Dopamine D2 Receptor Occupancy Levels Research Articles

The effects of illness severity, cognition, and estimated antipsychotic dopamine receptor occupancy on insight into the illness in schizophrenia: An analysis of clinical antipsychotic trials of intervention effectiveness (CATIE) data

BackgroundThe relationship between dopamine D2 receptor (D2R) occupancy and impaired illness awareness (IIA) remains unclear. While IIA is associated with illness severity and cognitive dysfunction, antipsychotic medication, the principal treatment for schizophrenia, indirectly improves IIA, but may simultaneously contribute to cognitive dysfunction at supratherapeutic doses. Aim and methodsWe investigated the influence of estimated D2R (Est.D2R) occupancy by antipsychotics on the relationships between IIA and illness severity, and IIA and cognition. IIA was assessed in 373 adult patients with schizophrenia (18−62 years) using data from CATIE. IIA was measured using the Positive and Negative Syndrome Scale (PANSS) item G12. D2R occupancy levels were estimated from plasma concentrations for risperidone, olanzapine, and ziprasidone. Correlation, regression, and path analyses were performed to examine IIA's relationship to illness severity, cognition, and Est.D2R. ResultsIllness severity was predictive of IIA. However, premorbid IQ, cognition, and Est.D2R did not predict IIA, and Est.D2R did not serve either a moderating or mediating role in both regression and path analyses. ConclusionsConsistent with previous literature, our results suggest that IIA is a function of illness severity in adult patients with schizophrenia. Future studies should explore whether D2R occupancy mediates the relationships between IIA and illness severity, and IIA and cognitive dysfunction, in late-life schizophrenia (i.e. ≥60 years) given the effects of aging on cognition, IIA, and antipsychotic sensitivity.

Plasma levels and estimated dopamine D2 receptor occupancy of long-acting injectable risperidone during maintenance treatment of schizophrenia: a 3-year follow-up study.

Dopamine D2 receptor occupancy levels needed for the maintenance treatment of schizophrenia remain to be elucidated. We examined 3-year clinical outcomes of patients with schizophrenia who received long-acting injectable risperidone (LAI risperidone) at baseline and investigated their dopamine D2 receptor occupancy levels, estimated from plasma drug concentrations. A chart review of 52 outpatients with schizophrenia who participated in the original cross-sectional study was conducted to examine their 3-year clinical outcomes between April and September 2015. Patients who continued outpatient treatment with LAI risperidone without any usage of concomitant chlorpromazine equivalent antipsychotic dosage at >200mg/day for the 3-year period were asked to participate in the follow-up assessments that included the Brief Psychiatric Rating Scale (BPRS) and estimated dopamine D2 receptor occupancy levels at trough, using plasma concentrations of risperidone plus 9-hydroxyrisperidone. Data were compared with the same patients collected 3years earlier. Among the original 52 participants, 14 participants (27%) continued outpatient treatment with LAI risperidone. Ten participants (19%) provided plasma samples; mean±SD measured trough concentration of risperidone plus 9-hydroxyrisperidone significantly increased from 22.9±15.6 to 31.8±17.5ng/mL (P=0.02). Estimated dopamine D2 receptor occupancy numerically increased from 63.0±10.9 to 69.0±11.0% (P=0.12). A significant worsening was observed in the BPRS total score among these patients (mean±SD, 34.3±12.7 to 46.5±16.9, P=0.003). Paradoxically, the increased plasma concentration was found to be associated with a significant worsening of the clinical outcome. More investigations are indicated to shed further light on optimal levels of D2 blockade in the maintenance treatment of schizophrenia.

Dose and dosing frequency of long-acting injectable antipsychotics: a systematic review of PET and SPECT data and clinical implications.

