Central D2-dopamine receptor occupancy in relation to antipsychotic drug effects: a double-blind PET study of schizophrenic patients

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.

The Role of Neuroimaging in Development of and Treatment With Antipsychotics

This article addresses how neuroimaging can impact the development of and therapy with antipsychotics. The article explains how drug development, disease pathophysiology and neuroimaging approaches can be understood within a single neurobiological framework. It then highlights the relative strengths and applicability of the two streams of neuroimaging: neurochemical neuroimaging that reveals regional concentrations of particular neurochemical species (receptors, transporters or enzymes) and functional neuroimaging that reveals the effects of drug or disease on regional indices of neuronal function such as blood flow and oxygen and glucose metabolism. The application of these techniques is exemplified with recent examples from development and therapeutic use of antipsychotics. To assist decision making in the context of these imaging possibilities, the article presents an algorithm that can be used to guide decisions regarding the application of neuroimaging in the development of and treatment with antipsychotics.

Probing targets for antipsychotic drug action with PET and SPET receptor imaging

The use of in vivo receptor imaging by positron emission tomography (PET) and single photon emission tomography (SPET) has permitted exploration of targets for antipsychotic drug action in living patients. Early PET and SPET studies focused on striatal D2 dopamine receptors. There is broad agreement that unwanted extrapyramidal (parkinsonian) side effects of antipsychotic drugs result from high striatal dopamine D2/D3 receptor blockade by these drugs. The dopamine hypothesis of antipsychotic drug action suggests that clinical response is directly related to the level of striatal D2/D3 receptor occupancy of antipsychotic drugs. This may be true for classical antipsychotic drugs, but recent evidence suggests that novel, atypical antipsychotic drugs produce efficacy in association with modest and transient striatal D2/D3 receptor occupancy levels. Furthermore, atypical antipsychotic drugs appear to show preferential occupancy of limbic cortical dopamine D2 receptors. Cortical dopamine D2/D2-like receptors may be a common site of action for all antipsychotic drugs. Data from receptor challenge paradigms has highlighted the need to explore the neurotransmitter systems involved in regulating or stabilising dopamine transmission, either via dopamine autoreceptors or non-dopaminergic pathways. These may be promising targets for drug development. In vivo PET and SPET imaging has produced unique data contributing to the design of better, less toxic drugs for schizophrenia.

D2 receptor occupancy under recommended and high doses of olanzapine: an iodine-123-iodobenzamide SPECT study

The aim of this study was to compare the degree of striatal dopamine D2 receptor availability in patients treated with recommended (5-20 mg, mean dose 11.9 +/- 6.3 mg daily) and higher doses (25-40 mg, mean 32.1 +/- 5.6 mg daily) of the novel antipsychotic drug olanzapine by means of [123I] IBZM Single photon emission computed tomography (SPECT). The results were compared to those of a group of 10 untreated, healthy, age- and sex-matched controls. The degree of dopamine D2 receptor occupancy in the patient group was correlated with the presence of extrapyramidal symptoms (EPS). A total of 20 patients who met the DSM III R criteria for schizophrenia or schizoaffective disorder received a clinically effective antipsychotic monotherapy with olanzapine. The mean daily dose of olanzapine ranged from 0.05-0.6 mg/kg body weight. The dopamine D2 receptor binding was reduced in all patients treated with olanzapine. Specific IBZM binding expressed as the [STR-BKG]/BKG ratio ranged from 0.13-0.61 (healthy controls 0.95). The D2 receptor availability revealed an exponential dose-response relationship (r = - 0.85, p < 0.001). The frequency of EPS induced by olanzapine was considerably lower. Only one patient, treated with 40 mg olanzapine, suffered from severe EPS symptoms and had to be given biperiden. There were no significant differences in the presence of EPS symptoms between patients with recommended doses and those with higher doses of olanzapine.

In vivo extrastriatal and striatal D2 dopamine receptor blockade by amisulpride in schizophrenia

Amisulpride, a substituted benzamide with high affinity for dopamine D2 and D3 receptors only, has been reported to have therapeutic effects on both negative and positive schizophrenic symptoms, although at distinct dose ranges (50-300 mg/day vs. 400-1,200 mg/day). The purpose of this study was to investigate the binding of amisulpride to extrastriatal (i.e., thalamus and temporal cortex) and striatal D2 dopamine receptors with respect to plasma amisulpride determinations. Ten patients with schizophrenia treated with amisulpride over a wide range of doses (25-1,200 mg/day) were studied. Positron emission tomography images were acquired by using 76Br-FLB-457, a highly specific antagonist of the D2 and D3 dopamine receptors. Binding indexes (BI) in the regions studied were estimated with reference to values from six healthy subjects. A curvilinear relationship was demonstrated between plasma concentration of amisulpride and the BI in extrastriatal regions. The BI also varied as a function of plasma concentration in striatum. Furthermore, the data provide evidence for different binding profiles: low plasma concentrations (28-92 ng/mL) induced marked extrastriatal binding and low striatal binding, whereas higher plasma concentrations (>153 ng/mL) induced marked binding both in extrastriatal and striatal regions. Dose-dependent differential binding profiles of amisulpride to D2 receptors in extrastriatal and striatal regions were demonstrated, and two therapeutic ranges of plasma concentrations for negative and positive schizophrenic symptoms, respectively, are suggested.

