Extrapyramidal side effects with risperidone and haloperidol at comparable D2 receptor occupancy levels

Predicting psychotic relapse following randomised discontinuation of paliperidone in individuals with schizophrenia or schizoaffective disorder: an individual participant data analysis

BACKGROUND

Predicting relapse for individuals with psychotic disorders is not well established, especially after discontinuation of antipsychotic treatment. We aimed to identify general prognostic factors of relapse for all participants (irrespective of treatment continuation or discontinuation) and specific predictors of relapse for treatment discontinuation, using machine learning.

METHODS

For this individual participant data analysis, we searched the Yale University Open Data Access Project's database for placebo-controlled, randomised antipsychotic discontinuation trials with participants with schizophrenia or schizoaffective disorder (aged ≥18 years). We included studies in which participants were treated with any antipsychotic study drug and randomly assigned to continue the same antipsychotic drug or to discontinue it and receive placebo. We assessed 36 prespecified baseline variables at randomisation to predict time to relapse, using univariate and multivariate proportional hazard regression models (including multivariate treatment group by variable interactions) with machine learning to categorise the variables as general prognostic factors of relapse, specific predictors of relapse, or both.

FINDINGS

We identified 414 trials, of which five trials with 700 participants (304 [43%] women and 396 [57%] men) were eligible for the continuation group and 692 participants (292 [42%] women and 400 [58%] men) were eligible for the discontinuation group (median age 37 [IQR 28-47] years for continuation group and 38 [28-47] years for discontinuation group). Out of the 36 baseline variables, general prognostic factors of increased risk of relapse for all participants were drug-positive urine; paranoid, disorganised, and undifferentiated types of schizophrenia (lower risk for schizoaffective disorder); psychiatric and neurological adverse events; higher severity of akathisia (ie, difficulty or inability to sit still); antipsychotic discontinuation; lower social performance; younger age; lower glomerular filtration rate; benzodiazepine comedication (lower risk for anti-epileptic comedication). Out of the 36 baseline variables, predictors of increased risk specifically after antipsychotic discontinuation were increased prolactin concentration, higher number of hospitalisations, and smoking. Both prognostic factors and predictors with increased risk after discontinuation were oral antipsychotic treatment (lower risk for long-acting injectables), higher last dosage of the antipsychotic study drug, shorter duration of antipsychotic treatment, and higher score on the Clinical Global Impression (CGI) severity scale The predictive performance (concordance index) for participants who were not used to train the model was 0·707 (chance level is 0·5).

INTERPRETATION

Routinely available general prognostic factors of psychotic relapse and predictors specific for treatment discontinuation could be used to support personalised treatment. Abrupt discontinuation of higher dosages of oral antipsychotics, especially for individuals with recurring hospitalisations, higher scores on the CGI severity scale, and increased prolactin concentrations, should be avoided to reduce the risk of relapse.

FUNDING

German Research Foundation and Berlin Institute of Health.

Effects of cannabidiol on vacuous chewing movements, plasma glucose and oxidative stress indices in rats administered high dose risperidone

Atypical antipsychotics, despite their rapid dissociation from dopamine receptors and reduced tendency to induce oxidative stress, have been associated with difficult-to-manage movement disorders, including tardive dyskinesia (TD). The study set out to investigate the effects of cannabidiol (CBD), a potent antioxidant, on risperidone-induced behavioural and motor disturbances; namely vacuous chewing movements (VCM), and oxidative stress markers (e.g. superoxide dismutase (SOD), catalase (CAT), reduced glutathione (GSH), malondialdehyde (MDA), Nitric oxide (NO), and DPPH (2,2-diphenyl-1-picrylhydrazyl)). Oral risperidone (10 mg/kg) or oral CBD (5 mg/kg) were administered to six experimental groups. While risperidone alone was administered for 28 days, CBD concomitantly or in sequential order with risperidone, was administered for 28 days; and CBD alone was administered for 21 days. Behavioural, motor, and specific biochemical parameters, which included VCM, muscle tone, fasting blood sugar (FBS), and oxidative stress markers were assessed at different time points after the last dose of medication. Oral CBD (5 mg/kg) significantly reduced risperidone-induced elevated FBS when given after the administration of risperidone. Oral CBD also had effects on VCM when administered before risperidone and similarly, attenuated risperidone-induced increased muscle tone. It was also established that concomitant or sequential administration of CBD and risperidone did not have any adverse effects on cognition or locomotion. Both CBD and risperidone increased the activity of antioxidant enzymes and decreased the activity of pro-oxidant enzymes. This study suggests CBD could mitigate metabolic dysregulation and extrapyramidal side effects associated with risperidone without producing cognitive impairments.

Chronic antipsychotic treatment exerts limited effects on the mania-like behavior of dopamine transporter knockdown mice

BACKGROUND

Bipolar disorder is a life-threatening disorder linked to dopamine transporter (DAT) polymorphisms, with reduced DAT levels seen in positron emission tomography and postmortem brains.

AIMS

The purpose of this study was to examine the effects of approved antipsychotics on DAT dysfunction-mediated mania behavior in mice.

METHODS

DAT knockdown mice received either D2-family receptor antagonist risperidone or asenapine and mania-related behaviors were assessed in the clinically-relevant behavioral pattern monitor to assess spontaneous exploration.

RESULTS

Chronic risperidone did not reverse mania-like behavior in DAT knockdown mice. Chronic asenapine reduced mania behavior but this effect was more pronounced in wild-type littermates than in DAT knockdown mice.

CONCLUSION

Taken together, these findings suggest that while acute antipsychotic treatment may be beneficial in management of bipolar mania, more targeted therapeutics may be necessary for long-term treatment. Specific investigation into DAT-targeting drugs could improve future treatment of bipolar mania.

Discovery of Piperidol Derivatives for Combinational Treatment of Azole-Resistant Candidiasis

Effective strategies are needed to deal with invasive fungal infections caused by drug-resistant fungi. Previously, we designed a series of antifungal benzocyclane derivatives based on the drug repurposing of haloperidol. Herein, further structural optimization and antifungal mechanism studies were performed, leading to the discovery of new piperidol derivative B2 with improved synergistic antifungal potency, selectivity, and water solubility. In particular, the combination of compound B2 and fluconazole showed potent in vitro and in vivo antifungal activity against azole-resistant Candida albicans. Compound B2 inhibited important virulence factors by regulating virulence-associated genes and improved the efficacy of fluconazole by down-regulating the CYP51-coding gene and efflux pump gene. Taken together, the piperidol derivative B2 represents a promising lead compound for the combinational treatment of azole-resistant candidiasis.

Inclusion of enclosed hydration effects in the binding free energy estimation of dopamine D3 receptor complexes

Confined hydration and conformational flexibility are some of the challenges encountered for the rational design of selective antagonists of G-protein coupled receptors. We present a set of C3-substituted (-)-stepholidine derivatives as potent binders of the dopamine D3 receptor. The compounds are characterized biochemically, as well as by computer modeling using a novel molecular dynamics-based alchemical binding free energy approach which incorporates the effect of the displacement of enclosed water molecules from the binding site. The free energy of displacement of specific hydration sites is obtained using the Hydration Site Analysis method with explicit solvation. This work underscores the critical role of confined hydration and conformational reorganization in the molecular recognition mechanism of dopamine receptors and illustrates the potential of binding free energy models to represent these key phenomena.

