Clozapine: new research on efficacy and mechanism of action

Second to none: rationale, timing, and clinical management of clozapine use in schizophrenia

Despite its enduring relevance as the single most effective and important evidence-based treatment for schizophrenia, underutilization of clozapine remains considerable. To a substantial degree, this is attributable to a reluctance of psychiatrists to offer clozapine due to its relatively large side-effect burden and the complexity of its use. This underscores the necessity for continued education regarding both the vital nature and the intricacies of clozapine treatment. This narrative review summarizes all clinically relevant areas of evidence, which support clozapine's wide-ranging superior efficacy - for treatment-resistant schizophrenia (TRS) and beyond - and make its safe use eminently feasible. Converging evidence indicates that TRS constitutes a distinct albeit heterogeneous subgroup of schizophrenias primarily responsive to clozapine. Most importantly, the predominantly early onset of treatment resistance and the considerable decline in response rates associated with its delayed initiation make clozapine an essential treatment option throughout the course of illness, beginning with the first psychotic episode. To maximize patients' benefits, systematic early recognition efforts based on stringent use of TRS criteria, a timely offer of clozapine, thorough side-effect screening and management as well as consistent use of therapeutic drug monitoring and established augmentation strategies for suboptimal responders are crucial. To minimize permanent all-cause discontinuation, re-challenges after neutropenia or myocarditis should be considered. Owing to clozapine's unique efficacy, comorbid conditions including substance use and most somatic disorders should not dissuade but rather encourage clinicians to consider clozapine. Moreover, treatment decisions need to be informed by the late onset of clozapine's full effects, which for reduced suicidality and mortality rates may not even be readily apparent. Overall, the singular extent of its efficacy combined with the high level of patient satisfaction continues to distinguish clozapine from all other available antipsychotics.

Main interactions of dopamine and risperidone with the dopamine D2 receptor

Psychosis is one of the psychiatric disorders that is controlled by dopaminergic drugs such as antipsychotics that have affinity for the dopamine D2 receptor (DRD2). In this investigation we perform quantum chemical calculations of two molecules [dopamine and risperidone] within a large cavity of DRD2 that represents the binding site of the receptor. Dopamine is an endogenous neurotransmitter and risperidone is a second-generation antipsychotic. Non-covalent interactions of dopamine and risperidone with DRD2 are analyzed using the Quantum Theory of Atoms in Molecules (QTAIM) and the Non-Covalent Interaction index (NCI). The QTAIM results show that these molecules strongly interact with the receptor. There are 22 non-covalent interactions for dopamine and 54 for risperidone. The electron density evaluated at each critical binding point is small in both systems but it is higher for dopamine than for risperidone, indicating that the interactions of DRD2 with the first are stronger than with the second molecule. However, the binding energy is higher for risperidone (-72.6 kcal mol-1) than for dopamine (-22.8 kcal mol-1). Thus, the strength of the binding energy is due to the number of contacts rather than the strength of the interactions themselves. This could be related to the ability of risperidone to block DRD2 and may explain the efficacy of this drug for controlling the symptoms of schizophrenia, but likewise its secondary effects.

New information of dopaminergic agents based on quantum chemistry calculations

Dopamine is an important neurotransmitter that plays a key role in a wide range of both locomotive and cognitive functions in humans. Disturbances on the dopaminergic system cause, among others, psychosis, Parkinson's disease and Huntington's disease. Antipsychotics are drugs that interact primarily with the dopamine receptors and are thus important for the control of psychosis and related disorders. These drugs function as agonists or antagonists and are classified as such in the literature. However, there is still much to learn about the underlying mechanism of action of these drugs. The goal of this investigation is to analyze the intrinsic chemical reactivity, more specifically, the electron donor-acceptor capacity of 217 molecules used as dopaminergic substances, particularly focusing on drugs used to treat psychosis. We analyzed 86 molecules categorized as agonists and 131 molecules classified as antagonists, applying Density Functional Theory calculations. Results show that most of the agonists are electron donors, as is dopamine, whereas most of the antagonists are electron acceptors. Therefore, a new characterization based on the electron transfer capacity is proposed in this study. This new classification can guide the clinical decision-making process based on the physiopathological knowledge of the dopaminergic diseases.

A quantum chemical approach representing a new perspective concerning agonist and antagonist drugs in the context of schizophrenia and Parkinson's disease

Schizophrenia and Parkinson’s disease can be controlled with dopamine antagonists and agonists. In order to improve the understanding of the reaction mechanism of these drugs, in this investigation we present a quantum chemical study of 20 antagonists and 10 agonists. Electron donor acceptor capacity and global hardness are analyzed using Density Functional Theory calculations. Following this theoretical approach, we provide new insights into the intrinsic response of these chemical species. In summary, antagonists generally prove to be better electron acceptors and worse electron donors than dopamine, whereas agonists present an electron donor-acceptor capacity similar to that of dopamine. The chemical hardness is a descriptor that captures the resistance of a chemical compound to change its number of electrons. Within this model, harder molecules are less polarizable and more stable systems. Our results show that the global hardness is similar for dopamine and agonists whilst antagonists present smaller values. Following the Hard and Soft Acid and Bases principle, it is possible to conclude that dopamine and agonists are hard bases while antagonists are soft acids, and this can be related to their activity. From the electronic point of view, we have evolved a new perspective for the classification of agonist and antagonist, which may help to analyze future results of chemical interactions triggered by these drugs.

Safety of antipsychotics for the treatment of schizophrenia: a focus on the adverse effects of clozapine

Clozapine, a dibenzodiazepine developed in 1961, is a multireceptorial atypical antipsychotic approved for the treatment of resistant schizophrenia. Since its introduction, it has remained the drug of choice in treatment-resistant schizophrenia, despite a wide range of adverse effects, as it is a very effective drug in everyday clinical practice. However, clozapine is not considered as a top-of-the-line treatment because it may often be difficult for some patients to tolerate as some adverse effects can be particularly bothersome (i.e. sedation, weight gain, sialorrhea etc.) and it has some other potentially dangerous and life-threatening side effects (i.e. myocarditis, seizures, agranulocytosis or granulocytopenia, gastrointestinal hypomotility etc.). As poor treatment adherence in patients with resistant schizophrenia may increase the risk of a psychotic relapse, which may further lead to impaired social and cognitive functioning, psychiatric hospitalizations and increased treatment costs, clozapine adverse effects are a common reason for discontinuing this medication. Therefore, every effort should be made to monitor and minimize these adverse effects in order to improve their early detection and management. The aim of this paper is to briefly summarize and provide an update on major clozapine adverse effects, especially focusing on those that are severe and potentially life threatening, even if most of the latter are relatively uncommon.

Genetics of tardive dyskinesia: Promising leads and ways forward

Tardive dyskinesia (TD) is a potentially irreversible and often debilitating movement disorder secondary to chronic use of dopamine receptor blocking medications. Genetic factors have been implicated in the etiology of TD. We therefore have reviewed the most promising genes associated with TD, including DRD2, DRD3, VMAT2, HSPG2, HTR2A, HTR2C, and SOD2. In addition, we present evidence supporting a role for these genes from preclinical models of TD. The current understanding of the etiogenesis of TD is discussed in the light of the recent approvals of valbenazine and deutetrabenazine, VMAT2 inhibitors, for treating TD.

