Population pharmacokinetic modeling of ziprasidone in patients with schizophrenia from the CATIE study

Unraveling the Influence of Age, IQ, Education, and Negative Symptoms on Neurocognitive Performance in Schizophrenia: A Conditional Inference Tree Analysis

INTRODUCTION

The complex nature of neurocognitive impairment in schizophrenia has been discussed in light of the mixed effects of antipsychotic drugs, psychotic symptoms, dopamine D2 receptor blockade, and intelligence quotient (IQ). These factors have not been thoroughly examined before.

METHODS

This study conducted a comprehensive re-analysis of the CATIE data using machine learning techniques, in particular Conditional Inference Tree (CTREE) analysis, to investigate associations between neurocognitive functions and moderating factors such as estimated trough dopamine D2 receptor blockade with risperidone, olanzapine, or ziprasidone, Positive and Negative Syndrome Scale (PANSS), and baseline IQ in 573 patients with schizophrenia.

RESULTS

The study reveals that IQ, age, and education consistently emerge as significant predictors across all neurocognitive domains. Furthermore, higher severity of PANSS-negative symptoms was associated with lower cognitive performance scores in several domains. CTREE analysis, in combination with a genetic algorithm approach, has been identified as particularly insightful for illustrating complex interactions between variables. Lower neurocognitive function was associated with factors such as age>52 years, IQ<94/95,<12/13 education years, and more pronounced negative symptoms (score<26).

CONCLUSIONS

These findings emphasize the multifaceted nature of neurocognitive functioning in patients with schizophrenia, with the PANSS-negative score being an important predictor. This gives rise to a role in addressing negative symptoms as a therapeutic objective for enhancing cognitive impairments in these patients. Further research must examine nonlinear relationships among various moderating factors identified in this work, especially the role of D2 occupancy.

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

BACKGROUND

The 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 METHODS

We 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.

RESULTS

Illness 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.

CONCLUSIONS

Consistent 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.

Optimal sampling of antipsychotic medicines: a pharmacometric approach for clinical practice

AIM

To determine optimal sampling strategies to allow the calculation of clinical pharmacokinetic parameters for selected antipsychotic medicines using a pharmacometric approach.

METHODS

This study utilized previous population pharmacokinetic parameters of the antipsychotic medicines aripiprazole, clozapine, olanzapine, perphenazine, quetiapine, risperidone (including 9-OH risperidone) and ziprasidone. d-optimality was utilized to identify time points which accurately predicted the pharmacokinetic parameters (and expected error) of each drug at steady-state. A standard two stage population approach (STS) with MAP-Bayesian estimation was used to compare area under the concentration-time curves (AUC) generated from sparse optimal time points and rich extensive data. Monte Carlo Simulation (MCS) was used to simulate 1000 patients with population variability in pharmacokinetic parameters. Forward stepwise regression analysis was used to determine the most predictive time points of the AUC for each drug at steady-state.

RESULTS

Three optimal sampling times were identified for each antipsychotic medicine. For aripiprazole, clozapine, olanzapine, perphenazine, risperidone, 9-OH risperidone, quetiapine and ziprasidone the CV% of the apparent clearance using optimal sampling strategies were 19.5, 8.6, 9.5, 13.5, 12.9, 10.0, 16.0 and 10.7, respectively. Using the MCS and linear regression approach to predict AUC, the recommended sampling windows were 16.5-17.5 h, 10-11 h, 23-24 h, 19-20 h, 16.5-17.5 h, 22.5-23.5 h, 5-6 h and 5.5-6.5 h, respectively.

CONCLUSION

This analysis provides important sampling information for future population pharmacokinetic studies and clinical studies investigating the pharmacokinetics of antipsychotic medicines.

Perphenazine for schizophrenia

BACKGROUND

Perphenazine is an old phenothiazine antipsychotic with a potency similar to haloperidol. It has been used for many years and is popular in the northern European countries and Japan.

