Population pharmacokinetic modelling of aripiprazole and its active metabolite, dehydroaripiprazole, in psychiatric patients

Therapeutic drug monitoring in children and adolescents with schizophrenia-spectrum, affective, behavioural, tic and other psychiatric disorders treated with aripiprazole: results of the TDM-VIGIL pharmacovigilance study

Aripiprazole is approved for various severe mental disorders in adults and adolescents. However, off-label prescribing is common, especially in children and adolescents (youth) in whom aripiprazole therapeutic serum level reference ranges are lacking for any disorders. The aim of the study was to evaluate the relationship between aripiprazole dose and serum concentrations and provide further knowledge on the use of aripiprazole in order to improve drug safety and effectiveness in the treatment of minors. The clinical course of youth treated with aripiprazole in the multicentre pharmacovigilance study TDM-VIGIL was systematically followed and serum concentrations measured. Sex, age, weight and comedications were analysed to identify possible effect modifiers. A preliminary therapeutic reference range was estimated for youth with schizophrenia-spectrum disorders, affective disorders and behavioural/emotional/tic disorders coded as treatment responders based on a Clinical-Global Impressions-Improvement (CGI-I) score of much or very much improved. In 93 youth (mean age = 15.2 ± 2.6, range = 7.4-18.2 years, females = 53%, CGI-Severity = 4.4 ± 1.1, responders = 64%), a positive, moderate correlation between the weight-normalized daily dose (WNDD) and aripiprazole serum concentration (=0.791, p < 0.0001) was found. The WNDD and co-medications that interact with CYP2D6 and CYP3A4 affected aripiprazole serum levels, explaining 64% of the variance. In patients within the preliminary therapeutic ranges determined by interquartile ranges (IQRs), slightly better outcomes and fewer adverse drug reactions were found versus patients within preliminary therapeutic ranges determined by the mean ± SD. The preliminary reference range for paediatric patients with schizophrenia-spectrum disorders calculated by the IQR showed an identical lower threshold (100-230 ng/ml) compared to adult schizophrenia-spectrum disorders patients (100-350 ng/ml). The preliminary therapeutic ranges for patients with affective disorders was: 60-160 ng/ml and for patients with behavioural/tic disorders 60-140 ng/ml. The therapeutic reference ranges for aripiprazole in youth estimated via the 25th and 75th IQRs may result in more clinically relevant therapeutic windows. Further studies need to confirm these results, especially in patients with affective and behavioural/tic disorder diagnoses.

Verification of successful maintenance by serum drug level during a guided antipsychotic reduction to reach minimum effective dose (GARMED) trial

BACKGROUND

Inconsistent results regarding the risk of relapse and better subjective outcomes of previous antipsychotic dose reduction trials in patients with remitted psychosis have not been verified using therapeutic drug monitoring (TDM). This study examined plasma drug concentrations of a dose-tapering trial which exhibited the potential of successful maintenance under lower antipsychotic dosages.

METHODS

A 2-year open-label randomized prospective trial recruited remitted patients to undergo guided antipsychotic tapering. Blood samples were collected at baseline, annually, and after each dose reduction. Plasma aripiprazole/dehydroaripiprazole concentrations were determined using LC-MS/MS. The relationship between the dose and serum drug levels was examined using Spearman's correlation. Divided at 120 ng/mL, relapse rate, global function, quality of life, and psychopathology were compared between high- and low- drug level groups.

RESULTS

A total of 126 blood samples were collected, after excluding13 samples due of non-adherence. The correlation coefficients between dosage and drug level were 0.853 (aripiprazole) and 0.864 (dehydroaripiprazole), and the dose and concentration plots were parallel along the tapering trajectories, except patients with non-adherence. The concentration-to-dose ratio of aripiprazole in this cohort, 17.79 ± 7.23 ng/mL/mg, was higher than that in Caucasian populations. No significant differences were observed in the clinical outcomes between the high- and low-level groups. Remarkably, 12 of 15 patients maintained remission at plasma aripiprazole concentrations of <120 ng/mL.

CONCLUSIONS

The lower-than-expected doses reached in our antipsychotic tapering trial were substantiated to provide adequate prophylactic effects by TDM results in a subset of patients treated with aripiprazole, even considering the differences in pharmacogenomics between ethnicities.

Drug-drug interaction and initial dosage optimization of aripiprazole in patients with schizophrenia based on population pharmacokinetics

Background

The present study aimed to investigate the drug-drug interaction and initial dosage optimization of aripiprazole in patients with schizophrenia based on population pharmacokinetics.

Research design and methods

A total of 119 patients with schizophrenia treated with aripiprazole were included to build an aripiprazole population pharmacokinetic model using nonlinear mixed effects.

Results

The weight and concomitant medication of fluoxetine influenced aripiprazole clearance. Under the same weight, the aripiprazole clearance rates were 0.714:1 in patients with or without fluoxetine, respectively. In addition, without fluoxetine, for the once-daily aripiprazole regimen, dosages of 0.3 and 0.2 mg kg-1 day-1 were recommended for patients with schizophrenia weighing 40-95 and 95-120 kg, respectively, while for the twice-daily aripiprazole regimen, 0.3 mg kg-1 day-1 was recommended for those weighing 40-120 kg. With fluoxetine, for the once-daily aripiprazole regimen, a dosage of 0.2 mg kg-1 day-1 was recommended for patients with schizophrenia weighing 40-120 kg, while for the twice-daily aripiprazole regimen, 0.3 and 0.2 mg kg-1 day-1 were recommended for those weighing 40-60 and 60-120 kg, respectively.

Conclusion

This is the first investigation of the effects of fluoxetine on aripiprazole via drug-drug interaction. The optimal aripiprazole initial dosage is recommended in patients with schizophrenia.

Towards precision medicine of long-acting aripiprazole through population pharmacokinetic modelling

Population pharmacokinetic (popPK) models constitute a valuable tool for characterizing the pharmacokinetic properties of once-monthly long-acting injectable aripiprazole (LAI aripiprazole) and quantifying the sources of variability in drug exposure. Our aim is to develop a popPK model of both aripiprazole and its metabolite dehydro-aripiprazole in patients treated with LAI aripiprazole, and to personalize the dosing regimen of aripiprazole across different sub-groups of patients. This is a prospective study investigating the pharmacokinetics of LAI aripiprazole. A total of 93 patients were included, 21 for model development and 71 for external model evaluation. A one-compartment model with linear absorption and elimination adequately described both aripiprazole and dehydro-aripiprazole concentrations. The weight of the patients has been shown to be the factor that most influences the absorption. However, the metabolizing phenotype for CYP2D6 and the concomitant treatment with strong inhibitors of this cytochrome have been shown to be the covariates that most influence total drug exposure. This is the first popPK model developed for LAI aripiprazole that includes aripiprazole and its main active metabolite, dehydroaripiprazole. It provides a personalized dosage recommendation that maximizes the probability of achieving optimal therapeutic concentrations and minimizes the difficulties associated with trial-and-error therapeutic strategies carried out in clinical practice.

