The relationship between risperidone plasma levels and dopamine D2 occupancy: a positron emission tomographic study

In-depth neuropharmacokinetic analysis of antipsychotics based on a novel approach to estimate unbound target-site concentration in CNS regions: link to spatial receptor occupancy

The current study provides a novel in-depth assessment of the extent of antipsychotic drugs transport across the blood-brain barrier (BBB) into various brain regions, as well as across the blood-spinal cord barrier (BSCB) and the blood-cerebrospinal fluid barrier (BCSFB). This is combined with an estimation of cellular barrier transport and a systematic evaluation of nonspecific brain tissue binding. The study is based on the new Combinatory Mapping Approach (CMA), here further developed for the assessment of unbound drug neuropharmacokinetics in regions of interest (ROI), referred as CMA-ROI. We show that differences exist between regions in both BBB transport and in brain tissue binding. The most dramatic spatial differences in BBB transport were found for the P-glycoprotein substrates risperidone (5.4-fold) and paliperidone (4-fold). A higher level of transporter-mediated protection was observed in the cerebellum compared with other brain regions with a more pronounced efflux for quetiapine, risperidone and paliperidone. The highest BBB penetration was documented in the frontal cortex, striatum and hippocampus (haloperidol, olanzapine), indicating potential influx mechanisms. BSCB transport was in general characterized by more efficient efflux compared with the brain regions. Regional tissue binding was significantly different for haloperidol, clozapine, risperidone and quetiapine (maximally 1.9-fold). Spatial differences in local unbound concentrations were found to significantly influence cortical 5-HT_2A receptor occupancy for risperidone and olanzapine. In conclusion, the observed regional differences in BBB penetration may potentially be important factors contributing to variations in therapeutic effect and side effect profiles among antipsychotic drugs.

D₂-receptor occupancy measurement of JNJ-37822681, a novel fast off-rate D₂-receptor antagonist, in healthy subjects using positron emission tomography: single dose versus steady state and dose selection

RATIONALE

JNJ-37822681 is a highly selective, fast dissociating dopamine D₂-receptor antagonist being developed for the treatment of schizophrenia. A single dose [¹¹C]raclopride positron emission tomography (PET) imaging study had yielded an estimated clinical dose range. Receptor occupancy at steady state was explored to test the validity of the single-dose estimates during chronic treatment.

OBJECTIVES

The aims of this study are to characterize single and multiple dose pharmacokinetics and obtain striatal D₂-receptor occupancies to predict doses for efficacy studies and assess the safety and tolerability of JNJ-37822681.

METHODS

An open-label single- and multiple-dose study with 10 mg JNJ-37822681 (twice daily for 13 doses) was performed in 12 healthy men. Twenty [¹¹C]raclopride PET scans (up to 60 h after the last dose) from 11 subjects were used to estimate D₂-receptor occupancy. A direct effect O (max) model was applied to explore the relationship between JNJ-37822681 plasma concentration and striatal D₂-receptor occupancy.

RESULTS

Steady state was reached after 4-5 days of twice daily dosing. JNJ-37822681 plasma concentrations of 3.17 to 63.0 ng/mL resulted in D₂ occupancies of 0 % to 62 %. The concentration leading to 50 % occupancy was 18.5 ng/mL (coefficient of variation 3.9 %) after single dose and 26.0 ng/mL (8.2 %) at steady state. JNJ-37822681 was well tolerated.

CONCLUSIONS

Receptor occupancy after single dose and at steady state differed for JNJ-37822681 and the robustness of the estimates at steady state will be tested in phase 2 studies. Dose predictions indicated that 10, 20, and 30 mg JNJ-37822681 twice daily could be suitable for these studies.

In vivo quantification of striatal dopamine D2 receptor occupancy by JNJ-37822681 using [11C]raclopride and positron emission tomography

JNJ-37822681 is a novel, fast-dissociating dopamine D(2) receptor antagonist, currently in development as an antipsychotic drug candidate. A previous first-in-human study demonstrated mild central nervous system effects of JNJ-37822681 in healthy male volunteers. Significant but transient serum prolactin elevations were demonstrated, whereas other neurophysiological effects were relatively small. To investigate striatal dopamine D(2) receptor occupancy by variable single doses of JNJ-37822681, an open-label [(11)C]raclopride positron emission tomography study was performed in 12 healthy male volunteers, using the simplified reference tissue model with cerebellum as reference tissue. Oral administration of JNJ-37822681 resulted in dose-dependent dopamine D(2) receptor occupancy. Receptor occupancy increased from 9-19% at 2 mg doses to 60-74% at 20 mg doses of JNJ-37822681. Therefore, single oral doses of JNJ-37822681 can produce occupancy levels that are generally associated with clinical efficacy for registered antipsychotic drugs.

