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

How Loading Dose Strategies for Depot Paliperidone Can Go Wrong

This column presents a real-life case of a patient who developed severe and prolonged Parkinsonism secondary to the loading dose strategy recommended in the prescribing information (package insert) for paliperidone palmitate (Invega Sustenna). This column presents 2 major points. First, the case illustrates what the practitioner must do before following the general guidelines for a loading dose approach to the administration of paliperidone palmitate as outlined in the package insert to decrease the likelihood of a serious and potentially fatal consequence. Second, the case illustrates how therapeutic drug monitoring can be useful in assessing and managing patients who develop an untoward reaction. In this case, therapeutic drug monitoring was done using serum prolactin levels because the available laboratory could not measure the level of the drug itself in plasma, and the case highlights some limitations to keep in mind when using plasma prolactin levels to do such monitoring. To put this case in context, a review of the literature was conducted which identified 3 related cases. The author also refers readers to previous articles on therapeutic drug monitoring and pharmacokinetic considerations that arise when using depot (long-acting injectable) antipsychotics.

Second-Generation Antipsychotics and Dysregulation of Glucose Metabolism: Beyond Weight Gain

Second-generation antipsychotics (SGAs) are the cornerstone of treatment for schizophrenia because of their high clinical efficacy. However, SGA treatment is associated with severe metabolic alterations and body weight gain, which can increase the risk of type 2 diabetes and cardiovascular disease, and greatly accelerate mortality. Several underlying mechanisms have been proposed for antipsychotic-induced weight gain (AIWG), but some studies suggest that metabolic changes in insulin-sensitive tissues can be triggered before the onset of AIWG. In this review, we give an outlook on current research about the metabolic disturbances provoked by SGAs, with a particular focus on whole-body glucose homeostasis disturbances induced independently of AIWG, lipid dysregulation or adipose tissue disturbances. Specifically, we discuss the mechanistic insights gleamed from cellular and preclinical animal studies that have reported on the impact of SGAs on insulin signaling, endogenous glucose production, glucose uptake and insulin secretion in the liver, skeletal muscle and the endocrine pancreas. Finally, we discuss some of the genetic and epigenetic changes that might explain the different susceptibilities of SGA-treated patients to the metabolic side-effects of antipsychotics.

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

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

Plasma prolactin levels are associated with the severity of illness in drug-naive first-episode psychosis female patients

Patients with schizophrenia frequently present hyperprolactinemia as a consequence of antipsychotic treatment. However, an increase in circulating prolactin levels has also been shown in patients without previous treatment. Our objective was to compare prolactin levels between antipsychotic-naive first-episode psychosis (AN-FEP) patients and healthy controls (HC). As part of an FEP program (Programa Asistencial Fases Iniciales de Psicosis [PAFIP]), 270 AN-FEP patients and 153 HC were eligible for this study. Serum prolactin levels were measured by an automated immunochemiluminescent assay. Subjects' sex and having an AN-FEP diagnosis both had an effect on prolactin levels, with higher levels in women than in men, and in AN-FEP patients than in HC. Moreover, plasma prolactin levels showed a negative correlation with the SAPS scores in AN-FEP female patients. AN-FEP patients have increased levels of prolactin, which might be stress-induced. This, together with the association of higher prolactin with a lower severity of the disease, suggests that prolactin might play a neuroprotective role, especially in women.

Dopamine D2 receptor occupancy of lumateperone (ITI-007): a Positron Emission Tomography Study in patients with schizophrenia

Dopamine D₂ receptor occupancy (D₂RO) is a key feature of all currently approved antipsychotic medications. However, antipsychotic efficacy associated with high D₂RO is often limited by side effects such as motor disturbances and hyperprolactinemia. Lumateperone (ITI-007) is a first-in-class selective and simultaneous modulator of serotonin, dopamine and glutamate in development for the treatment of schizophrenia and other disorders. The primary objective of the present study was to determine D₂RO at plasma steady state of 60 mg ITI-007, a dose that previously demonstrated antipsychotic efficacy in a controlled trial, administered orally open-label once daily in the morning for two weeks in patients with schizophrenia (N = 10) and after at least a two-week washout period from standard of care antipsychotics. D₂RO was determined using positron emission tomography with ¹¹C-raclopride as the radiotracer. Mean peak dorsal striatal D₂RO was 39% at 60 mg ITI-007 occurring 1 h post-dose. Lumateperone was well-tolerated with a favorable safety profile in this study. There were no clinically significant changes in vital signs, ECGs, or clinical chemistry laboratory values, including prolactin levels. There were no adverse event reports of akathisia or other extrapyramidal motor side effects; mean scores on motor function scales indicated no motor disturbances with lumateperone treatment. This level of occupancy is lower than most other antipsychotic drugs at their efficacious doses and likely contributes to the favorable safety and tolerability profile of lumateperone with reduced risk for movement disorders and hyperprolactinemia. If approved, lumateperone may provide a new and safe treatment option for individuals living with schizophrenia.

Review of serum prolactin levels as an antipsychotic-response biomarker

Antipsychotics acting as antagonists at dopamine D2 receptors concentrated in the striatum are the cornerstone of effective treatment of psychosis. Substantial progress in treating persons with schizophrenia could be achieved by the identification of biomarkers which reliably determine the lowest efficacious dose of antipsychotics. Prolactin levels have been considered a promising treatment-response biomarker due to dopamine’s regulation of serum prolactin levels through D2 receptors in the hypothalamic-pituitary pathway. Prolactin secretion in response antipsychotic administration is associated with the antipsychotics affinity for D2 receptors. This review assesses the available literature on the use of serum prolactin levels as an antipsychotic-response biomarker. Articles were identified through PubMed as well as the reference lists of full text articles available online. Relevant publications were summarized briefly to define the limitations and utility of serum prolactin levels as a tool for improving antipsychotic dosing. Serum prolactin levels in combination with prolactin-inducing potencies for each antipsychotic may help identify the lowest effective dose of antipsychotic medications. , In addition to the fact that prolactin secretion is dependent on serum antipsychotic levels and not brain levels, recent findings show that prolactin release is independent of the β-arrestin-2 pathway and GSK3β regulation, one branch of the pathway that has been implicated in antipsychotic efficacy. Therefore, serum prolactin is an indirect biomarker for treatment response. Further investigations are warranted to characterize prolactin-antipsychotic dose-response curves and systematically test the utility of measuring prolactin levels in patients to identify a person’s lowest efficacious dose.

