Population Pharmacokinetics and Dosing Simulations for Aripiprazole 2-Month Ready-to-Use Long-Acting Injectable in Adult Patients With Schizophrenia or Bipolar I Disorder.

A ready-to-use (RTU) long-acting injectable (LAI) formulation of aripiprazole monohydrate for administration once every 2 months, available in 960 mg (Ari 2MRTU 960) or 720 mg doses, has been developed for the treatment of schizophrenia or bipolar I disorder. A previously developed and validated population pharmacokinetic model for characterizing aripiprazole plasma concentrations following administration of oral aripiprazole or aripiprazole once-monthly (AOM) intramuscular injection was expanded to include the RTU LAI formulation of aripiprazole (Ari RTU LAI). Overall, 8899 aripiprazole pharmacokinetic samples from 1191 adults from 10 clinical trials were included in the final combined analysis data set. Aripiprazole plasma concentration-time profiles were simulated for various Ari RTU LAI initiation and maintenance scenarios in 1000 virtual patients. Diagnostic plots demonstrated that the final population pharmacokinetic model, which incorporated data for oral aripiprazole, AOM, and Ari RTU LAI, adequately described aripiprazole concentrations following Ari RTU LAI administration. Absorption of Ari RTU LAI was modeled by a parallel zero-order and lagged first-order process. Simulations across multiple scenarios were performed to inform dosing recommendations, including various treatment initiation regimens for a 2-monthly formulation of Ari RTU LAI in patients with or without prior stabilization on oral aripiprazole, and for patients switching from AOM. Additional simulations accounted for missed/delayed doses, cytochrome (CYP) 2D6 metabolizer status, and concomitant use of CYP2D6 or CYP3A4 inhibitors. Overall, simulations across a variety of scenarios demonstrated an Ari RTU LAI pharmacokinetic exposure profile that was comparable to AOM, with a longer dosing interval.

Population Pharmacokinetic Analysis of Brexpiprazole to Support its Indication and Dose Selection in Adolescents With Schizophrenia.

Due to the customary delay between medication approvals in adult and adolescent populations, adolescents with schizophrenia may receive off-label antipsychotic treatment, without empirically justified dosing recommendations. In order to accelerate pediatric drug development, the US Food and Drug Administration (FDA) released a general advice letter to sponsors permitting the effectiveness of atypical antipsychotics for the treatment of schizophrenia in adults to be extrapolated to adolescents based on a pharmacokinetic (PK) analysis to support dose selection, plus a safety study. The aim of the present article is to describe the population PK analysis that was submitted to the FDA to inform brexpiprazole dose selection in adolescents with schizophrenia. Using a population PK model with brexpiprazole clearance and volume of distribution allometrically scaled by body weight, PK simulations showed comparable brexpiprazole dose-exposure between adults and adolescents aged 13-17 years following oral daily doses of brexpiprazole 1-4 mg, indicating that the target brexpiprazole dose of 2-4 mg/day in adults with schizophrenia is also suitable for adolescents. Based on this population PK analysis, together with a safety study in adolescents, the FDA approved brexpiprazole for the treatment of schizophrenia in adolescents aged 13-17 years, via extrapolation of the efficacy of brexpiprazole from adults to adolescents.

Estimating the In Vivo Function of CYP2D6 Alleles through Population Pharmacokinetic Modeling of Brexpiprazole.

Accurate prediction of CYP2D6 phenotype from genotype information is important to support safe and efficacious pharmacotherapy with CYP2D6 substrates. To facilitate accurate CYP2D6 genotype-phenotype translation, there remains a need to investigate the enzyme activity associated with individual CYP2D6 alleles using large clinical data sets. This study aimed to quantify and compare the in vivo function of different CYP2D6 alleles through population pharmacokinetic (PopPK) modeling of brexpiprazole using data from 13 clinical studies. A PopPK model of brexpiprazole and its two metabolites, DM-3411 and DM-3412, was developed based on plasma concentration samples from 826 individuals. As the minor metabolite, DM-3412, is formed via CYP2D6, the metabolic ratio of DM-3412:brexpiprazole calculated from the PopPK parameter estimates was used as a surrogate measure of CYP2D6 activity. A CYP2D6 genotype-phenotype analysis based on 496 subjects showed that the CYP2D6*2 allele (n = 183) was associated with only 10% enzyme activity relative to the wild-type allele (CYP2D6*1) and a low enzyme activity was consistently observed across genotypes containing CYP2D6*2. Among the decreased function alleles, the following enzyme activities relative to CYP2D6*1 were estimated: 23% for CYP2D6*9 (n = 20), 32% for CYP2D6*10 (n = 62), 64% for CYP2D6*14 (n = 1), 4% for CYP2D6*17 (n = 37), 4% for CYP2D6*29 (n = 13), and 9% for CYP2D6*41 (n = 64). These findings imply that a lower functional value would more accurately reflect the in vivo function of many reduced function CYP2D6 alleles in the metabolism of brexpiprazole. The low enzyme activity observed for CYP2D6*2, which has also been reported by others, suggests that the allele exhibits substrate-specific enzyme activity.