Medications development for food-based and drug use disorders

Despite decades of research, few medications have gained Food and Drug Administration (FDA) approval for the management of substance abuse disorder. The paucity of successful medications can be attributed, in part, to the lack of clearly identified neurobiological targets for addressing the core pathology of addictive behavior. Commonalities in the behavioral and brain processes involved in the rewarding effects of drugs and foods has prompted the evaluation of candidate medications that target neural pathways involved in both drug and eating disorders. Here, pharmacological strategies for the development of novel medications for drug addiction are presented in the context of potential overlapping neurobiological targets identified for eating disorders (e.g., obesity, overeating, binge-eating) and substance abuse. Mechanisms discussed in this chapter include modulators of the gut-brain axis (e.g., leptin, ghrelin, cholecystokinin, cocaine- and amphetamine-regulated transcript, and pancreatic peptides) and neurotransmitter systems (e.g., opioids, cannabinoids, dopamine, serotonin, and acetylcholine).

Antipsychotics: Mechanisms underlying clinical response and side-effects and novel treatment approaches based on pathophysiology

Antipsychotic drugs are central to the treatment of schizophrenia and other psychotic disorders but are ineffective for some patients and associated with side-effects and nonadherence in others. We review the in vitro, pre-clinical, clinical and molecular imaging evidence on the mode of action of antipsychotics and their side-effects. This identifies the key role of striatal dopamine D2 receptor blockade for clinical response, but also for endocrine and motor side-effects, indicating a therapeutic window for D2 blockade. We consider how partial D2/3 receptor agonists fit within this framework, and the role of off-target effects of antipsychotics, particularly at serotonergic, histaminergic, cholinergic, and adrenergic receptors for efficacy and side-effects such as weight gain, sedation and dysphoria. We review the neurobiology of schizophrenia relevant to the mode of action of antipsychotics, and for the identification of new treatment targets. This shows elevated striatal dopamine synthesis and release capacity in dorsal regions of the striatum underlies the positive symptoms of psychosis and suggests reduced dopamine release in cortical regions contributes to cognitive and negative symptoms. Current drugs act downstream of the major dopamine abnormalities in schizophrenia, and potentially worsen cortical dopamine function. We consider new approaches including targeting dopamine synthesis and storage, autoreceptors, and trace amine receptors, and the cannabinoid, muscarinic, GABAergic and glutamatergic regulation of dopamine neurons, as well as post-synaptic modulation through phosphodiesterase inhibitors. Finally, we consider treatments for cognitive and negative symptoms such dopamine agonists, nicotinic agents and AMPA modulators before discussing immunological approaches which may be disease modifying. This article is part of the issue entitled 'Special Issue on Antipsychotics'.

Optimization of maintenance therapy of Risperidone with CYP2D6 genetic polymorphisms through an extended translational framework-based prediction of target occupancies/clinical outcomes

Risperidone, one of the second-generation antipsychotics, can efficiently target dopamine D₂ and serotonin 5-HT_2A receptors. There actually exists significant implication of CYP2D6 genetic polymorphisms on the metabolic kinetics of risperidone, little is known about the extent of CYP2D6 impacting human D2 and 5-HT2A receptor occupancies as well as the clinical efficacy and efficacy in schizophrenia treatment. Here we assessed the influences of CYP2D6 gene polymorphisms on human target occupancies/clinical outcomes and optimized the maintenance therapy of risperidone. A translational framework, previously developed using in vitro and in vivo information in rats, was used as the basis for integrating the effects of CYP2D6 genetic polymorphisms on target occupancies and clinical outcomes. D₂ occupancy as a biomarker was related to Positive and Negative Syndrome Scale (PANSS) response and Simpson-Angus Scale (SAS). The population approach was applied to characterize pharmacokinetic and pharmacodynamic (PK/PD) profiles of risperidone. Non-compartment analysis method was performed to calculate the steady state PK/PD parameters of both risperidone and 9-hydroxyrisperidone. The predictive power of this extended translational framework was determined by comparing the predictions of target occupancies and clinical outcomes with the reported human values of risperidone at clinically suggested dosage of 4.0 mg/day. This extended translational framework was adequately used to predict human target occupancies and clinical outcomes. At the steady state, D₂ ROs were 75.8%, 79.3% and 86.0% for CYP2D6 poor metabolizer (PM), intermediate metabolizer (IM) and extensive metabolizer (EM), respectively; 5-HT_2A ROs were 96.4%, 97.2% and 98.4% for CYP2D6 PM, IM and EM, respectively; PANSS changes from placebo were -5.3, -7.7 and -11.3 for CYP2D6 PM, IM and EM, respectively; SAS changes from placebo were 0.13, 0.15 and 0.18 for CYP2D6 PM, IM and EM, respectively. The predictions of human D₂, 5-HT_2A RO, PANSS and SAS changes for risperidone with CYP2D6 genetic polymorphisms were well in line with the reported values in clinic. 5.0, 4.0 and 2.5 mg/day were the equivalent dosages of risperidone for CYP2D6 PM, IM and EM, respectively. The optimized maintenance therapy of risperidone was provided through the Three-Step method and the dosage range was 2.5-5.0 mg/day for three CYP2D6 gene groups in the present study. Taken together, our findings demonstrate that this extended translational framework not only differentiates the effects of CYP2D6 genetic polymorphisms on target occupancies and clinical outcomes, but also constitutes a scientific basis to optimize the maintenance therapy of neuropsychiatric patients in clinic.

Treating Hallucinations and Delusions Associated With Parkinson's Disease Psychosis

PURPOSE OF REVIEW

We discuss features of Parkinson's disease psychosis (PDP) including symptomology and pathophysiology. Treatment options, including non-pharmacologic strategies, dose reduction of offending agents, and the addition of non-dopaminergic antipsychotics, are addressed. The efficacy of second-generation antipsychotics and novel agents is examined.

RECENT FINDINGS

Pimavanserin, a 5-HT_2A/C receptor inverse agonist with no other receptor activity, has shown efficacy and tolerability and is now FDA approved for PDP treatment. Research into novel targets is ongoing. PDP is a morbid complication of Parkinson's disease with complex incompletely understood mechanisms. Treatment is directed towards mitigation of psychosis without worsening of motor features.

Drug-induced supersensitivity psychosis revisited: characteristics of relapse in treatment-compliant patients

BACKGROUND

An association between abnormal involuntary movements and psychotic relapse was previously reported in a group of patients compliant with antipsychotic medication (Fallon and Dursun 2011). This was interpreted as the presence of an antipsychotic medication-induced supersensitivity psychosis.

METHOD

From the results of that study and the Chouinard diagnostic criteria for supersensitivity psychosis an abbreviated diagnostic checklist was developed to identify the phenomenon. In the present study the checklist was used on a larger sample of medication-compliant individuals experiencing a psychotic relapse.

RESULTS

The checklist demonstrated its utility by identifying a cause of relapse in 70% (29/41) of patients. Furthermore, it identified the presence of supersensitivity psychosis in 39% (16/41) of patients. This study also replicated a number of findings from the previous paper supporting the idea that supersensitivity psychosis is one cause of relapse in psychosis.

DISCUSSION

These results suggested that clinicians should exercise caution in prescribing and may have to augment treatment with other agents or switch to low dopamine-affinity antipsychotics.