Brain imaging data of antipsychotics have mainly been derived from oral antipsychotic drugs, which hampers our understanding of the requirement of dose/dosing frequency of long-acting injectable (LAI) antipsychotics for the maintenance treatment of schizophrenia. A systematic literature search was performed to identify positron emission tomography (PET) and single-photon emission computed tomography (SPECT) studies that assessed dopamine D2 receptor occupancy levels with LAI antipsychotic drugs in humans, using PubMed, EMBASE, and PsycINFO (last search, February 2013). Twenty studies (15 PET and 5 SPECT studies) were identified. The most investigated drug in these PET and SPECT studies was haloperidol decanoate (44 subjects; 11 studies), followed by risperidone LAI (24 subjects; 3 studies), olanzapine pamoate (14 subject; 1 study), and fluphenazine decanoate (12 subjects; 3 studies). The data have demonstrated high and continuous D2 receptor blockade with LAIs; the effects of LAI first-generation antipsychotics on the central nervous system may persist for several months. The prospective and cross-sectional studies showed that continuous dopamine D2 receptor blockade above 65% (ie, the lower end of the established therapeutic window for the acute phase treatment) was not always necessary for maintenance treatment for at least some of the patients. In conclusion, because of the limited brain imaging data on LAI antipsychotics, we still do not know the best way to dose them. Still, the currently available brain imaging data raises a possibility that the dosing interval of LAI antipsychotics may be extended beyond the currently indicated range in some patients.

Tardive dyskinesia in relation to estimated dopamine D2 receptor occupancy in patients with schizophrenia: Analysis of the CATIE data

ObjectiveThe objective of this study was to evaluate the relationship between antipsychotic-induced tardive dyskinesia (TD) and estimated dopamine D2 receptor occupancy levels in patients with schizophrenia, using the dataset from the Clinical Antipsychotic Trials in Intervention Effectiveness (CATIE). MethodsThe dataset from 218 subjects (risperidone, N=78; olanzapine, N=100; ziprasidone, N=40) who presented with a score of zero on the Abnormal Involuntary Movement Scale (AIMS) at baseline in Phase 1 of the CATIE study, and remained for ≥6months, was used. Peak and trough dopamine D2 receptor occupancy levels on the day of the AIMS assessment at the endpoint were estimated from plasma antipsychotic concentrations, using population pharmacokinetic analysis and our D2 prediction model. The estimated dopamine D2 receptor occupancy levels were compared between patients who presented an AIMS score of ≥2 at endpoint and those with a score of zero, using the Mann–Whitney U test. ResultsEstimated dopamine D2 receptor occupancy levels at trough were significantly higher in subjects who developed involuntary movements (N=23) than those who did not (N=195) (71.7±14.4% vs. 64.3±19.3%, p<0.05) while no significant difference was found in the estimated peak D2 receptor occupancy between them (75.4±8.7% vs. 72.1±9.9%, p=0.07). When the analyses were separately conducted for the three drugs, there were no significant differences in estimated peak or trough D2 occupancy although the values were consistently numerically higher among those developing involuntary movements. ConclusionGreater dopamine D2 receptor blockade with antipsychotics at trough might increase the risk of tardive involuntary movements although this finding needs to be replicated in larger trials.

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

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. 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. 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.). 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.

A Cross-Sectional Study of Plasma Risperidone Levels With Risperidone Long-Acting Injectable

While 65%-80% occupancy of dopamine D2 receptors with antipsychotics has been proposed to achieve optimal therapeutic response during acute treatment of schizophrenia, it remains unclear as to whether it is also necessary to maintain D2 receptor occupancy within this "safe" window for ongoing maintenance treatment. The data are especially scarce for long-acting antipsychotic formulations. Clinically stable patients with schizophrenia (DSM-IV) receiving a stable dose of risperidone long-acting injectable (LAI) as antipsychotic monotherapy for at least 3 months and free of any psychiatric hospitalization over the past 6 months were included. Dopamine D2 receptor occupancy levels at trough were estimated from plasma concentrations of risperidone plus 9-hydroxyrisperidone immediately before the intramuscular injection of risperidone LAI, using a 1-site binding model derived from our previous positron emission tomography data. This study was conducted from October to December 2011. 36 patients were included in this study (mean ± SD age, 49.3 ± 14.0 years; mean ± SD dose and interval of injections, 38.2 ± 11.6 mg and 16.5 ± 14.0 days, respectively). Mean ± SD D2 receptor occupancy was 62.1% ± 15.4%; 52.8% of the subjects (n = 19) did not demonstrate an occupancy of ≥ 65%. On the other hand, 13.9% (n = 5) showed a D2 occupancy as high as over 80% at the estimated trough. More than half of patients taking risperidone LAI maintained clinical stability without achieving continuous blockade of dopamine D2 receptors ≥ 65% in real-world clinical settings. Results suggest that sustained dopamine D2 receptor occupancy levels of ≥ 65% may not be necessary for maintenance treatment with risperidone LAI in schizophrenia.