Evidence for Therapeutic Drug Monitoring of Atypical Antipsychotics

Second-generation antipsychotics (SGAs), also known as atypical antipsychotics, are a newer class of antipsychotic drugs used to treat schizophrenia, bipolar disorder, and related psychiatric conditions. The plasma concentration of antipsychotic drugs is a valid measure of the drug at its primary target structure in the brain, and therefore determines the efficacy and safety of these drugs. However, despite the well-known high variability in pharmacokinetics of these substances, psychiatric medication is usually administered in uniform dosage schedules. Therapeutic drug monitoring (TDM), as the specific method that can help personalised medicine in dose adjustment according to the characteristics of the individual patient, minimizing the risk of toxicity, monitoring adherence, and increasing cost-effectiveness in the treatment, thus seems to be an elegant tool to solve this problem. Non-response to therapeutic doses, uncertain adherence to medication, suboptimal tolerability, or pharmacokinetic drug-drug interactions are typical indications for TDM of SGAs. This review aims to summarize an overview of the current knowledge and evidence of the possibilities to tailor the dosage of selected SGAs using TDM, including the necessary pharmacokinetic parameters for personalised pharmacotherapy.

CYP1A2*F Polymorphism Contributes at Least Partially to the Variability of Plasma Levels of Dehydroaripiprazole, an Active Metabolite of Aripiprazole, in Schizophrenic Patients

AIM

The relationship between CYP1A2 polymorphisms and the steady-state plasma levels of aripiprazole and its active metabolite, dehydroaripiprazole, were investigated in Japanese schizophrenic patients.

BACKGROUND

It has been implied that cytochrome P450 (CYP) 1A2 may play a role in the metabo-lism of aripiprazole. Genetic variations in the CYP1A2 gene have been reported.

OBJECTIVE

The authors investigated the relationship between 2 CYP1A2 polymorphisms, CYP1A2*C (-3860G>A) and CYP1A2*F (-163C>A), and the steady-state plasma levels/dose (C/D) ratios of aripiprazole and dehydroaripiprazole in Japanese schizophrenic patients.

METHODS

All 89 subjects (46 males and 43 females) had been receiving 2 fixed daily doses of aripiprazole (24 mg; n=56 and 12 mg: n=33) for more than 2 weeks. No other drugs were used except flunitrazepam and biperiden. The plasma drug levels were determined by LC/MS/MS. These CYP1A2 polymorphisms were detected using polymerase chain reaction analysis.

RESULTS

The mean C/D ratios of dehydroaripiprazole were significantly (P < 0.05) lower in patients with the A/A allele of CYP1A2*F than in those without the allele. No differences were found in the values of aripiprazole and the combination of aripiprazole and dehydroaripiprazole among the CYP1A2*F genotype. There were no differences in the values of aripiprazole, dehydroaripiprazole, or the combination of the 2 compounds among the CYP1A2*C genotype. The absence of the A allele of CYP1A2*F was correlated with the mean C/D ratios of dehydroaripiprazole (standardized partial correlation coefficient = 0.276, P < 0.01) by multiple regression analysis.

CONCLUSION

The findings of this study suggest that the CYP1A2*F polymorphism contributes at least partially to the variability in the steady-state plasma levels of dehydroaripiprazole.

Understanding inter-individual variability in pharmacokinetics/pharmacodynamics of aripiprazole in children with tic disorders: Individualized administration based on physiological development and CYP2D6 genotypes

Objective: This study aims to develop a combined population pharmacokinetic (PPK) model for aripiprazole (ARI) and its main active metabolite dehydroaripiprazole (DARI) in pediatric patients with tic disorders (TD), to investigate the inter-individual variability caused by physiological and genetic factors in pharmacokinetics of ARI and optimize the dosing regimens for pediatric patients. Methods: A prospective PPK research was performed in Chinese children with TD. Totally 84 patients aged 4.83-17.33 years were obtained for the pharmacokinetic analysis. 27 CYP2D6 and ABCB1 gene alleles were detected. Moreover, the clinical efficacy was evaluated according to reduction rate of Yale Global Tic Severity Scale (YGTSS) score at the 12th week comparing with the baseline. Monte Carlo simulations were used to evaluate and optimize dosing regimens. Results: The PPK model was established to predict the concentrations of ARI and DARI. Body weight and CYP2D6 genotype were the significant covariates affecting the clearance of ARI. The DARI/ARI metabolic ratios (MRs) of AUC24h, Cmin and Cmax at the steady state of results were ultra-rapid metabolizers (UMs) > normal metabolizers (NMs) > intermediated metabolizers (IMs). MRs could be used to distinguish UMs or IMs from other patients. The best predictor of clinical efficacy for TD was the trough concentration of ARI and the cut-off point was 101.636 ng/ml. Conclusion: The pharmacokinetics of ARI and DARI in pediatric TD were significantly influenced by body weight and CYP2D6 genotype. Individualized dosing regimens were recommended for pediatric patients with TD to ensure clinical efficacy.

Therapeutic Reference Range for Aripiprazole in Schizophrenia Revised: a Systematic Review and Metaanalysis

RATIONALE

While one of the basic axioms of pharmacology postulates that there is a relationship between the concentration and effects of a drug, the value of measuring blood levels is questioned by many clinicians. This is due to the often-missing validation of therapeutic reference ranges.

OBJECTIVES

Here, we present a prototypical meta-analysis of the relationships between blood levels of aripiprazole, its target engagement in the human brain, and clinical effects and side effects in patients with schizophrenia and related disorders.

METHODS

The relevant literature was systematically searched and reviewed for aripiprazole oral and injectable formulations. Population-based concentration ranges were computed (N = 3,373) and pharmacokinetic influences investigated.

RESULTS

Fifty-three study cohorts met the eligibility criteria. Twenty-nine studies report blood level after oral, 15 after injectable formulations, and nine were positron emission tomography studies. Conflicting evidence for a relationship between concentration, efficacy, and side effects exists (assigned level of evidence low, C; and absent, D). Population-based reference ranges are well in-line with findings from neuroimaging data and individual efficacy studies. We suggest a therapeutic reference range of 120-270 ng/ml and 180-380 ng/ml, respectively, for aripiprazole and its active moiety for the treatment of schizophrenia and related disorders.