The role of striatal dopamine D2 receptors in the occurrence of extrapyramidal side effects: iodine-123-iodobenzamide single photon emission computed tomography study

Levels above 75% of striatal dopamine 2 receptor occupancy (D2RO) have been associated with extrapyramidal symptoms (EPS). The aim of the present study is to investigate the relationship between D2RO and EPS in a sample of psychotic patients in current treatment with both typical and atypical antipsychotics. Brain iodine-123-iodobenzamide single photon emission computed tomography ((123)I-IBZM SPECT) was performed in 81 patients taking stable doses of haloperidol, risperidone, olanzapine, quetiapine, clozapine or ziprasidone. First, the degree of D2RO and Positive and Negative Syndrome Scale (PANSS) scores was compared between the group of patients who presented EPS and the group free of EPS. Afterwards, these variables were compared among the different antipsychotic medications. The group with EPS presented means of D2RO significantly higher than the group free of EPS. Significant differences in D2RO were found in clozapine, quetiapine and ziprasidone groups compared with the haloperidol group. No differences were observed between either olanzapine or risperidone and haloperidol. No quetiapine- or clozapine-treated patients developed EPS. Haloperidol and risperidone demonstrated a relationship between striatal D2RO and EPS. The findings suggest that higher D2RO is related to appearance of EPS. Occupancy in the group with EPS was in agreement with previous studies that suggested a high degree of D2RO is necessary for the occurrence of EPS.

Role of dopamine D(2) receptors for antipsychotic activity

This review summarizes the current state of knowledge regarding the proposed mechanisms by which antipsychotic agents reduce the symptoms of schizophrenia while giving rise to adverse side effects. The first part summarizes the contribution of neuroimaging studies to our understanding of the neurochemical substrates of schizophrenia, putting emphasis on direct evidence suggestive of a presynaptic rather than a postsynaptic dysregulation of dopaminergic neurotransmission in this disorder. The second part addresses the role of D(2) and non-D(2) receptor blockade in the treatment of schizophrenia and highlights a preponderant role of D(2) receptors in the mechanism of antipsychotic action. Neuroimaging studies have defined a narrow, but optimal, therapeutic window of 65-78 % D(2) receptor blockade within which most antipsychotics achieve optimal clinical efficacy with minimal side effects. Some antipsychotics though do not conform to that therapeutic window, notably clozapine. The reasons for its unexcelled clinical efficacy despite subthreshold levels of D(2) blockade are unclear and current theories on clozapine's mechanisms of action are discussed, including transiency of its D(2) receptor blocking effects or preferential blockade of limbic D(2) receptors. Evidence is also highlighted to consider the use of extended antipsychotic dosing to achieve transiency of D(2) blockade as a way to optimize functional outcomes in patients. We also present some critical clinical considerations regarding the mechanisms linking dopamine disturbance to the expression of psychosis and its blockade to the progressive resolution of psychosis, keeping in perspective the speed and onset of antipsychotic action. Finally, we discuss potential novel therapeutic strategies for schizophrenia.

Mechanisms of action of antipsychotic drugs of different classes, refractoriness to therapeutic effects of classical neuroleptics, and individual variation in sensitivity to their actions: Part II

Rapid-onset psychotic rebound is uncommon on discontinuation of most antipsychotic drugs, as might be expected for antipsychotic drugs with (hypothetically) indirect actions at their final target receptors. Rapid-onset psychosis is more common on withdrawal of clozapine, which might be expected if its action is direct. Drugs other than clozapine (notably thioridazine) may have hitherto unrecognised similarities to clozapine (but without danger of agranulocytosis), and may be useful in treatment of refractory psychosis. Quetiapine fulfils only some criteria for a clozapine-like drug. Clinical response to neuroleptics varies widely at any given plasma level. Haase's "neuroleptic threshold" concept suggests that the dose producing the slightest motor side effects produces most or all of the therapeutic benefit, but analyses presented here suggest that antipsychotic actions are not subject to a sharp "all-or-none" threshold but increase over a small dose range. This concept could provide a method for quantitative determination of individualized optimal doses.

Postsynaptic nigrostriatal dopamine receptors and their role in movement regulation

The article presents the hypothesis that nigrostriatal dopamine may regulate movement by modulation of tone and contraction in skeletal muscles through a concentration-dependent influence on the postsynaptic D1 and D2 receptors on the follow manner: nigrostriatal axons innervate both receptor types within the striatal locus somatotopically responsible for motor control in agonist/antagonist muscle pair around a given joint. D1 receptors interact with lower and D2 receptors with higher dopamine concentrations. Synaptic dopamine concentration increases immediately before movement starts. We hypothesize that increasing dopamine concentrations stimulate first the D1 receptors and reduce muscle tone in the antagonist muscle and than stimulate D2 receptors and induce contraction in the agonist muscle. The preceded muscle tone reduction in the antagonist muscle eases the efficient contraction of the agonist. Our hypothesis is applicable for an explanation of physiological movement regulation, different forms of movement pathology and therapeutic drug effects. Further, this hypothesis provides a theoretical basis for experimental investigation of dopaminergic motor control and development of new strategies for treatment of movement disorders.

Neurochemical imaging in schizophrenia

Recent advances in the development and applications of neurochemical brain imaging methods have improved the ability to study the neurochemistry of the living brain in normal processes as well as psychiatric disorders. In particular, positron emission tomography (PET) and single photon emission computed tomography (SPECT) have been used to determine neurochemical substrates of schizophrenia and to uncover the mechanism of action of antipsychotic medications. The growing availability of radiotracers for monoaminergic neurotransmitter synthesis, transporters and receptors, has enabled the evaluation of hypotheses regarding neurotransmitter function in schizophrenia derived from preclinical and clinical observations. This chapter reviews the studies using neurochemical brain imaging methods for (1) detection of abnormalities in indices of dopamine and serotonin transmission in patients with schizophrenia compared to controls, (2) development of new tools to study other neurotransmitters systems, such as gamma-aminobutyric acid (GABA) and glutamate, and (3) characterization of target occupancy by antipsychotic drugs, as well as its relationship to efficacy and side effects. As more imaging tools become available, this knowledge will expand and will lead to better detection of disease, as well as better therapeutic approaches.

Systematic overview of Cochrane reviews for anticholinergic effects of antipsychotic drugs

BACKGROUND

Despite much being written on the topic, there are few surveys investigating the prevalence of anticholinergic adverse effects of antipsychotic drugs. One study, however, used trial-derived data to calculate estimates.

OBJECTIVES

To investigate the prevalence/incidence rates of anticholinergic effects as viewed from within relevant randomized trials.

METHODS

Data were extracted from each relevant study included in Cochrane reviews. Data were checked, extracted, and simple frequencies, and 95% confidence intervals (CIs) were calculated.

RESULTS

Many trials in relevant reviews reported no data on anticholinergic effects (estimate 40,000 participants). However, data were extracted from 177 studies within 54 reviews (N = 27,328 participants). Most data are short-term (<12 weeks). For blurred vision, the newer generations of drugs have rates of between 10% and 20% (eg, risperidone, n = 1460, 6 randomized controlled trials [RCTs], 11.9% prevalence; CI, 10-14; olanzapine, n = 1584; 4 RCTs, 12.2% prevalence; CI, 11-14). These estimates are similar to those of sulpiride (n = 186; 2 RCTs, 12.4%; CI, 8-18) and chlorpromazine (n = 294; 10 RCTs, 11.2%; CI, 8-15), less than trifluoperazine (n = 167; 8 RCTs, 31.1%; CI, 25-39), but considerably more than perphenazine (n = 410; 8 RCTs, 3.7%; CI, 2-6). Data are presented on a range of anticholinergic effects across different periods.

