudes toward atypical LAI antipsychotics. Our assessment referenced concerns identified in a study conducted in Japan a decade ago, which found significant differences when compared with a survey of German psychiatrists. We also identified the factors influencing these negative attitudes. Additionally, the results were compared with those of previous Japanese and German studies. RESULTS: More than 50% of Japanese psychiatrists expressed negative attitudes toward atypical LAI antipsychotics in various areas. These concerns included apprehensions about cost, reluctance to recommend them initially, pain from injections, complexity of switching to LAI, usage in first-episode cases, and sufficient medication adherence with oral drugs. In all three studies, cost and adequate adherence to oral medication were concerns that exceeded the average of the three negative comments. Age and experience in psychiatry influenced the psychiatrists' attitudes toward using these drugs in first-episode cases. CONCLUSIONS: These findings shed light on the reasons for the underutilization of atypical LAI antipsychotics and suggest opportunities to enhance their appropriate use in clinical settings.

Long-acting injectable antipsychotics as maintenance therapy for schizophrenia during the COVID-19 pandemic: A micro-narrative review.

The coronavirus disease pandemic has presented healthcare systems with unprecedented challenges globally and substantially impacted the management of chronic diseases such as schizophrenia. This narrative review highlights the usefulness of long-acting injectable antipsychotics (LAIs) as maintenance therapy for patients with schizophrenia during the pandemic. The analysis of relevant literature and psychiatric survey data revealed diverse trends in LAIs prescription and patient adherence with oral antipsychotics. Although some studies have reported a decrease in LAIs prescriptions owing to pandemic-related disruptions, others have suggested stable patient adherence with oral antipsychotics. Approximately 70% of Japanese psychiatrists reported an increase in schizophrenia relapse rates in a survey, underscoring the critical role of LAIs in maintaining therapeutic stability. The potential benefits of LAIs with extended dosing intervals have been highlighted, including improving oral medication adherence and reducing the frequency of hospital visits. In conclusion, this review emphasizes the continued need for uninterrupted LAIs therapy in conjunction with community and home-based care despite the disruptions caused by the coronavirus disease pandemic. Further development of LAIs maintenance therapy strategies considering the ongoing pandemic and potential future public health emergencies are required.

Newer antidepressant for Japanese adults with major depressive disorder: A systematic review and meta-analysis.

INTRODUCTION: The question remains to be elucidated: "Is treatment with antidepressants at doses approved in Japan effective for Japanese patients with MDD?" It is crucial to confirm this in order to provide appropriate treatments for Japanese patients with major depressive disorder (MDD). Therefore, we conducted a systematic review and random-effects pairwise meta-analysis including these nine double-blind, randomized, placebo-controlled trials. METHODS: We calculated the standardized mean difference (SMD) and risk ratio (RR) with a 95% confidence interval (95% CI). RESULTS: Pooled newer antidepressants outperformed placebo regarding improvement of depressive symptom scale scores [SMD (95% CI) = -0.20 (-0.27, -0.12), p < 0.00001], response to treatment [RR (95% CI) = 1.23 (1.13, 1.32), p < 0.00001], and remission rate [RR (95% CI) = 1.30 (1.16, 1.45), p < 0.00001]. Although all-cause discontinuation was not significantly different between the treatment groups, the pooled antidepressant group showed a higher discontinuation rate due to adverse event [RR (95% CI) = 1.60 (1.13, 2.26), p = 0.007] and a higher incidence of at least one adverse event than the placebo group [RR (95% CI) = 1.13 (1.08, 1.18), p < 0.00001]. DISCUSSION: We concluded that newer antidepressants are effective for Japanese adults with MDD although the clinicians must monitor the health conditions of these individuals.

Effects of a conventional mood stabilizer alone or in combination with second-generation antipsychotics on recurrence rate and discontinuation rate in bipolar I disorder in the maintenance phase: A systematic review and meta-analysis of randomized, placebo-controlled trials.

