Dopamine D₂/₃ occupancy of ziprasidone across a day: a within-subject PET study

Optimisation of pharmacotherapy in psychiatry through therapeutic drug monitoring, molecular brain imaging and pharmacogenetic tests: Focus on antipsychotics

BACKGROUND

For psychotic disorders (i.e. schizophrenia), pharmacotherapy plays a key role in controlling acute and long-term symptoms. To find the optimal individual dose and dosage strategy, specialised tools are used. Three tools have been proven useful to personalise drug treatments: therapeutic drug monitoring (TDM) of drug levels, pharmacogenetic testing (PG), and molecular neuroimaging.

METHODS

In these Guidelines, we provide an in-depth review of pharmacokinetics, pharmacodynamics, and pharmacogenetics for 45 antipsychotics. Over 30 international experts in psychiatry selected studies that have measured drug concentrations in the blood (TDM), gene polymorphisms of enzymes involved in drug metabolism, or receptor/transporter occupancies in the brain (positron emission tomography (PET)).

RESULTS

Study results strongly support the use of TDM and the cytochrome P450 (CYP) genotyping and/or phenotyping to guide drug therapies. Evidence-based target ranges are available for titrating drug doses that are often supported by PET findings.

CONCLUSION

All three tools discussed in these Guidelines are essential for drug treatment. TDM goes well beyond typical indications such as unclear compliance and polypharmacy. Despite its enormous potential to optimise treatment effects, minimise side effects and ultimately reduce the global burden of diseases, personalised drug treatment has not yet become the standard of care in psychiatry.

Update Lessons from Positron Emission Tomography Imaging Part I: A Systematic Critical Review on Therapeutic Plasma Concentrations of Antipsychotics

BACKGROUND

Positron emission tomography (PET) and single photon emission tomography (SPECT) of molecular drug targets (neuroreceptors and transporters) provide essential information for therapeutic drug monitoring-guided antipsychotic drug therapy. The optimal therapeutic windows for D 2 antagonists and partial agonists, as well as their proposed target ranges, are discussed based on an up-to-date literature search.

METHODS

This part I of II presents an overview of molecular neuroimaging studies in humans and primates involving the target engagement of amisulpride, haloperidol, clozapine, aripiprazole, olanzapine, quetiapine, risperidone, cariprazine, and ziprasidone. The systemic review particularly focused on dopamine D 2 -like and 5-HT 2A receptors. Target concentration ranges were estimated based on receptor occupancy ranges that relate to clinical effects or side effects (ie, extrapyramidal side effects). In addition, findings for other relevant receptor systems were included to further enrich the discussion.

RESULTS

The reported reference ranges for aripiprazole and clozapine align closely with findings from PET studies. Conversely, for haloperidol, risperidone, and olanzapine, the PET studies indicate that a lowering of the previously published upper limits would be necessary to decrease the risk of extrapyramidal side effect.

CONCLUSIONS

Molecular neuroimaging studies serve as a strong tool for defining target ranges for antipsychotic drug treatment and directing therapeutic drug monitoring.

Beyond monoamines: I. Novel targets and radiotracers for Positron emission tomography imaging in psychiatric disorders

