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Robert R Bies

Publications and source records attributed to Robert R Bies.

16 recordsLinked to original sources
PubMed2006

A model of anticholinergic activity of atypical antipsychotic medications.

BACKGROUND: Atypical antipsychotics clozapine, olanzapine, and quetiapine have significant affinity for the muscarinic receptors in vitro, while aripiprazole, risperidone, and ziprasidone do not. Dissimilarity in binding profiles may contribute to the reported differences in the anticholinergic effects of these antipsychotics. However, it is difficult with the available data to predict the likelihood of anticholinergic effects occurring with various doses of an atypical antipsychotic. METHODS: We developed a model to assess the potential anticholinergic activity (AA) of atypical antipsychotics at therapeutic doses. A radioreceptor assay was used to measure in vitro AA at 6 clinically relevant concentrations of aripiprazole, clozapine, olanzapine, quetiapine, risperidone, and ziprasidone. Using published pharmacokinetic data, in combination with the measured in vitro AA, dose-AA curves were generated. RESULTS: Clozapine, and to a lesser extent olanzapine and quetiapine showed dose-dependent increases in AA. At therapeutic doses, the AA (in pmol/mL of atropine equivalents) was estimated to range from 27-250, 1-15, and 0-5.4 pmol/mL for clozapine, olanzapine, and quetiapine, respectively. Aripiprazole, risperidone, and ziprasidone did not demonstrate AA at any of the concentrations studied. CONCLUSIONS: Therapeutic doses of clozapine, olanzapine, and, to a lesser extent, quetiapine are associated with clinically relevant AA.

Adult↗
PubMed2006

Protective effect of the 20-HETE inhibitor HET0016 on brain damage after temporary focal ischemia.

Cytochrome P450 metabolism of arachidonic acid produces the potent vasoconstrictive metabolite, 20-hydroxyeicosatetraenoic acid (20-HETE). Recent studies have implicated 20-HETE as a vasoconstrictive mediator in hemorrhagic stroke. The purpose of this study was to determine the effect of the 20-HETE inhibitor, HET0016, on lesion volume and cerebral blood flow (CBF) after temporary middle cerebral artery occlusion (MCAO) in rats. Plasma pharmacokinetics and tissue concentrations of HET0016 were determined after a 10 mg/kg intraperitoneal dose. Separate rats were treated with HET0016 or vehicle before 90 mins of MCAO. Lesion volume was assessed by 2,3,5-triphenyl-tetrazolium-chloride and cerebral flow was determined using laser Doppler flow. The effect of MCAO on in vitro microsomal formation of mono-oxygenated arachidonic acid metabolites was also determined. Results show that HET0016 has a short biologic half-life, distributes into the brain, and is associated with a 79.6% reduction in 20-HETE concentration in the cortex. Lesion volume was greatly reduced in HET0016-treated (9.1%+/-4.9%) versus vehicle-treated (57.4%+/-9.8%; n=6; P<0.001) rats. An attenuation of the observed decrease in CBF was observed in HET0016-treated (180 mins 89.2%+/-6.2%; 240 mins 88.1%+/-5.7% of baseline flow) versus vehicle control (180 mins 57.6%+/-19.0%; 240 mins 53.8%+/-20.0% of baseline flow; n=6; P<0.05). Brain cortical microsomal formation rate of 20-HETE was also reduced at 24 h in the ipsilateral hemisphere after MCAO. These data support a significant role for 20-HETE in the pathogenesis of ischemic stroke.

Amidines↗
PubMed2006

Therapeutic hypothermia-induced pharmacokinetic alterations on CYP2E1 chlorzoxazone-mediated metabolism in a cardiac arrest rat model.