The modulation of adult neuroplasticity is involved in the mood-improving actions of atypical antipsychotics in an animal model of depression

Depression is a prevalent psychiatric disorder with an increasing impact in global public health. However, a large proportion of patients treated with currently available antidepressant drugs fail to achieve remission. Recently, antipsychotic drugs have received approval for the treatment of antidepressant-resistant forms of major depression. The modulation of adult neuroplasticity, namely hippocampal neurogenesis and neuronal remodeling, has been considered to have a key role in the therapeutic effects of antidepressants. However, the impact of antipsychotic drugs on these neuroplastic mechanisms remains largely unexplored. In this study, an unpredictable chronic mild stress protocol was used to induce a depressive-like phenotype in rats. In the last 3 weeks of stress exposure, animals were treated with two different antipsychotics: haloperidol (a classical antipsychotic) and clozapine (an atypical antipsychotic). We demonstrated that clozapine improved both measures of depressive-like behavior (behavior despair and anhedonia), whereas haloperidol aggravated learned helplessness in the forced-swimming test and behavior flexibility in a cognitive task. Importantly, an upregulation of adult neurogenesis and neuronal survival was observed in animals treated with clozapine, whereas haloperidol promoted a downregulation of these processes. Furthermore, clozapine was able to re-establish the stress-induced impairments in neuronal structure and gene expression in the hippocampus and prefrontal cortex. These results demonstrate the modulation of adult neuroplasticity by antipsychotics in an animal model of depression, revealing that the atypical antipsychotic drug clozapine reverts the behavioral effects of chronic stress by improving adult neurogenesis, cell survival and neuronal reorganization.

An update of safety of clinically used atypical antipsychotics

INTRODUCTION

The atypical antipsychotic (APs) drugs have become the most widely used agents to treat a variety of psychoses because of their superiority with regard to safety and tolerability profile compared to conventional/'typical' APs.

AREAS COVERED

We aimed at providing a synthesis of most current evidence about the safety and tolerability profile of the most clinically used atypical APs so far marketed. Qualitative synthesis followed an electronic search made inquiring of the following databases: MEDLINE, Embase, PsycINFO and the Cochrane Library from inception until January 2016, combining free terms and MESH headings for the topics of psychiatric disorders and all atypical APs as following: ((safety OR adverse events OR side effects) AND (aripiprazole OR asenapine OR quetiapine OR olanzapine OR risperidone OR paliperidone OR ziprasidone OR lurasidone OR clozapine OR amisulpride OR iloperidone)).

EXPERT OPINION

A critical issue in the treatment with atypical APs is represented by their metabolic side effect profile (e.g. weight gain, lipid and glycaemic imbalance, risk of diabetes mellitus and diabetic ketoacidosis) which may limit their use in particular clinical samples. Electrolyte imbalance, ECG abnormalities and cardiovascular adverse effects may recommend a careful baseline and periodic assessments.

Structural and functional neuroimaging findings associated with the use of clozapine in schizophrenia: a systematic review

OBJECTIVE

Schizophrenia is one of the most severe psychiatric disorders, and its current treatment relies on antipsychotic medications with only partial effectiveness. Clozapine is an atypical antipsychotic with a specific profile of action indicated for treatment-resistant schizophrenia. Neuroimaging studies assessing the effects of clozapine could help shed light on the neural underpinnings of the effects of this drug in the brain. The objective of this study was to review the available literature on the structural and functional neuroimaging findings associated with use of clozapine.

METHOD

We conducted a systematic review of the indexed literature using the PubMed, BIREME, and ISI Web of Knowledge search engines and the following keywords: clozapine, neuroimaging, computed tomography, MRI, functional magnetic resonance, PET, SPECT, and DTI.

RESULTS

A total of 23 articles were included in the review. In structural studies, the use of clozapine was associated with volume reductions in the basal ganglia, especially the caudate nucleus, where functional neuroimaging studies also found decreased perfusion. In the frontal lobe, clozapine treatment was associated with increased gray matter volume and reduced perfusion.

CONCLUSION

The results of the studies reviewed suggest that the use of clozapine is associated with distinctive structural and functional neuroimaging findings that are not shared with other antipsychotics.

Olanzapine/fluoxetine combination for bipolar depression

Bipolar depression remains one of the most difficult to treat of all mental disorders. Until recently, no treatments, including antidepressants, have consistently shown to be effective in this condition. Olanzapine, an atypical antipsychotic, has been approved by the US Food and Drug Administration for the acute treatment of mania and maintenance prevention of relapse into depression or mania. A clinical trial tested the relative effectiveness of the combination of olanzapine and fluoxetine in bipolar type I depression, against olanzapine alone or placebo. The combination produced a very robust clinical effect acutely and a long-term follow-up study indicated that there was a low rate of induction of mania or mixed states. Therefore, the olanzapine/fluoxetine combination represents a viable alternative for bipolar depression. However, uptake of this combined product in practice has been modest. This is likely to be the result of several factors, including resistance to the use of fixed combination preparations and, more recently, evidence of effectiveness of the atypical quetiapine and the anticonvulsant lamotrigine. Perhaps the greatest resistance to the use of olanzapine alone or in combination has been the problem of weight gain and the attendant risk of type 2 diabetes and the metabolic syndrome. Vigorous management of this problem has been shown to mitigate the potential for weight gain and is required if this combination is to be used. However, many clinicians find management of weight gain in olanzapine treated patients a challenge. In addition, weight, waist circumference, lipids and glucose should be monitored.

The effectiveness of treatments for cocaine dependence in schizophrenic patients: a systematic review

Objectives:

To evaluate and compare the effectiveness of available treatments for cocaine dependence in schizophrenic patients.

Method:

We searched articles published between May 2002 and June 2012 in the following databases: Scopus, Pubmed and Web of Knowledge. The key words utilised were “schizophrenia”, "dementia praecox", "schizophrenic disorder", "cocaine related disorder", "cocaine abuse", "cocaine addiction", "cocaine dependence", “treatment”, “therapeutic”, and "drug therapy”.

Selection of studies and data extraction:

Original articles in English, Portuguese and Spanish were selected. Controlled, double-blind and open-label studies involving only human subjects were included in this review.

Data Synthesis:

We found studies on typical and atypical antipsychotics and one monoamine transporter antagonist. There were few indications of the effectiveness of atypical antipsychotic medications for the treatment of cocaine dependence in patients with schizophrenia.

Conclusions:

We suggest that further studies be conducted with atypical antipsychotic medicationsand greater methodological strictness, including using a placebo group in the studies, so that health professionals can determine the real effectiveness of this class of medication for the treatment of cocaine dependence in schizophrenic patients.

Co-administration of 5-HT6 receptor antagonists with clozapine, risperidone, and a 5-HT2A receptor antagonist: effects on prepulse inhibition in rats

RATIONALE

Some novel antipsychotics manifest antagonistic activity at serotonin-6 receptors; however, little is known about the role of 5-HT6 receptors in ameliorating sensory gating deficits.