CONCLUSIONS

High interindividual variability and the influence of CYP2D6 genotypes gives a special indication for Therapeutic Drug Monitoring of oral and long-acting aripiprazole. A starting dose of 10 mg will in most patients result in effective concentrations in blood and brain. 5 mg will be sufficient for known poor metabolizers.

Racial/Ethnic Differences in the Pharmacokinetics of Antipsychotics: Focusing on East Asians

Empirical clinical studies have suggested that East Asian patients may require lower dosages of psychotropic drugs, such as antipsychotics, lithium, and antidepressants, than non-Asians. Both the pharmacokinetic and pharmacodynamic properties of a drug can affect the clinical response of an illness. The levels of antipsychotics used for the treatment of schizophrenia may affect patient clinical responses; several factors can affect these levels, including patient medication adherence, body weight (BW) or body mass index, smoking habits, and sex. The cytochrome P450 (CYP) system is a major factor affecting the blood levels of antipsychotics because many antipsychotics are metabolized by this system. There were notable genetic differences between people of different races. In this study, we determined the racial or ethnic differences in the metabolic patterns of some selected antipsychotics by reviewing therapeutic drug monitoring studies in East Asian populations. The plasma concentrations of haloperidol, clozapine, quetiapine, aripiprazole, and lurasidone, which are metabolized by specific CYP enzymes, were determined to be higher, under the same daily dose, in East Asian populations than in Western populations.

Effects of the combination of second-generation antipsychotics on serum concentrations of aripiprazole and dehydroaripiprazole in Chinese patients with schizophrenia

Background

Aripiprazole (ARI) is often prescribed alone or in combination with other second-generation antipsychotics (SGAs) to treat patients with schizophrenia. However, this may increase the potential clinical significance of drug–drug interactions. Therapeutic drug monitoring (TDM) is an important and fundamental tool both when administering ARI alone and in combination with other SGAs to monitor ARI pharmacokinetics, adjust the dosage and thereby achieve more effective and safer treatment.

Aims

This study retrospectively investigated the effects of four SGA comedications (clozapine, risperidone, quetiapine (QTP) and olanzapine) and other potential factors (sex, age and ARI dose) on the serum concentrations of ARI and dehydroaripiprazole (DARI) in Chinese patients with schizophrenia using TDM data.

Methods

High-performance liquid chromatography was used to test the serum concentrations of ARI, DARI and ARI+DARI. In addition, steady-state dose-adjusted serum concentrations (ie, concentration-to-dose ratios, C:D ratios) of ARI, DARI and ARI+DARI; sex; age; ARI dose and SGA comedication dose between 299 inpatients with schizophrenia who received ARI or SGA comedication were all collected and analysed. Spearman’s correlation and multiple linear regression analysis were used to evaluate bivariate associations between ARI dose and serum ARI and DARI concentrations and describe the effect of independent variables on serum ARI and DARI concentrations, respectively.

Results

There were significant differences in the C:D ratios of ARI (χ²=−3.21, p=0.001) and ARI+DARI (χ²=−2.50, p=0.01) between the ARI and SGA groups, as well as in the C:D ratios of ARI (χ²=−3.59, p<0.001) and ARI+DARI (χ²=−3.10, p=0.002) between the female patients in the two groups. Of the four SGAs, only QTP had significant effects on the C:D ratios of ARI (Z=−4.12, p<0.001) and ARI+DARI (Z=−3.62, p<0.001) when compared with the ARI group in the whole sample and on the C:D ratios of ARI, DARI and ARI+DARI (Z=−3.96, p<0.001; Z=−2.22, p=0.03; Z=−3.75, p<0.001, respectively) in women when compared with their counterparts in the ARI group.

Conclusion

Comedication with SGAs resulted in lower C:D ratios of ARI and ARI+DARI compared with ARI monotherapy, and comedication with QTP resulted in lower C:D ratios of ARI and ARI+DARI than ARI monotherapy. Despite this statistical significance of our findings, whether the presently observed effect has clinical significance requires exploration by further research. TDM and dosage regulation of ARI should be performed in Chinese inpatients with schizophrenia who are receiving SGA comedication (especially QTP) to maintain a safe and effective dose-adjusted serum concentration of ARI and DARI.

Safety and cardiovascular effects of multiple-dose administration of aripiprazole and olanzapine in a randomised clinical trial

OBJECTIVE

To assess adverse events (AEs) and safety of aripiprazole (ARI) and olanzapine (OLA) treatment.

METHODS

Twenty-four healthy volunteers receiving five daily oral doses of 10 mg ARI and 5 mg OLA in a crossover clinical trial were genotyped for 46 polymorphisms in 14 genes by qPCR. Drug plasma concentrations were measured by high-performance liquid chromatography tandem mass spectrometry. Blood pressure (BP) and 12-lead electrocardiogram were measured in supine position. AEs were also recorded.

RESULTS

ARI decreased diastolic BP on the first day and decreased QTc on the third and fifth day. OLA had a systolic and diastolic BP, heart rate and QTc lowering effect on the first day. Polymorphisms in ADRA2A, COMT, DRD3 and HTR2A genes were significantly associated to these changes. The most frequent adverse drug reactions (ADRs) to ARI were somnolence, headache, insomnia, dizziness, restlessness, palpitations, akathisia and nausea while were somnolence, dizziness, asthenia, constipation, dry mouth, headache and nausea to OLA. Additionally, HTR2A, HTR2C, DRD2, DRD3, OPRM1, UGT1A1 and CYP1A2 polymorphisms had a role in the development of ADRs.

CONCLUSIONS

OLA induced more cardiovascular changes; however, more ADRs were registered to ARI. In addition, some polymorphisms may explain the difference in the incidence of these effects among subjects.

Therapeutic drug monitoring of children and adolescents treated with aripiprazole: observational results from routine patient care

Although aripiprazole is one of the most used antipsychotics, knowledge about serum concentrations in children and adolescents is scarce and age-specific therapeutic ranges have not been established yet. Data of a routine therapeutic drug monitoring service were analyzed in order to evaluate the relationship between dose and serum concentration of aripiprazole in children and adolescents. The study also aimed to evaluate whether the therapeutic reference range defined for adults with schizophrenia (100-350 ng/ml) is applicable for minors. Data from 130 patients (aged 7-19 years) treated with aripiprazole for different indications in doses of 2-30 mg/day were evaluated. Patient characteristics, doses, serum concentrations and therapeutic outcome were assessed by standardized measures. A positive mean correlation between body weight-corrected daily dose and aripiprazole concentration was found (r_p = 0.59, p < 0.001) with variation in dose explaining 35% of the variability in serum concentrations. Girls had on average 41% higher dose-corrected concentrations than boys (244.9 versus 173.4 mg/l; p = 0.006). Aripiprazole concentrations did not vary with co-medication (p = 0.22). About 70% of all measured serum concentrations were within the recommended therapeutic range for adults. Using a calculation method in all responding patients with an ICD-10 F2 diagnosis for a rough estimation of a preliminary therapeutic window also demonstrated a similar therapeutic range of aripiprazole in minors (105.9-375.3 ng/ml) than for adults. If confirmed in larger samples and more controlled study designs, these data may contribute to the definition of a therapeutic range of aripiprazole concentrations in children and adolescents.