CONCLUSIONS

Anticholinergic symptoms are common adverse effects associated with the use of all antipsychotic drugs, and newer-generation drugs are not clearly distinguishable from many older compounds. Adverse effect data should be more accessible.

Within-subject comparison of striatal D2 receptor occupancy measurements using [123I]IBZM SPECT and [11C]Raclopride PET

Antipsychotic-induced D2 receptor occupancy values tend to be lower when measured with [(123)I]IBZM SPECT than with [(11)C]Raclopride PET. To clarify this issue, D2 receptor occupancy was measured in the same subjects using both techniques. Twenty patients with schizophrenia on monotherapy with risperidone (n=7; 3-9 mg/d), olanzapine (n=5; 5-20 mg/d) or clozapine (n=8; 150-450 mg/d) at stable doses, and ten healthy volunteers (HV) underwent both a [(123)I]IBZM SPECT and a [(11)C]Raclopride PET examinations in random order on different days within a week. Patients with schizophrenia were scanned at a fixed interval after last dose administration. Quantification of receptor availability was performed using the most conventional methods from the literature: the tissue ratio derived specific uptake ratios (SUR) were used for SPECT, and simplified reference tissue model (SRTM) derived binding potentials (BP(ND)) for PET. Analysis was performed using both occipital cortex and cerebellum as reference regions for both modalities. Striatal D2 receptor occupancy was measured as the percentage reduction of [(123)I]IBZM SUR or [(11)C]Raclopride BP(ND) compared to the population average measured in HV using the same modality. Occupancy values measured by SPECT were lower than those measured with PET, by 12.4% and 13.8% when occipital cortex and cerebellum were used as reference regions. This difference should be taken in consideration when interpreting reported antipsychotic striatal D2 receptor occupancy values from the literature.

The 'atypicality' of antipsychotics: a concept re-examined and re-defined

Recent clinical trials have raised questions over the perceived advantages of second-generation 'atypical' antipsychotics over those from the first generation. An atypical antipsychotic in its original sense is one that lacks extrapyramidal side effects. However, the addition of other clinical features to the original concept of atypicality, such as efficacy against negative and cognitive symptoms, seems to have become a feature of searches for novel antipsychotics in the past two decades. Although this approach has led to some therapeutic advances, we propose that it has also hampered antipsychotic drug research and that reframing the concept of atypicality could have a key role in making genuine breakthroughs in schizophrenia therapy.

Pharmacokinetics and time-course of D(2) receptor occupancy induced by atypical antipsychotics in stabilized schizophrenic patients

The (123)I-IBZM SPECT measured D(2) receptor occupancy (D(2)RO) in chronically dosed, stabilized schizophrenic patients and its relationship with antipsychotic (AP) pharmacokinetics (PK) over time is still unclear. The aims of this study were: 1) To define the relationship between striatal D(2) receptor occupancy (D( 2)RO) and plasma concentration (C(P)) in stabilized schizophrenic patients on clinically relevant doses using (123)I-IBZM SPECT; 2) To investigate the time course of AP-induced D(2)RO and corresponding C(P). Forty-six schizophrenic patients on their clinically required doses of risperidone, olanzapine, clozapine or quetiapine were included. D( 2)RO and C(P) were measured over time following a sparse-sampling experimental design, and individual PK and D(2)RO-time profiles were estimated using a population approach. Observed striatal D(2)RO and C(P) ranges were 28-75% and 9.4-60.5 ng/mL for risperidone, 22-84% and 8.6-89.5 ng/mL for olanzapine, 5-53% and 41.6-818.2 ng/mL for clozapine and 0-64% and 37.9-719.6 ng/mL for quetiapine. A PK-D(2)RO relationship was found for the four APs. D(2)RO pattern over time was stable for risperidone, olanzapine and clozapine but fluctuating for quetiapine. Stabilized schizophrenic patients show a wide range of both D(2)RO and C(P) at clinically effective doses of the four AP, suggesting that clinical response to these AP may be maintained with D(2)RO below 65%. D(2)RO patterns over time differ between AP. These results should be considered for accurate interpretation of D(2)RO measurements, proper design of studies and optimization of drug regimens for patients on AP treatment.

Neuroreceptor imaging studies in schizophrenia

The ability of SPECT and PET to image specific biomolecules in the living brain provides a unique tool for clinical researchers. It is therefore not surprising that the use of neuroreceptor-imaging techniques has become more widespread over the past decade. This article reviews the application of these techniques to the study of schizophrenia. The design of neuroreceptor-imaging studies performed in the field of schizophrenia research can be broadly divided into two categories: (1) studies of pathophysiology and (2) studies of pharmacology. The former examines neuroreceptor and neurotransmitter parameters in individuals with schizophrenia compared to control subjects in order to provide a better understanding of the disease process. Studies of pharmacology seek to elucidate the mechanism of action for the treatments utilized in schizophrenia. This review will consider both studies of pathophysiology and pharmacology, with a discussion of the application of these techniques to drug development.

Alterations of serotonin transmission in schizophrenia

A role for serotonin alterations in the pathophysiology of schizophrenia has long been suspected because of the psychotogenic effects of serotonergic agonists and the therapeutic effects of 5-HT(2) antagonism. This chapter is a review of the evidence derived from pharmacological studies, postmortem, and imaging studies that have assessed the role of serotonin transmission in schizophrenia. While a clear picture of specific serotonergic alterations in schizophrenia has not emerged despite much research, this review reinforces a modulatory role of serotonergic agents on dopamine transmission in schizophrenia, which may contribute to the therapeutic effects of atypical antipsychotics.

Serotonin transporter occupancy induced by paroxetine in patients with major depression disorder: a 123I-ADAM SPECT study

RATIONALE

To assess the paroxetine-induced serotonin transporter (SERT) occupancy (SERTocc) using in vivo (123)I-ADAM SPECT.

OBJECTIVES

(123)I-ADAM SPECT was used to investigate the SERTocc induced by paroxetine in major depression disorder (MDD) patients, to compare the SERT availability in drug-free MDD patients and healthy volunteers, and to study the relationship between paroxetine plasma concentrations (Cp) and SERTocc.

MATERIALS AND METHODS

Measures of SERT availability by means of (123)I-ADAM SPECT were obtained in ten MDD patients before and after 4- to 6-week treatment with paroxetine 20 mg/day. (123)I-ADAM SPECT measures of SERT availability from a group of ten previously studied age-matched healthy volunteers were used for comparison. The relationship between percentages of SERTocc and paroxetine Cp was studied using an E (max) model.

RESULTS

Mean SERTocc values were 66.4 +/- 9.5% in midbrain, 63.0 +/- 9.6% in thalamus, and 61.3 +/- 10.9% in striatum. No significant differences in SERTocc were found among these three regions. No significant differences in mean SERT availability were found in any region between drug-free MDD patients (midbrain = 1.14 +/- 0.15; thalamus = 0.85 +/- 0.13; striatum = 0.70 +/- 0.07) and healthy volunteers (midbrain = 1.19 +/- 0.22; thalamus = 0.96 +/- 0.14; striatum = 0.67 +/- 0.15). The E (max) model returned a SERTocc(max) = 70.5% and a Cp(50) = 2.7 ng/ml.