Advancing psychiatric pharmacogenomics using drug development paradigms

Drugs used to treat psychiatric disorders, even when taken as directed, fail to provide adequate relief for a sizeable proportion of patients. Despite our advancements in understanding human genetics and development of high-throughput tools to probe variation, pharmacogenomics has yielded marginal ability to predict drug response for psychiatric disorders. Here, I review the current pharmacogenomics paradigm, identifying opportunities to incorporate drug development strategies designed to increase the probability of delivering a successful molecule to the clinic. This includes using in-depth pharmacokinetic profiles, clear measures of target engagement and target-specific pharmacodynamic responses orthogonal to clinical response. The complex pharmacological profiles psychiatric drugs require re-examination of simplified clinical response-oriented pharmacogenetic hypotheses, in favor of a more complete patient profile.

d-Lysergic Acid Diethylamide (LSD) as a Model of Psychosis: Mechanism of Action and Pharmacology

d-Lysergic Acid Diethylamide (LSD) is known for its hallucinogenic properties and psychotic-like symptoms, especially at high doses. It is indeed used as a pharmacological model of psychosis in preclinical research. The goal of this review was to understand the mechanism of action of psychotic-like effects of LSD. We searched Pubmed, Web of Science, Scopus, Google Scholar and articles' reference lists for preclinical studies regarding the mechanism of action involved in the psychotic-like effects induced by LSD. LSD's mechanism of action is pleiotropic, primarily mediated by the serotonergic system in the Dorsal Raphe, binding the 5-HT2A receptor as a partial agonist and 5-HT1A as an agonist. LSD also modulates the Ventral Tegmental Area, at higher doses, by stimulating dopamine D₂, Trace Amine Associate receptor 1 (TAAR₁) and 5-HT2A. More studies clarifying the mechanism of action of the psychotic-like symptoms or psychosis induced by LSD in humans are needed. LSD's effects are mediated by a pleiotropic mechanism involving serotonergic, dopaminergic, and glutamatergic neurotransmission. Thus, the LSD-induced psychosis is a useful model to test the therapeutic efficacy of potential novel antipsychotic drugs, particularly drugs with dual serotonergic and dopaminergic (DA) mechanism or acting on TAAR₁ receptors.

Adjunctive metformin for antipsychotic-induced hyperprolactinemia: A systematic review

This systematic review examines adjunctive metformin therapy for the treatment of antipsychotic-induced hyperprolactinemia. A computerized search of databases in Chinese and the international databases in English provided three trials with a total of 325 patients including one randomized clinical trial (RCT) and two observational studies (single-group, before-after design). A meta-analysis could not be conducted. The quality of evidence ranged from "very low" to "moderate". Metformin patients had a significant decrease in serum prolactin level with a mean of 54.6μg/l in the three trials. In the RCT, menstruation restarted in 67% of those with menstrual disturbances versus 5% in placebo. In one observational study, 91% of patients no longer had signs or symptoms of galactorrhea. In the RCT, adverse drug reactions (ADRs) occurred at similar incidence rates among metformin and placebo patients, except that no significant increases in nausea, insomnia and agitation occurred which were not associated with discontinuations. Our systematic review indicated that adjunctive metformin significantly lowered prolactin level and relieved prolactin-related symptoms in patients with antipsychotic-induced hyperprolactinemia. Future higher quality RCTs need to verify the currently available limited evidence based on three trials which suggest that adjunctive metformin may be used effectively and safely for antipsychotic-induced hyperprolactinemia.

Dopamine Targeting Drugs for the Treatment of Schizophrenia: Past, Present and Future

Schizophrenia is a chronic and debilitating neuropsychiatric disorder affecting approximately 1% of the world's population. This disease is associated with considerable morbidity placing a major financial burden on society. Antipsychotics have been the mainstay of the pharmacological treatment of schizophrenia for decades. The traditional typical and atypical antipsychotics demonstrate clinical efficacy in treating positive symptoms, such as hallucinations and delusions, while are largely ineffective and may worsen negative symptoms, such as blunted affect and social withdrawal, as well as cognitive function. The inability to treat these latter symptoms may contribute to social function impairment associated with schizophrenia. The dysfunction of multiple neurotransmitter systems in schizophrenia suggests that drugs selectively targeting one neurotransmission pathway are unlikely to meet all the therapeutic needs of this heterogeneous disorder. Often, however, the unintentional engagement of multiple pharmacological targets or even the excessive engagement of intended pharmacological targets can lead to undesired consequences and poor tolerability. In this article, we will review marketed typical and atypical antipsychotics and new therapeutic agents targeting dopamine receptors and other neurotransmitters for the treatment of schizophrenia. Representative typical and atypical antipsychotic drugs and new investigational drug candidates will be systematically reviewed and compared by reviewing structure-activity relationships, pharmacokinetic properties, drug metabolism and safety, pharmacological properties, preclinical data in animal models, clinical outcomes and associated side effects.

Increased serum prolactin levels in drug-naive first-episode male patients with schizophrenia

BACKGROUND

Prolactin is a hormone receiving considerable attention in psychiatry. Increased serum prolactin level is frequently associated with dopamine blocking antipsychotics. Furthermore, decreased prolactin level was considered a reflector of the effect of antipsychotics. However, there is restricted numbers of investigations that researched baseline prolactin levels in first-episode patients with schizophrenia.

AIMS

We purpose to investigate serum baseline prolactin levels in drug-naive first-episode patients with schizophrenia (FES) and to explore the differences in serum prolactin levels between FES, drug-free schizophrenic patients (DFS) and healthy controls (HC).

MATERIAL AND METHODS

The study was conducted in the Departments of Psychiatry, Gölbaşı Hasvak and Kırklareli State Hospitals, Turkey. Thirty male FES, 41 male DFS and 32 male HC were included in study. All participants were clinically examined and individually interviewed. Before initiating any pharmacological treatment, 5 ml of venous blood was collected to measure serum prolactin levels between 08:00 and 10:00 h, which was determined by radioimmunoassay (RIA). Prolactin levels were also collected from the consenting HC using the same assay.

RESULTS

The mean age was higher in the DFS group. The mean score of Brief Psychiatric Rating Scale was higher in the FES group and mean score of Scale for the Assessment of Negative Symptoms was higher in the DFS group. The mean value of prolactin was higher in the FES group (34.1 ± 19.9 ng/dl) compared with DFS (17.9 ± 6.5 ng/dl) and HC (9.7 ± 2.3 ng/dl) (F = 35.5, P < 0.001). Additionally, the mean value of serum prolactin is higher in the DFS group compared with HC (P < 0.001).

