Viloxazine in the Management of CNS Disorders: A Historical Overview and Current Status.

Viloxazine has a long history of clinical use in Europe as an antidepressant, and has recently been repurposed into an extended-release form for the treatment of attention-deficit/hyperactivity disorder in the USA. An immediate-release formulation was approved for the treatment of depression in the UK in 1974, and was subsequently marketed there and in several European countries for 30 years with no major safety concerns. In contrast to first-generation antidepressants (e.g., tricyclic antidepressants, monoamine oxidase inhibitors), viloxazine was associated with a relatively low risk for cardiotoxicity. Gastrointestinal symptoms were the most commonly reported side effects. The therapeutic effects of viloxazine are thought to be primarily the result of its action as a norepinephrine reuptake inhibitor, although in vitro and preclinical in vivo animal data suggest that viloxazine may also impact the serotoninergic system. This review summarizes the evolving knowledge of viloxazine based on information from previously published preclinical and clinical investigations, and acquired unpublished historical study reports from both open-label and blinded controlled clinical trials. We review the chemical properties, mechanism of action, safety, and tolerability across these studies, and discuss the contemporary rationale for the development of this agent as an extended-release oral formulation for the treatment of attention-deficit/hyperactivity disorder.

Efficacy, Safety, and Tolerability of RBP-7000 Once-Monthly Risperidone for the Treatment of Acute Schizophrenia: An 8-Week, Randomized, Double-Blind, Placebo-Controlled, Multicenter Phase 3 Study.

RBP-7000 is a sustained-release formulation of risperidone for the treatment of schizophrenia, designed to be administered by once-monthly subcutaneous injection using the ATRIGEL delivery system. This study assessed the efficacy, safety, and tolerability of RBP-7000 compared with placebo in subjects with acute exacerbation of schizophrenia. Inpatients were randomly assigned to 8 weeks of double-blind treatment with subcutaneous 90 or 120 mg of RBP-7000 or placebo. Efficacy was evaluated using a mixed-model repeated-measures analysis of the change from baseline (the last nonmissing value before the first dose of RBP-7000 or placebo on day 1) to end of the study in Positive and Negative Syndrome Scale (PANSS) total score (primary efficacy measure) and Clinical Global Impression-Severity score (secondary efficacy measure). The least-squares means from the repeated-measures analysis for the change from baseline in the PANSS total scores for placebo was -9.219 (SE, 1.2162). RBP-7000 produced statistically and clinically significant differences in mean reductions from baseline in PANSS total scores (90-mg RBP-7000 compared with placebo, -6.148 [-9.982 to -2.314], P = 0.0004; 120-mg RBP-7000 compared with placebo, -7.237 [-11.045 to -3.429], P < 0.0001) and significantly improved Clinical Global Impression-Severity scores (90-mg RBP-7000 compared with placebo, -0.350 [-0.557 to -0.143], P = 0.0002; 120-mg RBP-7000 compared with placebo, -0.396 [-0.602 to -0.190], P < 0.0001). Both RBP-7000 dosages were generally well tolerated. The most frequently reported treatment-emergent adverse events in RBP-7000 groups compared with placebo were somnolence, weight gain, and akathisia. The overall incidence of extrapyramidal syndrome-related effects was low and similar across groups. RBP-7000 may provide a new, long-acting alternative treatment for use in adults with acute schizophrenia.

Simultaneous determination of buprenorphine, norbuprenorphine and naloxone in human plasma by liquid chromatography/tandem mass spectrometry.

A simple, sensitive and rapid liquid chromatography/electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) method was developed and validated for simultaneous quantification of naloxone, buprenorphine and its metabolite norbuprenorphine in human plasma. Human plasma samples were extracted using a single step liquid-liquid extraction, and then separated on an Imtakt Unison UK-C18 column (2.1×50mm, 3µm) using alkaline mobile phases with gradient elution. All of the analytes were detected in positive ion mode using multiple reaction monitoring (MRM). The method was validated and the specificity, linearity, lower limit of quantitation, precision, accuracy, recoveries and stability were determined. The linear range was 20-10000pg/mL for buprenorphine and norbuprenorphine; and 1-500pg/mL for naloxone. The correlation coefficient (R(2)) values for all three analytes were ≥0.995. The precision and accuracy for intra-day and inter-day were <11.0%. The recoveries were >63% and matrix effects were tracked by the deuterated internal standards (IS) with the IS-normalized matrix factor ranging from 0.96 to 1.33 for all three analytes. The validated method was successfully applied in a clinical pharmacokinetic study with low dose administration of sublingual buprenorphine and naloxone.