OBJECTIVES: Therapeutic hypothermia has demonstrated considerable benefit in patients experiencing cardiac arrest. Despite increasing clinical use, there is a paucity of information regarding the effect of hypothermia on the disposition of medications, specifically cytochrome P450-mediated drug metabolism. The objective was to determine the effect of hypothermia after cardiac arrest on the in vivo kinetics of a cytochrome P450 (CYP2E1) probe drug, chlorzoxazone, and to investigate the mechanism of these alterations. DESIGN: Laboratory investigation. SETTING: University pharmacy school and animal research facility. SUBJECTS: Sixteen male Sprague-Dawley rats. INTERVENTIONS: An asphyxial arrest rat model was used and moderate hypothermia was induced immediately postinsult via surface cooling. Chlorzoxazone was administered as an intravenous bolus, and plasma concentrations were analyzed using high-performance liquid chromatography methods. Protein binding was analyzed using rat control plasma, and Michaelis-Menten enzyme kinetic analysis was performed at 37 degrees C and 30 degrees C using control rat microsomes at varying concentrations of chlorzoxazone. MEASUREMENTS AND MAIN RESULTS: Moderate hypothermia after cardiac arrest in rats markedly decreased the systemic clearance of the CYP2E1 substrate, chlorzoxazone, when compared with normothermia after cardiac arrest, 1.26+/-0.34 mL/min vs. 0.580+/-0.37 mL/min (p<.001). No changes in chlorzoxazone protein binding were observed at 37 degrees C and 30 degrees C, and CYP2E1 enzyme capacity (maximum velocity) was not altered at these different incubation temperatures. However, Michaelis-Menten constant was significantly increased at 30 degrees C (551+/-150 microM) compared with incubations at 37 degrees C (255+/-52 microM, p<.01). CONCLUSIONS: Moderate hypothermia markedly reduces the systemic clearance of chlorzoxazone in cardiac arrest rats. This results from hypothermia-induced decreases in the CYP2E1 enzyme affinity for the substrate chlorzoxazone. This is the first systematic mechanistic investigation of the effect of hypothermia on CYP2E1-mediated metabolism.

Analysis of Variance↗
PubMed2006

Population pharmacokinetics in geriatric psychiatry.

Although geriatric patients are the major recipients of drugs, most research during drug development is conducted in healthy younger adults. Safe and effective drug therapy in the elderly requires an understanding of both drug disposition and response in older individuals. One of the major issues in studying the elderly relates to the ability to study a large number of people in a minimally invasive way. Population pharmacokinetics can be used to model drug concentrations from a large population of sparsely sampled individuals. Population pharmacokinetics characterizes both the interindividual (between-subject) and intraindividual (within-subject) variability, and can identify factors that contribute to pharmacokinetic and pharmacodynamic variability. Population pharmacokinetics can be used to aid in designing large clinical trials by simulating virtual data based on the study design. It can also be used to assess consistency of drug exposure and evaluate its effect on clinical outcome. This article reviews the methods used in pharmacokinetic modeling, as well as providing examples of population pharmacokinetic modeling, highlighting its application to geriatric psychiatry.

Adult↗
PubMed2006

Paroxetine: population pharmacokinetic analysis in late-life depression using sparse concentration sampling.

AIM: To develop a population pharmacokinetic (PK) model using sparse sampling of long-term treatment with paroxetine in elderly depressed subjects, incorporating CYP2D6 genotype as well as other covariates. METHODS: Elderly subjects (age>or=70 years) with nonpsychotic, nonbipolar major depressive disorder from the inpatient and outpatient clinic were treated with paroxetine in a 5-year clinical trial investigating 'Maintenance Therapies in Late-Life Depression' (MTLD-2). Plasma concentrations were collected during regular visits. CYP2D6 genotype was determined using polymerase chain reaction (PCR) for each individual. A nonlinear mixed-effects model was developed with NONMEM for these subjects who received 10-40 mg day-1 of paroxetine during treatment. One- and two-compartment models with linear and nonlinear elimination (Michaelis-Menten) were evaluated. PK parameters as well as interindividual and residual variability were estimated. The effects of age, weight, sex, race and CYP2D6 genotypes on the pharmacokinetics of paroxetine were evaluated. RESULTS: One hundred and seventy-one subjects with a mean age of 77 years (range 69-95) and a mean weight of 72.0 kg (range 32.9-137.0) were enrolled in the MTLD-2 clinical trial. A total of 1970 paroxetine concentrations were available for population PK analyses. Approximately 10 samples were taken per subject. A two-compartment nonlinear PK model with additive and proportional error provided the best base model for description of the data. Weight and CYP2D6 polymorphisms were found to have a significant effect on maximal velocity (Vm), whereas sex had an effect on volume of distribution of the central compartment. The Vm estimates in each of the CYP2D6 phenotypic groups were: 125 microg h-1 in poor metabolizer (n=1), 182 microg h-1 in intermediate metabolizers (n=28), 454 microg h-1 in extensive metabolizers (n=36) and 3670 microg h-1 in ultra-rapid metabolizers (n=5). CONCLUSIONS: The population PK model adequately described paroxetine data in this elderly depressed population. The data indicate that female and male subjects with different CYP2D6 polymorphisms have different elimination rates and therefore may need to be dosed differently based on metabolizer genotype.