CONCLUSION

To our knowledge, this study is the first to demonstrate higher serum prolactin levels in male FES compared with male DFS and male HC. Prolactin might act as a protective factor while first episode of schizophrenia is experienced. Future studies are needed to provide the role of prolactin in schizophrenia.

Long-term effect of haloperidol, olanzapine, and risperidone on plasma prolactin levels in patients with first-episode psychosis

OBJECTIVE

The main goal of this study was to assess the long-term effect of haloperidol, olanzapine, and risperidone on serum prolactin levels in a naturalistically treated first-episode psychosis population.

METHODS

Patients included in this study were drawn from a prospective, randomized, open-label clinical trial. Prolactin levels were measured in 110 patients with medication-naive first-episode psychosis at baseline, 3 months, and 1 year.

RESULTS

A repeated-measures analysis of variance revealed a significant difference between treatments (F = 17.28, P < 0.001). At 1-year follow-up, most patients in the haloperidol and olanzapine arms had prolactin values that fell within the reference range. Patients treated with risperidone experienced a significant increase at 3 months resulting in prolactin levels above the reference range in 90% of men and 87% of women. The levels showed a tendency to decrease at 1 year, although still more than 70% of the values remained above the normative range. Sexual adverse drug reactions at 1 year assessed by the Udvalg for Kliniske Undersogelser scale showed that a higher percentage (39.3%) of patients had symptoms in the risperidone group compared to the olanzapine group (24%) or haloperidol group (20%), but the difference did not reach statistical significance (P = 0.281).

CONCLUSION

Olanzapine and haloperidol treatments do not significantly affect serum prolactin levels at long term. After 1 year, elevated prolactin levels persist in most patients treated with risperidone.

Sex steroids and schizophrenia

The peak in incidence for schizophrenia is during late adolescence for both sexes, but within this time frame the peak is both earlier and steeper for males. Additionally, women have a second peak in incidence following menopause. Two meta-analyses have reported that men have an overall ∼40% greater chance of developing schizophrenia than do women (Aleman et al., 2003; McGrath et al., 2004). These and other findings have led to the suggestion that ovarian hormones may be protective against schizophrenia. Less explored is the potential role of testosterone in schizophrenia, although disruptions in steroid levels have also been reported in men with the illness. The relationship between increased gonadal hormone release per se and peri-adolescent vulnerability for psychiatric illness is difficult to tease apart from other potentially contributory factors in clinical studies, as adolescence is a turbulent period characterized by many social and biological changes. Despite the obvious opportunity provided by animal research, surprisingly little basic science effort has been devoted to this important issue. On the other hand, the animal work offers an understanding of the many ways in which gonadal steroids exert a powerful impact on the brain, both shaping its development and modifying its function during adulthood. Recently, investigators using preclinical models have described a greater male vulnerability to neurodevelopmental insults that are associated with schizophrenia; such studies may provide clinically relevant insights into the role of gonadal steroids in psychiatric illness.

Schizophrenia as a disorder of too little dopamine: implications for symptoms and treatment

Antipsychotics represent the first effective therapy for schizophrenia, with their benefits linked to dopamine D2 blockade. Schizophrenia was soon identified as a hyperdopaminergic disorder, and antipsychotics proved to be reasonably effective in controlling positive symptoms. However, over the years, schizophrenia has been reconceptualized more broadly, now defined as a heterogeneous disorder with multiple symptom domains. Negative and cognitive features, not particularly responsive to antipsychotic therapy, have taken on increased importance--current thinking suggests that these domains predate the onset of positive symptoms and are more closely tied to functional outcome. That they are better understood in the context of decreased dopamine activity suggests that schizophrenia may fundamentally represent a hypodopaminergic disorder. This shift in thinking has important theoretical implications from the standpoint of etiology and pathophysiology, but also clinically in terms of treatment and drug development.

Central nervous system drug evaluation using positron emission tomography

In conventional pharmacological research in the field of mental disorders, pharmacological effect and dose have been estimated by ethological approach and in vitro data of affinity to the site of action. In addition, the frequency of administration has been estimated from drug kinetics in blood. However, there is a problem regarding an objective index of drug effects in the living body. Furthermore, the possibility that the concentration of drug in blood does not necessarily reflect the drug kinetics in target organs has been pointed out. Positron emission tomography (PET) techniques have made progress for more than 20 years, and made it possible to measure the distribution and kinetics of small molecule components in living brain. In this article, we focused on rational drug dosing using receptor occupancy and proof-of-concept of drugs in the drug development process using PET.

Striatal D₂ receptor binding in 22q11 deletion syndrome: an [¹²³I]IBZM SPECT study

It has been hypothesised that in subjects with 22q11 deletion syndrome (22q11DS) disturbances of the dopamine (DA) system contribute to their increased risk for cognitive deficits and psychiatric problems. However, central DAergic neurotransmission in 22q11DS has not been investigated. We measured striatal D₂ receptor binding potential (D₂R BP(ND)) using (S)-(-)-3-iodo-2-hydroxy-6-methoxy-N-[(1-ethyl-2-pyrrolidinyl)methyl] benzamide-single photon emission computed tomography ([¹²³I]IBZM SPECT) in 12 adults with 22q11DS and 12 matched controls. Correlations between D₂R BP(ND) and plasma prolactin (pPRL) levels were also determined. 22q11DS subjects and controls had similar D₂R BP( ND). There was a positive correlation between D₂R BP( ND) and pPRL values in controls, but no such relation was found in 22q11DS subjects. This study suggests that a 22q11 deletion does not affect striatal DAergic neurotransmission in the living human brain. However, the disturbed relationship between D₂R BP(ND) and pPRL values suggests DAergic dysfunction at a different level. Further studies on DAergic function in extra-striatal brain regions and under challenged conditions are needed.