OBJECTIVE

We evaluated the effects of the combined administration of the 5-HT6 receptor antagonist SB 271046 with clozapine and haloperidol, as well as the co-administration of SB 271046 or SB 399885 with risperidone and the 5-HT2A antagonist M100907, to overcome the deficits induced by MK-801 in the prepulse inhibition (PPI) test.

RESULTS

MK-801 (0.1 mg/kg) produced reliable PPI deficits. Administration of SB 271046 (6 and 9 mg/kg), SB 399885 (3 and 6 mg/kg), clozapine (2.5 mg/kg), haloperidol (0.1 and 0.2 mg/kg), risperidone (0.25-1 mg/kg), and M100907 (0.5 and 1 mg/kg) did not affect the MK-801-induced deficits, but the administration of clozapine (5 mg/kg) did reverse the effects of MK-801. In MK-801-treated rats, the co-administration of inactive doses of clozapine (2.5 mg/kg) and SB 271046 (6 mg/kg) reversed the PPI impairments compared to animals that were administered inactive doses of either clozapine or SB 271046 alone. Co-administration of risperidone (1 mg/kg) or M100907 (0.5 mg/kg) with SB 271046 (6 mg/kg) or SB 399885 (3 mg/kg) also attenuated the MK-801-induced PPI deficits. In contrast, joint administration of haloperidol and SB 271046 had no effect on the PPI deficit.

CONCLUSION

The present results suggest that the 5-HT6 receptors may play adjunctive roles in antipsychotic drug action, and that the combination of 5-HT2A and 5-HT6 antagonism may represent an important element in the pharmacological profile of antipsychotic drugs.

Serotonergic hallucinogens as translational models relevant to schizophrenia

One of the oldest models of schizophrenia is based on the effects of serotonergic hallucinogens such as mescaline, psilocybin, and (+)-lysergic acid diethylamide (LSD), which act through the serotonin 5-HT(2A) receptor. These compounds produce a 'model psychosis' in normal individuals that resembles at least some of the positive symptoms of schizophrenia. Based on these similarities, and because evidence has emerged that the serotonergic system plays a role in the pathogenesis of schizophrenia in some patients, animal models relevant to schizophrenia have been developed based on hallucinogen effects. Here we review the behavioural effects of hallucinogens in four of those models, the receptor and neurochemical mechanisms for the effects and their translational relevance. Despite the difficulty of modelling hallucinogen effects in nonverbal species, animal models of schizophrenia based on hallucinogens have yielded important insights into the linkage between 5-HT and schizophrenia and have helped to identify receptor targets and interactions that could be exploited in the development of new therapeutic agents.

Drug-induced dyskinesia in Parkinson's disease. Should success in clinical management be a function of improvement of motor repertoire rather than amplitude of dyskinesia?

BACKGROUND

Dyskinesia, a major complication in the treatment of Parkinson's disease (PD), can require prolonged monitoring and complex medical management.

DISCUSSION

The current paper proposes a new way to view the management of dyskinesia in an integrated fashion. We suggest that dyskinesia be considered as a factor in a signal-to-noise ratio (SNR) equation where the signal is the voluntary movement and the noise is PD symptomatology, including dyskinesia. The goal of clinicians should be to ensure a high SNR in order to maintain or enhance the motor repertoire of patients. To understand why such an approach would be beneficial, we first review mechanisms of dyskinesia, as well as their impact on the quality of life of patients and on the health-care system. Theoretical and practical bases for the SNR approach are then discussed.

SUMMARY

Clinicians should not only consider the level of motor symptomatology when assessing the efficacy of their treatment strategy, but also breadth of the motor repertoire available to patients.

The return of fixed combinations in psychiatry: fluoxetine and olanzapine combination

Fixed combination psychotropics, such as a combination of a tricyclic and a typical antipsychotic, were widely prescribed a generation ago. These products were plagued by a number of problems, including serious side effects, which caused them to fall out of favor. More recently, a fixed combination of the atypical antipsychotic olanzapine and the serotonin selective reuptake inhibitor (SSRI) fluoxetine has been approved in the US for the treatment of bipolar I depression. Although the combination produced a robust clinical response relative to placebo or olanzapine alone, the response from practitioners has been mixed. The reasons for this are likely to be varied. Some practitioners who remember the earlier era of fixed combinations may simply be resistant to using products of this type. Moreover, the two constituents are available and many clinicians prescribe them independently. Finally, adverse events associated with olanzapine may make practitioners hesitant. For example, weight gain is a common side effect with olanzapine, and may be associated with hyperlipidemia or type II diabetes. Aggressive management of this problem appears to be helpful in preventing or reversing weight gain. It is not clear how weight gain is going to impact the uptake of this effective treatment.

Behavioral changes and mitochondrial dysfunction in a rat model of schizophrenia induced by ketamine

Evidence from the literature indicates that mitochondrial dysfunction occurs in schizophrenia and other psychiatric disorders. To produce an animal model that simulates psychotic symptoms analogous to those seen in schizophrenic patients, sub-anesthetic doses of N-methyl-D-aspartate (NMDA) receptor antagonists (such as ketamine) have been used. The aim of this study was to evaluate behavioral changes and mitochondrial dysfunction in rats administered ketamine for 7 consecutive days. Behavioral evaluation was performed using an activity monitor 1, 3 and 6 h after the last injection. The activities of mitochondrial respiratory chain complexes I, II, I-III and IV in multiple brain regions (prefrontal cortex, striatum and hippocampus) were also evaluated. Our results showed that hyperlocomotion occurred in the ketamine group 1 and 3 h after the last injection. Stereotypic movements were elevated only when animals were evaluated 1 h after receiving ketamine. In addition, we found that ketamine administration affects the respiratory chain, altering the activity of respiratory chain complexes in the striatum and hippocampus after 1 h, those in the prefrontal cortex and hippocampus after 3 h and those in the prefrontal cortex and striatum 6 h after the last administration of ketamine. These findings suggest that ketamine alters the behavior of rats and changes the activity of respiratory chain complexes in multiple brain regions at different time points.

Amisulpride the 'atypical' atypical antipsychotic--comparison to haloperidol, risperidone and clozapine

INTRODUCTION

Amisulpride's high and selective affinity for dopamine D2/3 (Ki 1.3/2.4 nM) receptors, lack of affinity for serotonin receptors, and its unusually high therapeutic doses (400-800 mg/day) makes it unique among atypical antipsychotics and prompted us to compare its actions with other antipsychotics in animal models.

METHODS

Amisulpride's effects on amphetamine and phencyclidine induced locomotor activity (AIL/PIL), conditioned avoidance response, catalepsy (CAT), subcortical Fos expression, and plasma prolactin was correlated to its time-course striatal D2/3 and prefrontal 5-HT2 receptor occupancy (D(2/3)/5-HT2RO); in comparison to haloperidol, clozapine, and risperidone.

RESULTS

Unlike the atypicals clozapine and risperidone, amisulpride lacked 5-HT2RO and showed a 'delayed' pattern of D2/3RO: 43, 60 and 88% after 1, 2 and 6 h (100 mg/kg), respectively, despite a quick onset (1 h) and decline (6 h) of prolactin elevation. While haloperidol and risperidone were effective at D2RO>60%, clozapine at D2/3RO<50%, amisulpride was effective only when its D2RO exceeded 60% with a delayed latency and lasted longer than other antipsychotics. CAT was observed for haloperidol and risperidone when D2RO exceeded 80%, while in the case of amisulpride, CAT was not observed even when doses exceeded 90% D2/3RO. Amisulpride also displayed functional limbic selectivity in Fos expression like the other atypicals.