Population Pharmacokinetic Modeling and Exposure-Response Analysis for Aripiprazole Once Monthly in Subjects With Schizophrenia.

An intramuscular formulation of aripiprazole monohydrate dosed once monthly (AOM) was developed to address nonadherence with the approved oral tablets. A 3-compartment linear population pharmacokinetic model for oral and AOM doses was developed; relative bioavailability was estimated for AOM relative to oral dosing and body mass index and sex were significant predictors of AOM absorption rate constant (longer absorption half-life for women and absorption half-life increases with increasing body mass index). Aripiprazole apparent oral clearance for subjects with cytochrome P450 (CYP) 2D6 poor metabolizer status and in the presence of strong CYP2D6 inhibitors was approximately half that of subjects with CYP2D6 extensive metabolizer status and 24% lower in the presence of strong CYP3A4 inhibitors. Simulations of the population pharmacokinetics were conducted to evaluate the effect of different dose initiation strategies for AOM, the effects of CYP2D6 metabolizer status, coadministration of CYP2D6 and CYP3A4 inhibitors, and missed doses. An exposure-response model with an exponential hazard function of the model-predicted minimum concentration (Cmin ) described the time to relapse. The hazard ratio (95% confidence interval) was 4.41 (2.89-6.75). Thus, a subject with a diagnosis of schizophrenia and Cmin  ≥ 95 ng/mL is 4.41 times less likely to relapse relative to a subject with Cmin  < 95 ng/mL.

An alternative start regimen with aripiprazole once-monthly in patients with schizophrenia: population pharmacokinetic analysis of a single-day, two-injection start with gluteal and/or deltoid intramuscular injection.

BACKGROUND: The single-injection start regimen for aripiprazole once-monthly 400 mg (AOM 400) in patients with schizophrenia requires a single intramuscular injection in the gluteal or deltoid site and 14 days of concurrent oral therapy. A simplified, single-day regimen of two injections at separate gluteal and/or deltoid injection sites, together with a single 20-mg dose of oral aripiprazole on the 1st day, was assessed. PATIENTS AND METHODS: A previously developed population-pharmacokinetic (popPK) model for characterizing aripiprazole PK following oral administration and gluteal intramuscular depot injection was expanded to include deltoid injection. Simulations were conducted to assess PK profiles following various (including two-injection) start regimens. Postmarketing data on patients who received higher-than-recommended AOM doses were used to assess overall safety/tolerability. RESULTS: The two-injection start regimen with a single concurrent oral dose displayed a comparable PK profile to the single-injection start regimen with concurrent 14-day oral administration in simulations. The safety assessment indicated the two-injection start regimen was unlikely to be associated with safety concerns beyond those expected with a single-injection start regimen. CONCLUSION: These data support use of the two-injection start regimen in clinical practice to reduce reliance on daily oral administration and optimize the therapeutic benefits of AOM 400 in patients with schizophrenia.

An open-label, positron emission tomography study of the striatal D2/D3 receptor occupancy and pharmacokinetics of single-dose oral brexpiprazole in healthy participants.

PURPOSE: The aim of this Phase 1, open-label, positron emission tomography (PET) study was to determine the degree of striatal D2/D3 receptor occupancy induced by the serotonin-dopamine activity modulator, brexpiprazole, at different single dose levels in the range 0.25-6 mg. METHODS: Occupancy was measured at 4 and 23.5 h post-dose using the D2/D3 receptor antagonist [11C]raclopride. The pharmacokinetics, safety and tolerability of brexpiprazole were assessed in parallel. RESULTS: Fifteen healthy participants were enrolled (mean age 33.9 years; 93.3% male). Mean D2/D3 receptor occupancy in the putamen and caudate nucleus increased with brexpiprazole dose, leveled out at 77-88% with brexpiprazole 5 mg and 6 mg at 4 h post-dose, and remained at a similar level at 23.5 h post-dose (74-83%). Estimates of maximum obtainable receptor occupancy (Omax) were 89.2% for the putamen and 95.4% for the caudate nucleus; plasma concentrations predicted to provide 50% of Omax (EC50) were 8.13 ng/mL and 7.75 ng/mL, respectively. Brexpiprazole area under the concentration-time curve (AUC∞) and maximum plasma concentration (Cmax) increased approximately proportional to dose. No notable subjective or objective adverse effects were observed in this cohort. CONCLUSION: By extrapolating the observed single-dose D2/D3 receptor occupancy data in healthy participants, multiple doses of brexpiprazole 2 mg/day and above are expected to result in an efficacious brexpiprazole concentration, consistent with clinically active doses in schizophrenia and major depressive disorder. TRIAL REGISTRATION: ClinicalTrials.gov NCT00805454 December 9, 2008.