OBJECTIVES

To examine the clinical effects and safety of perphenazine for those with schizophrenia and schizophrenia-like psychoses.

SEARCH METHODS

We updated our original search using the Cochrane Schizophrenia Group's register (September 2013), references of all included studies and contacted pharmaceutical companies and authors of included studies in order to identify further trials.

SELECTION CRITERIA

We included all randomised controlled trials that compared perphenazine with other treatments for people with schizophrenia and/or schizophrenia-like psychoses. We excluded trials of depot formulations of perphenazine.

DATA COLLECTION AND ANALYSIS

Two review authors independently inspected citations and, where possible, abstracts. We ordered papers, inspected and quality assessed them. We extracted data, again working independently. If loss to follow-up was greater than 50% we considered results as 'prone to bias'. For dichotomous data, we calculated risk ratios (RR) and for continuous data we calculated mean differences (MD), both with the 95% confidence intervals (CI). We assessed quality of data using the GRADE (Grading of Recommendations Assessment, Development and Evaluationtool) and assessed risk of bias for included studies.

MAIN RESULTS

Thirty-one studies fulfilled the inclusion criteria, with a total of 4662 participants (of which 4522 were receiving the drugs relevant to our comparison) and presented data that could be used for at least one comparison. The trial centres were located in Europe (especially Scandinavia), Japan and Northern America.When comparing perphenazine with placebo, for our primary outcome of clinical response, results favoured perphenazine with significantly more people receiving placebo rated as either 'no better or deterioration' for global state than people receiving perphenazine (1 RCT, n = 61 RR 0.32 CI 0.13 to 0.78, very low quality evidence). More people receiving placebo relapsed, although not a statistically significant number (1 RCT, n = 48, RR 0.14 CI 0.02 to 1.07, very low quality evidence). Death was not reported in the perphenazine versus placebo comparison. Experiences of dystonia were equivocal between groups (1 RCT, n = 48, RR 1.00 CI 0.07 to 15.08, very low quality evidence); other outcomes not reported in this comparison include serious adverse events, economic outcomes, and service use and hospitalisation.For the comparison of perphenazine versus any other antipsychotic drugs, no real differences in effect between the drugs were found. There was no significant difference between groups for those considered 'no better or deterioration' (17 RCTs, n = 1879, RR 1.04 CI 0.91 to 1.17, very low quality evidence). For mental state outcome of 'no effect' of the study drug, there was again no significant difference between groups (4 RCTs, n = 383, RR 1.24 CI 0.61 to 2.52, very low quality evidence). Death was not reported in any of the included studies. There was no significant difference in rates of dystonia with perphenazine versus any other antipsychotic drugs (4 RCTs, n = 416, RR 1.36 CI 0.23 to 8.16, very low quality evidence), nor was there a significant difference between groups for serious adverse events (2 RCTs, n = 1760, RR 0.98 CI 0.68 to 1.41, very low quality evidence).

AUTHORS' CONCLUSIONS

Although perphenazine has been used in randomised trials for more than 50 years, incomplete reporting and the variety of comparators used make it impossible to draw clear conclusions. All data for the main outcomes in this review were of very low quality evidence. At best we can say that perphenazine showed similar effects and adverse events as several of the other antipsychotic drugs. Since perphenazine is a relatively inexpensive and frequently used compound, further trials are justified to clarify the properties of this classical antipsychotic drug.

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

OBJECTIVE

The 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).

METHODS

The 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.

RESULTS

Estimated 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.

CONCLUSION

Greater 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.

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.