Population Pharmacokinetic Modeling After Repeated Administrations of RBP-6000, a New, Subcutaneously Injectable, Long-Acting, Sustained-Release Formulation of Buprenorphine, for the Treatment of Opioid Use Disorder.

RBP-6000 is a novel sustained-release formulation of buprenorphine for the treatment of opioid use disorder, which has been designed for once-monthly (28 days) subcutaneous (SC) injections. A population pharmacokinetic (PK) model was developed to describe the time course of buprenorphine plasma concentrations after repeated SC injections of RBP-6000 at 50 mg, 100 mg, 200 mg, or 300 mg in treatment-seeking opioid-dependent subjects previously on sublingual buprenorphine (Subutex(®) ) treatment. The µ-opioid receptor occupancy was predicted using a previously developed PK/PD Emax model. The results of the population PK analysis jointly with the predicted level of µ-opioid receptor occupancy provided quantitative criteria for clinical dose selection for RBP-6000: the dose of 300 mg every 28 days seems appropriate for immediately achieving an effective exposure after the first SC injection and to maintain effective levels of exposure during chronic treatment. Furthermore, simulations conducted to evaluate the potential impact of a holiday in drug intake indicated that in the unexpected event of a 2-week holiday, levels of µ-opioid receptor occupancy remained consistently above 70% with no significant loss of drug efficacy. This analysis indicated that RBP-6000 has the potential for becoming an effective treatment for opioid-dependent subjects by addressing compliance issues associated with the current once-a-day treatments.

Sustained-Release Buprenorphine (RBP-6000) Blocks the Effects of Opioid Challenge With Hydromorphone in Subjects With Opioid Use Disorder.

A major goal for the treatment of opioid use disorder is to reduce or eliminate the use of illicit opioids. Buprenorphine, a µ-opioid receptor partial agonist and kappa opioid receptor antagonist, is now being developed as a monthly, sustained-release formulation (RBP-6000). The objective of this study was to demonstrate that RBP-6000 blocks the subjective effects and reinforcing efficacy of the µ-opioid receptor agonist hydromorphone (intramuscularly administered) in subjects with moderate or severe opioid use disorder. Subjects were first inducted and dose stabilized on sublingual buprenorphine/naloxone (8-24 mg daily; dose expressed as the buprenorphine component), then received two subcutaneous injections of RBP-6000 (300 mg) on Day 1 and Day 29. Hydromorphone challenges (6 mg, 18 mg or placebo administered in randomized order) occurred on 3 consecutive days of each study week before and after receiving RBP-6000. Subjects reported their responses to each challenge on various 100-mm Visual Analogue Scales (VAS). Subjects also completed a choice task to assess the reinforcing efficacy of each hydromorphone dose relative to money. At baseline, mean "drug liking" VAS scores for hydromorphone 18 mg and 6 mg versus placebo were 61 mm (95% confidence interval, 52.3-68.9) and 45 mm (95% confidence interval, 37.2-53.6), respectively. After 300 mg RBP-6000 was administered, mean VAS score differences from placebo were less than 10 mm through week 12. The reinforcing efficacy of hydromorphone decreased in a parallel manner. This study demonstrated that RBP-6000 at a 300 mg dose provides durable and potent blockade of the subjective effects and reinforcing efficacy of hydromorphone in subjects with moderate or severe opioid use disorder.

Pharmacokinetics of Sublingual Buprenorphine and Naloxone in Subjects with Mild to Severe Hepatic Impairment (Child-Pugh Classes A, B, and C), in Hepatitis C Virus-Seropositive Subjects, and in Healthy Volunteers.