A comparison of serum prolactin concentrations after administration of paliperidone extended-release and risperidone tablets in patients with schizophrenia

Increases in serum prolactin concentrations after administration of risperidone have been attributed, by some, to the availability of paliperidone in plasma. This double-blind, randomized, parallel-group study in patients with schizophrenia compared serum prolactin concentrations following the administration of paliperidone extended-release and risperidone immediate-release tablets. At steady state, the doses administered resulted in a similar exposure to paliperidone and the pharmacologically active fraction of risperidone (i.e. risperidone + paliperidone), respectively. Eligible patients were randomized to either paliperidone extended-release 12 mg on days 1-6 or risperidone immediate-release 2 mg on day 1 and 4 mg on days 2-6. Mean serum prolactin concentrations increased on day 1 (C(max): 71.8 ng/ml and 89.7 ng/ml reached at 6.5 hours and 2.6 hours for paliperidone extended-release and risperidone immediate-release, respectively). On day 6, serum prolactin concentration-time profiles were similar for both treatments, with overall higher serum prolactin concentrations than on day 1 (AUC(0-24 h): 1389 and 842 ng h/ml, and 1306 and 741 ng.h/ml on day 6 and day 1 for paliperidone extended-release and risperidone immediate-release, respectively). These results indicate that paliperidone extended-release 12 mg and risperidone immediate-release 4 mg, administered over a period of 6 days, lead to similar elevations in serum prolactin concentrations.

Switching to quetiapine for risperidone-induced amenorrhea: Report of two cases

Almost all the antipsychotics can cause hyperprolactinemia-related side-effects like amenorrhea. Quetiapine has been reported to have minimal propensity to cause hyperprolactinemia. We report here two cases of risperidone-induced amenorrhea, who resumed their normal cycle on switching over the medication to quetiapine.

Gender-specific prolactin response to antipsychotic treatments with risperidone and olanzapine and its relationship to drug concentrations in patients with acutely exacerbated schizophrenia

Hyperprolactinemia is a frequent consequence of treatment with antipsychotic agents, partially because the prolactin response to antipsychotics is related to dopamine blockade. Recent studies have suggested that the prolactin response to olanzapine is weaker than that to risperidone. Thus, we studied the effects of various factors on the elevated plasma prolactin levels caused by these medications. The subjects were 94 patients with acutely exacerbated schizophrenia (46 males, 48 females). For four weeks, they received 6mg of risperidone and 20mg of olanzapine daily. Plasma samples were collected before the medications were given and 12h after the bedtime dosing each week. Treatment with either risperidone or olanzapine boosted plasma prolactin levels above baseline in both males and females. Prolactin levels were significantly higher in females than in males at all sampling points in both treatments. Risperidone increased prolactin significantly more than did olanzapine in both males and females. Delta prolactin (prolactin level at four weeks minus the baseline prolactin level) during olanzapine treatment significantly correlated with olanzapine concentration at 4th week (r=-0.518, p<0.01) only in males. Multiple regression analyses showed that delta prolactin during risperidone was significantly correlated with gender (p<0.001) and age (p<0.05) and that delta prolactin during olanzapine significantly correlated with gender (p<0.001) and drug concentration (p<0.01). The present study suggests that the predominant factors influencing hyperprolactinemia are young female for risperidone treatment, and being female and lower drug concentration as a predictor for hyperprolactinemia under olanzapine.

Prolactin fluctuation over the course of a day during treatments with three atypical antipsychotics in schizophrenic patients

Hyperprolactinemia is a frequent consequence of treatment with some antipsychotic agents. Although prolactin secretion varies over the course of a day and during psychological circumstances, there is little information in the literature regarding the time dependence of the prolactin response to antipsychotics. We evaluated prolactin levels in schizophrenic patients receiving risperidone (3 mg twice daily), olanzapine (10 mg twice daily), or perospirone (16 mg twice daily) for at least 4 weeks. The subjects were compared to matched healthy controls. Plasma sample collection for quantification of drug and prolactin levels was conducted before and 2, 4, 6, 8, and 12 h after the morning dosing. Prolactin concentrations before dosing during risperidone treatment were significantly higher than during treatment with olanzapine and perospirone in females. The daily fluctuation of prolactin concentration after perospirone treatment was larger than that observed after risperidone and olanzapine treatments. Areas under the plasma concentration-time curves was greatest in subjects treated with risperidone, followed by perospirone and finally by olanzapine. These findings suggest that daily fluctuations in prolactin concentration after perospirone treatment are larger than following treatment with risperidone and olanzapine. The plasma concentration of prolactin during perospirone treatment therefore depends on the time of sampling.

Mechanisms underlying psychosis and antipsychotic treatment response in schizophrenia: insights from PET and SPECT imaging

Molecular imaging studies have generated important in vivo insights into the etiology of schizophrenia and treatment response. This article first reviews the PET and SPECT evidence implicating dopaminergic dysfunction, especially presynaptic dysregulation, as a mechanism for psychosis. Second, it summarises the neurochemical imaging studies of antipsychotic action, focussing on D2/3 receptors. These studies show that all currently licensed antipsychotic drugs block striatal D2/3 receptors in vivo- a site downstream of the likely principal dopaminergic pathophysiology in schizophrenia- and that D2/3 occupancy above a threshold is required for antipsychotic treatment response. However, adverse events, such as extra-pyramidal side-effects or hyperprolactinemia, become much more likely at higher occupancy levels, which indicates there is an optimal 'therapeutic window' for D2/3 occupancy, and questions the use of high doses of antipsychotic treatment in clinical practice and trials. Adequate D2/3 blockade by antipsychotic drugs is necessary but not always sufficient for antipsychotic response. Molecular imaging studies of clozapine, the one antipsychotic licensed for treatment resistant schizophrenia, have provided insights into the mechanisms underlying its unique efficacy. To link this pharmacology to the phenomenology of the illness, we discuss the role of dopamine in motivational salience and show how i) psychosis could be viewed as a process of aberrant salience, and ii) antipsychotics might provide symptomatic relief by blocking this aberrant salience. Finally, we discuss the implications of these PET and SPECT findings for new avenues of drug development.

Variants of the dopamine D2 receptor gene and risperidone-induced hyperprolactinemia in children and adolescents

OBJECTIVE

To investigate the association between hyperprolactinemia and variants of the dopamine D2 receptor (DRD2) gene in children and adolescents in long-term treatment with risperidone.

METHODS

Medically healthy 7 to 17-year-old patients chronically treated with risperidone but receiving no other antipsychotics were recruited in a cross-sectional study. Four DRD2 variants were genotyped and prolactin concentration was measured. Medication history was obtained from the medical records. The effect of the TaqIA variants of the DRD2 on the risk of risperidone-induced hyperprolactinemia was the primary outcome measure.