State of the art of drug treatment of schizophrenia and the future position of the novel/atypical antipsychotics

Neuroleptic medication is the most important part of the treatment regimen for schizophrenic patients. The efficacy of neuroleptics in the acute and long-term treatment of schizophrenia is very well proven and the effect size is comparatively high. After more than 40 years of clinical practice with the classical neuroleptics, several more or less generally accepted rules for the management of drug treatment in schizophrenia have been established. The paper aims to describe these standards, discussing, among other things, developments which have appeared in the last 10 to 20 years, e.g. the tendency to a lower daily dose during acute treatment and the tendency to alternative strategies during long-term treatment. The paper especially also takes into consideration the benefits of the novel/atypical antipsychotics as compared to the classical neuroleptics, which will change the current treatment standards under several aspects--a change which is already ongoing. The novel/atypical antipsychotics will be much better accepted by patients, thus leading to increased compliance, will be associated with a better quality of life and will possibly change the long-term outcome of schizophrenic patients in a very important manner. It should be considered that the so-called novel/atypical neuroleptics do not constitute a homogeneous group but are a group of individual drugs, each with their own advantages and disadvantages. As was the situation with the classical neuroleptics, the physician also has to choose the most adequate drug under consideration of the risk/benefit profile of each drug in relation to the disposition of the individual patient.

Clinical pharmacology of psychotropic drugs

No Abstract

Are animal studies of antipsychotics appropriately dosed? Lessons from the bedside to the bench

Animal models are crucial for understanding the mechanism of action of antipsychotics. However, the dose of an antipsychotic in animal studies is often arbitrarily chosen, with haloperidol 1 mg/kg being a rather common standard. Recent clinical positron emission tomography (PET) studies in patients show all antipsychotics to block dopamine D2 receptors, and most are effective at doses that lead to 60% to 80% D2 occupancy. When occupancy exceeds 80%, the incidence of side effects rises sharply. To use this "bedside" information to inform the "bench," we measured D2 occupancy in rats using a method similar in principle to the [11C]-raclopride PET method in humans. We found that: 1) as in humans, haloperidol is effective in animal models of antipsychotic action when D2 occupancy > 70% and leads to effects in models of extrapyramidal side effects when D2 occupancy is > 80%; 2) very low doses, 0.06 mg/kg/sc, cause acute D2 occupancy of 75%; 3) and even doses that acutely saturate D2 receptors give little D2 occupancy after 24 hours due to the very short half-life of haloperidol in rats (2.5 hours versus 24 hours in humans). We conclude that most previous animal studies of antipsychotics have used doses giving rise to inappropriately high acute D2 occupancy and inappropriately low D2 occupancy between doses. We exemplify how this dosing confounder could lead to inappropriate conclusions. Data from the bedside translated to the bench--using D2 occupancy as a mediating variable--will lead to more valid animal models.

In vivo monitoring of drugs using radiotracer techniques

There is an increasing realization of the role of non-invasive monitoring of drug pharmacology. In this review, we discuss the role of positron emission tomography in such monitoring of tumour and normal tissue drug pharmacokinetics as well as assessment of tumour response, drug-receptor interactions and mechanisms of drug action and resistance. These studies represent a multidisciplinary research effort involving radiochemists, imaging scientists, clinicians, pharmacologists and mathematical modellers. This review evaluates achievements in the field from assessment of commonly used therapeutic agents such as 5-fluorouracil to target specific molecules such as markers for gene expression. It is envisaged that application of this technology will facilitate rational drug design and rapid translation of new ideas to the bedside.

Long-acting antipsychotic medication, restraint and treatment in the management of acute psychosis

OBJECTIVE

Zuclopenthixol acetate (ZA) is the first parenteral antipsychotic medication introduced for clinical use in the treatment of aggression and agitation that has a relatively prolonged duration of action. The aim of this paper is to explore a number of important ethical and clinical issues that are raised by the use of this novel therapeutic formulation.

METHOD

Relevant literature is explored and several issues are identified from which arguments for and against the use of medication of this type are raised. These issues are considered in general and with the use of a number of stylised clinical scenarios.

RESULT

The use of long-acting antipsychotic medication is complicated by its impact upon patient autonomy, by considerations of informed consent and by the need to provide justice to all patients and staff in a psychiatric treatment setting. The use of ZA in the emergency treatment of psychotic patients may only be justified under specific clinical circumstances and its use is not appropriate as routine chemical restraint.

CONCLUSIONS

Zuclopenthixol acetate is a novel and potentially useful treatment alternative in the acutely disturbed patient. Institutions in which ZA is used in emergency settings should develop protocols to guide clinicians in its appropriate use and provide monitoring.

Nuclear medicine in neurology and psychiatry

Progress in nuclear medicine has always been a function of technological advances, and applications in neurology and psychiatry illustrate the point. Improvements in radiation detectors now allow for three-dimensional and quantitative mapping of the distribution of a labelled compound in the human brain. New ligands permit the study of specific functioning signals of the blood/brain barrier, blood flow, metabolism (oxygen, glucose, aminoacids), and neurotransmission (dopamine, benzodiazepine, serotonin receptors). The picomolar sensitivity of nuclear medicine can now be coupled to a wide group of ligands which offer specific information that can be obtained in no other way in the living patient.

In vivo occupancy of striatal and temporal cortical D2/D3 dopamine receptors by typical antipsychotic drugs. [123I]epidepride single photon emission tomography (SPET) study

BACKGROUND

The dopamine hypothesis proposes that antipsychotic drugs act primarily through limbic cortical D2/D2-like dopamine receptor blockade.

AIM

To evaluate this hypothesis with the D2/D3-selective SPET probe [123I]-epidepride.