OBJECTIVES: A systematic review and meta-analysis of double-blind, randomized placebo-controlled trials were conducted to examine how soon an increase in recurrence risk could be observed among bipolar I disorder (BDI) patients who were clinically stable with the combination therapy of mood stabilizers with second-generation antipsychotics (SGA+MS) treatment following second-generation antipsychotics discontinuation (i.e., MS alone) compared with SGA+MS maintenance. METHODS: Embase, PubMed, and CENTRAL databases were used for systematic literature searches until May/22/2020. The primary outcome was the recurrence rate of any mood episode at 6 months. The secondary outcomes were the recurrence rates of manic/hypomanic/mixed and depressive episodes and all-cause discontinuation at 6 months. The recurrence rates at 1, 2, 3, 9, and 12 months were also investigated. RESULTS: Eight studies (mean study duration = 58.25 ± 33.63 weeks) were identified (SGA+MS group [n = 1,456: 3 aripiprazole+MS studies, 1 lurasidone+MS study, 1 olanzapine+MS study, 2 quetiapine+MS studies, 1 ziprasidone+MS study] and placebo+MS group [n = 1,476]). Pooled SGA+MS exhibited lower recurrence rates of any mood episode, manic/hypomanic/mixed episodes, and depressive episodes as well as reduced all-cause discontinuation at every observational point. The risk ratios (95% confidence interval) of the recurrence rate at 6 months were 0.51 (0.39-0.86) for any mood episode, 0.42 (0.30-0.59) for manic/hypomanic/mixed episodes, and 0.39 (0.28-0.54) for depressive episodes. The RR for all-cause discontinuation was 0.67 (0.50-0.89). Both aripiprazole+MS and quetiapine+MS outperformed placebo+MS in the recurrence of any mood, manic/hypomanic/mixed, and depressive episodes at 6 months. CONCLUSIONS: SGA+MS prevented recurrence for up to 12 months for BDI compared with placebo+MS.

N-acetylcysteine as an adjunctive treatment for bipolar depression and major depressive disorder: a systematic review and meta-analysis of double-blind, randomized placebo-controlled trials.

RATIONALE: It remains unclear whether using N-acetylcysteine as an adjunctive treatment has any benefit for bipolar depression and major depressive disorder. OBJECTIVES: A systematic review and random-effect meta-analysis of double-blind, randomized placebo-controlled trials was conducted to explore the clinical question. METHODS: Outcomes included improvement in depression scale scores (primary), Young Mania Rating Scale score, Hamilton Anxiety Rating Scale score, Clinical Global Impression-Severity Scale (CGI-S) score, Global Assessment of Functioning Scale score, Social and Occupational Functioning Assessment Scale score, Range of Impaired Functioning Tool score, Streamed Longitudinal Interval Clinical Evaluation for the Longitudinal Interview Follow-Up Evaluation score, quality of life scales scores, and the incidence of all-cause discontinuation and individual adverse events. RESULTS: Seven studies (n = 728, 8-24 weeks, mean age = 46.81, % female = 58.45%) were included. N-acetylcysteine did not improve depressive symptoms compared with placebo (N = 7, n = 579, standardized mean difference (SMD) = - 0.12, 95% confidence interval (95% CI) = - 0.38, 0.14, p = 0.38, I2 = 52.74%). The meta-regression analysis detected an association between effect size and publication year (coefficient = 0.06, 95% CI = 0.00, 0.11, p = 0.04, I2 = 27.56%). Although N-acetylcysteine was superior to placebo in CGI-S score (N = 6, n = 563, SMD = - 0.28, 95% CI = - 0.47, - 0.10, p < 0.01, I2 = 14.88%), there was no significant difference in the other efficacy outcomes between the treatment groups. Although N-acetylcysteine was associated with a higher incidence of gastrointestinal adverse events compared with placebo (N = 4, n = 537, risk ratio = 1.79, 95% CI = 1.37, 2.32, p < 0.01, I2 = 0.00%, number needed to treat to harm = 7), there was no significant difference in all-cause discontinuation and other safety outcomes between the treatments. CONCLUSIONS: Although N-acetylcysteine decreased CGI-S score, no specific improvements in symptoms were identified.