RESULTS

Hyperprolactinemia was present in 50% of 107 patients (87% males) treated with risperidone for an average of 2.9 years. Age, stage of sexual development, and the dose of risperidone independently predicted a higher prolactin concentration, whereas the dose of psychostimulants was negatively correlated with it. However, these four predictors became nonsignificant when risperidone serum concentration was entered into the model. Adverse events potentially related to hyperprolactinemia were more common in participants with elevated prolactin concentration and in girls (45%) compared with boys (10%). After controlling for risperidone concentration and the dose of psychostimulants, the TaqIA A1 and the A-241G alleles were associated with higher prolactin concentration, whereas the -141C Ins/Del and C957T variants had no significant effect. In addition, adverse events potentially related to hyperprolactinemia were four times more common in TaqIA A1 allele carriers.

CONCLUSION

Prolactin concentration is closely related to central DRD2 blockade, as reflected by risperidone serum concentration. Furthermore, the TaqIA and A-241G variants of the DRD2 gene could be useful in predicting the emergence of hyperprolactinemia and its potential adverse events.

Menstrual cycle dysfunction associated with neurologic and psychiatric disorders: their treatment in adolescents

Epilepsy, bipolar disorder, and migraines are common disorders that are often associated with disturbances in menstrual function in adolescent girls. Women with untreated epilepsy are more likely to have irregular menstrual cycles than are nonepileptic controls, indicating that the disease itself plays a role in the etiology of these reproductive abnormalities. In addition, many girls with these disorders require chronic maintenance treatment with agents that may perturb the hypothalamic-pituitary-ovarian axis. Valproate is a highly effective antiepileptic drug used widely to treat epilepsy, bipolar disorder, and migraines. Valproate induces features of the polycystic ovary syndrome (PCOS) in approximately 7% of women. Girls with epilepsy, and possibly bipolar disorder, appear particularly susceptible to developing PCOS features on valproate, perhaps on account of the relative immaturity of their hypothalamic-pituitary-ovarian axes. Antipsychotics are highly effective drugs used widely to treat adolescents with bipolar disorder, psychotic disorders, and behavioral disturbances. Some, but not all of the antipsychotic, induce hyperprolactinemia, which may result in oligo- or amenorrhea. Prolonged amenorrhea in association with hyperprolactinemia incurs significant risks for bone health in adolescent girls. Because of the potential reproductive health risks associated with use of specific antiepileptic drugs and selective antipsychotics, these agents are vital treatments for adolescents with severe illnesses. Use of these agents should be considered and weighed against the risk of using alternative agents, which have their own side effects, or not treating these serious neurologic and psychiatric disorders.

Association between dopamine-related polymorphisms and plasma concentrations of prolactin during risperidone treatment in schizophrenic patients

Hyperprolactinemia is an inevitable consequence of treatment with antipsychotic agents to some extent because prolactin response to antipsychotics is related to dopamine blockade. Recent studies have suggested that polymorphisms of the dopamine receptors are associated with therapeutic response to antipsychotics. Thus, we studied the effects of major polymorphisms of dopamine-related genes on plasma concentration of prolactin. Subjects were 174 schizophrenic patients (68 males, 106 females) receiving 3 mg twice daily of risperidone for at least 4 weeks. Sample collections were conducted 12 h after the bedtime dosing. Five dopamine-related polymorphisms (Taq1A, -141C ins/del for DRD2, Ser9Gly for DRD3, 48 bp VNTR for DRD4, Val158Met for COMT) were identified. The mean (+/-SD) plasma concentration of prolactin in females was significantly higher than males (54.3+/-27.2 ng/ml versus 126.8+/-70.2 ng/ml, p<0.001). No dopamine-related polymorphisms differed the plasma concentration of prolactin in males or females. Multiple regression analyses including plasma drug concentration and age revealed that plasma concentration of prolactin correlated with gender (standardized partial correlation coefficients (beta)=0.551, p<0.001) and negatively with age (standardized beta=-0.202, p<0.01). No correlations were found between prolactin concentration and dopamine-related polymorphisms. These findings suggest that plasma prolactin concentrations in females are much higher than in males but the dopamine-related variants are not predominantly associated with plasma concentration of prolactin.

The effects of herkinorin, the first mu-selective ligand from a salvinorin A-derived scaffold, in a neuroendocrine biomarker assay in nonhuman primates

Herkinorin is the first mu-opioid receptor-selective ligand from the salvinorin A diterpenoid scaffold. Herkinorin has relative mu > kappa > delta binding selectivity, and it can act as an agonist at both mu- and kappa-receptors, in vitro. These studies were the first in vivo evaluation of the effects of herkinorin in nonhuman primates, using prolactin release, a neuroendocrine biomarker assay that is responsive to both mu- and kappa-agonists, as well as to compounds with limited ability to cross the blood-brain barrier. In cumulative dosing studies (0.01-0.32 mg/kg i.v.), herkinorin produced only small effects in gonadally intact males (n = 4), but a more robust effect in females (n = 4). Time course studies with herkinorin (0.32 mg/kg) confirmed this greater effectiveness in females and revealed a fast onset after i.v. administration (e.g., by 5-15 min). Antagonism experiments with different doses of nalmefene (0.01 and 0.1 mg/kg) caused dose-dependent and complete prevention of the effect of herkinorin in females. This is consistent with a principal mu-agonist effect of herkinorin, with likely partial contribution by kappa-agonist effects. The peripherally selective antagonist quaternary naltrexone (1 mg/kg s.c.) caused approximately 70% reduction in the peak effect of herkinorin (0.32 mg/kg) in females, indicating that this effect of herkinorin is prominently mediated outside the blood-brain barrier.

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.

Association between major Multidrug Resistance 1 (MDR1) gene polymorphisms and plasma concentration of prolactin during risperidone treatment in schizophrenic patients

An in vitro study has suggested that risperidone is a substrate of P-glycoprotein, which is coded by MDR1gene. The rate of P-glycoprotein efflux transport can mediate brain penetration of lipophilic drugs. We therefore studied the effects of major polymorphisms of MDR1 gene on plasma concentrations of prolactin. Subjects included 175 schizophrenic patients (68 males, 107 females) who were receiving 3 mg of risperidone twice daily for at least 4 weeks. Sample collections were conducted 12 h after the bedtime dosing. The plasma concentrations of prolactin in females were significantly higher than in males (54.3+/-27.2 versus 126.8+/-70.2 ng/ml, p<0.001). There was no difference in mean (+/-SD) plasma concentration of prolactin between C3435T genotypes [C/C, C/T, T/T; 62.3+/-33.3, 49.4+/-15.6, 53.2+/-33.2 ng/ml, ns] or G2677T/A genotypes [G/G, G/T or A, T or A/T or A; 58.0+/-27.7, 58.5+/-35.0, 46.1+/-20.7 ng/ml, ns] in males nor between C3435T genotypes (123.6+/-65.0, 127.8+/-79.2, 130.4+/-49.7 ng/ml, ns) or G2677T/A genotypes (123.3+/-67.0, 97.7+/-71.2, 144.9+/-69.9 ng/ml, ns) in females. Multiple regression analyses including plasma drug concentration and age revealed that plasma concentration of prolactin correlated with gender (standardized beta=0.540, p<0.001) and negatively with age (standardized beta=-0.183, p<0.01). No correlations were found between prolactin concentration and MDR1 genotypes. These findings suggest that prolactin concentrations in females are much higher than in males but the major MDR1 variants are not associated with the plasma concentration of prolactin.