METHOD

[123I]-epidepride SPET scans were performed on 12 patients with schizophrenia treated with antipsychotics and II age-matched healthy controls. [123I]-epidepride 'specific binding' to D2/D3 dopamine receptors was estimated, and relative percentage D2/D3 receptor occupancy by typical antipsychotic drugs determined.

RESULTS

Mean (s.d.) daily dose was 669.12 (516.8) mg chlorpromazine equivalents. Mean percentage D2/D3 receptor occupancy was 81.6 (8.1) and 73.2 (13.9) in the temporal cortex and striatum respectively.

CONCLUSIONS

Typical antipsychotic drug treatment is associated with substantial temporal cortical D2/D3 receptor occupancy. The relationship between this and efficacy is poor in patients with treatment-resistant schizophrenia.

Optimal haloperidol dosage in first-episode psychosis

OBJECTIVE

To determine optimal doses of haloperidol for the treatment of a first episode of psychosis.

METHOD

A 4-week prospective controlled clinical trial with "optimal dose" defined as the dose at which either of the following occurs: 1) significant improvement, defined as a 15% or greater decrease in scores on the Positive And Negative Syndrome Scale (PANSS), or 2) the onset of extrapyramidal symptoms. Beginning with 2 mg daily, haloperidol was increased weekly to 5 mg, 10 mg, and finally 20 mg daily until either 1) or 2) occurred.

RESULTS

Optimal doses for the 36 subjects were 2 mg daily for 15 subjects, 5 mg daily for 11, 10 mg daily for 7, and 20 mg daily for 3. On average, subjects whose optimal dose was 2 mg daily showed the greatest improvement. Among the 27 subjects evidencing clinical response to treatment, 20 had plasma haloperidol levels below 5 ng/ml.

CONCLUSION

Many people suffering a first psychotic episode respond to haloperidol doses well below levels in common use.

Clinical and theoretical implications of 5-HT2 and D2 receptor occupancy of clozapine, risperidone, and olanzapine in schizophrenia

OBJECTIVE

Dopamine D2 receptor occupancy measurements provide a valid predictor of antipsychotic response, extrapyramidal side effects, and elevation of prolactin levels. The new antipsychotics clozapine, risperidone, and olanzapine obtain antipsychotic response with few extrapyramidal side effects and little prolactin elevation. The purpose of this study was to compare the D2 and serotonin 5-HT2 receptor occupancies of these drugs in patients receiving multiple-dose, steady-state regimens.

METHOD

Forty-four patients with schizophrenia (16 taking risperidone, 2-12 mg/day; 17 taking olanzapine, 5-60 mg/day; and 11 taking clozapine, 75-900 mg/day) had their D2 and 5-HT2 occupancies determined with the use of [11C]raclopride and [18F]setoperone, respectively, and positron emission tomography imaging.

RESULTS

Clozapine showed a much lower D2 occupancy (16%-68%) than risperidone (63%-89%) and olanzapine (43%-89%). Risperidone and olanzapine gave equal D2 occupancies at doses of 5 and 20 mg/day, respectively. All three drugs showed greater 5-HT2 than D2 occupancy at all doses, although the difference was greatest for clozapine.

CONCLUSIONS

Clozapine, at doses known to be effective in routine clinical settings, showed a D2 occupancy clearly lower than that of typical antipsychotics, while risperidone and olanzapine at their usual clinical doses gave the same level of D2 occupancy as low-dose typical antipsychotics. The results also suggest that some previous clinical comparisons of antipsychotics may have been confounded by different levels of D2 occupancy. Clinical comparisons of these drugs, matching for D2 occupancy, may provide a better measure of their true "atypicality" and will help in understanding the contribution of non-D2 receptors to antipsychotic effects.

An investigation of ethnic and gender differences in the pharmacodynamics of haloperidol

The objective of this study was to examine neuroleptic effectiveness among Asians and Caucasians, and to investigate inter-ethnic pharmacodynamic differences. Asians and Caucasians suffering a first episode of psychosis were maintained on low oral doses of haloperidol (2 mg/day) for the first week of treatment. Doses were increased weekly until the optimal therapeutic dosage was achieved. This was defined as the point at which subjects: (a) experienced significant clinical improvement; or (b) developed extrapyramidal side effects. Plasma haloperidol and prolactin were measured at intake, at the end of first week of the treatment on haloperidol 2 mg/day, and at optimal therapeutic dosage. The average optimal dosage for Asians and Caucasians was equal. However, at the end of the first week of haloperidol at a fixed dose of 2 mg, Caucasian males had significantly lower plasma haloperidol levels than Asian males while no ethnic differences in haloperidol levels were found among females. There were no ethnicity or gender effects on plasma prolactin response after 1 week of treatment. Ethnicity and gender may affect haloperidol metabolism.

Differential sensitivities to risperidone and olanzapine in a human immunodeficiency virus patient

BACKGROUND

Neuroleptic sensitivity presents a considerable problem for the treatment of psychosis in the acquired immunodeficiency syndrome (AIDS) and human immunodeficiency virus (HIV)-positive patient population. As yet, there are few data on the response of these patients to newer atypical antipsychotic medications.

METHODS

We present the detailed medication history of a 33-year-old man with AIDS, who had a prior history of extrapyramidal symptoms (EPS) with both typical antipsychotics and risperidone, and was treated with olanzapine for major depression with psychotic features.

RESULTS

The patient developed akathisia in a dose-dependent manner at dosages between 10 and 15 mg daily of olanzapine, but no EPS. Akathisia responded to dose reduction and use of beta-adrenergic blockade.