CONCLUSIONS

Using (123)I-ADAM SPECT, treatment with paroxetine 20 mg/day leads to more than 60% SERTocc on average in cerebral regions with known high SERT density. Data from this study do not support the existence of SERT availability differences between drug-free MDD patients and healthy volunteers. Finally, the E (max) model is suitable for the study of paroxetine Cp relationship to (123)I-ADAM SPECT-measured SERTocc. This approach may be useful for pharmacokinetic-pharmacodynamic relationships in drug development.

Dopamine D2 receptor occupancy by risperidone: implications for the timing and magnitude of clinical response

The objective of the study is to investigate whether dopamine D2 receptor occupancy by risperidone and plasma levels over time can account for therapeutic efficacy and the latency period to response. Thirty-eight examinations with (123)I-IBZM single photon emission computed tomography were performed on 22 patients with schizophrenia, at diagnosis, 48 h after starting risperidone treatment and at a stable dose. Risperidone plasma levels were determined and psychopathologic evaluations (Brief Psychiatric Rating Scale, Positive and Negative Syndrome Scale) were carried out. No differences in the striatal/occipital (S/O) ratio or plasma levels were found between examinations at the 48-h time point and when a stable dose level had been established, so these parameters could not account for the latency period required for clinical response. D2 receptor occupancy at 48 h correlated positively with clinical improvement after 2 weeks of treatment. Therefore, if these results are confirmed, D2 receptor occupancy at the beginning of treatment with risperidone may be a predictor of subsequent clinical response.

Effects of chronic risperidone treatment on the striatal protein profiles in rats

Extrapyramidal symptoms (EPS) commonly occur as side effects of antipsychotic drugs (APDs) and are most likely to arise when the occupancy of dopamine D(2) receptors in the striatum by these drugs exceeds 80%. We aimed to characterize changes in the protein expression profile in the striatum of rats after chronic (4 week) supra-therapeutic (EPS-inducing) treatment with risperidone (RIS), an atypical antipsychotic drug. Administration of RIS (2.1 mg/kg/day, via subcutaneous osmotic minipumps) induced significant vacuous chewing movements and catalepsy in male Sprague-Dawley rats over a 28-day treatment period compared with a vehicle (VEH) control group (n=12) (Karl et al., unpublished observation). Using two-dimensional gel electrophoresis (2DE), total protein extracts from the rat brain striatum were separated and protein expression was analyzed by Phoretix 2D Expression and Image Beta V4.02 software followed by matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). 2DE gels resolved up to 450 protein spots, presumably different proteins and/or their isoforms. There were 30 protein spots showing statistically significant different densities between the RIS- and VEH-treated groups. All 30 proteins were successfully identified by MALDI-TOF MS, 28 of these were divided into groups based on their known functions. These included metabolic, signaling, transport, protein metabolism, chaperone, DNA binding and cell cycle categories. We conclude that chronic risperidone treatment accompanied by an EPS-like behavioral phenotype results in alterations in the striatal protein profile possibly subsequent to blockade of dopaminergic systems. These results suggest that possible mechanisms involved in APD-induced EPS include metabolic dysfunction and oxidative stress.

Combating psychosis in Parkinson's disease patients: the use of antipsychotic drugs

Parkinson's disease (PD) patients commonly experience psychotic symptoms, with the most frequent manifestation being visual hallucinations. In PD, psychosis is predominantly drug induced and an important issue for clinicians to address as it increases the risk of nursing home placement as well as mortality. This review summarises the current knowledge regarding the clinical manifestations, pathophysiology and risk factors for drug-induced psychosis in patients with PD and focuses on treatment, especially with regard to the atypical antipsychotics.

PD-related psychosis: pathophysiology with therapeutical strategies

Parkinson's disease (PD) is a chronic, neurodegenerative disease with degeneration of the central dopaminergic neurons in the substantia nigra, leading to a depletion of dopamine (DA) in the striatum. This depletion causes the clinical hallmarks of this disease: bradykinesia, hypokinesia, rigidity, tremor and postural instability. Besides these well known motor symptoms, non-motor symptoms may develop, such as hyposmia, sleep disorders, autonomic disturbances, depression, cognitive impairment and psychosis. Pathophysiological mechanisms underlying these symptoms not only comprise Lewy body pathology in the central dopaminergic system, but also in the noradrenergic, serotinergic and cholinergic transmittersystems. Indeed, in Parkinson's disease, about 30-40% of the patients suffers fluctuating psychotic symptoms, mainly paranoid delusions and/or visual or acoustic hallucinations, symptoms considered to represent major contributors to patient and caregiver distress and nursing home placement. Endogenous (related to the disease process itself) as well as exogenous (related to therapeutical interventions) psychotogenic factors may contribute to the development of psychotic symptoms in PD. Therapeutical strategies, therefore, are aimed to reduce both endogenous and exogenous factors. To reduce endogenous psychotogenic factors, cholinesterase inhibitors, suggested to reduce cognitive deterioration, now seem to be the drugs of choice. In exogenously induced psychotic symptoms, atypical antipsychotics are considered the most effective. However, as psychotic symptoms in PD are often influenced by both endogenous and exogenous factors, a combination of both strategies may be preferred.

HPLC-DAD determination of plasma levels of the antipsychotic risperidone and its main metabolite for toxicological purposes

A new, rapid analytical method, based on liquid chromatography with diode array detection, has been developed and applied to the determination of risperidone and its main active metabolite 9-hydroxyrisperidone in human plasma. The chromatographic separation was obtained on a C8 (150 x 4.6 mm, 5 microm) column, using a mobile phase composed of acetonitrile (27%) and a pH 3.0 phosphate buffer (73%). A sample clean-up procedure was carried out by using C8 cartridges and eluting the analytes with methanol. The extraction yield was highly satisfactory for both analytes, with average absolute recovery values of about 95%. The experimental conditions permitted the quantitative determination of risperidone and 9-hydroxyrisperidone with high precision (RSD < 3.6%) and satisfactory sensitivity (LOQ = 4 ng mL(-1)). The method was applied to plasma samples from a patient who had tried to poison himself with 150 mg of risperidone, and was undergoing polypharmacy.

Striatal dopaminergic D2 receptor occupancy and clinical efficacy in psychosis exacerbation: a 123I-IBZM study with ziprasidone and haloperidol

OBJECTIVE

The aim of this study was to compare striatal dopaminergic D2 receptor occupancy (D2 RO) induced by ziprasidone and haloperidol and its relationship with clinical response and extrapyramidal side effects (EPS) in patients with acute psychosis exacerbation.

METHOD

Twenty patients hospitalized with an acute psychosis exacerbation were randomised in a single-blind study to receive either ziprasidone (80-120 mg/day) or haloperidol (5-20 mg/day) for more than 2 weeks. When stable doses were achieved, data on 123I-IBZM single-photon emission computed tomography (SPECT), as well as data on clinical efficacy (positive and negative symptoms scale [PANSS]) and EPS (Simpson Angus scale [SAS]), were compared between the two groups of patients. Clinical response was defined as a percentage of change of >30% in PANSS. Striatal D2 RO and clinical data were also compared between responders and nonresponders on each treatment group.