CONCLUSIONS

Amisulpride's "delayed" functional profile on acute administration and the need for high doses is most likely due to its poor blood-brain-barrier penetration; however, it is distinct from other atypicals in showing low motor side-effects, activity against phencyclidine, and a mesolimbic preference, despite no action on serotonin receptors.

Augmentation of antidepressants with atypical antipsychotics for treatment-resistant major depressive disorder

OBJECTIVE

Atypical antipsychotics (AAPs) have been hypothesized to be beneficial in treatment-resistant depression (TRD). This paper will review a biochemical rationale and will summarize the data regarding the effectiveness of AAPs in TRD.

METHOD

Studies were identified using searches of Pubmed/Medline, EMBase and the Cochrane databases by cross-referencing the term 'depression' with each of the six AAPs.

RESULTS

After initial positive, short case reports and clinical trials, larger studies failed to show the effectiveness of AAPs combined with antidepressants for TRD. More recently, larger scale clinical trials have supported the effectiveness of at least some of these medications. While AAPs have gained in popularity for TRD, there are nagging concerns regarding risks such as metabolic syndrome and tardive dyskinesia.

CONCLUSION

The existing research provides some support for the beneficial effects of AAPs when combined with SSRI's in TRD. These medications pose significant risks that must be considered in their use.

Prolactin and dopamine: what is the connection? A review article

Dopamine (DA) holds a predominant role in the regulation of prolactin (PRL) secretion. Through a direct effect on anterior pituitary lactotrophs, DA inhibits the basally high-secretory tone of the cell. It accomplishes this by binding to D2 receptors expressed on the cell membrane of the lactotroph, activation of which results in a reduction of PRL exocytosis and gene expression by a variety of intracellular signalling mechanisms. The hypothalamic dopaminergic neurons, which provide DA to the anterior pituitary gland, are themselves regulated by feedback from PRL through a 'short-loop feedback mechanism'. A variety of other modulators of prolactin secretion act at the hypothalamic level by either disinhibition of the dopaminergic tone (e.g. serotonin, GABA, oestrogens and opioids) or by reinforcing it (e.g. substance P). All typical antipsychotic medications are associated with sustained hyperprolactinaemia due to their high affinity for the D2 receptor and their slow dissociation from the receptor once bound, but atypicals differ quite dramatically in their propensity to cause prolonged high prolactin levels. Of those atypicals that are associated with prolactin elevation, the main causative factor appears to be a higher peripheral-to-central dopamine receptor potency of either the parent drug or its active metabolite (e.g. risperidone, 9-hydroxy-risperidone and amisulpride). Antipsychotics that easily cross the blood-brain barrier and exhibit fast dissociation from the dopamine receptor once bound do not result in sustained hyperprolactinaemia.

PET analysis of the 5-HT2A receptor inverse agonist ACP-103 in human brain

The mechanisms underlying the clinical properties of atypical antipsychotics have been postulated to be mediated, in part, by interactions with the 5-HT2A receptor. Recently, it has been recognized that clinically effective antipsychotic drugs are 5-HT2A receptor inverse agonists rather than neutral antagonists. In the present study, which is part of the clinical development of the novel, selective 5-HT2A receptor inverse agonist ACP-103, we applied positron emission tomography (PET) with the radioligand [11C]N-methylspiperone ([11C]NMSP) to study the relationship between oral dose, plasma level, and uptake of ACP-103 in living human brain. The safety of drug administration was also assessed. Four healthy volunteers were examined by PET at baseline, and after the oral administration of various single doses of ACP-103. Two subjects each received 1, 5, and 20 mg doses, and two subjects each received 2, 10, and 100 mg doses, respectively. ACP-103 was well tolerated. Detectable receptor binding was observed at very low ACP-103 serum levels. Cortical [11C]NMSP binding was found to be dose-dependent and fitted well to the law of mass action. A reduction in binding was detectable after an oral dose of ACP-103 as low as 1 mg, and reached near maximal displacement following the 10-20 mg dose. In conclusion, administration of ACP-103 to healthy volunteers was found to be safe and well tolerated, and single oral doses as low as 10 mg were found to fully saturate 5-HT2A receptors in human brain as determined by PET.

Clinical Pharmacokinetics of Atypical Antipsychotics

In the past, the information about the dose-clinical effectiveness of typical antipsychotics was not complete and this led to the risk of extrapyramidal adverse effects. This, together with the intention of improving patients' quality of life and therapeutic compliance, resulted in the development of atypical or second-generation antipsychotics (SGAs). This review will concentrate on the pharmacokinetics and metabolism of clozapine, risperidone, olanzapine, quetiapine, amisulpride, ziprasidone, aripiprazole and sertindole, and will discuss the main aspects of their pharmacodynamics. In psychopharmacology, therapeutic drug monitoring studies have generally concentrated on controlling compliance and avoiding adverse effects by keeping long-term exposure to the minimal effective blood concentration. The rationale for using therapeutic drug monitoring in relation to SGAs is still a matter of debate, but there is growing evidence that it can improve efficacy, especially when patients do not respond to therapeutic doses or when they develop adverse effects. Here, we review the literature concerning the relationships between plasma concentrations of SGAs and clinical responses by dividing the studies on the basis of the length of their observation periods. Studies with clozapine evidenced a positive relationship between plasma concentrations and clinical response, with a threshold of 350-420 ng/mL associated with good clinical response. The usefulness of therapeutic drug monitoring is well established because high plasma concentrations of clozapine can increase the risk of epileptic seizures. Plasma clozapine concentrations seem to be influenced by many factors such as altered cytochrome P450 1A4 activity, age, sex and smoking. The pharmacological effects of risperidone depend on the sum of the plasma concentrations of risperidone and its 9-hydroxyrisperidone metabolite, so monitoring the plasma concentrations of the parent compound alone can lead to erroneous interpretations. Despite a large variability in plasma drug concentrations, the lack of studies using fixed dosages, and discrepancies in the results, it seems that monitoring the plasma concentrations of the active moiety may be useful. However, no therapeutic plasma concentration range for risperidone has yet been clearly established. A plasma threshold concentration for parkinsonian side effects has been found to be 74 ng/mL. Moreover, therapeutic drug monitoring may be particularly useful in the switch between the oral and the long-acting injectable form. The reviewed studies on olanzapine strongly indicate a relationship between clinical outcomes and plasma concentrations. Olanzapine therapeutic drug monitoring can be considered very useful in assessing therapeutic efficacy and controlling adverse events. A therapeutic range of 20-50 ng/mL has been found. There is little evidence in favour of the existence of a relationship between plasma quetiapine concentrations and clinical responses, and an optimal therapeutic range has not been identified. Positron emission tomography studies of receptor blockade indicated a discrepancy between the time course of receptor occupancy and plasma quetiapine concentrations. The value of quetiapine plasma concentration monitoring in clinical practice is still controversial. Preliminary data suggested that a therapeutic plasma amisulpride concentration of 367 ng/mL was associated with clinical improvement. A therapeutic range of 100-400 ng/mL is proposed from non-systematic clinical experience. There is no direct evidence concerning optimal plasma concentration ranges of ziprasidone, aripiprazole or sertindole.