BACKGROUND AND OBJECTIVES: Suboxone(®) is a sublingual tablet of buprenorphine/naloxone, approved for the treatment of opioid dependence. The objective of this study was to quantify the impact of hepatic impairment or hepatitis C virus infection on the pharmacokinetics of buprenorphine or naloxone and their major metabolites. METHODS: Forty-three subjects received a single dose of a Suboxone 2.0/0.5-mg tablet. Blood samples were collected up to 168 h and pharmacokinetic parameters were calculated using non-compartmental analysis. Statistical analysis was performed using analysis of covariance. RESULTS: Pharmacokinetic parameters were derived from 33 subjects. Compared with healthy subjects, for patients with severe hepatic impairment, total and peak exposures increased to 281.4 % [90 % confidence interval 187.1-423.3] and 171.8 % [117.9-250.2] for buprenorphine, 1401.9 % [707.6-2777.5] and 1129.8 % [577.2-2211.4] for naloxone. For moderate hepatic impaired subjects, naloxone total and peak exposure increased to 317.6 % [164.9-611.5] and 270.0  % [141.9-513.9]. For buprenorphine, only total exposure increased to 163.9 % [110.8-242.3]. Changes in maximum observed plasma concentration, area under the plasma concentration-time curve from time zero to time of the last quantifiable concentration, and area under the plasma concentration-time curve from time zero to infinity of buprenorphine or naloxone in subjects with mild hepatic impairment or with hepatitis C virus infection were within twofold of those of healthy subjects. Serious adverse events were not observed. CONCLUSIONS: Severe and moderate hepatic impairment significantly increased exposure of naloxone and to a lesser extent of buprenorphine. Therefore, buprenorphine/naloxone combination products should generally be avoided in patients with severe hepatic impairment and may not be appropriate for patients with moderate hepatic impairment. However, buprenorphine/naloxone products may be used with caution for maintenance treatment in patients with moderate hepatic impairment who have initiated treatment on a buprenorphine product without naloxone [Registered at ClinicalTrials.gov as NCT01846455].

Population pharmacokinetic modeling and simulation to guide dose selection for RBP-7000, a new sustained-release formulation of risperidone.

RBP-7000 is a long-acting formulation of risperidone designed for once-monthly subcutaneous injection for the treatment of schizophrenia. The objective was to estimate clinically effective doses of RBP-7000 based on model simulations and on the comparison with other long-acting injectable antipsychotics. A population pharmacokinetic model of RBP-7000 was developed in 90 clinically stable schizophrenic patients having received single/repeated doses of 60, 90, or 120 mg. Model simulations were conducted to compare active moiety plasma exposure after repeated RBP-7000 administrations to the published data of long-acting risperidone injection (Risperdal® Consta®) at 25 and 50 mg, and of paliperidone palmitate (Invega® Sustenna®) at 50 and 100 mg equivalent paliperidone. Predictions of dopamine D2 receptor occupancy were derived from the simulated active moiety concentrations. Simulations showed similar active moiety plasma exposure at steady-state for 90 mg of RBP-7000 and 25 mg of long-acting risperidone. In comparison to risperidone, RBP-7000 reached effective concentrations immediately after the first administration. RBP-7000 at the doses of 60 and 90 mg provided similar active moiety plasma concentrations at steady-state compared to 50 and 100 mg equivalent paliperidone, respectively. These findings provide guidance for dose selection in Phase III clinical trials and suggest potential benefits for RBP-7000 over competitors.

A randomized, double-blind, placebo-controlled trial of RBP-8000 in cocaine abusers: pharmacokinetic profile of rbp-8000 and cocaine and effects of RBP-8000 on cocaine-induced physiological effects.

RBP-8000 is a double mutant cocaine esterase that rapidly metabolizes cocaine. This study was conducted to assess the pharmacokinetics of cocaine and cocaine-induced physiological effects in the absence (placebo) or presence of RBP-8000. Twenty-nine cocaine abusers were randomized 1:1 (active: placebo) to 4 sequences and 2 treatment periods. In the presence of RBP-8000, cocaine plasma exposures dropped by 90% within 2 min; cocaine-induced physiological effects were significantly reduced with higher extent and faster decrease in systolic blood pressure and pulse rate compared to placebo. This study provides strong evidence in support to use RBP-8000 as a pharmacotherapy for cocaine intoxication.