CONCLUSIONS

The AIDS patient may exhibit sensitivity even to newer atypical antipsychotics. The lack of EPS and response to a beta-blocker underscore the different mechanisms causing akathisia and EPS.

Functional imaging of the brain in the evaluation of drug response and its application to the study of aging

Functional neuroimaging techniques including single photon emission computerised tomography (SPECT), positron emission tomography (PET) and functional magnetic resonance imaging (FMRI) can provide insight into the functional connectivity of the human brain in both health and disease, including the effects of aging and drugs on brain function. Neuroimaging measurement techniques can either be direct, using radio-specific ligands, or indirect, using the neurophysiological consequences of pharmacological interventions. Both approaches can be combined with sensorimotor or cognitive activation to examine the interaction between the targeted receptor function and the sensorimotor or cognitive process implicit in the study design. Using radionuclides, PET can provide absolute measurement of cerebral blood flow to regions of interest and can measure changes in cerebral metabolism using labelled fluorodeoxyglucose. PET offered the first opportunity to image brain activation caused by a variety of stimuli and hence to measure the effect of drugs on brain activation. PET also enables the study of drug disposition within the brain. SPECT has been used to study relative changes in cerebral blood flow associated with disease processes and also receptor occupancy. FMRI, by contrast, does not involve ionising radiation and has better spatial and temporal resolution. It is still a relatively new technique and limited by its ability to only measure haemodynamic changes through the blood oxygen level-dependent (BOLD) signal. The effects of aging on drug responsiveness and the effects of drug treatment of diseases associated with old age are relatively unexplored areas of functional neuroimaging research.

Comparison of the transient equilibrium and continuous infusion method for quantitative PET analysis of [11C]raclopride binding

Several approaches have been applied for quantification of D2 dopamine receptors in positron emission tomography studies using [11C]raclopride. Initial approaches were based on analyses of data obtained after rapid bolus injection of [11C]raclopride. A continuous infusion paradigm has more recently been applied. The current study compares these approaches in healthy men. Two positron emission tomography measurements were performed in each of six healthy men, the first with rapid bolus injection and the second with continuous infusion of [11C]raclopride. In rapid bolus injection, the binding potential was calculated by the following methods. One approach is the kinetic analysis using the standard three-compartment model. Another is to define a transient equilibrium at the moment when the specific binding reaches its maximum. In continuous infusion, binding potential was calculated by using time-activity data at equilibrium condition. All methods gave almost identical binding potential, representing cross-validation of these methods. The continuous infusion method can provide "true" equilibrium condition. The kinetic analysis is a sophisticated approach but requires determination of an arterial input function. The transient equilibrium method thus is suitable for routine clinical research, since it does not require determination of an arterial input function.

Plasma prolactin and central D2 receptor occupancy in antipsychotic drug-treated patients

Previous studies of the relationship between plasma prolactin and clinical effects in patients treated with antipsychotic drugs have yielded inconsistent results. A possible explanation may be that most studies have not included subtherapeutic or low doses of antipsychotics. In this exploratory, double-blind study, the relationship between plasma prolactin concentration and central D2 receptor occupancy was examined in 13 schizophrenic patients treated with the experimental antipsychotic drug raclopride (2, 6, or 12 mg daily). D2 receptor occupancy was determined by positron emission tomography and was related to antipsychotic effect as measured by the Brief Psychiatric Rating Scale. Plasma prolactin concentration was increased in eight of nine patients with a D2 receptor occupancy greater than 50%, whereas it was normal among patients with a D2 receptor occupancy less than 50% (p < 0.01). Plasma prolactin concentration measured 4 hours after the morning dose of raclopride correlated significantly with plasma raclopride concentration (r = 0.92, p < 0.01), the degree of D2 receptor occupancy (r = 0.81,p < 0.01), and the antipsychotic effect (r = 0.79, p < 0.01). Further controlled studies that include low doses of antipsychotic drugs may warrant a reconciliation of plasma prolactin as a useful tool in clinical monitoring of antipsychotic drug treatment.

Typical and atypical antipsychotics in adolescent schizophrenia: efficacy, tolerability, and differential sensitivity to extrapyramidal symptoms

OBJECTIVE

To review the existing literature on the efficacy and tolerability of antipsychotics for adolescent psychosis. The review focuses in particular on literature regarding adverse effects that are thought to have an increased incidence in young patients and on the possible neurobiological bases for such differential sensitivity.

METHOD

Pertinent studies were sought using Medline searches, supplemented by selected bibliographies, and reviewed.

RESULTS

There is a relative paucity of research in this area; in particular, well-controlled trails are lacking. The existing literature suggests fairly good efficacy of both typical and atypical antipsychotics in the treatment of psychotic disorders in children and adolescents. However, the incidence of certain side effects, particularly extrapyramidal symptoms (EPS). is found to be higher in younger patients compared with adults. Positron emission tomography (PET) receptor studies in adults have demonstrated that the incidence of EPS is related to dose-dependent dopamine type-2 (D2) receptor occupancy and that there is a significant relationship between the number of these receptors and age.

CONCLUSIONS

Improved tolerability is leading to the increasing us of atypical antipsychotics for adolescent patients, though these new drugs to have specific adverse effects of their own. There is a need for more controlled studies of atypical antipsychotics in children and adolescents. In particular, dose-finding studies are needed to determine the optimal dose range to produce the greatest improvement with the least side effects for each of these drugs.