Age Factors↗
PubMed2006

Development of a dosage strategy in patients receiving enoxaparin by continuous intravenous infusion using modelling and simulation.

AIM: To develop an appropriate dosing strategy for continuous intravenous infusions (CII) of enoxaparin by minimizing the percentage of steady-state anti-Xa concentration (C(ss)) outside the therapeutic range of 0.5-1.2 IU ml(-1). METHODS: A nonlinear mixed effects model was developed with NONMEM for 48 adult patients who received CII of enoxaparin with infusion durations that ranged from 8 to 894 h at rates between 100 and 1600 IU h(-1). Three hundred and sixty-three anti-Xa concentration measurements were available from patients who received CII. These were combined with 309 anti-Xa concentrations from 35 patients who received subcutaneous enoxaparin. The effects of age, body size, height, sex, creatinine clearance (CrCL) and patient location [intensive care unit (ICU) or general medical unit] on pharmacokinetic (PK) parameters were evaluated. Monte Carlo simulations were used to (i) evaluate covariate effects on C(ss) and (ii) compare the impact of different infusion rates on predicted C(ss). The best dose was selected based on the highest probability that the C(ss) achieved would lie within the therapeutic range. RESULTS: A two-compartment linear model with additive and proportional residual error for general medical unit patients and only a proportional error for patients in ICU provided the best description of the data. Both CrCL and weight were found to affect significantly clearance and volume of distribution of the central compartment, respectively. Simulations suggested that the best doses for patients in the ICU setting were 50 IU kg(-1) per 12 h (4.2 IU kg(-1) h(-1)) if CrCL < 30 ml min(-1); 60 IU kg(-1) per 12 h (5.0 IU kg(-1) h(-1)) if CrCL was 30-50 ml min(-1); and 70 IU kg(-1) per 12 h (5.8 IU kg(-1) h(-1)) if CrCL > 50 ml min(-1). The best doses for patients in the general medical unit were 60 IU kg(-1) per 12 h (5.0 IU kg(-1) h(-1)) if CrCL < 30 ml min(-1); 70 IU kg(-1) per 12 h (5.8 IU kg(-1) h(-1)) if CrCL was 30-50 ml min(-1); and 100 IU kg(-1) per 12 h (8.3 IU kg(-1) h(-1)) if CrCL > 50 ml min(-1). These best doses were selected based on providing the lowest equal probability of either being above or below the therapeutic range and the highest probability that the C(ss) achieved would lie within the therapeutic range. CONCLUSIONS: The dose of enoxaparin should be individualized to the patients' renal function and weight. There is some evidence to support slightly lower doses of CII enoxaparin in patients in the ICU setting.

Adolescent↗
PubMed2006

Relevance of assessing drug concentration exposure in pharmacogenetic and imaging studies.

Pharmacodynamic differences are difficult to interpret without drug concentration data. In particular, variability in drug exposure may confound the interpretation of pharmacogenetic, therapeutic outcome, and neuroimaging studies. Inter-individual variability in concentrations can be quite high due to variable adherence and pharmacokinetics. For example, clearance may be influenced by genetics, drug interactions, age and illness. We review findings that acute responses to selective serotonin reuptake inhibitors can have a concentration-response relationship using positron emission tomography and neuroendocrine measures. We also present preliminary evidence that the concentration-response relationship for paroxetine is influenced by genotypic differences at the serotonin transporter promoter. In large clinical studies, the accurate assessment of drug exposure can be challenging, with several techniques used to assess exposure. Population pharmacokinetics (Pop PK) is a method that is ideally suited for analysing concentration data from large trials because both patient-specific and population parameters can be determined with only a small number of plasma samples per patient. As opposed to relying on prescribed doses or a single trough level, the ability to determine more accurately exposure with Pop PK reduces the heterogeneity introduced by exposure variability. Pop PK hierarchic Bayesian approaches have been effective for characterizing anticonvulsants, antibiotics, antineoplastics and antiarrhythmics. We have recently successfully incorporated these pop PK analyses into routine assessments of elderly patients in clinical trials of selective serotonin reuptake inhibitors (SSRIs) and second generation antipsychotics. For the design and interpretation of neuroimaging, pharmacogenetic, and behavioural studies, the assessment of drug concentration exposure is therefore feasible and has potentially important ramifications.