A population pharmacokinetic and pharmacodynamic modelling approach to support the clinical development of RBP-6000, a new, subcutaneously injectable, long-acting, sustained-release formulation of buprenorphine, for the treatment of opioid dependence.

BACKGROUND AND OBJECTIVES: This study implemented pharmacokinetic/pharmacodynamic modelling to support the clinical development of RBP-6000, a new, long-acting, sustained-release formulation of buprenorphine for the treatment of opioid dependence. Such a formulation could offer advantages over existing buprenorphine pharmacotherapy by improving patient compliance and reducing the diversion of the product. METHODS: A population pharmacokinetic model was developed using 36 opioid-dependent subjects who received single subcutaneous doses of RBP-6000. Another pharmacokinetic/pharmacodynamic model was developed using µ-opioid receptor occupancy (µORO) data to predict efficacy of RBP-6000 after repeated doses. It was also assessed how buprenorphine plasma concentrations were correlated with opioid withdrawal symptoms and hydromorphone agonist blockade data from 15 heroin-dependent subjects. RESULTS: The resulting pharmacokinetic model accurately described buprenorphine and norbuprenorphine plasma concentrations. A saturable maximum effect (E max) model with 0.67 ng/mL effective concentration at 50 % of maximum (EC50) and 91 % E max best described µORO versus buprenorphine plasma concentrations. Linear relationships were found among µORO, withdrawal symptoms and blockade of agonist effects. CONCLUSION: Previously published findings have demonstrated µORO ≥70 % is needed to achieve withdrawal suppression and blockade of opioid agonist subjective effects. Model simulations indicated that a 200 mg RBP-6000 dose should achieve 2­3 ng/mL buprenorphine average concentrations and desired efficacy.

Population pharmacokinetics and prediction of dopamine D2 receptor occupancy after multiple doses of RBP-7000, a new sustained-release formulation of risperidone, in schizophrenia patients on stable oral risperidone treatment.

BACKGROUND AND OBJECTIVES: RBP-7000 is a long-acting formulation of risperidone administered once monthly via subcutaneous (SC) injections for the treatment of schizophrenia. The objectives of the present study were to characterize the pharmacokinetics of RBP-7000 after multiple doses in schizophrenic patients on stable oral risperidone therapy and to evaluate the switch between oral risperidone and SC injections of RBP-7000. METHODS: Data were collected in a phase IIa, open-label, multiple-ascending-dose study where 45 patients clinically stabilized on oral risperidone (2, 3 or 4 mg/day) were switched to receive 60, 90 or 120 mg/month SC injections of RBP-7000, respectively. Patients were thereafter switched back to oral risperidone. An integrated population pharmacokinetic model describing simultaneously risperidone and 9-hydroxyrisperidone after risperidone oral intake and RBP-7000 administration was developed in NON-MEM using 5,232 quantifiable plasma concentrations. Predictions of dopamine D2 receptor occupancy were derived using a previously published model. RESULTS: A two-compartment model with first-order absorption was selected for oral risperidone, while a three-compartment model with first-order absorption and a transit compartment absorption model was selected for RBP-7000. Body mass index was identified as a significant covariate affecting the initial absorption of risperidone following RBP-7000 injection. Steady state was reached after the second or third RBP-7000 injection but plasma concentrations close to steady-state values were obtained right after the first injection when switching from oral risperidone therapy. Predicted dopamine D2 receptor occupancy after repeated doses of 90 and 120 mg showed less fluctuation than after oral risperidone with acceptable ranges for clinical efficacy and a potentially safer profile with respect to extrapyramidal side effects. CONCLUSION: This analysis provided additional insight into the pharmacokinetics of RBP-7000 and for the comparison with oral risperidone treatment. The established model was used to support the design of a planned phase III study.