Prominence of the dopamine D2 short isoform in dopaminergic pathways

As a result of alternative splicing, the D2 gene of the dopamine receptor family exists in two isoforms. The D2 long is characterized by the insertion of 29 amino acids in the third cytoplasmic loop, which is absent in the short isoform. We have produced subtype-specific antibodies against both the D2 short and D2 long isoforms and found a unique compartmentalization between these two isoforms in the primate brain. The D2 short predominates in the cell bodies and projection axons of the dopaminergic cell groups of the mesencephalon and hypothalamus, whereas the D2 long is more strongly expressed by neurons in the striatum and nucleus accumbens, structures targeted by dopaminergic fibers. These results show that the splice variants of the dopamine D2 receptor are differentially distributed and possess distinct functions. The strategic localization of the D2 short isoform in dopaminergic cell bodies and axons strongly suggests that this isoform is the likely dopamine autoreceptor, whereas the D2 long isoform is primarily a postsynaptic receptor.

D2 dopamine receptor up-regulation, treatment response, neurological soft signs, and extrapyramidal side effects in schizophrenia: a follow-up study with 123I-iodobenzamide single photon emission computed tomography in the drug-naive state and after neuroleptic treatment

BACKGROUND

Animal and postmortem studies indicate that neuroleptic therapy may induce D2 dopamine receptor up-regulation in the basal ganglia.

METHODS

To address this phenomenon in a clinical study, we investigated the D2 dopamine receptor binding in 15 DSM-III-R schizophrenics in the drug-naive state and 3 days after completion of a standardized neuroleptic therapy (benperidol 12-16 mg/day, for 25 days) using single photon emission computed tomography (SPECT). SPECT scans were obtained 2 hours after intravenous injection of 185 MBq 123I-iodobenzamide. For analysis, basal ganglia to frontal cortex (BG/FC) ratios were calculated and the patient sample was subgrouped into patients with a favorable versus a poor treatment response.

RESULTS

Neuroleptic treatment led to decreased BG/FC ratios in patients with a favorable response, but increased ratios in the poor responders (df = 1, F = 4.1, p = .06). Changes of BG/FC ratios were significantly correlated with extrapyramidal side effects but not with neurological soft signs.

CONCLUSIONS

Our findings suggest that neuroleptic therapy may induce D2 dopamine receptor up-regulation in a subgroup of patients characterized by poor treatment response and pronounced extrapyramidal side effects.

The relationship between serum concentration and therapeutic effect of haloperidol in patients with acute schizophrenia

Haloperidol is the most commonly used antipsychotic drug in the therapy of acute schizophrenia. Clinicians have been using therapeutic drug monitoring in an attempt to improve clinical application of this drug. The scale of interest in this area is emphasised by the large number of studies (about 50) concerning the serum concentration-therapeutic effect relationship (SCTER) of haloperidol, including 35 studies on patients with acute schizophrenia. However, conflicting results concerning the existence and position of a therapeutic window have emerged. This article aims to provide a comprehensive review of the study design of studies in patients with acute schizophrenia before the study data are used for decision-making. For this purpose, a reproducible system for the evaluation of studies in this special area, a so-called total study score (TSS), was developed on an empirical basis. Thus, insufficient study design was found to be a reason for negative results. On the other hand, in spite of a great variability, the majority of studies with good design provided evidence for a significant SCTER: a bisigmoidal dependence of clinical effect on haloperidol serum concentration. The therapeutic effects of haloperidol increase at low concentrations, and the concentration has a maximum effect at about 10 micrograms/L and again decreasing at higher concentrations. The data of 552 patients also fit to this model in a single scatter plot (pseudo-r2 = 0.076, p < 0.001). The position of the therapeutic window was determined at about 5.6 to 16.9 micrograms/L. Patients treated with serum concentrations within this optimal range had a significantly better response compared with outside this range (p < 0.001, Student t-test). Therefore, a quantitative synthesis of all available data by means of effect-size analysis provides a mean effect-size (g) = 0.499 +/- 0.182 (standard deviation) for the comparison of haloperidol-treatment with serum concentrations within versus outside the therapeutic window. Thus, because of this moderate positive effect, serum concentration assay of haloperidol is recommended for patients with acute schizophrenia in a therapeutic drug monitoring programme. The modalities of haloperidol therapeutic drug monitoring in clinical practice are discussed, e.g. patient selection, method and time for serum concentration measurement, influence of premedication and comedication, interpretation of results and dose adjustment. Clinical investigations into this subject should focus on covariates which are responsible for the variability of the SCTER. Serum concentration assay is advised for investigations of nonresponse to exclude patients with pseudo-drug resistance.

Dose-response relationships for the antipsychotic effects and Parkinsonian side-effects of typical neuroleptic drugs: practical and theoretical implications

1. From a review of published literature it is concluded that the minimum dose of a neuroleptic drug (NLD) required to alleviate psychosis is very similar to that producing minimal parkinsonian side effects (PSE). This conclusion is reached both from group comparisons and individual comparisons of dose/response relations (DRR) for the two effects. 2. A lower dose of NLD is usually sufficient to prevent relapse in well stabilized patients than is needed to check an active psychotic state. 3. Anticholinergic agents used to reduce side effects of typical NLD can retard the therapeutic process during neuroleptic treatment of acute psychosis. Although it is not fully established that this is a central interaction, it is consistent with the idea that minimal side effects are a necessary condition for therapeutic effectiveness with typical antipsychotic drugs. 4. In relapse-free maintenance of psychosis-prone patients, tolerance occurs to PSE. Thus few patients need experience prolonged side effects during maintenance treatment with neuroleptics. 5. The evidence reviewed is discussed with respect to a previous hypothesis of the supposedly "indirect" action of typical neuroleptic drugs in therapy for psychosis. The evidence is consistent with the idea of a close causal relation between minimal PSE of these drugs, and their therapeutic effectiveness in the acute stage of treatment.