Recurrence of Mania or Depression Among Adult Bipolar Patients Who Continued Using Lithium: A Single-group Summary Meta-analysis of Randomized Trials.

BACKGROUND: The exact recurrence rate of bipolar disorder in patients receiving lithium maintenance phase treatment and the modifiers associated with recurrence are still unknown. METHODS: We searched Embase, PubMed, and CENTRAL from inception until April 28, 2020. Outcomes included recurrence rate of any mood episode, depressive episodes, and manic/hypomanic/mixed episodes; all-cause discontinuation rate; and discontinuation rate due to adverse events. A random-effects model, single-group summary meta-analysis was conducted. A meta-regression analysis to examine whether the modifiers (total number of patients, %female, mean age, duration of study, duration of preliminary phase, publication year, bipolar disorder type, mood status at recruitment, presence of a placebo arm, sponsorship, enrichment design, number of treatment arms, and risk of bias for blinding or randomization) were associated with the event rate of the outcomes was also performed. RESULTS: We identified 21 randomized trials (n = 1,415; mean study duration, 78.40 ± 32.10 weeks; %female, 54.85%; mean age, 43.47 ± 4.88 years). The event rates (95% confidence interval [CI]) were as follows: recurrence of any mood episode, 39.8% (32.8%, 47.1%); depressive episodes, 25.6% (18.8%, 34.0%); manic/hypomanic/mixed episodes, 18.5% (13.7%, 24.7%); all-cause discontinuation rate, 67.0% (57.2%, 75.5%); and discontinuation rate due to adverse events, 8.7% (5.1%, 14.7%). After adjusting for multiple testing, our meta-regression analysis showed association only between the all-cause discontinuation rate and presence of a placebo arm. CONCLUSIONS: The recurrence rate of depressive episodes seemed to be higher than the recurrence rate of manic/hypomanic/mixed episodes. The all-cause discontinuation rate was high. However, the studies included in our meta-analysis were of short duration.

Efficacy and safety of lithium and lamotrigine for the maintenance treatment of clinically stable patients with bipolar disorder: A systematic review and meta-analysis of double-blind, randomized, placebo-controlled trials with an enrichment design.

AIM: Whether patients with adult bipolar disorder (BD) who have been clinically stabilized with lithium or lamotrigine should continue this medication is not established fully. This systematic review and meta-analysis evaluated the efficacy and safety of lithium and lamotrigine for maintenance treatment in clinically stable patients with adult BD. METHODS: This meta-analysis included only double-blind, randomized, placebo-controlled trials with an enrichment design that selected patients who responded acutely to lithium or lamotrigine. Reports prior to November 15, 2018, were retrieved from the PubMed/Cochrane Library/Embase. The primary outcome was the relapse rate due to any mood episode at the study endpoint. Other outcomes were relapse rates due to a manic/hypomanic/mixed episode or depression at the study endpoint, discontinuation rate, death, and death by suicide. Risk ratios (RRs) (95% confidence intervals) were calculated. When the random-effects model showed significant differences between groups, the number-needed-to-treat (NNT) was estimated. RESULTS: The search retrieved two studies regarding lithium (N = 218) and four evaluating lamotrigine (N = 706). Both drugs were superior to placebo for reducing the relapse rate due to any mood episode [lithium: RR = 0.52 (0.41-0.66), P < 0.00001, I2  = 0%, NNT = 2.3 (1.6-4.2); lamotrigine: RR = 0.81 (0.70-0.93), P = 0.004, I2  = 0%, NNT = 8.3 (5.0-25.0)] and all-cause discontinuation. There were no significant differences in other outcomes between lithium or lamotrigine and the placebo groups. CONCLUSION: Both drugs showed benefit for preventing relapse in clinically stable patients with adult BD. However, the number of studies and patients in this analysis was small.