Plasma concentrations and dosing of 2 long-acting injectable formulations of aripiprazole.

Maintaining therapeutic plasma concentrations of an antipsychotic agent is essential in preventing relapse of symptoms in schizophrenia. Long-acting injectable (LAI) formulations provide extended exposure to antipsychotic therapy and have been useful in addressing treatment nonadherence. Aripiprazole is an atypical antipsychotic used in the treatment of schizophrenia and is available in 2 chemically different (aripiprazole monohydrate and aripiprazole lauroxil [AL]) and pharmaceutically different LAI formulations (aripiprazole once-monthly 400 mg [AOM 400] and AL). The pharmaceutical difference is that AL, unlike AOM 400, is a prodrug that requires additional metabolic steps to form the active drug aripiprazole. We present data demonstrating that aripiprazole plasma concentrations are similar for AOM 400 and the 882 mg dose of AL when administered once every 4 weeks and that both provide similar therapeutic plasma concentrations of aripiprazole when compared with therapeutic oral doses.

Aripiprazole Once-Monthly 400 mg: Comparison of Pharmacokinetics, Tolerability, and Safety of Deltoid Versus Gluteal Administration.

Background: Two open-label, randomized, parallel-arm studies compared pharmacokinetics, safety, and tolerability of aripiprazole once-monthly 400 mg following deltoid vs gluteal injection in patients with schizophrenia. Methods: In the single-dose study, 1 injection of aripiprazole once-monthly 400 mg in the deltoid (n=17) or gluteal (n=18) muscle (NCT01646827) was administered. In the multiple-dose study, the first aripiprazole once-monthly 400 mg injection was administered in either the deltoid (n=71) or gluteal (n=67) muscle followed by 4 once-monthly deltoid injections (NCT01909466). Results: After single-dose administration, aripiprazole exposure (area under the concentration-time curve) was similar between deltoid and gluteal administrations, whereas median time to maximum plasma concentration was shorter (7.1 [deltoid] vs 24.1 days [gluteal]) and maximum concentration was 31% higher after deltoid administration. In the multiple-dose study, median time to maximum plasma concentration for deltoid administration was shorter (3.95 vs 7.1 days), whereas aripiprazole mean trough concentrations, maximum concentration, and area under the concentration-time curve were comparable between deltoid and gluteal muscles (historical data comparison). Multiple-dose pharmacokinetic results for the major metabolite, dehydro-aripiprazole, followed a similar pattern to that of the parent drug for both deltoid and gluteal injection sites. Safety and tolerability profiles were similar after gluteal or deltoid injections. Based on observed data, minimum aripiprazole concentrations achieved by aripiprazole once-monthly 400 mg are comparable with those of oral aripiprazole 15 to 20 mg/d. Conclusions: The deltoid muscle is a safe alternative injection site for aripiprazole once-monthly 400 mg in patients with schizophrenia.

Initiation of aripiprazole once-monthly in patients with schizophrenia.

OBJECTIVE: This article provides rationale for recommendations on how to initiate aripiprazole once-monthly 400 mg (AOM 400), an injectable suspension, in patients with schizophrenia, supported by pharmacokinetic (PK) data and based on clinical studies. METHODS: An overview of data from a PK study, PK simulations, controlled clinical trials, and a naturalistic study is presented. RESULTS: Pharmacokinetic data support 400 mg as the starting and maintenance dose of AOM; the plasma concentration profile of aripiprazole after initiating AOM 400 was consistent with therapeutic concentrations observed with oral aripiprazole 10 to 30 mg/d. PK simulations and observed data from a single-dose clinical trial indicate that median aripiprazole plasma concentrations reach therapeutic levels within 7 days of initiating AOM 400. Because of interpatient variability, a 14-day overlap with oral aripiprazole or another antipsychotic medication is considered sufficient to ensure therapeutic concentrations. In clinical studies, when patients initiated AOM 400 with concomitant oral aripiprazole (10-15 mg/d based on stabilized dose) or continued their previous antipsychotic for ≤14 days, mean aripiprazole plasma concentration after 4 weeks (93 to 112 ng/mL) was in range of the therapeutic window established for aripiprazole (94.0-534.0 ng/mL). In clinical studies, the 400-mg starting dose of AOM was efficacious and well tolerated. Across studies of variable duration and design, 1296/1439 (90.1%) patients initiated AOM 400 and required no dose change. Overall rates of discontinuation due to lack of efficacy across clinical studies were low in patients treated with AOM 400 (range, 2.3%-10.0%). In a post hoc analysis from a naturalistic study, cross-titration from other oral antipsychotic therapies to oral aripiprazole before initiating AOM 400 was better tolerated with a >1- to 4-week cross-titration period versus a ≤1-week period, as evidenced by lower rates of discontinuation due to adverse events during cross-titration (2.7% [7/239] vs 10.4% [5/48]). The efficacy and safety of AOM 400 in the month after initiation in the pivotal maintenance studies were comparable between subpopulations of patients previously stabilized on 10- or 30-mg doses of oral aripiprazole. CONCLUSIONS: Findings from PK data, PK simulations, and clinical studies all support that 400 mg is the appropriate initiation dose of AOM for patients with schizophrenia. When switching to oral aripiprazole before initiating AOM 400, tapering the prior oral antipsychotic while titrating up the oral aripiprazole dose (target dose 10-30 mg/d) over >1 to 4 weeks may be an effective strategy. The efficacy, safety, and tolerability of AOM 400 were comparable regardless of whether patients were previously stabilized on oral aripiprazole 10 or 30 mg/d or other antipsychotic therapy and continued to receive the same oral antipsychotic for the first 14 days after initiating AOM 400.