Antipsychotic efficacy: relationship to optimal D2-receptor occupancy

Clinically important differences exist between antipsychotic agents and formulations in terms of safety and tolerability. Features of the biochemical interaction between the antipsychotic and the D2-receptor may underlie these differences. This article reviews current information on the relationship between antipsychotic receptor occupancy and clinical response. A literature search was performed using the keywords 'antipsychotic or neuroleptic', 'receptor' and 'occupancy' and 'dopamine' and 'D2' supplemented by the authors' knowledge of the literature. Imaging and clinical data have generally supported the hypotheses that optimal D2-receptor occupancy in the striatum lies in a 'therapeutic window' between approximately 65 and approximately 80%, however, pharmacokinetic and pharmacodynamic properties of a drug should also be taken into account to fully evaluate its therapeutic effects. Additional research, perhaps in preclinical models, is needed to establish D2-receptor occupancy in various regions of the brain and the optimal duration of D2-receptor blockade in order to maximise efficacy and tolerability profiles of atypical antipsychotics and thereby improve treatment outcomes for patients with schizophrenia.

Prolactin levels in male schizophrenic patients treated with risperidone and haloperidol: a double-blind and randomized study

RATIONALE

There are few data from systematic, double-blind clinical trials that have compared the effect of the typical and the atypical antipsychotics on serum prolactin (PRL) levels in patients with schizophrenia.

OBJECTIVES

The goal of this study was to compare the effect of risperidone and haloperidol on serum PRL and investigate the relationship between serum PRL levels and clinical response in patients with schizophrenia.

METHODS

Seventy-eight inpatients with a diagnosis of schizophrenia (according to DSM-III-R) were randomly assigned to 12 weeks of treatment with 6 mg/day of risperidone or 20 mg/day of haloperidol after a 2-week washout period, using a randomized, double-blind design. Clinical efficacy was determined using the positive and negative syndrome scale (PANSS). Their serum PRL was assayed by means of radioimmunometric assay (RIA) between pre-treatment and post-treatment, and compared with 30 sex-matched and age-matched normal subjects.

RESULTS

Both risperidone and haloperidol treatment significantly increased serum PRL levels in drug-free chronic schizophrenia patients (both P<0.001). Hyperprolactinemia induced by risperidone 6 mg/kg was comparable to levels produced by haloperidol 20 mg/day. Considering dose-adjusted serum PRL levels, risperidone treatment induced a significant elevation of PRL levels compared with haloperidol treatment at the haloperidol equivalent (P<0.001). Change in PRL levels at pre-treatment and post-treatment were related to positive symptom improvement seen in the risperidone group (r=0.51, P=0.016), but not in the haloperidol group (P>0.05). Female patients showed both a higher baseline and post-treatment PRL level and a greater increase in PRL than men (all P<0.05).

CONCLUSIONS

Risperidone is associated with a robust effect on prolactin secretion in contrast to the conventional antipsychotic haloperidol. Prolactin monitoring during risperidone treatment should be performed.

Antipsychotic-induced hyperprolactinaemia: mechanisms, clinical features and management

Hyperprolactinaemia is an important but neglected adverse effect of antipsychotic medication. It occurs frequently with conventional antipsychotics and some atypical antipsychotics (risperidone and amisulpride) but is rare with other atypical antipsychotics (aripiprazole, clozapine, olanzapine, quetiapine, ziprasidone). For this reason the terms 'prolactin-sparing' and 'prolactin-raising' are more useful than 'atypical' and 'conventional' when considering the effect of antipsychotic drugs on serum prolactin. During antipsychotic treatment prolactin levels can rise 10-fold or more above pretreatment values. In a recent study approximately 60% of women and 40% of men treated with a prolactin-raising antipsychotic had a prolactin level above the upper limit of the normal range. The distinction between asymptomatic and symptomatic hyperprolactinaemia is important but is often not made in the literature. Some symptoms of hyperprolactinaemia result from a direct effect of prolactin on target tissues but others result from hypogonadism caused by prolactin disrupting the normal functioning of the hypothalamic-pituitary-gonadal axis. Symptoms of hyperprolactinaemia include gynaecomastia, galactorrhoea, sexual dysfunction, infertility, oligomenorrhoea and amenorrhoea. These symptoms are little researched in psychiatric patients. Existing data suggest that they are common but that clinicians underestimate their prevalence. For example, well conducted studies of women treated with conventional antipsychotics have reported prevalence rates of approximately 45% for oligomenorrhoea/amenorrhoea and 19% for galactorrhoea. An illness-related under-function of the hypothalamic-pituitary-gonadal axis in female patients with schizophrenia may also contribute to menstrual irregularities. Long-term consequences of antipsychotic-related hypogonadism require further research but are likely and include premature bone loss in men and women. There are conflicting data on whether hyperprolactinaemia is associated with an increased risk of breast cancer in women. In patients prescribed antipsychotics who have biochemically confirmed hyperprolactinaemia it is important to exclude other causes of prolactin elevation, in particular tumours in the hypothalamic-pituitary area. If a patient has been amenorrhoeic for 1 year or more, investigations should include bone mineral density measurements. Management should be tailored to the individual patient. Options include reducing the dose of the antipsychotic, switching to a prolactin-sparing agent, prescribing a dopamine receptor agonist and prescribing estrogen replacement in hypoestrogenic female patients. The efficacy and risks of the last two treatment options have not been systematically examined. Antipsychotic-induced hyperprolactinaemia should become a focus of interest in the drug treatment of psychiatric patients, particularly given the recent introduction of prolactin-sparing antipsychotics. Appropriate investigations and effective management should reduce the burden of adverse effects and prevent long-term consequences.