Differently lasting effects of prenatal and postnatal chronic clozapine/haloperidol on activity and memory in mouse offspring

We evaluated the behavioral effects of chronic haloperidol (HAL) and clozapine (CLO) during gestation and CNS development, compared with transient treatments that stopped 1-3 weeks before the test.

RESULTS

1) Chronic HAL (6 mg/l in drinking water) but not HAL-withdrawal caused hypo-activity in open-field test on postnatal days (PNDs) 35, 42 and 56. However, hyper-activity was found in both CLO (90 mg/l) and CLO-withdrawal pups. 2) In the step-through test, retention performance was significantly higher in HAL-treated mice than in the controls on PND 42, as well as in withdrawal mice on PNDs 35 and 42. However, both chronic CLO (90 mg/l) exposure and CLO-withdrawal tended to improve the acquisition of memory. Furthermore, chronic CLO (180 mg/l) ameliorated scopolamine (3 mg/kg)-induced impairment of memory on PND 56. 3) In the water-maze test, both chronic HAL and HAL-withdrawal treatments significantly impaired performance on the 4th training day at PND 35, but not PNDs 42 and 56. Neither chronic CLO exposure nor CLO-withdrawal affected spatial memory. 4) Body weight following HAL/CLO administration decreased when compared with the controls during PND 21-35, but approached control levels at PND 40.

CONCLUSION

HAL doesn't elicit permanent behavioral changes in offspring. By contrast, CLO had longer-lasting effects than HAL. The pups at age before PND 35 seem more sensitive to HAL/CLO than elder pups.

Sensorimotor gating and habituation of the startle response in schizophrenic patients randomly treated with amisulpride or olanzapine

BACKGROUND

Schizophrenic patients exhibit impairments in prepulse inhibition (PPI) and habituation of the acoustic startle response (ASR). Recent studies suggested that PPI deficits and habituation deficits are normalized after antipsychotic treatment. Despite clear evidence of gating and habituation mechanisms in animal models, it is still unknown which neurotransmitter systems are involved in schizophrenic patients. Thus, we compared the effects of a combined 5-HT2A/D2 and a pure D2/D3 antagonist on PPI and habituation of ASR in patients with schizophrenia.

METHODS

The ASR was measured in 37 acute schizophrenic patients who were randomized and double-blinded as to treatment with amisulpride or olanzapine. Patients were assessed during the first week and after four and eight weeks of treatment. Twenty healthy matched control subjects were examined likewise.

RESULTS

Schizophrenic patients showed a significant PPI deficit and significantly decreased startle amplitude at baseline. The gating deficit disappeared after antipsychotic treatment in both treatment groups. Amisulpride sensitized the startle amplitude, whereas startle amplitude was not changed by olanzapine. After correcting for startle amplitude, patients did not show a habituation deficit; however, amisulpride accelerated habituation, whereas olanzapine had no effect.

CONCLUSIONS

Our findings suggest that the PPI-restoring effect of antipsychotics is probably attributed to a dopamine D2 receptor blockade.

Tardive dyskinesia in the era of typical and atypical antipsychotics. Part 2: Incidence and management strategies in patients with schizophrenia

OBJECTIVE

Tardive dyskinesia (TD), the principal adverse effect of long-term conventional antipsychotic treatment, can be debilitating and, in many cases, persistent. We sought to explore the incidence and management of TD in the era of atypical antipsychotics because it remains an important iatrogenic adverse effect.

METHODS

We conducted a review of TD incidence and management literature from January 1, 1965, to January 31, 2004, using the terms tardive dyskinesia, management, therapy, neuroleptics, antipsychotics, clozapine, olanzapine, risperidone, quetiapine, ziprasidone, and aripiprazole. Additional articles were obtained by searching the bibliographies of relevant references. We considered articles that contributed to the current understanding of both the incidence of TD with atypical antipsychotics and management strategies for TD.

RESULTS

The incidence of TD is significantly lower with atypical, compared with typical, antipsychotics, but cases of de novo TD have been identified. Evidence suggests that atypical antipsychotic therapy ameliorates long-standing TD. This paper outlines management strategies for TD in patients with schizophrenia.

CONCLUSION

The literature supports the recommendation that atypical antipsychotics should be the first antipsychotics used in patients who have experienced TD as a result of treatment with conventional antipsychotic agents. The other management strategies discussed may prove useful in certain patients.

First- and second-generation antipsychotic medication and cognitive processing in schizophrenia

Schizophrenia has been consistently characterized by deficits in the cognitive domains of executive function, working memory, attention, and episodic memory. Although some cognitive abnormalities, such as motor slowing, may be associated with antipsychotic medication administration, generally the cognitive deficits shown by patients with schizophrenia can be attributed at least in part to the disease process. Modulation of the dopamine neurotransmitter system, notably through D2 receptor blockade, has been associated with psychotic symptom reduction and cognitive performance improvements in patients with schizophrenia. Although first-generation antipsychotic medication treatment initially was thought not to result in cognitive improvement, recent studies comparing second-generation antipsychotics to low doses of first-generation antipsychotic medication showed cognitive benefits for first-generation drugs, although perhaps not as great as that found after treatment with second-generation medication. Cognitive improvement associated with administration of antipsychotic medication may be a manifestation of improvement in general cortical information processing. Recent work has shown that specific genetic polymorphisms may interact with antipsychotic medication treatment to influence the degree to which cognitive abilities display improvement after treatment. In particular, the catechol-O-methyltransferase val108/158met polymorphism has been shown to predict working memory improvement after administration of antipsychotic medication to patients with schizophrenia.

Cognitive improvement in schizophrenic patients does not require a serotonergic mechanism: randomized controlled trial of olanzapine vs amisulpride

Combined serotonin-2A (5-HT(2A)) and dopamine-2 (D2) receptor blockade has been proposed as a candidate mechanism by which second-generation antipsychotics (SGAs) improve both cognition and negative symptoms in schizophrenic patients, in contrast to antipsychotics of the first generation. The SGA amisulpride, however, only binds to D2/D3 receptors, which makes it an interesting tool to test this assumption. In a randomized controlled trial, 52 schizophrenic patients were allocated to treatment with either olanzapine (10-20 mg/day) or amisulpride (400-800 mg/day). A comprehensive neuropsychological test battery and clinical ratings were used to assess participants at inclusion and after 4 and 8 weeks. Cognitive improvements of moderate size were observed, with effect sizes similar to those obtained in previous studies on the cognitive effects of SGAs. Importantly, amisulpride was not inferior to olanzapine for any cognitive domain. Combined 5-HT(2A)/D2 receptor blockade is probably not necessary for cognitive improvement by SGAs.

Cerebral metabolic changes induced by clozapine in schizophrenia and related to clinical improvement

RATIONALE

The study of the different effects on brain metabolism between typical and atypical antipsychotics would aid in understanding their mechanisms of action. Clozapine is of special interest, since it is one of the most effective antipsychotic drugs and demonstrates a distinctive mechanism of action in pre-clinical studies with respect to typical neuroleptics.