With the emergence of positron emission tomography (PET) in the late 1970s, psychiatry had access to a tool capable of non-invasive assessment of human brain function. Early applications in psychiatry focused on identifying characteristic brain blood flow and metabolic derangements using radiotracers such as [¹⁵ O]H₂ O and [¹⁸ F]FDG. Despite the success of these techniques, it became apparent that more specific probes were needed to understand the neurochemical bases of psychiatric disorders. The first neurochemical PET imaging probes targeted sites of action of neuroleptic (dopamine D₂ receptors) and psychoactive (serotonin receptors) drugs. Based on the centrality of monoamine dysfunction in psychiatric disorders and the measured success of monoamine-enhancing drugs in treating them, the next 30 years witnessed the development of an armamentarium of PET radiopharmaceuticals and imaging methodologies for studying monoamines. Continued development of monoamine-enhancing drugs over this time however was less successful, realizing only modest gains in efficacy and tolerability. As patent protection for many widely prescribed and profitable psychiatric drugs lapsed, drug development pipelines shifted away from monoamines in search of novel targets with the promises of improved efficacy, or abandoned altogether. Over this period, PET radiopharmaceutical development activities closely paralleled drug development priorities resulting in the development of new PET imaging agents for non-monoamine targets. Part one of this review will briefly survey novel PET imaging targets with relevance to the field of psychiatry, which include the metabotropic glutamate receptor type 5 (mGluR5), purinergic P₂ X₇ receptor, type 1 cannabinoid receptor (CB₁ ), phosphodiesterase 10A (PDE10A), and describe radiotracers developed for these and other targets that have matured to human subject investigations. Current limitations of the targets and techniques will also be discussed.

In Vivo Receptor Visualization and Evaluation of Receptor Occupancy with Positron Emission Tomography

Positron emission tomography (PET) is useful for noninvasive in vivo visualization of disease-related receptors, for evaluation of receptor occupancy to determine an appropriate drug dosage, and for proof-of-concept of drug candidates in translational research. For these purposes, the specificity of the PET tracer for the target receptor is critical. Here, we review work in this area, focusing on the chemical structures of reported PET tracers, their K_i/K_d values, and the physical properties relevant to target receptor selectivity. Among these physical properties, such as cLogP, cLogD, molecular weight, topological polar surface area, number of hydrogen bond donors, and pK_a, we focus especially on LogD and LogP as important physical properties that can be easily compared across a range of studies. We discuss the success of PET tracers in evaluating receptor occupancy and consider likely future developments in the field.

Dopamine D2 Receptor Occupancy Estimated From Plasma Concentrations of Four Different Antipsychotics and the Subjective Experience of Physical and Mental Well-Being in Schizophrenia: Results From the Randomized NeSSy Trial

BACKGROUND

Impaired subjective well-being in schizophrenia patients treated with antipsychotics has often been linked inter alia to the antidopaminergic effects of medication. Thus, it is important to capture the association between striatal dopamine D2 receptor occupancy (D2-RO) and global subjective well-being. We examined this association using data from our multicenter, randomized, double-blind Neuroleptic Strategy Study (NeSSy).

METHODS

An innovative double randomization process was used for allocation of patients to the specific treatment groups. Plasma drug concentrations were measured after 6 and 24 weeks of treatment to obtain the estimated D2-RO (eD2-RO) relative to literature values. We made an exploratory analysis of associations between eD2-RO and subjective well-being scores. One hundred two blood samples from 69 patients were available for the analysis. Because of the lack of a satisfactory occupancy model for quetiapine, only haloperidol, flupentixol, and olanzapine treatment groups were pooled, whereas aripiprazole data were analyzed separately, because of its partial agonistic properties.

RESULTS

In the pooled antagonist group, eD2-RO correlated negatively with the summarized well-being score. In a more detailed analysis, this association could be confirmed for all first-generation antipsychotic-treated patients, but not for the separate second-generation antipsychotic groups. In the aripiprazole group, higher eD2-RO was associated with impaired physical well-being, but had no association with mental well-being.

CONCLUSIONS

Our results suggest that high plasma levels and consequently high occupancy at D2 receptors are disadvantageous for subjective well-being, as distinct from the objective extrapyramidal side effects. To minimize patients' malaise, which disfavors adherence, implementation of therapeutic drug monitoring in the clinical routine may be useful.