Prolactinemia is uncoupled from central D2/D3 dopamine receptor occupancy in amisulpride treated patients

RATIONALE

Atypical antipsychotic drugs are classically associated with lower propensity to extrapyramidal symptoms (EPS) and hyperprolactinemia than typical antipsychotic drugs. It has not been clarified why some atypical antipsychotic drugs, such as amisulpride, induce prolactin plasma concentration (PRL) elevation, but little EPS. Previous studies have found an association between striatal D2/D3 receptor occupancy and PRL in typical antipsychotic treated patients suggesting that PRL is a marker of central D2/D3 receptors blockade.

OBJECTIVE

We have evaluated the relationship between PRL and central (striatum, temporal cortex and thalamus) D2/D3 receptor occupancy in amisulpride treated schizophrenic patients.

METHODS

Single photon emission tomography (SPET) and [123I]-epidepride were used to determine D2/D3 receptor occupancy in eight amisulpride treated patients. PRL was measured concurrently with the scans.

RESULTS

The mean PRL was 1166 (range 499-1892 mIU/l) for a mean amisulpride dose of 406 mg/day (range 150-600 mg/day). Amisulpride plasma concentration and central D2/D3 receptor occupancy were positively correlated (r=0.83-0.89, df=4, P<0.05). No significant correlations were observed between PRL and amisulpride (daily dose or plasma concentration, P>0.05), or between PRL and central D2/D3 receptor occupancy (P>0.05).

CONCLUSIONS

Our findings show that amisulpride-induced hyperprolactinemia is uncoupled from central D2/D3 receptor occupancy. Amisulpride has poor blood-brain barrier penetration and reaches much higher concentration at the pituitary, which is outside the blood-brain barrier. Higher D2/D3 receptor occupancy at the pituitary gland than at central regions is a possible explanation for amisulpride PRL elevation with low EPS. Further studies evaluating pituitary D2/D3 receptor occupancy in vivo are necessary to confirm this hypothesis.

Serum prolactin levels in unmedicated first-episode and recurrent schizophrenia patients: a possible marker for the disease's subtypes

Various studies indicate that we must consider schizophrenia not as a single disease but as several distinct etiological processes that give rise to characteristic symptoms. In the current study, we aimed to examine prolactin serum levels in unmedicated first-episode and recurrent schizophrenic patients. The prolactin levels were compared among the different schizophrenia subtypes, i.e. paranoid, schizoaffective and disorganized. Prolactin serum samples were assessed on the morning after the admission in 48 first-episode and 38 recurrent unmedicated hospitalized schizophrenia patients. Two psychiatrists made the diagnosis without knowledge of laboratory results and completed the rating scales. Despite all prolactin levels being within or close to the normal range, we found significant differences in prolactin serum levels among schizophrenia subtype patients: the lowest values were for the paranoid type, intermediate for the schizoaffective and the highest for the disorganized patients. The results seem to indicate a pronounced hyperdopaminergic activity in paranoid schizophrenia, suggesting differences in dopaminergic tone between the schizophrenia subtypes, and support the clinical and the neuropsychological individuality of disease subtypes. There were no significant differences in prolactin serum levels of the schizophrenia subtypes between the first-episode and the recurrent patients. It appears that there are constant patterns of dopamine bioactivity in acutely psychotic unmedicated schizophrenia patients, whether the patients are first admitted or recurrent.

Single oral dose safety, tolerability, and pharmacokinetics of PNU-96391 in healthy volunteers

The safety, tolerability, and pharmacokinetics of PNU-96391, an orally active weak dopamine D2 receptor antagonist with modulatory properties of central dopaminergic function, was characterized. Fifty-three healthy normal volunteers were enrolled in this randomized, double-blinded, placebo-controlled, single-dose study. Subjects were assigned to single oral doses of placebo and 1, 3, 10, 30, 100, 150, and 200 mg PNU-96391. Safety and tolerability were assessed using telemetry, Holter monitoring, surface ECG, vital signs, safety laboratories, and adverse event reports. Pharmacokinetic parameters were determined by model-independent techniques. Adverse events were infrequent, of mild to moderate intensity, and in the dose range of 1 to 150 mg. Dose escalation was stopped at 200 mg because of severe nausea, dizziness, lightheadedness, and tachycardia. Besides the increase in heart rate, no other drug-related effects on vital signs were observed. Safety laboratory measurements were not significantly changed. Evidence of drug activity was demonstrated by a dose-dependent elevation in serum prolactin. PNU-96391 was rapidly absorbed, with maximum concentrations achieved between 0.5 and 4 hours in all subjects. The half-life of the drug was short (2 to 6 h). The main metabolite, PNU-100014, was rapidly formed, with a t(max) ranging from 1 to 6 hours. Peak levels of the metabolite are approximately half of the parent drug, and the half-life is slightly longer (4 to 10 h). Increases in dose resulted in linear increases in exposure for both PNU-96391 and PNU-100014. Hence, PNU-96391 was well tolerated at doses ranging from 1 to 150 mg.

Are dopamine antagonists a risk factor for breast cancer? An answer from Parkinson's disease

Women undergoing chemotherapy for breast cancer are often administered dopamine antagonist adjuvant medications that may increase levels of prolactin potentially increasing the risk of cancer. Using nationwide computerized registers of death data for the years 1991 through 1996 we examined 12,430,473 deaths of persons over 40 years of age and extracted 144,364 cases with Parkinson's disease (PD), a dopamine deficient population. Patients with PD had lower rates of breast and other types of malignancies, even in the presence of depression and suicide.

Schizophrenia and osteoporosis

Although it has been suggested that antipsychotic-induced hyperprolactinaemia in schizophrenic patients may lead to an increased risk of osteoporosis, this has not been proven. Osteoporosis is a multifactorial disease, and untreated patients with schizophrenia are at risk due to both the consequences of the disease and related lifestyle factors. Evidence from available studies does not show that antipsychotic-induced hyperprolactinaemia is an independent risk factor for osteoporosis in schizophrenic patients. Osteoporosis would be expected in women who develop amenorrhoea as a result of hyperprolactinaemia secondary to antipsychotics, but there is no plausible mechanism in men. The uncertainty over this issue underlines the need for full medical and metabolic assessment and monitoring of psychiatric patients.