Estimated dopamine D₂ receptor occupancy and remission in schizophrenia: analysis of the CATIE data

In treating schizophrenia, 65% to 80% occupancy of dopamine D₂ receptors optimizes therapeutic efficacy while minimizing risks of extrapyramidal symptoms and cognitive impairments. However, it is unclear as to whether it is necessary to keep D₂ receptor occupancy within this therapeutic window to maintain clinical response. The data set from phase 1 of the Clinical Antipsychotic Trials in Intervention Effectiveness (CATIE) trial was reappraised. Thirty patients receiving risperidone (12 patients), olanzapine (12 patients), or ziprasidone (6 patients) fulfilled the following definition of remission and were included: a score of 3 or less on the 8 specific items in the Positive and Negative Syndrome Scale (ie, P1, P2, P3, N1, N4, N6, G5, and G9; adopted from Andreasen et al, 2005) at the initial assessment and months 1, 2, and 6. Peak and trough D₂ receptor occupancy levels at month 6 were estimated from plasma antipsychotic concentrations using population pharmacokinetic analysis and our D₂ prediction model. Estimated mean ± SD peak and trough D₂ receptor occupancy levels at month 6 were 70.3% ± 9.8% and 60.5% ± 20.2%, respectively; among these individuals, 46.7% (14 patients) did not achieve continuous blockade of 65% or greater (ie, trough D₂ occupancy of <65%). In conclusion, approximately half of patients with remission did not achieve continuous blockade of estimated D₂ receptor occupancy 5% or greater. These results extend our previous findings and suggest that sustained D₂ receptor occupancy greater than 65% may not always be necessary for the maintenance treatment of schizophrenia.

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.

High-dose oral ziprasidone versus conventional dosing in schizophrenia patients with residual symptoms: the ZEBRAS study

Uncontrolled studies have suggested that increasing the dose of ziprasidone above the standard maximum daily dose of 160 mg may be more effective for some patients with schizophrenia. To test this hypothesis, we conducted an 8-week, placebo-controlled, fixed-dose escalation trial comparing ziprasidone 160 versus 320 mg/d in individuals with schizophrenia or schizoaffective disorder who remained symptomatic despite treatment with ziprasidone 160 mg/d for at least 3 weeks. Of 75 randomized patients, 42 completed the study. Serum ziprasidone concentrations increased significantly in the high-dose group compared with the standard-dose group at week 4 but did not differ between groups at week 8. Both treatment groups exhibited significant symptomatic improvement. Response did not differ between treatment groups; however, in the high-dose group, higher ziprasidone serum concentrations were associated with better response at a trend level. Higher ziprasidone concentrations were also associated with reductions in diastolic blood pressure and, at a trend level, with more prominent negative symptoms and greater QTc prolongation. In summary, increasing the ziprasidone dose to 320 mg/d did not produce a sustained elevation in serum concentrations or symptomatic improvement compared with a standard ziprasidone dose of 160 mg/d.

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

RATIONALE

Ziprasidone is an atypical antipsychotic recommended to be administered twice daily.

OBJECTIVES

The purpose of this study was to investigate whether occupancy of the dopamine D2/3 receptors by ziprasidone is maintained across a day employing a within subject design.

METHODS

Positron emission tomography (PET) scans with [(11)C]-raclopride were performed in 12 patients with schizophrenia while treated with ziprasidone 60 mg twice daily. Each patient completed [(11)C]-raclopride PET scans at 5, 13 and 23 h after the last dose of ziprasidone. Dopamine D2/3 receptor occupancy was estimated with reference to binding potential data of 44 age- and sex-matched control subjects in the caudate, putamen and ventral striatum.

RESULTS

Eleven scans were available at each time point, and the mean occupancies at 5-, 13- and 23-h scans were 66, 39 and 2 % in the putamen; 62, 35 and -6 % in the caudate; and 68, 47 and 11 % in the ventral striatum, respectively. The time-course of receptor occupancy across the regions indicated an occupancy half-life of 8.3 h. The serum level of ziprasidone associated with 50 % D2/3 receptors occupancy was estimated to be 204 nmol/L (84 ng/ml). Prolactin levels were highest at 5-h post-dose and none showed hyperprolactinemia at 23-h scans.