Dose reduction of high-dose first-generation antipsychotics or switch to ziprasidone in long-stay patients with schizophrenia: A 1-year double-blind randomized clinical trial

Long-stay patients with severe schizophrenia are frequently treated with high doses of first-generation antipsychotics (FGA). Dose reduction or switching to ziprasidone may reduce the severity of negative symptoms and side effects. We investigated in a randomized double-blind trial whether a dose-reduction strategy to achieve an adequate dose of a FGA (5 mg/day haloperidol equivalents, n = 24) or switching to ziprasidone (160 mg/day, n = 24) in treatment resistant patients would decrease negative symptoms after 1 year of treatment. We found that negative symptoms did not change significantly in either condition. Positive symptoms, excited symptoms, and emotional distress worsened over time with ziprasidone, resulting in a significant difference between conditions in favour of FGA dose reduction. Relapse and treatment failure, defined as a prolonged or repeated relapse, occurred more often with ziprasidone than with FGA (45.8% versus 20.8%, and 25.0% versus 16.7%, respectively). Treatment with ziprasidone was superior for extrapyramidal symptoms. Our study establishes that lowering high FGA doses to an equivalent of 5 mg/day haloperidol or switching to ziprasidone is feasible in the vast majority of patients but does not improve negative or other symptoms. Neither FGA dose reduction nor switching to ziprasidone is an adequate alternative to clozapine for long-stay patients with severe treatment resistant schizophrenia.

Amotivation is associated with smaller ventral striatum volumes in older patients with schizophrenia

OBJECTIVE

Motivational deficits are prevalent in patients with schizophrenia, persist despite antipsychotic treatment, and predict long-term outcomes. Evidence suggests that patients with greater amotivation have smaller ventral striatum (VS) volumes. We wished to replicate this finding in a sample of older, chronically medicated patients with schizophrenia. Using structural imaging and positron emission tomography, we examined whether amotivation uniquely predicted VS volumes beyond the effects of striatal dopamine D2/3 receptor (D2/3 R) blockade by antipsychotics.

METHODS

Data from 41 older schizophrenia patients (mean age: 60.2 ± 6.7; 11 female) were reanalysed from previously published imaging data. We constructed multivariate linear stepwise regression models with VS volumes as the dependent variable and various sociodemographic and clinical variables as the initial predictors: age, gender, total brain volume, and antipsychotic striatal D2/3 R occupancy. Amotivation was included as a subsequent step to determine any unique relationships with VS volumes beyond the contribution of the covariates. In a reduced sample (n = 36), general cognition was also included as a covariate.

RESULTS

Amotivation uniquely explained 8% and 6% of the variance in right and left VS volumes, respectively (right: β = -.38, t = -2.48, P = .01; left: β = -.31, t = -2.17, P = .03). Considering cognition, amotivation levels uniquely explained 9% of the variance in right VS volumes (β = -.43, t = -0.26, P = .03).

CONCLUSION

We replicate and extend the finding of reduced VS volumes with greater amotivation. We demonstrate this relationship uniquely beyond the potential contributions of striatal D2/3 R blockade by antipsychotics. Elucidating the structural correlates of amotivation in schizophrenia may help develop treatments for this presently irremediable deficit.

Representativeness of clinical PET study participants with schizophrenia: A systematic review

While positron emission tomography (PET) studies have provided invaluable data on antipsychotic effects, selection bias remains a serious concern. A systematic review of PET studies that measured dopamine D₂ receptor blockade with antipsychotics was conducted to examine their inclusion/exclusion criteria, using PubMed, EMBASE, and ClinicalTrials.gov (last search, September 2016). PET studies were included if they measured D₂ receptor occupancy in patients with schizophrenia and included introduction of antipsychotic treatment or antipsychotic regimen change in a systematic manner. Twenty-six studies were identified. Age limit was included in 13 studies; one study solely included geriatric patients while others targeted younger adults. Eleven, 6, and 3 studies specifically targeted clinically stable patients, patients with severe psychopathology, and antipsychotic-free patients, respectively. Nineteen and 18 studies excluded patients with physical comorbidity and substance abuse, respectively. As a result, the mean age of subjects ranged from 23 to 42 years when one study that targeted geriatric patients was excluded. Mean Positive and Negative Syndrome Scale total scores ranged from 54 to 95. No comparison active-drug or placebo arm was employed in 24 studies. Blind assessment of symptomatology was performed in 5 studies. In general, subjects participating in clinical PET studies were relatively young, presented with mild symptomatology, and were free from substance abuse or physical comorbidities. These characteristics need to be taken into account when clinical PET data are interpreted. On the other hand, it should also be noted that this study was only qualitative and conservative interpretation is necessary for possibility of subjective bias.