Dopamine D2 receptor occupancy with risperidone or olanzapine during maintenance treatment of schizophrenia: A cross-sectional study

In treating schizophrenia, it has been established that 65-80% occupancy of dopamine D2 receptors optimizes therapeutic efficacy while minimizing risks of extrapyramidal symptoms. However, it is unclear as to whether it is necessary to keep D2 receptor occupancy within this therapeutic window to maintain response. In this study, daily peak and trough D2 receptor occupancy levels were estimated in clinically stable patients with schizophrenia (DSM-IV) who were receiving risperidone or olanzapine. Using two collected plasma samples, plasma antipsychotic concentrations at peak and trough were estimated with population pharmacokinetic techniques. Corresponding dopamine D2 receptor occupancy levels were then estimated, using a recently developed model. 35 subjects with stable schizophrenia completed the study (mean±SD age, 48.8±13.8years; male [N=14]; Asians [N=23], Caucasians [N=12]; risperidone [N=20] at 3.2±2.3mg/day, and olanzapine [N=15] at 9.2±4.9mg/day) between September and December 2010. 48.6% (N=17) did not achieve a continuous blockade of ≥65%. Moreover, 11.4% (N=4) did not achieve the 65% threshold at estimated peak concentrations. In conclusion, approximately half the subjects with stable schizophrenia did not achieve estimated continuous blockade of D2 receptor occupancy of ≥65%. The results suggest that sustained D2 receptor occupancy levels of ≥65% may not always be necessary for the maintenance treatment of schizophrenia.

Predicting Dopamine D2 Receptor Occupancy From Plasma Levels of Antipsychotic Drugs

Measuring dopamine D₂ receptor occupancy levels using positron emission tomography (PET) is still widely unavailable. The objective of this study was to evaluate the accuracy of predicting D2 occupancy from the antipsychotic plasma level in patients with schizophrenia. Positron emission tomographic studies that measured plasma levels of antipsychotics and their corresponding D₂ occupancy levels were identified, using MEDLINE and EMBASE (last search: March 2010). Antipsychotics that were investigated in a total of 20 subjects or more were included. All data points for each antipsychotic were fit to a one-site binding model to estimate the total plasma concentration of each antipsychotic associated with a 50% occupancy (ED₅₀) of brain D₂ receptors. The mean prediction error and the root mean squared prediction error were used to measure the predictive performance of individual D₂ receptor occupancies from plasma drug levels derived from a one-site occupancy model using an ED₅₀ value calculated for each data point. A total of 34 treatment arms from 23 studies involving 281 subjects were included. The mean (95% confidence interval) prediction errors and root squared prediction errors were as low as 0.0 (-1.8 to 1.8) and 8.9 (7.6-10.2) for risperidone (n = 98); 0.0 (-3.5 to 3.5) and 15.1 (12.9-17.3) for clozapine (n = 75); -0.1 (-1.2 to 1.2), 0.0 (-1.9 to 1.9), and 4.6 (3.5-5.8) for olanzapine (n = 42); 0.1 (-3.4 to 3.5) and 9.9 (7.3-12.5) for haloperidol (n = 35); and -0.1 (-3.3 to 3.1) and 12.3 (8.8-15.7) for ziprasidone (n = 31), respectively. These findings suggest that D₂ occupancy of antipsychotics could be estimated with a high degree of accuracy using widely available plasma levels.

Using pharmacokinetic–pharmacodynamic modelling as a tool for prediction of therapeutic effective plasma levels of antipsychotics