RESULTS

All patients on haloperidol and four patients on ziprasidone showed EPS. Mean D2 RO was significantly higher in the haloperidol (74.7+/-3.5) than in the ziprasidone (60.2+/-14.4) group (Mann Whitney U-test [M-W U-test] 8.50; p=0.002). Five patients were responders, and five were nonresponders on each group of treatment. Haloperidol responders and nonresponders did not differ in D2 RO, duration of treatment, doses or EPS. Ziprasidone responders were on higher doses than nonresponders and showed higher D2 RO although below 74%. A positive correlation of ziprasidone D2 RO was found with dose (r Spearman 0.87; p=0.001) and with SAS scores (r Spearman 0.88; p=0.001).

CONCLUSIONS

Ziprasidone induces lower D2 RO and EPS than haloperidol, which is consistent with an atypical antipsychotic profile. A direct relationship of ziprasidone D2 RO with dose, clinical efficacy and EPS has been found in this study. These data suggest that high ziprasidone doses might be more beneficial in patients with psychosis exacerbation and claim for caution regarding EPS appearance with such high dosages.

Thiethylperazine-induced parkinsonism: in vivo demonstration of dopamine D2 receptors blockade

Thiethylperazine (Torecan) is a piperazine phenothiazine employed to relieve vertigo. Its use may be associated with extrapyramidal side effects (dystonia, akathisia, tardive dyskinesia) (Sulkava, 1984), but parkinsonism has rarely been described. We describe a woman who, 1 month after the onset of thiethylperazine treatment, developed parkinsonism that disappeared 2 months after withdrawal of the drug. However, cerebral single-photon emission computed tomography (SPECT) with the dopamine (DA) D2 receptors ligand 123I-iodobenzamide (123I-IBZM) revealed a persistent reduced DA D2 receptors activity (by 45%) in the basal ganglia (BG), which may be clinically not effective.

Occupancy of dopamine D2 receptors by the atypical antipsychotic drugs risperidone and olanzapine: theoretical implications

RATIONALE

To examine the D2 occupancy of two commonly used antipsychotic medications and relate this to the D2 occupancy by endogenous dopamine in schizophrenia.

OBJECTIVES

The aim of this study is to compare the occupancy of striatal D2 receptors by the atypical antipsychotic medications risperidone and olanzapine at fixed dosages and to estimate the effect on D2 occupancy by dopamine as a result of these treatments.

METHODS

Seven patients with schizophrenia taking risperidone 6 mg/day and nine patients with schizophrenia taking olanzapine 10 mg/day underwent an [123I]IBZM SPECT scan after 3 weeks of treatment. The specific to non-specific equilibrium partition coefficient (V3") after bolus plus constant infusion of the tracer was calculated as [(striatal activity)/(cerebellar activity)]-1. D2 receptor occupancy was calculated by comparing V3" measured in treated patients to an age-corrected V3" value derived from a group of untreated patients with schizophrenia, previously published, according to the following formula: OCC=1-(V3" treated/V3" drug free).

RESULTS

V3" was significantly lower in risperidone treated patients compared with olanzapine treated patients (0.23+/-0.06 versus 0.34+/-0.08, P=-0.01), which translated to a significantly larger occupancy in schizophrenic patients treated with risperidone compared to olanzapine (69+/-8% versus 55 +/-11%, P=0.01). Data from our previous study were used to calculate the occupancy of striatal D2 receptors by antipsychotic medications required to reduce the occupancy of these receptors by endogenous dopamine to control values. In medication-free patients with schizophrenia, the occupancy of striatal D2 receptors by endogenous dopamine is estimated at 15.8%. In healthy controls, the occupancy of striatal D2 receptors by dopamine is estimated at 8.8%. In order to reduce the dopamine occupancy of striatal D2 receptors in patients with schizophrenia to control values, 48% receptor occupancy by antipsychotic medications is required.

CONCLUSIONS

These data indicate that the dosage of these medications, found to be effective in the treatment of schizophrenia, reduces DA stimulation of D2 receptors to levels slightly lower than those found in unmedicated healthy subjects.

Significance of non-presynaptic SPECT tracer methods in Parkinson's disease

Tropane-related tracers for SPECT and PET scanning have shown their value in assessing the in vivo striatal presynaptic status of the dopaminergic neurotransmitter system in man. Previously, there were a few other tracers suggested to be useful in the study of in vivo brain biochemistry in humans, particularly in patients afflicted with Parkinson's disease (PD) or parkinsonian syndromes. We summarize the work concerning the two main tracers applied in that context using single photon emission tomography (SPECT) scanning in patients with PD: IBZM and HMPAO. IBZM binds specifically to striatal dopamine D(2) receptors and HMPAO uptake is a measure of cerebral tissue perfusion.

Positron emission tomography and single photon emission CT molecular imaging in schizophrenia

We reviewed findings from PET and SPECT studies that have contributed to our understanding of the pathophysiology and treatment of schizophrenia. The most robust set of findings pertains to imaging of presynaptic dopaminergic function in the striatum. The results of these studies have been consistent in showing that schizophrenia, at least during episodes of illness exacerbation, is associated with increased activity of DA neurons; this increased presynaptic activity is associated with positive symptoms and good therapeutic response. Studies of cortical DA function are less numerous and less consistent. In the future, technical advances in PET instrumentation and radioligand development should contribute to a clarification of the role of prefrontal DA in the cognitive impairment that is presented by these patients. An important drawback of the literature in this field is the generally low number of subjects that are included in studies (typically less than 20 per group). Small samples are necessitated by the cost of these investigations, but also, in some instances, to the difficulty in recruiting appropriate clinical subjects (such as drug-free patients who have schizophrenia). In conditions that are characterized by marked heterogeneity, such as major depressive disorders, this factor is bound to yield divergent results across studies. Another source of discrepancy is the variety of technical approaches to data acquisition and analysis. For example, analytical methods range from "empirical" or "semiquantitative" (typically a region of interest to a region of reference ratio measured at one time point) to model-based methods that use an arterial input function. The limitations that are associated with empirical analytical methods might account for artifactual results, especially when the effect size of the between-group difference and the number of subjects are small [149]. In addressing these limitations it will be important to increase the availability of these techniques beyond a few academic centers, to promote multi-center studies in well-characterized populations, and to standardize analytical methods. Until recently, SPECT was the only widely available technique, and SPECT studies have provided a substantial contribution to this field. With the current increase in PET camera availability, the development of [18F]-based molecular imaging probes will provide unique opportunities for further dissemination of these techniques. The article reviewed seminal findings obtained with PET and SPECT molecular imaging of schizophrenia. These techniques do not play a major role in the diagnosis and treatment of this disorder, remain essentially research tools. The results that have been produced by this field to date suggest that PET will significantly contribute to unraveling the biologic bases of psychiatric disorders and may contribute to their clinical management. Moreover, it is foreseeable that PET will become increasingly involved in the development of new psychiatric medications. Expanding the availability of PET and the current radiopharmaceutical portfolio will be critical for these predictions to become reality.

Can antipsychotic drugs be classified by their effects on a particular group of dopamine neurons in the brain?