Retraction: 'Effect of blonanserin on cognitive function in antipsychotic-naïve first-episode schizophrenia'.

The above article from Human Psychopharmacology, first published on 25 January 2012 in Wiley OnlineLibrary (onlinelibrary.wiley.com), and in Volume 90, pp. 90-100, has been retracted by agreement between the authors, the journal Editor in Chief, David Baldwin, and John Wiley & Sons Ltd. The retraction has been agreed following an investigation by the St Marianna University Ethics Committee which determined that the paper was not as originally designed and approved. REFERENCES: Tenjin, T., Miyamoto, S., Miyake, N., Ogino, S., Kitajima, R., Ojima, K., … Yamaguchi, N. (2012). Effect of blonanserin on cognitive function in antipsychotic-naïve first-episode schizophrenia. Hum. Psychopharmacol Clin Exp, 27, 90-100. https://doi.org/10.1002/hup.1276.

[Effectiveness of N-acetylcysteine in the treatment of schizophrenia].

Oxidative stress and neuroinflammation have recently been focused on the pathological hypotheses of schizophrenia. N-acetylcysteine (NAC) is a precursor of endogenous antioxidant glutathione and has antioxidant, anti-inflammatory, and neuroprotective properties. NAC is widely available as an over-the-counter nutritional supplement. Increasing lines of evidence suggest that NAC is effective for various mental disorders. In randomized controlled trials, treatment with NAC as an add-on to antipsychotics showed beneficial effects and safety profiles in patients with chronic schizophrenia. The results of a recent preclinical study using a neurodevelopmental model of schizophrenia suggest that NAC may have promising effects in an early stage of schizophrenia and an at-risk mental state. However, there is little clinical evidence for the efficacy and safety of NAC at these stages of schizophrenia. In this review, we summarize the evidence regarding the effectiveness of NAC for the treatment of schizophrenia and its prodromal stage. We also introduce the preliminary results of our research on NAC.

Long-term efficacy and safety of blonanserin in patients with first-episode schizophrenia: a 1-year open-label trial.

AIMS: The purpose of this study was to evaluate the long-term effectiveness and safety of blonanserin, a second-generation antipsychotic drug developed in Japan, in patients with first-episode schizophrenia. METHODS: Twenty-three antipsychotic-naïve patients with first-episode schizophrenia were treated within an open-label, 1-year, prospective trial of blonanserin (2-24 mg/day). Clinical evaluations were conducted at baseline and 2, 6, and 12 months after the start of treatment. The main outcome measures were changes in subjective well-being and subjective quality of life, as assessed by the Subjective Well-being under Neuroleptic treatment scale Short form-Japanese version and the Schizophrenia Quality of Life Scale-Japanese version, respectively. Secondary outcome measures included the Positive and Negative Syndrome Scale, the Brief Assessment of Cognition in Schizophrenia-Japanese version, laboratory tests, bodyweight, and extrapyramidal symptoms. RESULTS: Fourteen patients (60.9%) remained on the study at 1 year. In the intention-to-treat analysis, significant improvements were observed in several subscales on the Subjective Well-being under Neuroleptic treatment scale Short form-Japanese version, the Schizophrenia Quality of Life Scale-Japanese version, and the Brief Assessment of Cognition in Schizophrenia-Japanese version, and in all factor scores on the Positive and Negative Syndrome Scale. Improvement in depressive symptoms with blonanserin treatment was positively correlated with improvements in subjective well-being and subjective quality of life, as well as verbal memory. No significant changes were noted for any safety measure during the 1-year study period. CONCLUSIONS: Blonanserin was well tolerated and effective for the treatment of first-episode schizophrenia in terms of subjective wellness, cognition, and a wide range of pathological symptoms. Further large-scale studies are warranted to confirm our findings.

Benefits and limits of anticholinergic use in schizophrenia: focusing on its effect on cognitive function.