Dopamine Receptor Partial Agonists for the Treatment of Bipolar Disorder

Bipolar disorder is a chronic, disabling, and costly illness with frequent relapses and recurrences, high rates of co-morbid conditions, and poor adherence to treatment. Mood stabilizers and antipsychotics are the cornerstones of treatment. Dopamine receptor partial agonists are a novel class of antipsychotic agents with original pharmacodynamic properties. Among them, two have been approved by the US Food and Drug Administration for the treatment of bipolar disorder. Aripiprazole (oral formulation) has been approved as monotherapy for the treatment of manic/mixed episodes in adult and pediatric populations and for maintenance treatment in adults, and as adjunctive treatment to mood stabilizers, for the acute treatment of manic/mixed episodes and for maintenance in adults. An intramuscular formulation of aripiprazole has been approved for the treatment of agitation in mania and a long-acting injectable formulation has been approved as maintenance treatment. In the USA, cariprazine has been approved as monotherapy for the acute treatment of manic/mixed as well as bipolar depressive episodes. Brexpiprazole is not yet approved to treat bipolar disorder. The evidence supporting these indications is reviewed via an analysis of clinical registration trials as well as additional studies, on the basis of a systematic literature search. Further studies dealing with other aspects of bipolar illness are also presented. Aripiprazole and cariprazine are efficacious and generally well tolerated agents that have shown cost effectiveness, and may therefore enrich our therapeutic armamentarium for bipolar illness. Brexpiprazole, which displays an overall promising tolerability profile, deserves further efficacy studies.

Understanding variability in the pharmacokinetics of atypical antipsychotics - focus on clozapine, olanzapine and aripiprazole population models

Antipsychotic medicines are widely used for the management of psychotic symptoms regardless of the underlying diagnosis. Most atypical antipsychotics undergo extensive metabolism prior to excretion. Various factors may influence their pharmacokinetics, particularly elimination, leading to highly variable drug concentrations between individual patients following the same dosing regimen. Population pharmacokinetic approach, based on nonlinear mixed effects modeling, is a useful tool to identify covariates explaining pharmacokinetic variability, as well as to characterize and distinguish unexplained residual and between-subject (interindividual) variability. In addition, this approach allows the use of both sparsely and intensively sampled data. In this paper, we reviewed the pharmacokinetic characteristics of clozapine, olanzapine and aripiprazole, focusing on a population modeling approach. In particular, models based on a nonlinear mixed effects approach performed by NONMEM^® software in order to identify and quantify sources of pharmacokinetic variability are presented. Population models were identified through systematic searches of PubMed and sixteen studies were selected. Some of the factors identified that significantly contribute to variability in elimination among clozapine, olanzapine, and aripiprazole are demographic characteristics, body weight, genetic polymorphism, smoking and in some cases drug interactions. Scientific research based on pharmacometric modeling is useful to further characterize sources of variability and their combined effect.

Impact of age and CYP2D6 genetics on exposure of aripiprazole and dehydroaripiprazole in patients using long-acting injectable versus oral formulation: relevance of poor and intermediate metabolizer status

PURPOSE

Tailoring medication dosing for the individual patient is complex, and many factors can influence drug exposure. We investigated the effect of age and CYP2D6 genotype on aripiprazole and dehydroaripiprazole exposure in patients using long-acting injectable (LAI) or oral aripiprazole.

METHODS

Matched data on serum concentration of aripiprazole and CYP2D6 genotype of patients using oral or LAI aripiprazole were included retrospectively from a therapeutic drug monitoring service. The patients were divided into the following CYP2D6 genotype-defined categories: poor metabolizers (PMs), intermediate metabolizers (IMs), normal metabolizers (NMs), and ultrarapid metabolizers (UMs). Linear mixed model analyses were used to evaluate the impact of CYP2D6 genotype on dose-adjusted serum concentrations of the active moiety of aripiprazole+dehydroaripiprazole in relation to age and formulation.

RESULTS

We identified 635 patients (mean age = 40.1 years, 9.4% ≥ 65 years, 53.7% females) using LAI (n = 166) or oral formulation (n = 469). The genotype-predicted CYP2D6 phenotype subgroups were 2.4% UMs, 82.0% NMs, 8.0% IMs, and 7.2% PMs. Age did not significantly affect exposure of the active moiety of aripiprazole+dehydroaripiprazole in the LAI (p = 0.071) or oral (p = 0.14) subgroups. Compared with CYP2D6 NMs, PMs and IMs had significantly increased exposure of the active moiety of aripiprazole+dehydroaripiprazole in the LAI (1.7-fold higher, p < 0.001, and 1.5-fold higher, p < 0.001) and oral (1.7-fold higher, p < 0.001, and 1.6-fold higher, p < 0.001) subgroups.

CONCLUSIONS

In conclusion, doses should be adjusted according to CYP2D6 genotype when initiating treatment with aripiprazole LAI or tablets, while advanced age do not affect the exposure of the active moiety of aripiprazole treatment regardless of formulation.

A Population Pharmacokinetic and Pharmacodynamic Analysis of RP5063 Phase 2 Study Data in Patients with Schizophrenia or Schizoaffective Disorder

Background and Objective

RP5063 is a novel multimodal dopamine (D)–serotonin (5-HT) stabilizer possessing partial agonist activity for D_2/3/4 and 5-HT_1A/2A, antagonist activity for 5-HT_2B/2C/7, and moderate affinity for the serotonin transporter. Phase 2 trial data analysis of RP5063 involving patients with schizophrenia and schizoaffective disorder defined: (1) the pharmacokinetic profile; and (2) the pharmacokinetic/pharmacodynamic relationships.

Methods

Pharmacokinetic sample data (175 patients on RP5063; 28 doses/patient) were analyzed, utilized one- and two-compartment models, and evaluated the impact of covariates. Pharmacodynamic analysis involved development of an E_max model.