During the four decades that research has been carried out on antipsychotic drugs, a variety of methods have been used to study the effects of these compounds on dopamine neurotransmission. An important issue in this research was to find an explanation for the difference between "typical" and "atypical" antipsychotic drugs. The hypothesis that the beneficial properties and the motor side effects of antipsychotic drugs result from their effects on different groups of dopamine neurons has received considerable attention. Numerous researchers have tried to discover regiospecific actions of antipsychotic drugs in mesolimbic and in mesocortical dopamine neurons. An overview of these research attempts is presented here. Electrophysiological studies showed a selective action of atypical antipsychotic drugs on A10 dopamine neurons. It was found that chronic treatment with these compounds induced a preferential depolarisation block of the A10 neurons that project to the mesolimbic areas. The model represents certain clinical features of antipsychotic drug use and offers a possible explanation for the lack of extrapyramidal side effects of atypical antipsychotic drugs. Dopamine neurons projecting from A10 to the frontal cortex are also considered as a possible site of action of atypical antipsychotic drugs. Microdialysis studies have shown that certain atypical antipsychotic drugs selectively enhance the release of dopamine in the prefrontal cortex when compared with typical antipsychotic drugs. The finding that repeated treatment with antipsychotic drugs increased dopamine D(2) receptor binding in the frontal cortex confirms the significance of this brain area. These properties might indeed explain certain beneficial effects of atypical antipsychotic drugs such as improvement of cognitive dysfunction. However the effects of typical and atypical antipsychotic drugs in the frontal cortex could not be fully differentiated, which illustrates the difficulty of localising clinical effects of antipsychotic drugs in terms of regional dopamine neurons. Recently new insights into the mechanism of action of typical and atypical antipsychotic drugs have been published. Clinical positron emission tomography (PET) studies have indicated that a moderate dopamine D(2) receptor occupancy, probably combined with a high dissociation rate, might provide the optimal clinical conditions for an antipsychotic drug, without inducing extrapyramidal side effects. Moreover the efficacy of benzamides as atypical antipsychotic drugs suggests that low to moderate dopamine D(2) blockade is probably the most important-if not the only-criterion that determines "atypicality". Interestingly these new insights are based on PET studies of the human basal ganglia and not on the comparison of different brain areas. Apparently, according to this concept an ideal antipsychotic drug need not to act on a particular type of dopamine neurons, as it is the moderate dopamine D(2) receptor occupancy that determines the desirable clinical effects. It is concluded that both beneficial actions and side effects, of antipsychotic drugs might be dose dependently localised in A9 as well as A10 dopamine neurons.

Neuroreceptor imaging in psychiatric disorders

Molecular imaging, the study of receptors, transporters and enzymes, as well as other cellular processes, has grown in recent years to be one of the most active neuroimaging areas. The application of single photon emission tomography (SPECT) and positron emission tomography (PET) techniques to the study of psychiatric illness has lead to increased understanding of disease processes as well as validated, in vivo, theories of illness etiology. Within the field of psychiatry these techniques have been applied most widely to the study of schizophrenia. Studies within schizophrenia are largely limited to either the dopamine or serotonin system. This is due in large part to the availability of suitable radiotracers as well as the current theories on the etiology of the illness. Two basic study designs are used when studying schizophrenia using molecular imaging and make up the majority of studies reviewed in this manuscript. The first type, termed "clinical studies," compares the findings from PET and SPECT studies in those with schizophrenia to normal controls in an attempt to understand the pathophysiology of the illness. The second study design, termed "occupancy studies," uses these techniques to enhance the understanding of the mechanism of action of the medications used in treating this illness. This review will focus on the findings of molecular imaging studies in schizophrenia, focusing, for the most part, on the serotonin and dopamine systems. Emphasis will be placed on how these findings and techniques are currently being used to inform the development of novel treatments for schizophrenia.

The effect of chronic treatment with typical and atypical antipsychotics on working memory and jaw movements in three- and eighteen-month-old rats

The effects of chronic treatment with typical and atypical antipsychotics on acquisition, working memory, motor activity, and rat tardive dyskinesia (TD) were studied in 3- and 18-month-old Sprague-Dawley rats. Acquisition and working memory were studied in eight-arm radial mazes. TD liability of antipsychotic drugs (APD) was evaluated in rat model of TD in which spontaneous repetitive jaw movements (RJM) occur during withdrawal from neuroleptic treatment. Motor behavior was assessed using the traverse beam test. D1 and D2 receptor occupancy was determined in the rat brain during treatment with typical and atypical antipsychotics. Chronic administration of clozapine, haloperidol, and risperidone impaired acquisition of the eight-arm radial maze in both young and aging rats while olanzapine had no effect. Retention tests showed that aging rats made more errors than the adults and that the antipsychotics haloperidol and risperidone significantly impaired retention in both age groups. Evaluation of motor behavior revealed that typical and atypical antipsychotics used in comparable doses in young rats had no effect on motor behavior, whereas in aging rats performance was impaired by clozapine, haloperidol, and risperidone but not by olanzapine. RJM responses were increased during washout from haloperidol treatment in young and aging rats whereas olanzapine, clozapine, and risperidone had no effect. D2 receptor occupancy in haloperidol- and risperidone-treated rats was above 70% while olanzapine and clozapine receptor occupancy was below 70%, which is the threshold for the appearance of extrapyramidal syndrome (EPS) and TD.

Increasing D2 affinity results in the loss of clozapine's atypical antipsychotic action

Typical antipsychotics (haloperidol) give rise to severe motor side-effects while atypical antipsychotics like clozapine do not. Action at several neurotransmitter receptors have been implicated. To identify the critical mechanisms involved we synthesized an 8-C1 isomer of clozapine which showed an equivalent affinity to clozapine on multiple receptors (5-HT1A, 5-HT2, D1, D4, M1) but differed in having a 10-fold higher affinity at the dopamine D2/3 receptor. When tested in a series of animal models indicative of the typical/atypical distinction (catalepsy, striatal gene-induction, prolactin elevation) isoclozapine lost atypical properties and behaved like a typical antipsychotic. Simultaneous in vivo receptor occupancy studies confirmed that alterations in D2 receptor occupancy were most closely related to loss of atypicality by clozapine's isomer isoclozapine. The implications for the design of future antipsychotics is discussed.

Double-blind olanzapine vs. haloperidol D2 dopamine receptor blockade in schizophrenic patients: a baseline-endpoint

The aim of this study was to compare in vivo striatal D2 dopamine receptor occupancy induced by olanzapine and haloperidol in schizophrenic patients using a baseline-endpoint [(123)I]IBZM single photon computed emission tomography (SPECT) design. The relationships of striatal D2 receptor occupancy with clinical efficacy and extrapyramidal symptoms (EPS) were also assessed. Twenty-seven inpatients with schizophrenia or schizophreniform disorder were included in a 4-week prospective, randomized, double-blind, parallel and comparative clinical trial. Thirteen patients were treated with haloperidol (10 mg/day) and 14 with olanzapine (10 mg/day). Ratings of clinical status and EPS were obtained weekly. The percentage of D2 receptor occupancy was estimated by using basal ganglia (striatum)/frontal cortex IBZM uptake ratios obtained from each patient before and after 4 weeks of maintained antipsychotic treatment. Olanzapine led to a mean striatal D2 receptor occupancy of 49% (range 28-69%), which was significantly lower than that induced by haloperidol (mean 64%, range 46-90%). The baseline-endpoint SPECT design used in this study revealed lower antipsychotic D2 occupancy percentage values than those reported in the literature, using other approaches. The degree of striatal D2 receptor occupancy correlated to the EPS, which predominantly appeared in patients on haloperidol. No relationship was found between the striatal D2 receptor occupancy and clinical improvement. Olanzapine induced a lower striatal D2 occupancy than haloperidol. This low striatal D2 occupancy, together with the lower incidence of EPS in olanzapine-treated patients, contributed to confirm the atypical behavior of this new antipsychotic drug. Nevertheless, conclusions based on SPECT-estimated percentages of antipsychotic D2 occupancy should be cautious, since the SPECT design could influence the results. In this regard, SPECT studies including baseline and endpoint examinations should be encouraged.