Hyperprolactinaemia and antipsychotic therapy in schizophrenia

Prolactin is a polypeptide hormone that exists as a number of isoforms and is involved in a multitude of physiological processes. Prolactin secretion is promoted by various physiological stimuli and pathological processes and is inhibited by the action of dopamine on the lactotroph cells of the hypothalamus. Hyperprolactinaemia, an elevation of prolactin levels above the norm, is a physiological occurrence and is not of concern (including sexual dysfunction and decreased bone mineral density). Treatment of hyperprolactinaemia is usually confined to the removal of the primary cause of the disease, but several dopamine agonists have been investigated. Hyperprolactinaemia is also a side-effect of the conventional, and some of the second-generation, antipsychotics used in the treatment of schizophrenia. These agents rely on their dopamine antagonistic properties to provide their antipsychotic effects. However, this also removes the brake on prolactin secretion, leading to hyperprolactinaemia. While antipsychotic use has been linked to certain hyperprolactinaemia-related side-effects (sexual dysfunction), its link to others (decreased bone mineral density) has proved more controversial. The association of symptoms with antipsychotic use is further complicated by the fact that patients with schizophrenia can suffer from some of these symptoms because of the disease itself. In managing antipsychotic-induced hyperprolactinaemia, the initial step is to exclude other causes of hyperprolactinaemia while monitoring the occurrence of adverse effects. The physician should also engage in close consultation with the patient with regard to the benefits of the antipsychotic medication and the impact of any adverse effects. A regular risk-benefit discussion will allow the clinician to achieve optimal outcomes in each case.

Hyperprolactinemia and bone mineral density: the potential impact of antipsychotic agents

The prevalence of schizophrenia is about 1% worldwide. Individuals with schizophrenia are at increased risk for osteoporosis and fractures for several reasons, including poor diet, lack of exercise, cigarette smoking, and polydipsia. Some antipsychotic medications may further increase the risk of fractures by causing dizziness, orthostatic hypotension, and falls. Studies in women with hyperprolactinemia resulting from pituitary tumors have demonstrated high rates of osteoporosis believed to result from hypoestrogenism. Similarly, hyperprolactinemia in men results in hypogonadism and bone loss. Preliminary surveys have indicated that schizophrenia patients also may have elevated rates of osteoporosis and pathological fractures, possibly resulting in part from the long-term administration of antipsychotic agents that produce hyperprolactinemia and secondarily lower estrogen and testosterone levels. This potential complication of treatment with certain antipsychotic agents requires careful study and could represent a serious public health problem.

Optimizing limbic selective D2/D3 receptor occupancy by risperidone: a [123I]-epidepride SPET study

Selective action at limbic cortical dopamine D2-like receptors is a putative mechanism of atypical antipsychotic efficacy with few extrapyramidal side effects. Although risperidone is an atypical antipsychotic with high affinity for D2 receptors, low-dose risperidone treatment is effective without inducing extrapyramidal symptoms. The objective was to test the hypothesis that treatment with low-dose risperidone results in 'limbic selective' D2/D3 receptor blockade in vivo. Dynamic single photon emission tomography (SPET) sequences were obtained over 5 hours after injection of [123I]-epidepride (approximately 150 MBq), using a high-resolution triple-headed brain scanner (Marconi Prism 3000XP). Kinetic modelling was performed using the simplified reference region model to obtain binding potential values. Estimates of receptor occupancy were made relative to a normal volunteer control group (n = 5). Six patients treated with low-dose risperidone (mean = 2.6 mg) showed moderate levels of D2/D3 occupancy in striatum (49.9%), but higher levels of D2/D3 occupancy in thalamus (70.8%) and temporal cortex (75.2%). Occupancy values in striatum were significantly different from thalamus (F (1,4) = 26.3, p < 0.01) and from temporal cortex (F (1,4) = 53.4, p < 0.01). This is the first study to evaluate striatal and extrastriatal occupancy of risperidone. Low dose treatment with risperidone achieves a similar selectivity of limbic cortical over striatal D2/D3 receptor blockade to that of atypical antipsychotics with lower D2/D3 affinity such as clozapine, olanzapine and quetiapine. This finding is consistent with the relevance of 'limbic selective' D2/D3 receptor occupancy to the therapeutic efficacy of atypical antipsychotic drugs.

Comparison of prolactin concentrations between haloperidol and bromperidol treatments in schizophrenic patients

The antipsychotic drug, bromperidol, is a close structural analogue of haloperidol. These two drugs also have similarities in metabolic pathways and pharmacological properties. In the present study, the prolactin concentrations in plasma during bromperidol versus haloperidol treatments were compared in the same individuals. The subjects were 22 schizophrenic inpatients, who first received bromperidol 12 mg/day for at least 2 weeks followed by haloperidol 12 mg/day. The prolactin concentration in plasma during bromperidol treatment (median and range; 24 and 7-93 ng/ml, respectively) was significantly (P< .01) lower than during haloperidol treatment (32 and 8-102 ng/ml), although the difference was small. The mean (+/- S.D.) plasma concentration of bromperidol was significantly lower than that of haloperidol (20.8+/-8.0 vs. 28.0+/-13.1 nmol/l, P<.05). Prolactin concentrations during both treatment phases correlated well in individuals (r's=.813, P<.001), while no correlation was observed between plasma concentrations of haloperidol and bromperidol (r=.053, ns). These findings suggest that slightly higher prolactin concentration does not necessarily lead to increased risk of hyperprolactinemia during bromperidol treatment compared with haloperidol treatment. In addition, it is suggested that both drugs show similar pharmacodynamic response despite the difference in pharmacokinetics in the same individuals.

Safety and tolerability: how do newer generation "atypical" antipsychotics compare?

Previously, clinicians worked with antipsychotic drugs that almost invariably caused extrapyramidal side effects (EPS) at the dose at which they were clinically effective. By definition, all newer generation atypical antipsychotic agents are significantly better than conventional agents with regard to EPS; i.e., they are clinically effective at doses at which they do not cause EPS. This EPS advantage of atypical antipsychotics translates into several important clinical benefits, including better negative symptom efficacy, lesser dysphoria, less impaired cognition, and a lower risk of tardive dyskinesia; in fact, this "EPS advantage" is the principal basis of the many clinical advantages provided by the class of atypical antipsychotics. While all atypical agents share this "EPS advantage," there are important differences between these agents with regard to the ease and consistency with which this EPS advantage can be realized. Pharmacologically, different atypical antipsychotics differ; these differences translate into differences in their side effect profiles. Five atypical antipsychotics are currently available: clozapine, risperidone, olanzapine, quetiapine, and ziprasidone. Meaningful differences between these agents with regard to weight gain, sedation, anticholinergic side effects, cardiovascular issues, endocrine side effects, hepatic and sexual issues, will be considered and their clinical implications discussed.