Results

The pharmacokinetic analysis identified a one-compartment model incorporating body mass index influence on volume as the optimum construct, with fixed-effect parameters: (1) oral clearance (Cl/F), 5.11 ± 0.11 L/h; (2) volume of distribution (V_c/F), 328.00 ± 31.40 L; (3) absorption constant (ka) 0.42 ± 0.17 h⁻¹; (4) lag time (t lag) of 0.41 ± 0.02 h; and (5) a calculated half-life of 44.5 h. Pharmacokinetics were linear related to dose. An E_max model for total Positive and Negative Syndrome Scale (PANSS) scores as the response factor against cumulative area under the curve (AUC) provided fixed-effect estimates: (1) E_o = 87.3 ± 0.71 (PANSS Units; pu); (2) E_max = − 31.60 ± 4.05 (pu); and (3) AUC₅₀ = 89.60 ± 30.10 (µg·h/mL). The predicted PANSS improvement reflected a clinical dose range of 5–30 mg.

Conclusions

Pharmacokinetics of RP5063 behaved predictably and consistently. Pharmacodynamics were characterized using an E_max model, reflecting total PANSS score as a function of cumulative AUC, that showed high predictability and low variability when correlated with actual observations.

Electronic supplementary material

The online version of this article (10.1007/s13318-018-0472-z) contains supplementary material, which is available to authorized users.

A quantitative systems pharmacology study on optimal scenarios for switching to paliperidone palmitate once-monthly

Long-acting injectable (LAI) antipsychotic formulations are increasingly used for improving patient compliance and long-term outcomes. Transitioning to LAIs raises questions regarding how optimum efficacy can be rapidly achieved while minimizing potential efficacy and safety concerns related to overlapping plasma levels of prior treatments and the new LAI. Ideally, randomized clinical trials would provide guidance regarding transition algorithms, but the number of studies and sample size required to address relevant questions makes this approach unachievable. We have used quantitative systems pharmacology, a clinically calibrated, mechanism-based computer model for schizophrenia to identify optimal switching scenarios to injectable paliperidone palmitate once-monthly (PP1M) from oral antipsychotics. We show that starting PP1M 1day after the last oral medication dose or 4weeks after the last LAI injection provides optimal benefit-risk compared to a delayed PP1M start after 1week with either a 1- or 2-week overlap with oral paliperidone. Although a similar or better therapeutic effect can be achieved within 2weeks for oral medications and LAI haloperidol decanoate and 8weeks for LAI aripiprazole, we identified a potential transient undertreatment liability in all cases except for risperidone. Switching from oral olanzapine may lead to a small reduction of antipsychotic efficacy in some patients. Switching to PP1M decreases extrapyramidal symptom liability in most cases, but increased dopamine D₂ receptor inhibition (except for haloperidol) might potentially increase prolactin synthesis. Overall, these results suggest time-windows for which the treating clinician must be most vigilant for potential efficacy and safety signals when switching to PP1M.

Comparison of Capillary and Venous Drug Concentrations After Administration of a Single Dose of Risperidone, Paliperidone, Quetiapine, Olanzapine, or Aripiprazole

Risperidone, paliperidone, quetiapine, olanzapine, and aripiprazole are antipsychotic drugs approved for treating various psychiatric disorders, including schizophrenia. The objective of this randomized, parallel‐group, open‐label study was to compare finger‐stick‐based capillary with corresponding venous whole‐blood and plasma concentrations for these drugs after administration of a single dose to healthy volunteers. All whole‐blood and plasma drug concentrations were measured with validated liquid chromatography–tandem mass spectrometry methods. Capillary and venous concentrations (both in plasma and whole blood) were in close agreement, although a time‐dependent difference was observed, most obviously for olanzapine and paliperidone, with slightly higher capillary versus venous drug concentrations during the first hours after administering a single dose. The observed difference between capillary and venous plasma drug concentrations is expected not to be relevant in clinical practice, considering the wide window of therapeutic concentrations and the wide range of drug concentrations in the patient population for a given dose. Based on these results, finger‐stick‐based capillary drug concentrations have been shown to approximate venous drug concentrations.

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.

Immunotoxicological Effects of Aripiprazole: In vivo and In vitro Studies

Aripiprazole (ARI) is a commonly prescribed medication used to treat schizophrenia and bipolar disorder. To date, there have been no studies regarding the molecular pathological and immunotoxicological profiling of aripiprazole. Thus, in the present study, we prepared two different formulas of aripiprazole [Free base crystal of aripiprazole (ARPGCB) and cocrystal of aripiprazole (GCB3004)], and explored their effects on the patterns of survival and apoptosis-regulatory proteins under acute toxicity and cytotoxicity test conditions. Furthermore, we also evaluated the modulatory activity of the different formulations on the immunological responses in macrophages primed by various stimulators such as lipopolysaccharide (LPS), pam3CSK, and poly(I:C) via toll-like receptor 4 (TLR4), TLR2, and TLR3 pathways, respectively. In liver, both ARPGCB and GCB3004 produced similar toxicity profiles. In particular, these two formulas exhibited similar phospho-protein profiling of p65/nuclear factor (NF)-κB, c-Jun/activator protein (AP)-1, ERK, JNK, p38, caspase 3, and bcl-2 in brain. In contrast, the patterns of these phospho-proteins were variable in other tissues. Moreover, these two formulas did not exhibit any cytotoxicity in C6 glioma cells. Finally, the two formulations at available in vivo concentrations did not block nitric oxide (NO) production from activated macrophage-like RAW264.7 cells stimulated with LPS, pam3CSK, or poly(I:C), nor did they alter the morphological changes of the activated macrophages. Taken together, our present work, as a comparative study of two different formulas of aripiprazole, suggests that these two formulas can be used to achieve similar functional activation of brain proteins related to cell survival and apoptosis and immunotoxicological activities of macrophages.

Effects of genetic polymorphisms of CYP2D6, CYP3A5, and ABCB1 on the steady-state plasma concentrations of aripiprazole and its active metabolite, dehydroaripiprazole, in Japanese patients with schizophrenia

BACKGROUND

We studied the effects of various factors, including genetic polymorphisms of the cytochrome P450 (CYP) 2D6, CYP3A5, and ABCB1, age, gender, and smoking habit on the steady-state plasma concentrations of aripiprazole and its active metabolite, dehydroaripiprazole, in 89 patients with schizophrenia (46 males, 43 females).

METHODS

All patients had been receiving fixed doses of aripiprazole for at least 2 weeks. The daily doses were 24 mg (n = 56) and 12 mg (n = 33). No other drugs except biperiden and flunitrazepam were coadministered. Plasma concentrations of aripiprazole and dehydroaripiprazole were measured using liquid chromatography with mass-spectrometric detection. The CYP2D6 (CYP2D6*5, CYP2D6*10, and CYP2D6*14), CYP3A5 (CYP3A5*3), and ABCB1 (C3435T and G2677T/A) genotypes were identified by PCR analyses.