All currently available antipsychotic drugs are the dopamine D2 receptor antagonists and are capable of producing extrapyramidal side-effects (EPS). Anticholinergic drugs are primarily used to treat EPS or prevent EPS induced by antipsychotics in the treatment of psychosis and schizophrenia. However, they can cause a variety of distressing peripheral side-effects (e.g. dry mouth, urinary disturbances, and constipation) and central adverse effects (e.g. cognitive impairment, worsening of tardive dyskinesia, and delirium). Disturbances in cognitive abilities are cardinal features of schizophrenia from its earliest phases and account for much of the functional disability associated with the illness. It is likely that long-term concomitant administration of anticholinergics exacerbates the underlying cognitive impairment in patients with schizophrenia and subsequently affects patients' quality of life. Thus, current treatment guidelines for schizophrenia generally do not recommend the prophylactic and long-term use of anticholinergics. However, the high use of long-term anticholinergic drugs with antipsychotics has been identified as an important issue in the treatment of schizophrenia in several countries. To assess the benefits and limits of anticholinergic use in psychosis and schizophrenia, this article will provide a brief review of the pharmacology and clinical profiles of anticholinergic drugs and will focus on their effects on cognitive function in schizophrenia, particularly during the course of the early phase of the illness. In addition, we will address the effects of discontinuation of anticholinergics on cognitive function in patients with schizophrenia and provide a strategy for adjunctive anticholinergic use in patients treated with long-acting injectable antipsychotics.

Profile of blonanserin for the treatment of schizophrenia.

Blonanserin was developed as an antipsychotic drug in Japan and approved for the treatment of schizophrenia. It belongs to a series of 4-phenyl-2-(1-piperazinyl)pyridines and acts as an antagonist at dopamine D2, D3, and serotonin 5-HT2A receptors. Blonanserin has low affinity for 5-HT2C, adrenergic α1, histamine H1, and muscarinic M1 receptors, but displays relatively high affinity for 5-HT6 receptors. In several short-term double-blind clinical trials, blonanserin had equal efficacy as haloperidol and risperidone for positive symptoms in patients with chronic schizophrenia and was also superior to haloperidol for improving negative symptoms. Blonanserin is generally well tolerated and has a low propensity to cause metabolic side effects and prolactin elevation. We recently reported that blonanserin can improve some types of cognitive function associated with prefrontal cortical function in patients with first-episode and chronic schizophrenia. Taken together, these results suggest that blonanserin may be a promising candidate for a first-line antipsychotic for acute and maintenance therapy for schizophrenia. Further comparative studies are warranted to clarify the benefit/risk profile of blonanserin and its role in the treatment of schizophrenia.

New serotonin/dopamine antagonists for the treatment of schizophrenia: are we making real progress?

The introduction of second-generation antipsychotics (SGAs), heralded by clozapine in 1990, represented an important advance in the pharmacologic treatment of schizophrenia. However, several recent comparative effectiveness trials found that non-clozapine SGAs provided little or no advantage in efficacy over first-generation antipsychotics, and all agents had substantial safety and tolerability concerns. Clearly, there remains a great unmet need for more effective and better-tolerated antipsychotics. Relatively potent antagonism of serotonin 5-HT2A receptors coupled with relatively weaker antagonism of dopamine D2 receptors is the central pharmacological characteristic shared by most SGAs. This profile continues to be a favored model for developing new SGAs, commonly defined as serotonin/dopamine antagonists. In the past ten years, aripiprazole, paliperidone, asenapine, iloperidone, and lurasidone have been introduced. Studies suggest that the newer agents have similar short-term efficacy to earlier serotonin/dopamine antagonists, and several demonstrate at least modest improvements in safety and tolerability profiles, particularly metabolic measures. However, as a group, the newer serotonin/dopamine antagonists are pharmacologically heterogeneous, and their side-effect burden can still be considerable. Moreover, their putative clinical advantages have not yet been well demonstrated via direct comparative studies. The absence of such evidence adds to the challenges in defining their place among more established treatment choices, or in providing clinicians with clear indications to guide treatment choices for individual patients. Long-term, head-to-head comparative studies are required to clarify the risk/benefit profiles of the newer antipsychotics and their roles in the treatment of schizophrenia.