In the rat, selective suppression of conditioned avoidance response has been widely reported as a test with high predictive validity for antipsychotic efficacy. Recent studies have shown that the relationship between dopamine D2 receptor occupancy and the suppression of conditioned avoidance response behaviour correlates well with the relationship between human dopamine D2 receptor occupancy and clinical effect. The aim of the present study was to evaluate how pharmacokinetic/pharmacodynamic (PK/PD) predictions of therapeutic effective steady-state plasma levels by means of conditioned avoidance response behaviour in rodents, correlate with clinically relevant plasma exposure for the classical antipsychotic drug haloperidol and four second generation antipsychotics: sertindole, clozapine, risperidone and olanzapine, including selected metabolites. In order to confirm the validity of the present conditioned avoidance response procedure, in vivo striatal dopamine D2 receptor occupancy was determined in parallel using 3H-raclopride as the radioligand. The PK/PD relationship was established by modelling the time–response and time–plasma concentration data. We found the order of dopamine D2 receptor occupancy required to suppress conditioned avoidance response behaviour according to EC50 measurements to be sertindole (+dehydrosertindole)=dehydrosertindole=paliperidone (the metabolite of risperidone)=haloperidol=olanzapine>risperidone≫clozapine. Overall, a good agreement was observed between the rat dopamine D2 receptor occupancy levels providing 50% response in the conditioned avoidance response test and the dopamine D2 receptor occupancy levels reported from responding schizophrenic patients treated with antipsychotics. Predictions of therapeutically effective steady-state levels for sertindole (+dehydrosertindole) and olanzapine were 3–4-fold too high whereas for haloperidol, clozapine and risperidone the predicted steady-state EC50 in conditioned avoidance responding rats correlated well with the therapeutically effective plasma levels observed in patients. Accordingly, the proposed PK/PD model may act as a guide for determining effective plasma concentrations of potential antipsychotics in the clinical setting and thereby accelerating the overall drug development process.

Dopamine D2 receptor occupancy levels of acute sulpiride challenges that produce working memory and learning impairments in healthy volunteers

In humans, the effects of dopaminergic agents administered systemically are less clear-cut than studies in experimental animals where agents can be applied locally in the brain. DA receptor occupancy could clearly contribute to the variance in findings, although this is typically not known. The objective of the study was to measure the DA D2 receptor occupancy of sulpiride 200 and 400 mg and relate this to changes in task performance. Positron emission tomography scans were acquired in ten healthy volunteers with [11C]-raclopride. Striatal drug occupancy was calculated as the percentage change in binding potential between placebo and drug scans. All volunteers received placebo and sulpiride 400 mg, with four receiving 200 mg on a third session. Immediate post-scan neuropsychological assessment included working memory and learning tasks. Striatal sulpiride occupancy was approximately 17% (200 mg) and approximately 28% (400 mg), with similar occupancy within the midbrain. Neuropsychological data analysis was restricted to the higher dose (n = 10). Accuracy on the spatial working memory and spatial learning tasks was impaired after the drug, and the former was inversely related to occupancy. Doses of sulpiride typically used in human cognitive studies produced low levels of DA D2 receptor occupancy compared to that considered efficacious in the treatment of schizophrenia. The levels of occupancy were sufficient to replicate impairments on a spatial working memory task and impair spatial learning. The relationship between occupancy and working memory was suggestive of presynaptic effects, although the precise mechanism underlying the impairment will require studies of wider ranges of occupancy within and outside of the striatum.

Continuous but not intermittent olanzapine infusion induces vacuous chewing movements in rats

Continuous, but not intermittent, infusion with a conventional antipsychotic (haloperidol, HAL) can induce the vacuous chewing movement (VCM) syndrome in rats. The objective of this study was to determine whether continuous, versus intermittent, olanzapine (OLZ) infusion differently affects the development of VCMs. Experiment 1: Animals were treated with 7.5 mg/kg/day of OLZ or vehicle (VEH) via either minipump (MP) or daily subcutaneous (SC) injections for 8 weeks. Experiment 2: A separate group of rats were treated with 15 mg/kg/day of OLZ, or 1 mg/kg/day of HAL or VEH via MP for 8 weeks. Dopamine D2 receptor occupancy levels were measured, ex vivo, with [3H]-raclopride. Experiment 1: Rats receiving 7.5 mg/kg/day of OLZ via MP (51% D2 occupancy), but not those receiving the same dose via daily SC injections (94% peak D2 occupancy), showed significant VCM levels compared with control animals (p = .02). Experiment 2: Both OLZ (67% D2 occupancy) and HAL (79% D2 occupancy) led to similar increases in VCMs compared with VEH (p = .005). This study provides strong evidence that even an atypical antipsychotic like OLZ, which rarely gives rise to tardive dyskinesia in the clinic, can lead to the VCM syndrome in rats if the antipsychotic is administered in a method (via MP) that leads to continuous presence of the drug in the brain.