RESULTS

The mean concentration/dose ratios of aripiprazole and the sum of aripiprazole and dehydroaripiprazole were significantly higher in patients with 1 (P < 0.01 and P < 0.01) or 2 (P < 0.001 and P < 0.05) mutated alleles for CYP2D6 than in those without mutated alleles. No differences were found in the values of dehydroaripiprazole among CYP2D6 genotypes. There were no differences in the values of aripiprazole, dehydroaripiprazole, and the sum of the 2 compounds among CYP3A5 or the 2 ABCB1 variants. Multiple regression analyses including these polymorphisms, age, gender, and smoking habit showed that only the number of mutated alleles for CYP2D6 was correlated with mean concentration/dose ratios of aripiprazole [standardized partial correlation coefficients (beta) = 0.420, P < 0.001] and the sum of the 2 compounds (standardized beta = 0.335, P < 0.01).

CONCLUSIONS

The findings of this study suggest that CYP2D6 genotypes play an important role in controlling steady-state plasma concentrations of aripiprazole and the sum of aripiprazole and dehydroaripiprazole in Asian subjects, whereas CYP3A5 and ABCB1 genotypes seemed unlikely to have an impact.

Update on the Mechanism of Action of Aripiprazole: Translational Insights into Antipsychotic Strategies Beyond Dopamine Receptor Antagonism

Dopamine partial agonism and functional selectivity have been innovative strategies in the pharmacological treatment of schizophrenia and mood disorders and have shifted the concept of dopamine modulation beyond the established approach of dopamine D2 receptor (D2R) antagonism. Despite the fact that aripiprazole was introduced in therapy more than 12 years ago, many questions are still unresolved regarding the complexity of the effects of this agent on signal transduction and intracellular pathways, in part linked to its pleiotropic receptor profile. The complexity of the mechanism of action has progressively shifted the conceptualization of this agent from partial agonism to functional selectivity. From the induction of early genes to modulation of scaffolding proteins and activation of transcription factors, aripiprazole has been shown to affect multiple cellular pathways and several cortical and subcortical neurotransmitter circuitries. Growing evidence shows that, beyond the consequences of D2R occupancy, aripiprazole has a unique neurobiology among available antipsychotics. The effect of chronic administration of aripiprazole on D2R affinity state and number has been especially highlighted, with relevant translational implications for long-term treatment of psychosis. The hypothesized effects of aripiprazole on cell-protective mechanisms and neurite growth, as well as the differential effects on intracellular pathways [i.e. extracellular signal-regulated kinase (ERK)] compared with full D2R antagonists, suggest further exploration of these targets by novel and future biased ligand compounds. This review aims to recapitulate the main neurobiological effects of aripiprazole and discuss the potential implications for upcoming improvements in schizophrenia therapy based on dopamine modulation beyond D2R antagonism.

Clinical validity of cytochrome P450 metabolism and serotonin gene variants in psychiatric pharmacotherapy

Adverse events, response failures and medication non-compliance are common in patients receiving medications for the treatment of mental illnesses. A systematic literature review assessed whether pharmacokinetic (PK) or pharmacodynamic (PD) responses to 26 commonly prescribed antipsychotic and antidepressant medications, including efficacy or side effects, are associated with nucleotide polymorphisms in eight commonly studied genes in psychiatric pharmacotherapy: CYP2D6, CYP2C19, CYP2C9, CYP1A2, CYP3A4, HTR2C, HTR2A, and SLC6A4. Of the 294 publications included in this review, 168 (57%) showed significant associations between gene variants and PK or PD outcomes. Other studies that showed no association often had insufficient control for confounding variables, such as co-medication use, or analysis of medications not substrates of the target gene. The strongest gene-outcome associations were for the PK profiles of CYP2C19 and CYP2D6 (93% and 90%, respectively), for the PD associations between HTR2C and weight gain (57%), and for SLC6A4 and clinical response (54%), with stronger SLC6A4 response associations for specific drug classes (60-83%). The preponderance of evidence supports the validity of analyzing nucleotide polymorphisms in CYP and pharmacodynamic genes to predict the metabolism, safety, or therapeutic efficacy of psychotropic medications commonly used for the treatment of depression, schizophrenia, and bipolar illness.

Towards the implementation of CYP2D6 and CYP2C19 genotypes in clinical practice: update and report from a pharmacogenetic service clinic

Genetic testing may help to improve treatment outcomes in order to avoid non-response or severe side effects to psychotropic medication. Most robust data have been obtained for gene variants in CYP2D6 and CYP2C19 enzymes for antipsychotics and antidepressant treatment. We reviewed original articles indexed in PubMed from 2008-2013 on CYP2D6 and CYP2C19 gene variants and treatment outcome to antidepressant or antipsychotic medication. We have started providing CYP2D6 and CYP2C19 genotype information to physicians and conducted a survey where preliminary results are reported. Studies provided mixed results regarding the impact of CYP2D6 and CYP2C19 gene variation on treatment response. Plasma levels were mostly found associated with CYP metabolizer status. Higher occurrence/severity of side effects were reported in non-extensive CYP2D6 or CYP2C19 metabolizers. Results showed that providing genotypic information is feasible and generally well accepted by both patients and physicians. Although currently available studies are limited by small sample sizes and infrequent plasma drug level assessment, research to date indicates that CYP2D6 and CYP2C19 testing may be beneficial particularly for non-extensive metabolizing patients. In summary, clinical assessment of CYP2D6 and CYP2C19 metabolizer status is feasible, well accepted and optimizes drug treatment in psychiatry.

Predicting brain occupancy from plasma levels using PET: superiority of combining pharmacokinetics with pharmacodynamics while modeling the relationship

Positron emission tomography (PET) studies of dopamine receptor occupancy can be used to assess dosing of antipsychotics. Typically, studies of antipsychotics have applied pharmacodynamic (PD) modeling alone to characterize the relationship between antipsychotic dose and its effect on the brain. However, a limitation of this approach is that it does not account for the discrepancy between the time courses of plasma concentration and receptor occupancy by antipsychotics. Combined pharmacokinetic-PD (PK-PD) modeling, by incorporating the time dependence of occupancy, is better suited for the reliable analysis of the concentration-occupancy relationship. To determine the effect of time on the concentration-occupancy relationship as a function of analysis approach, we measured dopamine receptor occupancy after the administration of aripiprazole using [(11)C]raclopride PET and obtained serial measurements of the plasma aripiprazole concentration in 18 volunteers. We then developed a PK-PD model for the relationship, and compared it with conventional approach (PD modeling alone). The hysteresis characteristics were observed in the competitor concentration-occupancy relationship and the value of EC(50) was different according to the analysis approach (EC(50) derived from PD modeling alone=11.1 ng/mL (95% confidence interval (CI)=10.1 to 12.1); while that derived from combined PK-PD modeling=8.63 ng/mL (95% CI=7.75 to 9.51)). This finding suggests that PK-PD modeling is required to obtain reliable prediction of brain occupancy by antipsychotics.