Effect of blonanserin on cognitive function in antipsychotic-naïve first-episode schizophrenia.

OBJECTIVE: The purpose of this study was to evaluate the effects of blonanserin, a novel antipsychotic, on cognitive function in first-episode schizophrenia. METHODS: Twenty-four antipsychotic-naïve patients with first-episode schizophrenia participated in the study. Blonanserin was given in an open-label design for 8 weeks. The Brief Assessment of Cognition in Schizophrenia-Japanese language version (BACS-J) was administered as the primary outcome measure at baseline and 8 weeks. Clinical evaluation included the Positive and Negative Syndrome Scale (PANSS), the Schizophrenia Quality of Life Scale-Japanese language version (SQLS-J), and the Clinical Global Impression-Severity of Illness Scale (CGI-S). To exclude the possibility of retest effects on the BACS-J, 10 age-matched patients with chronic schizophrenia treated with blonanserin were tested at baseline and after an 8-week interval. RESULTS: Twenty first-episode patients completed the study. Repeated measures analysis of covariance revealed a significant group-by-time interaction effect on the letter fluency task due to better performance in the first-episode group, but not in the control group. Main effect of time or group-by-time interaction effect on the Tower of London task was not significant; however, the first-episode group, but not the control group, showed substantial improvement with a moderate effect size. All items on the PANSS, SQLS-J, and CGI-S significantly improved after 8 weeks of treatment. CONCLUSIONS: These results suggest that blonanserin improves some types of cognitive function associated with prefrontal cortical function.

Effects of tapering of long-term benzodiazepines on cognitive function in patients with schizophrenia receiving a second-generation antipsychotic.

BACKGROUND: The high use of long-term benzodiazepines (BZDs) with second-generation antipsychotics (SGAs) has been identified as an important issue in the treatment of schizophrenia in Japan. The aim of this study was to evaluate the effects of gradual reduction or discontinuation of daytime BZD use on cognitive function and quality of life (QOL) in patients with chronic schizophrenia receiving an SGA. METHODS: Thirty schizophrenic patients who had received an SGA with concomitant BZDs for at least 3 months were enrolled. Before and 4 weeks after tapering of daytime BZDs, the Brief Assessment of Cognition in Schizophrenia Japanese-language version (BACS-J) and the Schizophrenia Quality of Life Scale Japanese-language version (SQLS-J) were administered. Clinical evaluation also included the Positive and Negative Syndrome Scale (PANSS). To compare for practice effects on the BACS-J, 10 patients with chronic schizophrenia were assessed without tapering BZDs. RESULTS: BZDs were reduced or discontinued safely in most patients, and no emergent withdrawal symptoms were observed. Significant improvements were shown in verbal memory, working memory, and composite score, as measured by the BACS-J without practice effects. In addition, the motivation/energy score on the SQLS-J, the negative symptoms and total scores on the PANSS significantly improved after tapering BZDs. CONCLUSION: Reduction or discontinuation of long-term daytime use of BZDs may be warranted in patients with schizophrenia treated with SGAs, as it may improve cognitive function, subjective QOL, and psychiatric symptoms with no significant adverse effects.

Imaging changes in glutamate transmission in vivo with the metabotropic glutamate receptor 5 tracer [11C] ABP688 and N-acetylcysteine challenge.