Safety and tolerability of once monthly aripiprazole treatment initiation in adults with schizophrenia stabilized on selected atypical oral antipsychotics other than aripiprazole.

OBJECTIVE: Safety and tolerability assessment of initiating treatment with a once monthly long-acting injectable form of aripiprazole (aripiprazole once monthly) in patients stabilized on oral antipsychotics other than aripiprazole. METHODS: Patients with schizophrenia treated with oral atypical antipsychotics other than aripiprazole and with a history of aripiprazole tolerability were enrolled. Patients were stabilized per investigator's judgment for ≥14 days on oral atypical antipsychotics during screening. Patients then received one dose of aripiprazole once monthly (400 mg). Concomitant with aripiprazole once monthly, subjects received their current oral atypical antipsychotic for 14 ± 1 days at doses reduced to the mid/lower recommended dose range. Safety and tolerability were assessed for the 28-day treatment phase. For pharmacokinetic analyses, aripiprazole plasma concentrations were measured on Days 7, 14, and 28. RESULTS: Sixty patients were enrolled and initiated with aripiprazole once monthly while continuing treatment with oral olanzapine (n = 3), quetiapine (n = 28), risperidone (n = 24) or ziprasidone (n = 5). Duration of co-administered oral antipsychotic treatment varied, ranging from 0 to 15 days. Treatment was well tolerated. Frequently reported treatment-emergent adverse events (TEAEs) were injection-site pain and toothache (4/60 subjects each, 6.7%), followed by dystonia, fatigue, increased blood creatine phosphokinase, insomnia and restlessness (3/60 subjects each, 5.0%). Most TEAEs occurred in the first 8 days of co-administration irrespective of days of oral overlap. No clinically relevant mean changes from baseline were observed for laboratory values or fasting metabolic parameters. Psychotic symptoms remained stable. Aripiprazole plasma concentrations were similar to those observed following daily doses of oral aripiprazole. CONCLUSIONS: The adverse-event profile of patients receiving aripiprazole once monthly concomitant with oral atypical antipsychotics other than aripiprazole was consistent with previous reports of aripiprazole once monthly concomitant with oral aripiprazole. Adverse events were similar irrespective of prior atypical antipsychotic and duration of oral antipsychotic overlap, suggesting that patients can be safely switched from their existing oral antipsychotic to aripiprazole once monthly without requiring an intermediate stabilization phase with oral aripiprazole. Aspects of the study design (open-label trial and short duration) and patient population (predominantly male and of African-American ethnicity) may limit the generalizability of these findings. CLINICAL TRIAL REGISTRATION: Safety and Tolerability Trial of Aripiprazole IM Depot Treatment in Adult Subjects With Schizophrenia Stabilized on Oral Antipsychotics Other Than Aripiprazole. ID number: NCT01552772. Registry: clinicaltrials.gov.

Steady-state pharmacokinetics of galantamine are not affected by addition of memantine in healthy subjects.

To evaluate the effect of multiple doses of memantine on the pharmacokinetics of galantamine and to assess the safety and tolerability of galantamine with adjunctive memantine treatment, an open-label, single-center, drug interaction study was conducted in 16 healthy adults. Subjects received an 8-mg dose of galantamine extended release once daily during week 1 and a 16-mg dose of galantamine extended release once daily during week 2. During weeks 3 and 4, they received a 16-mg dose of galantamine extended release once daily and a 10-mg dose of memantine twice daily, except on days 1 and 2 of week 3, when memantine was given as 10 mg once daily. The pharmacokinetic profile and parameters of galantamine at steady state were similar after administration of a 16-mg dose of galantamine once daily alone and after administration with a 10-mg dose of memantine twice daily. Galantamine 16 mg once daily with adjunctive memantine 10 mg twice daily was well tolerated and safe in healthy subjects.