OBJECTIVE

To study the differences in cerebral activity induced by clozapine as compared to those produced by haloperidol.

METHODS

[18F]Fluoro-deoxy-glucose (FDG)-positron emission tomography (PET) scans were obtained in the resting condition before and after 6 months of treatment with clozapine in 22 treatment-resistant patients with schizophrenia. Before inclusion, patients had been chronically treated with classical drugs, and all of them received haloperidol during the last month. Data were analyzed with statistical parametric mapping (SPM'99) methods, comparing pre-treatment and post-treatment conditions. The association between the changes in symptom scores and metabolism was also assessed to corroborate the functional relevance of possible metabolic changes.

RESULTS

Clozapine decreased prefrontal and basal ganglia activity, and increased occipital metabolism, including primary and association visual areas. The change in negative symptoms was related with the decrease of basal ganglia activity; the improvement in disorganization related to the metabolic decrease in the motor area, and the change in positive symptoms was associated to the increase of activity in the visual area.

CONCLUSIONS

These results show that haloperidol and clozapine produce different patterns of metabolic changes in schizophrenia. Compared to the haloperidol baseline, clozapine inhibited the metabolic activity of the prefrontal and motor cortical regions and basal ganglia and induced a higher activation of the visual cortex. The improvement in disorganization, negative and positive syndromes with clozapine may be respectively associated with metabolic changes in the motor area, basal ganglia, and visual cortex.

N-methyl-D-aspartate antagonists as drug models of schizophrenia: a surprising link to tobacco smoking

The pros and cons of N-methyl-D-aspartate (NMDA) antagonists as drug models of schizophrenia are discussed in relation to the neuropathology of this complex mental spectrum of diseases. The role of acetylcholine, dopamine, gamma aminobutyric acid, glutamic acid, and serotonin emphasizes that multiple neurotransmitter system abnormalities are involved, even though current drug therapy involves primarily dopamine (D(2))/serotonin (5 HT(2)) antagonists. Only some of the fundamental aspects of schizophrenia are replicated by NMDA receptor antagonists of glutamic acid. Subchronic NMDA antagonism in an animal model results in decreased levels of dopamine in prefrontal cortex and increased D(1) receptor binding. The results of PET studies of schizophrenic patients imply decreased dopamine levels in their prefrontal cortex. Tobacco-smoking schizophrenic patients transiently normalize prepulse inhibition. Nicotine appears to be one factor that may help explain some of these phenomena.

Comparison of cognitive performances during a placebo period and an atypical antipsychotic treatment period in schizophrenia: critical examination of confounds

Although previous studies report cognitive improvement following atypical antipsychotic administration in schizophrenia (SC), few placebo-controlled within-subject studies with examination of confounds (symptom reduction, cooperation, learning, and outliers) have been reported. The present study examines the effects of atypicals and confounds upon cognition in SC. The hypothesis tested was that relative to placebo, atypicals as a general class of medication would elicit cognitive improvement in SC. In all, 19 patients with SC (15 males) completed the double-blind, counterbalanced, randomized within-subject study of the effects of atypical antipsychotics (risperidone, clozapine, olanzapine, or quetiapine) vs placebo administration upon cognitive performance in the domains of executive function, attention, memory, language, visual perception, and general intellect. Significant cognitive improvement during atypical antipsychotic administration relative to placebo withdrawal occurred in most cognitive domains with robust improvements in intelligence (p=0.001), memory (p=0.0009), and fluency (p <0.002) even after outliers and unmotivated performances were excluded. These findings suggest that relative to placebo withdrawal, atypicals improve cognitive performance in SC. However, this finding may not be specific to atypicals, since analogous studies of typicals have not been performed.

Serotonergic effects of clozapine and its metabolites in hippocampal HT22 cells

In the hippocampal neuronal in vitro system of HT22 cells, we studied the effects of clozapine (Cloz) and its metabolites clozapine-N-oxide (Cloz-N-oxide) and norclozapine (Norcloz) on 5-HT transporter affinity (K(M)) and uptake (V(max)), MAO-B affinity (K(M)) and maximal velocity (V(max)), as well as on 5-HT(2) receptor affinity and density. Clinically relevant concentrations of Cloz (200 and 400 ng/ml) and its metabolites (100 and 200 ng/ml) were used for the examination of the effects after short-term (4 h) and long-term (24 h) incubation. Statistical evaluation revealed that a significantly lowered 5-HT transporter affinity (higher K(M)) was related to higher concentrations of Cloz and its metabolites. A significantly higher 5-HT transporter uptake was dependent on both high concentrations of drugs and an increased time of incubation. No significant influence of the investigated independent variables on MAO-B affinity could be demonstrated, whereas a significant drug-related increase of MAO-B velocity was detectable. Additionally, low and high concentrations of Cloz and its metabolites induced a higher 5-HT(2) receptor affinity (lower K(D)). No significant influences of the investigated independent variables on 5-HT(2) receptor density were detectable. The results of the present study show that Cloz and its metabolites induce significant alterations in serotoninergic parameters of hippocampal HT22 cells, validating the system of hippocampal HT22 cells for further examinations of the mechanisms of action of atypical neuroleptics.

Effects of the selective dopamine D(1) antagonists NNC 01-0112 and SCH 39166 on latent inhibition in the rat

Dopamine D(1) receptor blockade does not appear to be a prerequisite for antipsychotic activity since many clinically effective antipsychotics have little or no affinity for this receptor subtype. Clozapine, however, which has minimal liability for extrapyramidal symptoms, possesses affinities of similar order for D(1) and D(2) receptors. In earlier animal models used to predict antipsychotic effect, selective D(1) antagonists have shown effects similar to standard antipsychotics with preferential D(2) or mixed D(1)/D(2) antagonism. We investigated the effects of haloperidol (0.1 mg/kg) and two selective D(1) antagonists, NNC 01-0112 (0.05, 0.1 and 0.2 mg/kg) and SCH 39166 (0.02, 0.2 and 2.0 mg/kg), on latent inhibition (LI) in rats. LI is a behavioural paradigm in which repeated nonreinforced preexposure to a stimulus retards subsequent associations to that stimulus. Disrupted LI has been suggested as a model for the attentional deficits in schizophrenia. Using preexposure to a flashing light stimulus, which subsequently served as a conditioned stimulus for suppression of water licking, we demonstrated a clear LI effect with haloperidol but with neither of the two D(1) antagonists. Since selective D(1) antagonists are not clinically effective, these results add further credibility for the relevance of LI as an animal model of psychosis.