BACKGROUND: An imaging method to probe glutamate levels in vivo would allow the study of glutamate transmission in disease states and in response to therapeutic interventions. Here we demonstrate the feasibility of this approach for the first time using positron emission tomography and [(11)C] ABP688, a radiotracer for an allosteric site on the metabotropic glutamate receptor 5. METHODS: We conducted two sets of experiments in anesthetized baboons: test and retest without pharmacologic challenge and in combination with N-acetylcysteine (NAC), a promoter of the cystine-glutamate antiporter that increases extrasynaptic glutamate release. The goal was to assess whether NAC-induced changes in [(11)C] ABP688 binding potential, ΔBP(ND), could be detected above the noise in the measurement. RESULTS: Linear mixed modeling comparing ΔBP(ND) from test-retest to ΔBP(ND) from NAC challenge across all brain regions showed a highly significant effect of treatment [F(1,40) = 21.2, p < .001]. ΔBP(ND) was significantly different from zero following NAC [F(1,20) = 76.6, p < .001] but not after test-retest studies. CONCLUSIONS: NAC induced decrease in [(11)C] ABP688 ΔBP(ND) may be the result of allosteric modulation, although other mechanisms may be at play. We outline steps needed to replicate and validate this method as a new tool to measure in vivo glutamate transmission.

Presynaptic dopamine in schizophrenia.

Presynaptic dopamine (DA) transmission has been measured in schizophrenia using different paradigms aimed at providing estimates of the integrity or the activity of the presynaptic dopaminergic neuron. RESEARCHERS HAVE MEASURED: (1) DA synthesis capacity with [(18) F]DOPA, a measure of the activity of dopa decarboxylase, (2) DA release with studies measuring the impact of a DA releasing stimulant challenge on the binding of a D(2) receptor radiotracer, (3) D(2) baseline occupancy by DA, a measure of baseline intrasynaptic DA, assessed by the changes in binding of D(2) radiotracer induced by DA depletion, and (4) the DA and the vesicular monoamine transporters, to assess the integrity of presynaptic terminals. The relationship between DA release and D(2) receptor occupancy at baseline by DA has also been assessed in the same patients. Overall, these different imaging modalities have converged to show a dysregulation of presynaptic dopaminergic activity in schizophrenia, leading to excessive DA release in the striatum, particularly in the projection to the associative striatum, an area of integration between cognitive and limbic cortical inputs. Excessive striatal presynaptic DA is linked to the emergence of acute psychotic symptoms and to their response to treatment in schizophrenia. Understanding the etiology of this dysregulation and its consequences on the rest of the circuitry is important for future drug development.

In vivo binding of antipsychotics to D3 and D2 receptors: a PET study in baboons with [11C]-(+)-PHNO.

Measuring the in vivo occupancy of antipsychotic drugs at dopamine D(2) and D(3) receptors separately has been difficult because of the lack of selective radiotracers. The recently developed [(11)C]-(+)-PHNO is D(3)-preferring, allowing estimates of the relative D(2) and D(3) binding of antipsychotic drugs. We used positron emission tomography (PET) imaging in baboons with [(11)C]-(+)-PHNO to examine the binding of clozapine and haloperidol to D(2) and D(3) receptors. Four animals were scanned with dynamically acquired PET and arterial plasma input functions. Test and retest scans were acquired in single scanning sessions for three subjects to assess the reproducibility of [(11)C]-(+)-PHNO scans. Four additional scans were acquired in each of three subjects following single doses of antipsychotic drugs (clozapine 0.5534 mg/kg, haloperidol 0.0109 mg/kg, two administrations per drug per subject) and compared with baseline scans. The percent change in binding (ΔBP(ND)) following challenges with antipsychotic drugs was measured. A regression model, based on published values of regional D(2) and D(3) fractions of [(11)C]-(+)-PHNO BP(ND) in six brain regions, was used to infer occupancy at D(2) and D(3) receptors. BP(ND) following antipsychotic challenge decreased in all regions. Estimated D(2) : D(3) selectivity was 2.38 for haloperidol and 5.25 for clozapine, similar to published in vitro values for haloperidol (3.03), but slightly higher for clozapine (2.82). These data suggest that acute doses of clozapine and haloperidol bind to D(3) receptors in vivo, and that the lack of D(3) occupancy by antipsychotics observed in some recent imaging studies may be because of other phenomena.