CONCLUSIONS

The absence of ziprasidone striatal D2/3 receptor binding 23 h after taking 60 mg under steady-state conditions is consistent with its peripheral half-life. The results support our earlier report that ziprasidone 60 mg administered twice daily appears to be the minimal dose expected to achieve therapeutic central dopamine D2/3 receptor occupancy (i.e. 60 %).

CLINICAL TRIALS REGISTRATION

24-Hour Time Course of Striatal Dopamine D2 Receptor Occupancy of Ziprasidone: A PET Study, www.clinicaltrials.gov/ct2/show/NCT00818298 , NCT00818298.

Dopamine D2 receptor occupancy and cognition in schizophrenia: analysis of the CATIE data

INTRODUCTION

Antipsychotic drugs exert antipsychotic effects by blocking dopamine D2 receptors in the treatment of schizophrenia. However, effects of D2 receptor blockade on neurocognitive function still remain to be elucidated. The objective of this analysis was to evaluate impacts of estimated dopamine D2 receptor occupancy with antipsychotic drugs on several domains of neurocognitive function in patients with schizophrenia in the Clinical Antipsychotic Trials in Intervention Effectiveness (CATIE) trial.

METHODS

The dataset from the CATIE trial was used in the present analysis. Data were extracted from 410 subjects who were treated with risperidone, olanzapine, or ziprasidone, received assessments for neurocognitive functions (verbal memory, vigilance, processing speed, reasoning, and working memory) and psychopathology, and provided plasma samples for the measurement of plasma antipsychotic concentrations. D2 receptor occupancy levels on the day of neurocognitive assessment were estimated from plasma antipsychotic concentrations, using population pharmacokinetic analysis and our recently developed model. A multivariate general linear model was used to examine effects of clinical and demographic characteristics, including estimated D2 occupancy levels, on neurocognitive functions.

RESULTS

D2 occupancy levels showed significant associations with the vigilance and the summary scores. Neurocognitive functions, including vigilance, were especially impaired in subjects who showed D2 receptor occupancy level of >77%.

DISCUSSION

These findings suggest a nonlinear relationship between prescribed antipsychotic doses and overall neurocognitive function and vigilance. This study shows that D2 occupancy above approximately 80% not only increases the risk for extrapyramidal side effects as consistently reported in the literature but also increases the risk for cognitive impairment.

Predicting plasma concentration of risperidone associated with dosage change: a population pharmacokinetic study

BACKGROUND

Due to high interindividual variability in peripheral pharmacokinetic parameters, dosing of antipsychotics relies on clinical trial and error. This blind process of upward or downward clinical dose titration carries a risk of relapse and adverse effects in the treatment of schizophrenia. Using population pharmacokinetic methods, the authors therefore sought to predict plasma concentrations of risperidone (RIS) plus 9-hydroxyrisperidone (9-OH-RIS) before a dosage change.

METHODS

Two plasma samples were collected at 2 separate given time points for the measurement of RIS and 9-OH-RIS concentrations from 50 patients with schizophrenia or schizoaffective disorder maintained on risperidone (mean ± SD age = 56 ± 15 years; 39 men). After an oral risperidone dose adjustment, a third sample was collected. The plasma concentration of the third sample was individually predicted in a blinded fashion with the 2 baseline plasma concentrations before dose adjustment and clinical and demographic information, using the mixed-effects model with NONMEM that was derived from the data of the Clinical Antipsychotic Trials in Intervention Effectiveness study.

RESULTS

The mean (95% confidence interval) prediction errors (in ng/mL) were as low as 0.0 (-1.3 to 1.4) for RIS and 1.0 (-1.1 to 3.0) for 9-OH-RIS. The observed and predicted concentrations of RIS and 9-OH-RIS were highly correlated (r = 0.96, P < 0.0001 and r = 0.92, P < 0.0001, respectively).

CONCLUSIONS

Antipsychotic plasma concentrations can be predicted before risperidone dose adjustment. In light of the known relationship between plasma drug concentration, dopamine D2 receptor occupancy, and clinical effects, our results confirm that individualized dosing with the measurement of antipsychotic plasma concentrations has the potential for bedside clinical application.