Aripiprazole and dehydroaripiprazole plasma concentrations and clinical responses in patients with schizophrenia

Aripiprazole is widely used to treat schizophrenia. Plasma levels of aripiprazole and its active metabolite dehydroaripiprazole and their clinical responses in patients were explored. Forty-five (male/female: 19/26) patients with schizophrenia were treated with aripiprazole after a washout period of at least 3 days. There was no concomitant psychotropic except benzodiazepines for insomnia. The Positive and Negative Syndrome Scale (PANSS) was used to measure the clinical response at baseline and at weeks 2, 4, and 6. Blood was drawn at week 6 to measure the plasma concentrations of aripiprazole and dehydroaripiprazole. Patients with a PANSS score that decreased by more than 20% were defined as responders after 6 weeks of treatment. There was no difference in baseline PANSS scores or the daily dosage used between responders (n = 28) and nonresponders (n = 17) (15.0 ± 5.9 vs 12.9 ± 6.9 mg, respectively; P = 0.203). The responders showed a trend toward a higher plasma concentration of aripiprazole than nonresponders (234.4 ± 156.7 vs 163.5 ± 77.2 ng/mL, respectively; P = 0.117) and a significantly higher plasma concentration of dehydroaripiprazole (101.6 ± 58.0 vs 66.0 ± 48.4, respectively; P = 0.023). Higher plasma concentrations of aripiprazole and its active metabolite dehydroaripiprazole were noted in responders than nonresponders. Compared with Western patients, Oriental patients had higher plasma concentrations of aripiprazole and dehydroaripiprazole at the same dose. We suggest that therapeutic drug monitoring of aripiprazole will help improve the response in clinical practice.

Partial agonists in schizophrenia--why some work and others do not: insights from preclinical animal models

While dopamine D2 receptor partial agonists (PAs) have been long considered for treating schizophrenia, only one, aripiprazole, is clinically available for therapeutic use. This raises critically important questions as to what is unique about aripiprazole and to what extent animal models can predict therapeutic success. A number of PAs whose clinical fate is known: aripiprazole, preclamol, terguride, OPC-4392 and bifeprunox were compared to haloperidol (a reference antipsychotic) in several convergent preclinical animal models; i.e. amphetamine-induced locomotion (AIL) and conditioned avoidance response (CAR), predictive of antipsychotic effects; unilateral nigrostriatal lesioned rats, a model of hypo-dopaminergia; striatal Fos induction, a molecular marker for antipsychotic activity; and side-effects common to this class of drugs: catalepsy (motor side-effects) and prolactaemia. The results were compared across drugs with reference to their measured striatal D2 receptor occupancy. All the PAs occupied striatal D2 receptors in a dose dependent manner, inhibited AIL and CAR, and lacked motor side-effects or prolactinaemia despite D2 receptor occupancy exceeding 80%. At comparative doses, aripiprazole distinguished itself from the other PAs by causing the least rotation in the hypo-dopaminergic model (indicating the least intrinsic activity) and showed the highest Fos expression in the nucleus accumbens (indicating functional D2 antagonism). Although a number of PAs are active in antipsychotic animal models, not all of them succeed. Given that only aripiprazole is clinically available, it can be inferred that low functional intrinsic activity coupled with sufficient functional antagonism as reflected in the animal models may be a marker of success.

Pharmacokinetics and metabolism update for some recent antipsychotics

INTRODUCTION

The search for drugs that reduce psychotic symptoms, with minimal adverse effects, has led to the development of new agents that act somewhat differently from their older antipsychotic counterparts. These agents, which include aripiprazole, lurasidone and perospirone, act by targeting both D₂ and 5-HT(1A) receptors, in addition to other characteristic receptors.

AREAS COVERED

This article covers the pharmacokinetics and metabolism of aripiprazole, perospirone, lurasidone and cariprazine. The review also describes the effects of physiological and pathological variables on these drugs as well as potential drug interactions. The author provides the reader with knowledge of the fundamental pharmacokinetic characteristics and metabolic pathways of these new antipsychotics, emphasizing the clinically important common features and differences compared to other older agents.

EXPERT OPINION

Aripiprazole, perospirone, lurasidone and cariprazine share some of the pharmacokinetic characteristics of older, lipophilic antipsychotics and, like these, each has some distinct pharmacokinetic features that are clinically beneficial and some that are not. We await the results of future practical effectiveness trials of these new antipsychotics and their follow-on derivatives to learn more about their benefit/risk profile compared with established antipsychotics. It is hoped that some of these newer antipsychotics will not only increase the range of pharmacotherapeutic options, but decisively improve the expectations of psychotherapy for schizophrenia.

Aripiprazole as adjunctive therapy for patients with major depressive disorder: overview and implications of clinical trial data

Aripiprazole was initially approved to treat schizophrenia and later approved for bipolar mania, as a monotherapy and an adjunctive therapy (manic or mixed episodes), and for irritability associated with autism. Aripiprazole is a partial agonist at dopamine D(2) and D(3) and serotonin 5-HT(1A) receptors, and is an antagonist at 5-HT(2A) receptors. This profile, and convincing preliminary data from small-scale studies, provided the rationale for the large-scale exploration of aripiprazole for unipolar depression. Recently, three 6-week, large-scale, randomized, double-blind, placebo-controlled clinical trials demonstrated clinically meaningful efficacy for aripiprazole as an adjunctive therapy to antidepressants for treating major depressive disorder (MDD). In November 2007, aripiprazole was approved by the US FDA as an adjunctive therapy to antidepressants for treating MDD, with support from two of the above-mentioned trials. In the trials, aripiprazole was demonstrated to be safe and well tolerated, and showed a minimal trend for weight gain over the course of a 6-week treatment. The incidence of akathisia was higher than that reported in studies of patients with schizophrenia; however, most cases were mild to moderate and infrequently lead to discontinuation (5/1090 from all three trials). This comprehensive review provides an overview of the data from all three 6-week studies (including a pooled analysis) and from an unpublished 52-week, open-label extension study, to inform physicians and facilitate reasonable treatment decisions. In addition, specific issues associated with the use of aripiprazole as an adjunctive therapy in patients with MDD, including possible early treatment effect, appropriate timing of therapy initiation, appropriate dosing and duration of treatment, possible differential effect on depressive subgroups and long-term tolerability, are also discussed.