Clozapine, norclozapine plasma levels, their sum and ratio in 50 psychotic patients: influence of patient-related variables

Steady-state plasma concentrations of clozapine and norclozapine, its major metabolite, as well as their sum and ratio (norclozapine/clozapine), were evaluated in 50 in- and outpatients taking clozapine and naturalistically recruited. Drug plasma concentrations were measured by means of a reversed-phase high-performance liquid chromatography (RPLC) method with an ultraviolet detection. Daily doses (milligrams per kilogram of body weight) of clozapine correlated positively with clozapine plasma parameters, except with the norclozapine/clozapine ratio, in all patients. When the patients were divided in subgroups with respect to gender, the corresponding plasma concentrations were no longer dose-related in men. A lack of significant correlation was observed also in patients (n=23) co-treated with typical neuroleptics. Conversely, dose-concentration correlations were significant in either smoker or nonsmoker patients. No significant relationship between body weight and clozapine plasma parameters was reported. Further, we observed (1) a trend towards higher medians of clozapine or total analytes in women than those reported in men (P=.09 and .07); (2) no significant difference in plasma levels obtained in subjects younger than 34 years and subjects 34 years old or older; (3) a trend towards higher norclozapine and clozapine plus norclozapine levels (P=.05 and .08) in nonsmoker than smoker patients; (4) no significant difference between clozapine plasma parameters measured in patients co-medicated with typical neuroleptics and in patients receiving clozapine alone.

Agranulocytosis during clozapine therapy

Granulocytopenia and agranulocytosis are considered among the most dangerous adverse effects of clozapine. During the last 15-year period, this atypical antipsychotic agent has been administered to 750 patients managed at the Emergency Psychiatry Services and Clinical Pharmacology Unit of the National Institute of Psychiatry and Neurology (NIPandN; Budapest, Hungary). Granulocytopenia was ascertained in seven, whereas agranulocytosis was diagnosed in two patients of this population. The latter two comprised a 42-year-old female with schizoaffective psychosis and a 35-year-old male with paranoid schizophrenia. The female patient received clozapine in a daily dose of 400 mg, which induced agranulocytosis after 2 months. The male patient was treated with 225-mg/day clozapine and the time to the diagnosis of agranulocytosis was 6 weeks. These adverse reactions were recognized early and the appropriate treatment of agranulocytosis resulted in complete recovery in both cases.

Relationship between patient variables and plasma clozapine concentrations: a dosing nomogram

BACKGROUND

Previous work has suggested factors such as gender, smoking behavior, dose, and age affect the amount of drug a patient requires to achieve a desired plasma concentration of clozapine. Plasma clozapine concentrations ranging from 350 to 504 ng/mL in treatment-refractory schizophrenics and schizoaffective patients produce response rates ranging approximately 55-80%. Without the aid of clozapine plasma concentration monitoring, 3-6 months are recommended for a therapeutic clozapine trial. Data suggest that the lag time to response can be reduced by administering a dose that produces a therapeutic clozapine concentration.

METHODS

To generate a clozapine dosing nomogram to predict clozapine steady-state plasma concentrations, a cohort of 71 patients was collected via retrospective chart review and/or patient interview. Clozapine steady-state plasma concentrations and demographic variables were obtained. Multiple-linear regression was utilized to examine the relationship between the plasma clozapine concentration and the independent variables.

RESULTS

The dosing model that optimally predicted steady-state clozapine plasma concentrations included the variables dose (mg/day), smoking (yes = 0 and no = 1), gender, and a dose-gender interaction variable. The model explained 47% of the variance in the clozapine concentrations (F = 14.42, p < .001, r2 = .47). Two equations, one for male subjects, i.e., clozapine (ng/mL) = 111 (smoke) + 0.464 (dose) + 145, and one for female subjects, i.e., clozapine (ng/mL) = 111 (smoke) + 1.590 (dose)-149, were derived to predict clozapine steady-state plasma concentrations to serve as a clozapine dosing guide for clinicians.

CONCLUSIONS

A clozapine dosing nomogram was constructed as a clinical aid to facilitate clozapine dosing.

Enhancement of latent inhibition in the rat at a high dose of clozapine

The present experiments investigated clozapine (2.5, 5 and 10 mg/kg) and haloperidol (0.1 mg/kg) administration on latent inhibition (LI) in rats. Clozapine's ability to antagonize amphetamine-induced disruption of LI was also assessed. A conditioned emotional response procedure was employed. In the pre-exposure stage, 'pre-exposed' rats received 10 (Experiment 1) or 40 (Experiment 2) presentations of a flashing light stimulus without reinforcement. During the conditioning phase, the light stimulus was paired with a footshock. At test, LI was expressed by the extent of suppression of water licking during flashing light presentation. Both clozapine (10 mg/kg) and haloperidol (0.1 mg/kg) significantly facilitated LI. In addition, clozapine significantly reversed the disruption of LI induced by amphetamine (1.0 mg/kg). These results with clozapine illustrate that LI is sensitive to antipsychotics which differ in their mode of action and furthermore emphasize the value of LI as a test model for detecting the antipsychotic potential of novel drugs.

Symptoms at index admission as predictor for 1-5 year outcome in schizophrenia

A total of 107 drug-free schizophrenic patients (76 males and 31 females) were consecutively admitted to an emergency ward and rated for psychotic symptoms by means of 32 items from the Comprehensive Psychopathological Rating Scale (CPRS). They were followed prospectively with ratings of social functioning by use of Strauss-Carpenter's outcome scale at 1, 3 and 5 years after index admission with the aim of determining possible early symptoms that are predictors of social outcome. In total, 59 of the patients were first admissions and had never been treated. At index admission, no difference was found in total CPRS scores between first-admission patients and chronic readmitted patients, or between male and female subjects. When subscales for positive symptoms (flights of ideas, feeling controlled, disrupted thoughts, auditory hallucinations, ideas of persecution) and negative symptoms (indecision, withdrawal, reduced speech, lack of appropriate emotions, slowness of movements) from the CPRS were applied, no relationship between the two subscales and outcome scores was found. However, in patients with a duration of the disorder of less than 24 months before index admission, high scores on both negative and positive subscales were significantly correlated with a poor 5-year outcome. No correlation was found in the group with a duration of illness of more than 24 months before index admission. It is concluded that symptoms at index admission have a predictive value for outcome in schizophrenic patients. Negative symptoms measured by use of a subscale of the CPRS have a predictive value for outcome up to 5 years after index admission, but high scores on both positive and negative symptoms are more strongly associated with a poor outcome. The duration of the symptoms before admission, as well as the kind of neuroleptic treatment given (clozapine vs. classical neuroleptics), seem to be important factors for prediction of outcome. Our data support the view that early negative symptoms in particular have a predictive value for the prognosis in schizophrenia for up to 5 years.

The latent inhibition model of schizophrenia: further validation using the atypical neuroleptic, clozapine

Latent inhibition (LI) refers to retarded conditioning to a stimulus that has been repeatedly presented without reinforcement. LI is impaired in schizophrenia patients and in rats treated with amphetamine. Neuroleptic drugs produce two effects in this test paradigm: antagonism of amphetamine-induced disruption of LI, and enhancement of LI when administered on their own. The present experiments tested the effects of the atypical neuroleptic, clozapine, on LI. The experiments used a conditioned emotional response procedure in rats licking for water, consisting of three stages: preexposure, in which the to-be-conditioned stimulus (tone) was repeatedly presented without reinforcement; conditioning, in which the preexposed stimulus was paired with reinforcement (foot shock); and test, in which LI was indexed by animals' degree of suppression of licking during tone presentation. In experiments 1 and 2, the effects of 5.0 and 10.0 mg/kg clozapine on LI were assessed following 20 or 10 tone preexposures, respectively. Experiments 3 and 4 used 40 preexposures and investigated antagonism of amphetamine-induced disruption of LI by 5.0 and 10.0 mg/kg clozapine, respectively. The results demonstrated that clozapine possesses a neuroleptic profile in the LI model, namely, it facilitates the development of LI and antagonizes amphetamine-induced disruption of LI.