Application of a single-objective, hybrid genetic algorithm approach to pharmacokinetic model building

A limitation in traditional stepwise population pharmacokinetic model building is the difficulty in handling interactions between model components. To address this issue, a method was previously introduced which couples NONMEM parameter estimation and model fitness evaluation to a single-objective, hybrid genetic algorithm for global optimization of the model structure. In this study, the generalizability of this approach for pharmacokinetic model building is evaluated by comparing (1) correct and spurious covariate relationships in a simulated dataset resulting from automated stepwise covariate modeling, Lasso methods, and single-objective hybrid genetic algorithm approaches to covariate identification and (2) information criteria values, model structures, convergence, and model parameter values resulting from manual stepwise versus single-objective, hybrid genetic algorithm approaches to model building for seven compounds. Both manual stepwise and single-objective, hybrid genetic algorithm approaches to model building were applied, blinded to the results of the other approach, for selection of the compartment structure as well as inclusion and model form of inter-individual and inter-occasion variability, residual error, and covariates from a common set of model options. For the simulated dataset, stepwise covariate modeling identified three of four true covariates and two spurious covariates; Lasso identified two of four true and 0 spurious covariates; and the single-objective, hybrid genetic algorithm identified three of four true covariates and one spurious covariate. For the clinical datasets, the Akaike information criterion was a median of 22.3 points lower (range of 470.5 point decrease to 0.1 point decrease) for the best single-objective hybrid genetic-algorithm candidate model versus the final manual stepwise model: the Akaike information criterion was lower by greater than 10 points for four compounds and differed by less than 10 points for three compounds. The root mean squared error and absolute mean prediction error of the best single-objective hybrid genetic algorithm candidates were a median of 0.2 points higher (range of 38.9 point decrease to 27.3 point increase) and 0.02 points lower (range of 0.98 point decrease to 0.74 point increase), respectively, than that of the final stepwise models. In addition, the best single-objective, hybrid genetic algorithm candidate models had successful convergence and covariance steps for each compound, used the same compartment structure as the manual stepwise approach for 6 of 7 (86 %) compounds, and identified 54 % (7 of 13) of covariates included by the manual stepwise approach and 16 covariate relationships not included by manual stepwise models. The model parameter values between the final manual stepwise and best single-objective, hybrid genetic algorithm models differed by a median of 26.7 % (q₁ = 4.9 % and q₃ = 57.1 %). Finally, the single-objective, hybrid genetic algorithm approach was able to identify models capable of estimating absorption rate parameters for four compounds that the manual stepwise approach did not identify. The single-objective, hybrid genetic algorithm represents a general pharmacokinetic model building methodology whose ability to rapidly search the feasible solution space leads to nearly equivalent or superior model fits to pharmacokinetic data.

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.

Genetic variation in CYP3A43 explains racial difference in olanzapine clearance

The antipsychotic drug, olanzapine, one of the most widely used drugs in clinical medicine, has a high rate of discontinuation due to inefficacy and/or adverse effects. We identified a single nucleotide polymorphism in the drug metabolizing enzyme, cytochrome P450 3A43 (CYP3A43; rs472660), that highly significantly predicted olanzapine clearance in the Clinical Antipsychotic Trials of Intervention Effectiveness trial (P=5.9e(-7)). Moreover, at standard antipsychotic doses, 50% of individuals with the high clearance genotype (AA) have trough blood levels below the therapeutic range. Interestingly, a much higher proportion of African Americans carry the A allele compared with Caucasians (allele frequency 67 vs 14%). After accounting for CYP3A43 genotype, race is no longer a significant predictor of olanzapine clearance. Olanzapine clearance was associated with measures of clinical response. Patients with greater clearance had higher symptom ratings and were more likely to discontinue treatment due to an inadequate response. Our data identify a genetic mechanism for variation in olanzapine response and demonstrate that blood level monitoring of olanzapine treatment is advisable.