Dopamine D2 occupancy as a biomarker for antipsychotics: quantifying the relationship with efficacy and extrapyramidal symptoms

For currently available antipsychotic drugs, blockade of dopamine D(2) receptors is a critical component for achieving antipsychotic efficacy, but it is also a driving factor in the development of extrapyramidal symptoms (EPS). To inform the clinical development of asenapine, generic mathematical models have been developed for predicting antipsychotic efficacy and EPS tolerability based on D(2) receptor occupancy. Clinical data on pharmacokinetics, D(2) receptor occupancy, efficacy, and EPS for several antipsychotics were collected from the public domain. Asenapine data were obtained from in-house trials. D(2) receptor occupancy data were restricted to published positron emission tomography studies that included blood sampling for pharmacokinetics. Clinical efficacy data were restricted to group mean endpoint data from short-term placebo-controlled trials, whereas EPS evaluation also included some non-placebo-controlled trials. A generally applicable model connecting antipsychotic dose, pharmacokinetics, D(2) receptor occupancy, Positive and Negative Syndrome Scale (PANSS) response, and effect on Simpson-Angus Scale (SAS) was then developed. The empirical models describing the D(2)-PANSS and D(2)-SAS relationships were used successfully to aid dose selection for asenapine phase II and III trials. A broader use can be envisaged as a dose selection tool for new antipsychotics with D(2) antagonist properties in the treatment of schizophrenia.

Long-acting injectable risperidone and metabolic ratio: a possible index of clinical outcome in treatment-resistant schizophrenic patients

RATIONALE

It is still common to encounter a partial or no response to antipsychotic treatment in clinical practice, but only individual case reports are currently available concerning the efficacy of long-acting risperidone (RLAI) in treatment-resistant schizophrenia. The relationship between RSP and 9-OH-RSP plasma levels, and clinical response or tolerability has not yet been thoroughly assessed.

METHODS

This open-label, non-randomised study involved 30 outpatients with treatment-resistant schizophrenia, who were prescribed RLAI for 6 months, and clinically evaluated using the Brief Psychiatric Rating Scale (BPRS), the Positive and Negative Symptoms Scale (PANSS), the Clinical Global Impression-Improvement Scale (CGI-I), and the Simpson and Angus Scale for Extrapyramidal Side Effects (EPSE). Plasma RSP and 9-OH-RSP levels were determined at steady-state, and the metabolic ratio (MR) was calculated as plasma 9-OH-RSP/RSP levels.

RESULTS

At the end of the study, 60% of the patients responded to RLAI (a >or=20% reduction in the PANSS score). Linear regression analysis showed a significant positive relationship between the RSP dose and active moiety (RSP + 9-OH-RSP) (r = 0.4; p = 0.02). There was a significant positive relationship between active moiety and EPSE scores (r = 0.6; p = 0.00). The BPRS responders had a significantly higher mean MR than the non-responders (3.41 +/- 1.87 SD vs 1.60 +/- 0.98 SD) (p = 0.00).

CONCLUSIONS

Therapeutic drug monitoring seems to be useful in optimising the dose of RLAI, especially in the case of tolerability problems. MR might be a better index of clinical response to RLAI than the value of the active moiety, although this needs to be confirmed by further data.

Sensitivity of older patients to antipsychotic motor side effects: a PET study examining potential mechanisms

OBJECTIVE

It is generally held that the elderly are more sensitive to motor side effects of antipsychotics, although the mechanisms for such an effect are not fully understood. The objective of this study was to examine whether this sensitivity is due to a central pharmacokinetic (i.e., higher occupancy for a given plasma level) or pharmacodynamic (i.e., greater functional effects for a given occupancy) effect.

DESIGN

Cross-sectional.

SETTING

Centre for Addiction and Mental Health, Toronto, Ontario, Canada.

PARTICIPANTS

Thirteen subjects aged 50 (mean +/- standard deviation age: 62 +/- 9 years) with schizophrenia or schizoaffective disorder who were receiving risperidone.

MEASUREMENTS

Dopamine D2 binding potential in the striatum, using [C]raclopride positron emission tomography scan. D2 receptor occupancy was calculated, using age-corrected measure from healthy individuals and region of interest analysis.

RESULTS

The authors observed the expected nonlinear relationship between total risperidone and 9-hydroxyrisperidone plasma level and striatal D2 receptor occupancy. The estimated plasma level of risperidone plus 9-hydroxyrisperidone associated with 50% maximal receptor occupancy was 7.3 ng/mL, which is similar to what has been reported in younger patients. However, extrapyramidal side effects (EPS) were observed in seven subjects at D2 occupancy of 34%-79%, occupancy levels that are lower than previously reported for younger patients in whom EPS are rare at occupancies lower than 80%.

CONCLUSION

The observation of greater functional effect (EPS in this case) for a given drug occupancy than the younger patients supports a pharmacodynamic mechanism for age-related antipsychotic drug sensitivity. This finding has important implications for dosing of antipsychotics in older patients with schizophrenia.