Imaging in drug development

Imaging has played an important part in the diagnosis of disease and development of the understanding of the underlying disease mechanisms and is now poised to make an impact in the development of new pharmaceuticals. This chapter discusses the underlying technologies that make the field ready for this challenge. In particular, the potentials of magnetic resonance imaging and functional magnetic resonance imaging are outlined, including the new methods developed to provide additional information from the scans carried out. The field of nuclear medicine has seen a rapid increase in interest as advances in radiochemistry have enabled a wide range of new radiotracers to be synthesised.

The effects of novel and newly approved antipsychotics on serum prolactin levels: a comprehensive review

Since the 1970s, clinicians have increasingly become more familiar with hyperprolactinemia (HPRL) as a common adverse effect of antipsychotic medication, which remains the cornerstone of pharmacological treatment for patients with schizophrenia. Although treatment with second-generation antipsychotics (SGAs) as a group is, compared with use of the first-generation antipsychotics, associated with lower prolactin (PRL) plasma levels, the detailed effects on plasma PRL levels for each of these compounds in reports often remain incomplete or inaccurate. Moreover, at this moment, no review has been published about the effect of the newly approved antipsychotics asenapine, iloperidone and lurasidone on PRL levels. The objective of this review is to describe PRL physiology; PRL measurement; diagnosis, causes, consequences and mechanisms of HPRL; incidence figures of (new-onset) HPRL with SGAs and newly approved antipsychotics in adolescent and adult patients; and revisit lingering questions regarding this hormone. A literature search, using the MEDLINE database (1966-December 2013), was conducted to identify relevant publications to report on the state of the art of HPRL and to summarize the available evidence with respect to the propensity of the SGAs and the newly approved antipsychotics to elevate PRL levels. Our review shows that although HPRL usually is defined as a sustained level of PRL above the laboratory upper limit of normal, limit values show some degree of variability in clinical reports, making the interpretation and comparison of data across studies difficult. Moreover, many reports do not provide much or any data detailing the measurement of PRL. Although the highest rates of HPRL are consistently reported in association with amisulpride, risperidone and paliperidone, while aripiprazole and quetiapine have the most favorable profile with respect to this outcome, all SGAs can induce PRL elevations, especially at the beginning of treatment, and have the potential to cause new-onset HPRL. Considering the PRL-elevating propensity of the newly approved antipsychotics, evidence seems to indicate these agents have a PRL profile comparable to that of clozapine (asenapine and iloperidone), ziprasidone and olanzapine (lurasidone). PRL elevations with antipsychotic medication generally are dose dependant. However, antipsychotics having a high potential for PRL elevation (amisulpride, risperidone and paliperidone) can have a profound impact on PRL levels even at relatively low doses, while PRL levels with antipsychotics having a minimal effect on PRL, in most cases, can remain unchanged (quetiapine) or reduce (aripiprazole) over all dosages. Although tolerance and decreases in PRL values after long-term administration of PRL-elevating antipsychotics can occur, the elevations, in most cases, remain above the upper limit of normal. PRL profiles of antipsychotics in children and adolescents seem to be the same as in adults. The hyperprolactinemic effects of antipsychotic medication are mostly correlated with their affinity for dopamine D2 receptors at the level of the anterior pituitary lactotrophs (and probably other neurotransmitter mechanisms) and their blood-brain barrier penetrating capability. Even though antipsychotics are the most common cause of pharmacologically induced HPRL, recent research has shown that HPRL can be pre-existing in a substantial portion of antipsychotic-naïve patients with first-episode psychosis or at-risk mental state.