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

Risperidone is an antipsychotic drug with high affinity at dopamine D2 and serotonin 5-HT2 receptors. Previous clinical studies have proposed that risperidone's pharmacologic profile may produce improved efficacy for negative psychotic symptoms and decreased propensity for extrapyramidal side effects; features shared by so-called 'atypical' neuroleptics. To determine if routine risperidone treatment is associated with a unique degree of D2 receptor occupancy and pattern of clinical effects, we used [123I]IBZM SPECT to determine D2 occupancy in subjects treated with routine clinical doses of risperidone (n = 12) or haloperidol (n = 7). Both risperidone and haloperidol produced D2 occupancy levels between approximately 60 and 90% at standard clinical doses. There was no significant difference between occupancy levels obtained with haloperidol or risperidone. Drug-induced parkinsonism was observed in subjects treated with risperidone (42%) and haloperidol (29%) and was observed at occupancy levels above 60%. Based on these observations, it is concluded that 5-HT2 blockade obtained with risperidone at D2 occupancy rates of 60% and above does not appear to protect against the risk for extrapyramidal side effects.

Guidelines for the use of antipsychotic drug studies in healthy volunteers. The BAP Consensus Group

The following article summarizes the background to a British Association for Psychopharmacology Workshop held at the Royal Society, London, on 15 March 1996. It includes abstracts of the papers presented at that meeting and concludes with a list of agreed guidelines for future studies with antipsychotic drugs in healthy volunteer subjects.

Paroxetine potentiates the central nervous system side effects of perphenazine: contribution of cytochrome P4502D6 inhibition in vivo

BACKGROUND

Paroxetine is a frequently used antidepressant and a potent inhibitor of the CYP2D6 isozyme in vitro (inhibition constant [Ki] = 0.15 micromol/L). Most classic antipsychotic agents such as perphenazine are metabolized by the CYP2D6 isozyme and are often coadministered with antidepressant agents. This study assessed the extent of changes in CYP2D6 isozyme activity in vivo after pretreatment with paroxetine and its consequences on perphenazine kinetics and central nervous system effects.

METHODS

Eight extensive metabolizers for CYP2D6 were administered a single dose of perphenazine (0.11 mg/kg orally) or placebo following a randomized double-blind design. Perphenazine plasma concentrations and effects were assessed for a period of 8 hours. Subsequently, subjects were treated with a standard therapeutic dose of paroxetine (20 mg/day orally) for 10 days and test sessions with perphenazine and placebo were repeated.

RESULTS

Paroxetine treatment resulted in a twofold to 21-fold decrease in CYP2D6 activity (p < 0.001). After pretreatment with paroxetine, perphenazine peak plasma concentrations increased twofold to 13-fold (p < 0.01). This was associated with a significant increase in central nervous system side effects of perphenazine, including oversedation, extrapyramidal symptoms, and impairment of psychomotor performance and memory (p < 0.05).

CONCLUSION

Coadministration of perphenazine after pretreatment with a standard therapeutic dose of paroxetine increased the plasma concentration and central nervous system side effects of perphenazine, primarily as a result of inhibition of the CYP2D6 isozyme. In patients who are at steady state with paroxetine, a reduction of perphenazine dose may be required to prevent central nervous system side effects.

In vivo kinetics of [18F](N-methyl)benperidol: a novel PET tracer for assessment of dopaminergic D2-like receptor binding

A novel D2-like receptor-binding radioligand, [18F](N-methyl)benperidol ([18F]NMB), was evaluated via positron emission tomographic (PET) imaging studies of baboons. [18F]NMB rapidly localized in vivo within dopaminergic receptor-rich cerebral tissues, and striatum-to-cerebellum ratios as high as 35 were achieved after 3 hours. Pretreatment of an animal with unlabeled receptor-specific antagonists before injection of [18F]NMB confirmed that the radioligand bound specifically to central D2-like receptors in vivo, and not to S2- or D1-like receptors. Unlabeled eticlopride displaced striatal [18F]NMB in vivo, showing that D2-like binding is reversible. Receptor-binding by the radioligand was resistant to competitive displacement by synaptic dopamine, as illustrated by the lack of effect of intravenous d-amphetamine on the in vivo localization of [18F]NMB. Studies involving sequential intravenous administration of [18F]NMB, d-amphetamine, and eticlopride show that the radioligand does not undergo agonist-mediated internalization with subsequent trapping. The feasibility of applying a three-compartment non-steady state model for quantification of [18F]NMB receptor binding was demonstrated. These in vivo characteristics give [18F]NMB distinct advantages over the PET radiopharmaceuticals currently used for clinical investigation of D2-like receptor binding.

Neuroleptic dosing in chronic schizophrenia: a 10-year follow-up

OBJECTIVE

To evaluate neuroleptic dosing patterns in individuals with schizophrenia over a 10-year interval.

METHOD

Changes in neuroleptic dosing between 1980 and 1990 were followed in 65 patients with a diagnosis of chronic schizophrenia.

RESULTS

According to more recent dosing guidelines, doses were already high at the time of initial evaluation, yet overall they continued to increase during the next decade of treatment for both males and females. Patients were almost equally divided, however, by those who underwent an increase (n = 33) and those whose dose remained stable (n = 4) or was decreased (n = 28).

CONCLUSION

A considerable number of patients with schizophrenia appear to receive progressively higher neuroleptic doses over the course of their illness, despite a lack of empirical data to support such an approach. Results are discussed in terms of current dosing recommendations and factors influencing dose changes.