Ziprasidone versus other atypical antipsychotics for schizophrenia

BACKGROUND

In many countries of the industrialised world second generation ('atypical') antipsychotics have become the first line drug treatment for people with schizophrenia. The question as to whether, and if so how much, the effects of the various new generation antipsychotics differ is a matter of debate. In this review we examined how the efficacy and tolerability of ziprasidone differs from that of other second generation antipsychotics.

OBJECTIVES

To evaluate the effects of ziprasidone compared with other atypical antipsychotics for people with schizophrenia and schizophrenia-like psychoses.

SEARCH STRATEGY

We searched the Cochrane Schizophrenia Group Specialised Register (April 2007) and references of all identified studies for further trial citations. We contacted pharmaceutical companies and authors of trials for additional information.

SELECTION CRITERIA

We included all randomised, at least single-blind, controlled trials comparing oral ziprasidone with oral forms of amisulpride, aripiprazole, clozapine, olanzapine, quetiapine, risperidone or zotepine in people with schizophrenia or schizophrenia-like psychoses.

DATA COLLECTION AND ANALYSIS

We extracted data independently. For continuous data, we calculated weighted mean differences (MD) for dichotomous data we calculated relative risks (RR) and their 95% confidence intervals (CI) on an intention-to-treat basis based on a random-effects model. We calculated numbers needed to treat/harm (NNT/NNH) where appropriate.

MAIN RESULTS

The review currently includes nine randomised controlled trials (RCTs) with 3361 participants. The overall rate of premature study discontinuation was very high (59.1%). Data for the comparisons of ziprasidone with amisulpride, clozapine, olanzapine, quetiapine and risperidone were available. Ziprasidone was a less acceptable treatment than olanzapine (leaving the studies early for any reason: 5 RCTs, n=1937, RR 1.26 CI 1.18 to 1.35, NNH 7 CI 5 to 10) and risperidone (3 RCTs, n=1029, RR 1.11 CI 1.02 to 1.20, NNH 14 CI 8 to 50), but not than the other second generation antipsychotic drugs. Ziprasidone was less efficacious than amisulpride (leaving the study early due to inefficacy: 1 RCT, n=123, RR 4.72 CI 1.06 to 20.98, NNH 8 CI 5 to 50) olanzapine (PANSS total score: 4 RCTs, n=1291, MD 8.32 CI 5.64 to 10.99) and risperidone (PANSS total score: 3 RCTs, n=1016, MD 3.91 CI 0.27 to 7.55). Based on limited data there were no significant differences in tolerability between ziprasidone and amisulpride or clozapine. Ziprasidone produced less weight gain than olanzapine (5 RCTs, n=1659, MD -3.82 CI -4.69 to -2.96), quetiapine (2 RCTs, n=754, RR 0.45 CI 0.28 to 0.74) or risperidone (3 RCTs, n=1063, RR 0.49 CI 0.33 to 0.74). It was associated with less cholesterol increase than olanzapine, quetiapine and risperidone. Conversely ziprasidone produced slightly more extrapyramidal side-effects than olanzapine (4 RCTs, n=1732, RR 1.43 CI 1.03 to 1.99, NNH not estimable) and more prolactin increase than quetiapine (2 RCTs, n=754, MD 4.77 CI 1.37 to 8.16), but less movement disorders (2 RCTs, n=822, RR 0.70 CI 0.51 to 0.97, NNT not estimable) and less prolactin increase (2 RCTs, n=767, MD -21.97 CI -27.34 to -16.60) than risperidone.

AUTHORS' CONCLUSIONS

Ziprasidone may be a slightly less efficacious antipsychotic drug than amisulpride, olanzapine and risperidone. Its main advantage is the low propensity to induce weight gain and associated adverse effects. However, the high overall rate of participants leaving the studies early limits the validity of any findings.