Structure-activity relationships of a series of novel (piperazinylbutyl)thiazolidinone antipsychotic agents related to 3-[4-[4-(6-fluorobenzo[b]thien-3-yl)-1-piperazinyl]butyl]-2,5,5- trimethyl-4-thiazolidinone maleate

HP-236 (3-[4-[4-(6-Fluorobenzo[b]thien-3-yl)-1-piperazinyl]butyl]-2,5,5- trimethyl-4-thiazolidinone maleate; P-9236) (54) displayed a pharmacological profile indicative of potential atypical antipsychotic activity. A series of piperazinyl butyl thiazolidinones structurally related to this compound were prepared and evaluated in vitro for dopamine D2 and serotonin 5HT2 and 5HT1A receptor affinity. The compounds were examined in vivo in animal models of potential antipsychotic activity and screened in models predictive of extrapyramidal side effect (EPS) liability. The synthesis of these compounds, details of their structure-activity relationships, and discovery of a new lead, compound 50, as well as further development of the profiles of compounds 50 and 54 are described.

Further evidence for clozapine as a dopamine D1 receptor agonist

Clozapine (0.625-10.0 mg kg-1 s.c.), but not the two major clozapine metabolites, N-desmethylclozapine (0.625-10.0 mg kg-1 s.c.) or clozapine-N-oxide (0.625-10.0 mg kg-1 s.c.), caused a dose-dependent decrease in core temperature in the rat. Furthermore, the clozapine-induced hypothermia (2.5 mg kg-1 s.c.) was fully antagonised by pretreatment with the selective dopamine D1 receptor antagonist (+)-5-(2,3-dihydrobenzofuran-7-yl)-3-methyl-8-nitro-2,3,4, 5-tetrahydro-1 H-3-benzazepine-7-ol, maleate (NNC 687) (4.0 mg kg-1 s.c.). NNC 687 by itself (2.0-8.0 mg kg-1 s.c.) did not affect core temperature. The present results provide further evidence for the dopamine D1 receptor agonist properties of clozapine.

Autoradiography with [3H]8-OH-DPAT reveals increases in 5-HT(1A) receptors in ventral prefrontal cortex in schizophrenia

We previously reported increased glutamatergic innervation in orbital frontal cortex in schizophrenia. In view of the evidence that one serotonin (5-HT) receptor, the 5-HT(1A) subtype, is associated with cortical glutamatergic neurons, we have used quantitative receptor autoradiography to measure the specific binding of the 5-HT(1A) receptor ligand [3H]8-OH-DPAT (2 nM) in sections of orbital frontal cortex taken from 18 control and 12 schizophrenic postmortem brains. Schizophrenic patients, as compared with controls, had increased 5-HT(1A) receptor binding in the three orbital frontal regions examined. These effects were pronounced in the male subgroup, and were most apparent in the outer cortical laminae. These data are consistent with the hypothesis that schizophrenia is associated with an abnormal glutamatergic afferent innervation of orbital frontal cortex.

Clozapine: current status and role in the pharmacotherapy of schizophrenia

OBJECTIVE

This study evaluates clozapine and its present role in the pharmacotherapy of schizophrenia.

METHOD

Clozapine's current clinical status is reviewed, as is its position with respect to other treatment options.

RESULTS

Clozapine represents the prototype of "atypical" neuroleptics, with evidence of clinical efficacy in both positive and negative symptoms, as well as a diminished risk of extrapyramidal side effects. It is the only neuroleptic to date that has established itself as having little, if any, risk of tardive dyskinesia. More recent research has focused on its potential for overall savings in health care costs, as well as possible benefits in the area of neuropsychological functioning.

CONCLUSION

Evidence suggesting that the course of schizophrenia can be altered by effective treatment favours a systematic approach that optimizes treatment options. While clozapine does not represent a 1st-line agent because of its risk of agranulocytosis, it has an integral role to play in treatment-resistant schizophrenia or in individuals experiencing intolerable side effects with conventional neuroleptics.

Potentiation of the effects of raclopride on sucrose consumption by the 5-HT2 antagonist ritanserin

We examined the effects on sucrose consumption of a dopamine (DA) D2/D3 antagonist (raclopride, 0-0.3 mg/kg), a serotonin 5-HT2/2c antagonist (ritanserin, 0-0.4 mg/kg), and raclopride (0.15 mg/kg) combined with ritanserin (0-0.4 mg/kg). Three different concentrations of sucrose solution (0.7%, 7.0% and 34%) were tested. The concentration-intake function in drug-free rats was an inverted-U, with 7.0% sucrose supporting the highest intake. Raclopride (0.3 mg/kg) inhibited intake of 7.0% sucrose, but its effect on 0.7% sucrose fell short of significance (P < 0.06) and intake of 34% sucrose was unchanged. Ritanserin did not affect sucrose intake when given on its own, but synergized with a previously ineffective dose of raclopride (0.15 mg/kg) so as to cause a significant inhibition of 7.0% sucrose intake and increase in 34% sucrose intake. These data indicate that 5-HT2 antagonism potentiated the behavioural effects of raclopride and we speculate that this interaction might contribute to the efficacy of atypical neuroleptic drugs.

Rebound insomnia after abrupt clozapine withdrawal

Rebound insomnia has been reported upon discontinuation of benzodiazepines. We describe the first case of a sleep polygraphically documented rebound insomnia with an unusual somatic fatigue syndrome after long-term use of clozapine in a 30-year-old schizophrenic male. The withdrawal symptoms occurred the first day after drug discontinuation and could be stopped by readministering clozapine. In our opinion, the sudden occurrence of the withdrawal symptoms cannot be explained by a dopaminergic hypersensitivity or a cholinergic rebound, but indicates an involvement of GABAergic and perhaps antiglutamatergic properties of clozapine.

Characterization of [3H]clozapine binding sites in rat brain

We examined the characteristics of [3H]clozapine binding sites in four rat brain regions (frontal cortex, limbic area, hippocampus and striatum) in order to elucidate the pharmacological profile of this unique atypical antipsychotic drug. The specific [3H]clozapine binding was found to be saturable and reversible in all these brain regions. Scatchard analysis of the saturation data indicated that the specific binding consisted of high- and low-affinity components. Displacement experiments showed that the muscarinic cholinergic receptor represented about 50% of [3H]clozapine binding in each brain area. Serotonin 5-HT2 and dopamine D4 receptor binding sites could also be detected by displacement experiments using ketanserin and nemonapride, respectively, in frontal cortex and limbic area, but not in hippocampus or striatum. Alpha-1, alpha-2, histamine H1, dopamine D1, D2, or D3 receptor components could not be determined within the high-affinity [3H]clozapine binding sites in any brain region. It is possible that the atypical property of clozapine may depend on the modulatory effect on dopaminergic function via 5-HT2 receptor blockade and/or may be mediated via D4 receptor blockade in the mesocortical and mesolimbic area.