The Dose Reduction in Schizophrenia (DORIS) Study: a final report

Twenty-one medication-free chronic schizophrenics were randomly assigned to three treatment groups: 50% blockade of the bromocriptine growth hormone (GH) response, 100% blockade or 10 ng/ml haloperidol. Only seven of the 21 patients showed a significant improvement after 6 weeks in positive psychotic symptoms; six of the seven responders came from the 50 and 100% blockade groups, suggesting greater efficacy at lower doses. Fifty percent blockade was associated with an average daily haloperidol dose of 3.2 mg and plasma haloperidol levels below the limit of detection (< 1 ng/ml). 100% blockade was associated with a daily dose of 6.5 mg and a plasma haloperidol level of 1 ng/ml. Negative symptoms significantly improved in only four of the 21 patients, and three of these patients were from the 100% blockade group. Twenty-nine patients currently receiving 20 mg/day haloperidol were randomly assigned to three treatment groups: placebo, 100% blockade of the GH response and 10 ng/ml. Patients in the placebo group showed significant deterioration along both the positive and negative symptom dimensions. There were no significant symptom differences between the 100% blockade and the 10 ng/ml groups. The patients in the 100% blockade group had on average a daily dose reduction from 20 to 11 mg/day and a 65% reduction in the plasma haloperidol level. There was a 70% difference in the average daily dose for 100% blockade between the two study arms. The higher daily dose in the dose-reduction arm may reflect receptor up-regulation and/or other "tolerance'-like mechanisms associated with chronic neuroleptic administration.

Perspectives on the role of serotonergic mechanisms in the pharmacology of schizophrenia

In recent years, a number of research findings has renewed interest in the possible role of serotonin (5-HT) in the pharmacology of schizophrenia. Atypical antipsychotics that potently block 5-HT receptors have been shown to be at least as effective as classical antipsychotics as well as producing fewer extrapyramidal side-effects. In addition, molecular biological studies have suggested that allelic variations of 5-HT receptor genes may affect both susceptibility to schizophrenia and clinical response to atypical antipsychotics. Building on these findings, this article proposes that 5-HT receptors are critical sites of antipsychotic action, and examines the implications of this to the treatment and pathophysiology of schizophrenia. Possible pharmacological mechanisms underlying the clinical efficacy of 5-HT blocking antipsychotics are discussed, and the potential of functional neuroimaging techniques to further elucidate these mechanisms is emphasized.

Effects of intermittent and continuous subchronic administration of raclopride on motor activity, dopamine turnover and receptor occupancy in the rat

With the purpose of finding means to circumvent the marked pharmacokinetic differences of raclopride between rats and man, the effects of intermittent and continuous administration of raclopride were compared in rats. Intermittent administration of raclopride via subcutaneous injections resulted in a prompt increase of dopamine (DA) turnover and decrease of motor activity but these effects were of short duration, probably due to rapidly decreasing raclopride DA D2 receptor occupancy. In contrast, but similar to schizophrenic patients on raclopride treatment, stable plasma raclopride levels and a steady DA D2 receptor occupancy above 70% were produced in the caudate-putamen and nucleus accumbens/olfactory tubercle, when raclopride was administered continuously via minipumps at daily doses above 2 mg/kg. Tolerance to the acute effects of raclopride on DA turnover and locomotion was found with both routes of administration but it was more marked with continuous administration. At continuous raclopride administration, tolerance to the effects of raclopride on DA turnover and spontaneous motor activity as well as supersensitivity to amphetamine-induced motor activity occurred when 70% or more of DA D2 receptor sites were occupied, i.e. the same degree of receptor occupancy as found in patients given therapeutic doses of raclopride.

Enhancement of antipsychotic-like properties of the dopamine D2 receptor antagonist, raclopride, by the additional treatment with the 5-HT2 receptor blocking agent, ritanserin, in the rat

The effects of 5-HT2 receptor blockade on the ability of a dopamine (DA) D2 receptor antagonist to produce suppression of conditioned avoidance response (CAR) and to produce catalepsy in rats were examined. It was found that ritanserin (2 mg kg-1 s.c.) enhanced the raclopride (0.1 mg kg-1 s.c.)-induced suppression of CAR without affecting raclopride-induced catalepsy at either maximal (4 mg kg-1 s.c.) or submaximal (0.2 mg kg-1 s.c.) doses. Considering the CAR performance as an index of mesocorticolimbic dopaminergic functions, it is concluded that 5-HT2 receptor blockade confers a limbic profile on the DA D2 receptor antagonist.

Test-retest reliability of central [11C]raclopride binding at high D2 receptor occupancy. A PET study in haloperidol-treated patients

Central D2 dopamine receptor occupancy may be a useful measure to establish clinical guidelines for optimal antipsychotic drug treatment. The use of positron emission tomography (PET) to explore quantitative relationships among D2 receptor occupancy and clinical effects depends on the reliability of such measurements. The calculation of D2 receptor occupancy using [11C]raclopride is routinely based on a ratio-equilibrium analysis, in which the ratio of radioactivity concentration in the striatum to that in the cerebellum is determined. To examine the reliability of such ratios, a test-retest analysis was performed in four schizophrenic patients treated with haloperidol decanoate. PET experiments with [11C]raclopride were repeated in each subject during the same day. The putamen to cerebellum ratio (P/C ratio) ranged from 1.44 to 1.07 among the four patients, corresponding to a D2 receptor occupancy of 62 to 71%. In each subject, the P/C ratios remained highly similar, with quotients 0.98, 1.01, 1.04 and 1.06 between the two experiments. The high test-retest reproducibility of the P/C ratios indicates that measurements of D2 receptor occupancy with the present methods are highly reliable, and support the further use of PET to optimize the drug treatment of schizophrenia.