Neuropharmacological studies with SPECT in neuropsychiatric disorders

The last decade saw a rapid development of single photon emission computed tomography (SPECT) from a tool to assess cerebral blood flow to the study of specific neurotransmitter systems. Because of the relatively long half-life of SPECT radioisotopes, it is practical to measure the availability of neuroreceptors and transporters in conditions approaching equilibrium. The cost-efficiency of SPECT allowed studies in relatively large samples of patients with various neuropsychiatric disorders. We have applied this approach in studies of dopaminergic, serotonergic, and muscarinergic neurotransmission in patients with dementia, extrapyramidal disorders, schizophrenia, and alcoholism. No simple associations were observed between a single defect in one neurotransmitter system and a certain neuropsychiatric disease. Instead, complex dysfunction of several neurotransmitter systems in multiple, partially connected brain circuits have been implicated. Treatment effects also have been characterized. Microdialysis and neurotransmitter depletion studies showed that most radioligands and endogenous neurotransmitters compete for binding at receptors and transporters. Future research directions include the assessment of endogenous neurotransmitter concentrations measured by depletion studies and of genetic effects on neuroreceptor and transporter expression.

Neuropsychological and conditioned blocking performance in patients with schizophrenia: assessment of the contribution of neuroleptic dose, serum levels and dopamine D2-receptor occupancy

Patients with schizophrenia show impairments of attention and neuropsychological performance, but the extent to which this is attributable to antipsychotic medication remains largely unexplored. We describe here the putative influence of the dose of antipsychotic medication (chlorpromazine equivalents, CPZ), the antipsychotic serum concentration of dopamine (DA) D2-blocking activity and the approximated central dopamine D2-receptor occupancy (DA D2-occupancy), on conditioned blocking (CB) measures of attention and performance on a neuropsychological battery, in 108 patients with schizophrenia (compared with 62 healthy controls). Antipsychotic serum concentration and D2-occupancy were higher in patients with a paranoid versus non-paranoid diagnosis, and in female versus male patients (independent of symptom severity). Controlling for D2-occupancy removed the difference between high CB in paranoid and impaired low CB in non-paranoid patients. Similar partial correlations for antipsychotic drug dose and serum levels of DA D2-blocking activity with performance of the trail-making and picture completion tests (negative) and the block-design task (positive) showed the functional importance of DA-related activity. High estimates of central DA D2-occupancy were related to impaired verbal fluency but were associated with improved recall of stories, especially in paranoid patients. This, the first study of its kind, tentatively imputes a role for DA D2-related activity in left frontal (e.g. CB, verbal fluency) and temporal lobe functions (verbal recall) as well as in some non-verbal abilities mediated more in the right hemisphere in patients with schizophrenia.

Risperidone treatment of drug-related psychosis in patients with parkinsonism

Risperidone, a novel neuroleptic with approximately equal D2 and 5HT2A receptor blocking properties, has been used to treat drug-related hallucinations in patients with Parkinson's disease. However, the results of only small numbers of patients have been reported with the drug demonstrating limited usefulness. We report our experience with this drug in 39 patients (25 women and 19 men) with parkinsonism. Monitored clinical data included duration of disease, Hoehn and Yahr score, Mini-Mental State Score, Unified Parkinson's Disease Rating Scale (UPDRS) prior to drug administration and after 3 and 6 months of treatment, and response to treatment. Twenty-three patients with Parkinson's disease had either complete or near-complete resolution of hallucinations whereas an unsatisfactory response (N = 6) or worsening of parkinsonism (N = 6) was noted in 12 patients, only six of whom had Parkinson's disease. Excluding patients with diffuse Lewy body disease, there was no significant worsening of the UPDRS scores after either 3 or 6 months of treatment. The presence of dementia did not predict response to treatment. Our results suggest that risperidone is a useful treatment for hallucinations in patients with parkinsonism.

Atypical antipsychotics in the treatment of drug-induced psychosis in Parkinson's disease

Our experience with atypical antipsychotics in patients with PD is that their motor effects are not predictable. The multiple reports concerning clozapine's beneficial effects on tremor, dystonia, nocturnal akathisia, and dyskinesias all underscore this observation. However, the appearance of even minor degrees of parkinsonism in normal volunteers or schizophrenics should suggest that an antipsychotic will not be well-tolerated in patients with PD. The treatment of PD is probably the most stringent test of a drug's freedom from parkinsonian side effects. The data from trials in schizophrenia concerning parkinsonian effects cannot always be confidently interpreted. Virtually all subjects in these trials have been treated with typical neuroleptics until shortly before study entry. Because the parkinsonian side effects of these drugs may persist for several months, patients may still show declining levels of parkinsonism even when placed on a drug that induces it if this effect is milder than that induced by the pre-study neuroleptic. Depending on the pre-study drug used and the duration of the study, distinguishing placebo from a low-potency neuroleptic may be impossible. Furthermore, the standard measure of parkinsonism in psychiatric studies is the Simpson-Angus scale which is heavily weighted toward rigidity and may underscore bradykinesia, gait, and posture abnormalities. The prolactin response to an antipsychotic drug may turn out to be a good predictor of its freedom from parkinsonian side effects. That would fit with the data presented above of clozapine and quetiapine having less parkinsonian effects, olanzapine having more but variable effects and risperidone being poorly tolerated. With the data presented above, comprising a current review of all reports of the use of atypical antipsychotics in PD that we could locate, we can say little with certainty. The only drug with confirmed benefit without worsening parkinsonism is clozapine. Open-label trials involving over 400 patients and two multicenter, placebo-controlled, double-blind trials have demonstrated that it is effective in treating the psychosis. It improves tremor, does not worsen other motor functions to any significant extent, and is safe at low doses. Limited data provide conflicting information on both risperidone and olanzapine. Quetiapine seems to be well-tolerated with some, but definitely less, worsening of PD motor features than risperidone and olanzapine. Based on the current literature, our personal experience, and anecdotal experience of other PD specialists which we solicited, we will venture our own interpretation and recommendations. We think risperidone is poorly tolerated and should be used only as a last resort; that olanzapine is better than risperidone but will, in a majority of patients with PD, worsen motor function. We are optimistic, but not yet convinced, that quetiapine may prove to be as effective and better tolerated than clozapine. It will not require cumbersome monitoring because it does not induce a blood dyscrasia. We therefore recommend that DP be treated in the following manner. First, the anti-PD medications should be simplified and reduced as much as tolerated. We think, in general, side effects multiply more with increasing numbers of drugs than with drug dose, so that patients are more likely to tolerate a higher dose of levodopa than a lower dose of levodopa combined with other adjunctive anti-PD medications. In reducing anti-PD medications, we recommend tapering and stopping, if necessary, the drugs with the highest risk-to-benefit ratio first. Anticholinergics are stopped first, then selegiline, dopamine agonists, amantadine, and finally COMT inhibitors, which have no psychotomimetic action of their own. Finally, levodopa is reduced. Generally, a point is reached at which the anti-PD medications cannot be reduced without jeopardizing motor function. If psychosis persists at this point, then an antipsychotic is added. (ABS