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

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

Antipsychotic augmentation of serotonergic antidepressants in treatment-resistant obsessive-compulsive disorder: a meta-analysis of the randomized controlled trials

This study aimed to determine the effectiveness of antipsychotic augmentation of serotonergic antidepressants in the management of treatment-resistant obsessive compulsive disorder by carrying out a meta-analysis of all randomized controlled trials. Studies selected through a literature search conducted in March 2006. Ten trials comparing antipsychotic drugs versus placebo met inclusion criteria (haloperidol [n=1], risperidone [n=3], olanzapine [n=2], quetiapine [n=4]). A total of 157 patients were randomized to study drug and 148 were randomized to placebo. Response occurred more often among patients randomized to antipsychotic drugs. The weighted combined response rate ratio by random effects meta-analysis was 3.31 (95% CI 1.40-7.84). Significant between studies heterogeneity was partly explained by the definition of refractoriness, the type and dose of the drug used and the inclusion or exclusion of patients with tic disorders. The study supports the use of antipsychotic drugs as an augmentation strategy but more and larger trials are needed.

Mechanisms of action of second generation antipsychotic drugs in schizophrenia: insights from brain imaging studies

Multiple lines of evidence including recent imaging studies suggest that schizophrenia is associated with an imbalance of the dopaminergic system, entailing hyperstimulation of striatal dopamine (DA) D2 receptors and understimulation of cortical DA D1 receptors. This DA endophenotype presumably emerges from the background of a more general synaptic dysconnectivity, involving alterations in N-methyl-d-aspartate (NMDA) and glutamatergic (GLU) functions. Equally important is the fact that this DA dysregulation might further impair NMDA transmission. The first generation antipsychotic (FGA) drugs are characterized by high affinity to and generally high occupancy of D2 receptors. The efficacy of FGAs is limited by a high incidence of extrapyramidal side-effects (EPS). Second generation antipsychotic (SGA) drugs display reduced EPS liability and modest but clinically significant enhanced therapeutic efficacy. Compared to FGAs, the improved therapeutic action of SGAs probably derives from a more moderate D2 receptor blockade. We will review the effects of SGAs on other neurotransmitter systems and conclude by highlighting the importance of therapeutic strategies aimed at directly increasing prefrontal DA, D1 receptor transmission or NMDA transmission to enhance the therapeutic effect of moderate D2 receptor antagonism.

Atypical antipsychotics and mood stabilization in bipolar disorder

The available literature on the use of atypical antipsychotics for the treatment of bipolar disorder was reviewed. All uncontrolled and controlled reports were identified through a comprehensive Medline search. Based on the available evidence, olanzapine was found to be the most appropriate atypical antipsychotic agent utilized for the treatment of manic bipolar patients, although there is also preliminary data suggesting the efficacy of risperidone and clozapine. The preliminary data evaluating the efficacy of quetiapine and ziprasidone in bipolar disorder are still very limited. Double-blind controlled studies with atypical antipsychotics in the long-term treatment of bipolar disorder are still largely not available, but will be critical to determine the effectiveness of these agents in the maintenance treatment of bipolar disorder. There are recent uncontrolled suggestions that olanzapine may have beneficial effects in depressed bipolar patients, which deserve further investigation in controlled studies. In conclusion, atypical antipsychotics, due to lower potential for neurotoxicity and preliminary evidence suggesting better efficacy than typical antipsychotics, are increasingly having a more prominent role in the pharmacological management of bipolar patients. Nonetheless, until there is systematic data from long-term controlled follow-up studies on the comparative efficacy of these agents with mood stabilizers, atypical antipsychotics should be cautiously utilized, and preferably in combination with a mood stabilizer for the maintenance phase of treatment.

Neuroreceptor imaging in psychiatric disorders

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

Risperidone pre-treatment reduces the euphoric effects of experimentally administered cocaine

Pre-clinical research implicates dopaminergic neurotransmission as critical in producing the effects of stimulants. Previous stimulant challenge studies using volunteers treated with dopaminergic antagonists have generally failed to demonstrate reduction of subjective effects. We performed this study to determine whether repeated dosing with risperidone reduced the subjective effects of experimentally administered cocaine. Nine non-treatment seeking hospitalized cocaine-dependent volunteers received 40 mg cocaine IV before and following 5 days of treatment with risperidone, 2 mg per day. Risperidone pre-treatment reduced the self-rated 'high' produced by cocaine. Repeated, rather than single, dosing with a D2 antagonist may be necessary to reduce the subjective effects produced by cocaine. The degree of D2 receptor blockade produced by risperidone appears to be greater than the reduction in euphoric effects produced by cocaine, suggesting that mechanisms other than those involving D2 receptors may be important in drug-induced euphoria.

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

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