Estimated dopamine D2 receptor occupancy from plasma concentrations of atypical antipsychotics and subjective experience/drug attitude in schizophrenia: an analysis of the CATIE data

OBJECTIVE

The objective of this analysis was to evaluate both cross-sectional and longitudinal relationships between estimated dopamine D2 receptor occupancy from plasma concentrations of atypical antipsychotics and subjective experience/drug attitude in patients with schizophrenia.

METHOD

The data from the Clinical Antipsychotic Trials in Intervention Effectiveness (CATIE) were used in this analysis. The cross-sectional data included 371 patients receiving risperidone, olanzapine, or ziprasidone, who had completed the Drug Attitude Inventory (DAI-10) at six months and provided plasma antipsychotic concentrations. Samples were analyzed to examine the relationship between DAI-10 total scores and estimated D2 occupancy using Spearman's rank correlations, followed by multiple regression analysis. In addition, to elucidate the relationship between changes in DAI-10 scores and estimated D2 occupancy, the longitudinal data from 45 patients who experienced an increase in antipsychotic dosage between six and 12months were analyzed. Mean peak and trough D2 occupancy levels were estimated from plasma antipsychotic concentrations using a population pharmacokinetic approach.

RESULTS

A positive association was found between estimated D2 occupancy and DAI-10 total scores in patients receiving ziprasidone in the cross-sectional dataset (rs=0.395, P=0.001). In contrast, a negative association was found in changes in estimated D2 occupancy and DAI-10 scores among patients receiving olanzapine in the longitudinal dataset (rs=-0.534, P=0.010). No significant associations were found in patients receiving risperidone, or in the whole sample regarding both cross-sectional and longitudinal datasets.

CONCLUSION

Dopamine D2 receptor occupancy may mediate subjective experience/drug attitude in patients with schizophrenia. The directionality may however differ between antipsychotics, which warrants further investigation.

Hyperprolactinemia and estimated dopamine D2 receptor occupancy in patients with schizophrenia: analysis of the CATIE data

BACKGROUND

Large-scale data are still lacking on the relationship between serum prolactin concentration and dopamine D2 receptor occupancy in patients with schizophrenia treated with antipsychotics.

METHODS

The dataset from 481 subjects (risperidone, N = 172, olanzapine, N = 211, and ziprasidone, N = 98) who participated in Phase 1 of the Clinical Antipsychotic Trials in Intervention Effectiveness (CATIE) was used in the present analysis. Dopamine D2 receptor occupancy levels on the day of the measurement of serum prolactin level were estimated from plasma antipsychotic concentrations. A multivariate general linear model was used to examine effects of clinical and demographic characteristics, including estimated D2 occupancy levels, on serum prolactin concentrations. Individual subjects were divided into two groups, stratified by the presence of hyperprolactinemia. To evaluate the performance of this binary classification, sensitivity, specificity, and accuracy of consecutive cut-off points in the D2 occupancy were calculated.

RESULTS

The multivariate general linear model revealed that estimated D2 occupancy levels had significant effects on serum prolactin concentrations while any other variables failed to show significant effects. The cut-off point associated with 0.5 or greater, in both sensitivity and specificity with the greatest accuracy, was 73% (sensitivity, 0.58; specificity, 0.68; accuracy = 0.64) (68-70% for risperidone, 77% for olanzapine, and 55% for ziprasidone.).

CONCLUSION

The threshold for hyperprolactinemia in D2 occupancy may lie somewhat on a lower side of the established therapeutic window with antipsychotics (i.e. 65-80%). This finding highlights the need for the use of the lowest possible dose to avoid this hormonal side effect in the treatment of schizophrenia.