Schizophrenia and antipsychotic somatic treatment

Schizophrenia typically affects individuals in early life and leads to long-term suffering at high cost to both the individual and the community. Structural, functional, and biochemical factors may play a role in the pathogenesis and perhaps the course, of schizophrenia. Although early research into the treatment of schizophrenia was not fruitful, the results of recent research, particularly the use of narcoleptics combined with new clinical appreciation of psychosocial factors in chronic psychotic disorders, give reason for hope and optimism.

The effects of raclopride on vacuous jaw movements in rats following acute administration

Classic neuroleptics produce a syndrome of vacuous jaw movements in rats, whereas atypical neuroleptics like clozapine do not. The present study compared the effects of repeated administration of raclopride, clozapine, haloperidol, or vehicle on vacuous jaw movements in rats over a 4-week period. Rats received an IP injection of drug once a day. On days 1, 8, 15, and 29 the rats were observed for a 5-min period by two trained observers who recorded their vacuous jaw movements. The dose-response curves at which each drug produced vacuous jaw movements are presented and discussed in terms of their predictive capabilities of early onset extrapyramidal side effects.

Subchronic administration of clozapine, but not haloperidol or metoclopramide, decreases dopamine D2 receptor messenger RNA levels in the nucleus accumbens and caudate-putamen in rats

The effects of unique profile antipsychotic drugs on dopamine D2 receptors and D2 receptor messenger RNA were assessed following subchronic administration in rats. Male, Sprague-Dawley rats were administered oral haloperidol, clozapine, metoclopramide or no drug for three weeks via their drinking water. Tissue from the medial nucleus accumbens and dorsolateral caudate-putamen was dissected and analyzed by Northern blot analysis for levels of dopamine D2 receptor messenger RNA and binding assays conducted with [3H]spiperone for dopamine D2 receptors. Haloperidol and metoclopramide, but not clozapine, significantly increased [3H]spiperone in the caudate-putamen, but not the nucleus accumbens. Clozapine significantly decreased D2 messenger RNA levels in the caudate-putamen and the nucleus accumbens, while metoclopramide and haloperidol had no significant effect in either brain region. The finding of decreased D2 receptor messenger RNA levels produced by subchronic clozapine may account for the lack of striatal D2 receptor up-regulation, which was robustly observed after subchronic haloperidol and metoclopramide. Furthermore, since haloperidol and metoclopramide have a high liability for motor side effects, the current results relate favorably to the low motor side effect profile of clozapine.

The modulation of brain dopamine and GABAA receptors by estradiol: a clue for CNS changes occurring at menopause

1. Tardive dyskinesia is more important in postmenopausal women than men of comparable age and a peak of first episodes of schizophrenia is observed in postmenopausal women. The effect of ovariectomy (2 weeks or 3 months) in rats was investigated as a model of decreased gonadal function associated with menopause. 2. Frontal cortex D1 receptor density and affinity were similar in intact male compared to intact female rats and progressively decreased in density with time after ovariectomy, with no change of affinity. Striatal D1 and D2 receptors also decreased in density after ovariectomy for both receptor subtypes, with no change of affinity. Striatal D1 receptor density and affinity were similar in intact male and female rats, whereas the density of D2 receptors was higher in females. Treatment with estradiol for 2 weeks restored the D2 but not the D1 receptor changes. 3. In the substantia nigra pars reticulata, striatum, nucleus accumbens, and entopeduncular nucleus, a progressive increase in [3H]flunitrazepam specific binding associated with GABAA receptors was observed as a function of time following ovariectomy; this was corrected with estradiol treatment. In contrast, the opposite was observed for [3H] flunitrazepam binding in the globus pallidus, where ovariectomy decreased binding, which was corrected with estradiol replacement therapy. 4. Low prefrontal cortex dopamine activity with implications of D1 receptors in negative symptoms of schizophrenia is hypothesized. Furthermore, GABAergic overactivity in the internal globus pallidus-substantia nigra pars reticulata complex is hypothesized in tardive dyskinesia. 5. The present data suggest that gonadal hormone withdrawal by reducing brain dopamine receptors and producing an imbalance of GABAA receptors in the output pathways of the striatum may predispose to schizophrenia and dyskinesia.

5-HT2 antagonism and EPS benefits: is there a causal connection?

This article examines the hypothesis that 5-HT2 antagonism ameliorates extrapyramidal side effects (EPS) induced by the blockade of D2 dopamine receptors by antipsychotics. Neuroanatomical and neurophysiological data confirm the existence of pathways whereby 5-HT2 antagonism may influence EPS. The experimental data in rodents is marginally positive, but shows that the net effect of 5-HT2 antagonism is dependent upon the precise conditions under which catalepsy is induced. The data in monkeys are mainly negative. Studies in patients who have received adjunct 5-HT2 antagonists in addition to typical neuroleptics lend some support the the hypothesis, but are not conclusive. It is reasoned that 5-HT2 antagonism plays no role in clozapine's freedom from EPS, but it may be responsible for risperidone's decreased propensity to cause EPS. The article concludes that there is support for a conditional role of 5-HT2 in decreasing EPS: 5-HT2 antagonists may delay the onset and decrease the severity of EPS but cannot totally eliminate its occurrence. The implications of these findings for the next generation of combined 5-HT2/D2 antagonists are discussed.