Neurobiological bases and clinical aspects of the use of aripiprazole in treatment-resistant major depressive disorder

Addition of atypical antipsychotics to the therapeutic regimen of patients with unipolar major depressive disorder not responding adequately to their treatment has become a common intervention. With all these agents the observation that low doses that are ineffective in schizophrenia, and thus not blocking dopamine D2 receptors effectively, indicate that their beneficial action is attributable to their action at other receptors. Preclinical research has shown that atypical antipsychotics can reverse the suppression of firing of norepinephrine neurons produced by selective serotonin reuptake inhibitors through their antagonism of 5-HT₂(A) receptors. In the case of aripiprazole, three large placebo-controlled studies in more than 1,000 patients individually concluded to significant antidepressant responses and remissions after a six-week treatment. Aripiprazole addition did not produce more discontinuations due to adverse events than placebo. The most frequently encountered adverse events were akathisia and restlessness. Weight gain was minimal but significant in two of the three studies, suggesting that this side effect is not major problem. There was no significant laboratory abnormalities noted with this strategy. It is proposed that because of its long half-life (approximately 3 days), the doses of aripiprazole were escalated too rapidly in these controlled trials. More gradual titration may lead in routine clinical practice to better outcomes, minimizing side effects and improving remission rates.

Not all partial dopamine D(2) receptor agonists are the same in treating schizophrenia. Exploring the effects of bifeprunox and aripiprazole using a computer model of a primate striatal dopaminergic synapse

Species differences in physiology and unique active human metabolites contribute to the limited predictive value of preclinical rodent models for many central nervous system (CNS) drugs. In order to explore possible drivers for this translational disconnect, we developed a computer model of a dopaminergic synapse that simulates the competition among three agents and their binding to pre- and postsynaptic receptors, based on the affinities for their targets and their actual concentrations. The model includes presynaptic autoreceptor effects on neurotransmitter release and modulation by presynaptic firing frequency and is calibrated with actual experimental data on free dopamine levels in the striatum of the rodent and the primate. Using this model, we simulated the postsynaptic dopamine D(2) receptor activation levels of bifeprunox and aripiprazole, two relatively similar dopamine D(2) receptor agonists. The results indicate a substantial difference in dose-response for the two compounds when applying primate calibration parameters as opposed to rodent calibration parameters. In addition, when introducing the major human and rodent metabolites of aripiprazole with their specific pharmacological activities, the model predicts that while bifeprunox would result in a higher postsynaptic D(2) receptor antagonism in the rodent, aripiprazole would result in a higher D(2) receptor antagonism in the primate model. Furthermore, only the highest dose of aripiprazole, but not bifeprunox, reaches postsynaptic functional D(2) receptor antagonism similar to 4 mg haloperidol in the primate model. The model further identifies a limited optimal window of functionality for dopamine D(2) receptor partial agonists. These results suggest that computer modeling of key CNS processes, using well-validated calibration paradigms, can increase the predictive value in the clinical setting of preclinical animal model outcomes.

Incorporating evidence from pharmacologic and pharmacogenetic studies of atypical antipsychotic drugs into advanced psychiatric nursing practice

PURPOSE

To present a conceptual framework for incorporating pharmacologic findings and pharmacogenetic evidence related to atypical antipsychotic drugs (AADs) into advanced psychiatric nursing practice.

CONCLUSIONS

Three evidence domains lend important information about differential AAD response. These include the pharmacology of AADs, the molecular genetics of metabolizing enzymes, and the molecular genetics of neurotransmitter receptor drug targets.

PRACTICE IMPLICATIONS

These evidence domains can be incorporated into nursing practice decisions related to medication planning, patient and family education, and medication monitoring processes. The central focus of the framework is patient outcomes, which include medication adherence, tolerability of the AADs, and demonstrated clinical effectiveness.

A review of the safety and tolerability of aripiprazole

It seems that the efficacy of aripiprazole for treating schizophrenia is mediated through a combination of partial agonism at dopamine D2 and serotonin 5-HT1A receptors and antagonism at serotonin 5-HT2A receptors. Aripiprazole has also received approval for the treatment of bipolar disorder as adjunctive therapy or monotherapy (manic or mixed episodes) as well as an augmentation therapy of major depressive disorder (MDD) by the US FDA. The overall safety and tolerability of aripiprazole is favorable compared to other atypical antipsychotics across the approved indications. Aripiprazole showed a minimal propensity for clinically significant weight gain and metabolic disruption. However, extrapyramidal side effects, such as akathisia, are reported and may limit its clinical use in some cases, particularly in patients with bipolar disorder and MDD. This review focuses on the tolerability and safety of aripiprazole across a broad spectrum of psychiatric disorders while taking into consideration results from registrational studies as well as findings from studies in the naturalistic setting. In conclusion, whereas the comparative safety and tolerability of aripiprazole has not been systematically evaluated in comparator studies, tolerability and safety issues commonly associated with atypical antipsychotics such as weight gain and metabolic syndrome are less prominent with aripiprazole.

Polymorphism of human cytochrome P450 enzymes and its clinical impact

Pharmacogenetics is the study of how interindividual variations in the DNA sequence of specific genes affect drug response. This article highlights current pharmacogenetic knowledge on important human drug-metabolizing cytochrome P450s (CYPs) to understand the large interindividual variability in drug clearance and responses in clinical practice. The human CYP superfamily contains 57 functional genes and 58 pseudogenes, with members of the 1, 2, and 3 families playing an important role in the metabolism of therapeutic drugs, other xenobiotics, and some endogenous compounds. Polymorphisms in the CYP family may have had the most impact on the fate of therapeutic drugs. CYP2D6, 2C19, and 2C9 polymorphisms account for the most frequent variations in phase I metabolism of drugs, since almost 80% of drugs in use today are metabolized by these enzymes. Approximately 5-14% of Caucasians, 0-5% Africans, and 0-1% of Asians lack CYP2D6 activity, and these individuals are known as poor metabolizers. CYP2C9 is another clinically significant enzyme that demonstrates multiple genetic variants with a potentially functional impact on the efficacy and adverse effects of drugs that are mainly eliminated by this enzyme. Studies into the CYP2C9 polymorphism have highlighted the importance of the CYP2C9*2 and *3 alleles. Extensive polymorphism also occurs in other CYP genes, such as CYP1A1, 2A6, 2A13, 2C8, 3A4, and 3A5. Since several of these CYPs (e.g., CYP1A1 and 1A2) play a role in the bioactivation of many procarcinogens, polymorphisms of these enzymes may contribute to the variable susceptibility to carcinogenesis. The distribution of the common variant alleles of CYP genes varies among different ethnic populations. Pharmacogenetics has the potential to achieve optimal quality use of medicines, and to improve the efficacy and safety of both prospective and currently available drugs. Further studies are warranted to explore the gene-dose, gene-concentration, and gene-response relationships for these important drug-metabolizing CYPs.