Clinical Trials as Topic↗
PubMed2006

Endothelin receptor A blockade enhances taxane effects in prostate cancer.

Endothelin (ET) 1 is important in the growth of prostate cancer cells through the activation of the endothelin A (ET(A)) receptor. ET receptor blockade is a new therapeutic target in treating advanced prostate cancer. This study investigates the impact of the combination of the ET(A) antagonist atrasentan (ABT-627) and taxane chemotherapy on prostate cancer cell survival in vitro and on the delay of prostate cancer in a xenograft mouse model. In vitro, PPC-1 cells transfected with an ET(A)-overexpressing vector were treated with ABT-627, paclitaxel/docetaxel, or both. Clonogenic viability and cell death assays were used to determine cell survival and apoptosis, respectively. ABT-627 and docetaxel combination treatment was used in vivo to treat mice with established ET(A)-overexpressing PPC-1 xenograft tumors, and tumor growth rates were assessed. Cell proliferation and vascularity were determined with Ki-67 and CD31 staining, respectively. Cells treated with combination therapy had significantly fewer viable cells and more programmed cell death than cells given monotherapy. Xenograft tumor growth rates were significantly lower in mice treated with combination therapy than in animals given a single agent. Ki-67 immunostaining demonstrated significantly fewer proliferative cells following combination therapy than following monotherapy. This study demonstrates ABT-627 to have additive antitumor effects when used in combination with taxane drugs both in vitro and in vivo.

Animals↗
PubMed2005

Role of endothelin axis in progression to aggressive phenotype of prostate adenocarcinoma.

BACKGROUND: Mitogenic and anti-apoptotic actions of endothelin-1 (ET-1) are mediated through endothelin A (ET(A)) receptors. We investigated endothelin receptor expression in increasingly aggressive phenotype and in vivo effects of combination therapy using ET(A) antagonist with paclitaxel. METHODS: Dunning prostate cancer cells ranged in aggressiveness from non-tumorigenic G, to tumorigenic, non-metastatic AT-1, and to tumorigenic and metastatic MLL. Binding assays were performed alongside Q-PCR to assess receptor density. MLL xenografts were treated with vehicle, atrasentan, paclitaxel, and paclitaxel+atrasentan. RESULTS: Saturation binding assays demonstrated endothelin receptor density of MLL and AT-1 cells seven- and threefold higher than G cells, respectively. Q-PCR showed 9- and 4.5-fold greater ET(A) mRNA expression in MLL and AT-1 than G cells, respectively and no endothelin receptor B (ET(B)) expression. Combination therapy had significant effect on reduction of tumor volume than paclitaxel or atrasentan alone. CONCLUSIONS: ET(A) expression increases in aggressive prostate carcinoma. ET(A) blockade combined with paclitaxel may reduce tumor growth in advanced prostate carcinoma.

Adenocarcinoma↗
PubMed2005

Population pharmacokinetics as a method to detect variable risperidone exposure in patients suffering from dementia with behavioral disturbances.

OBJECTIVE: This study was intended to compare the consistency of risperidone exposure in patients who have dementia and behavioral disturbances treated in a psychiatric hospital versus a community care setting. METHODS: Population pharmacokinetic modeling was used to assess the consistency of risperidone exposure in Alzheimer's disease patients with agitation. The ratio of predicted to observed drug concentrations (Cpred/Cobs) derived from this model was used to compare exposure in the inpatient versus long-term/home care settings using both the mean and the variance of this term across groups. RESULTS: The modeled Cpred/Cobs ratios had a much higher within-subject variance in the inpatients than in the community care patients (117.03% vs 72.35%; P < 0.001). The central tendencies of the Cpred/Cobs ratios across the 2 groups were not significantly different. CONCLUSIONS: Exposure to risperidone was more variable in a psychiatric hospital than in a community care setting. Future research may help to identify the specific contributors to the increased variance observed in this pilot study.

Aged↗
PubMed2004

Population pharmacokinetic analysis of 17-(allylamino)-17-demethoxygeldanamycin (17AAG) in adult patients with advanced malignancies.

PURPOSE: 17-(Allylamino)-17-demethoxygeldanamycin (17AAG) is a novel anticancer agent in clinical development. The objectives of this study were to develop a population pharmacokinetic model for 17AAG and its major metabolite, 17AG, and to investigate influences of patient characteristics and biochemical markers on pharmacokinetic parameters estimated for 17AAG and 17AG. EXPERIMENTAL DESIGN: In a phase I clinical study, 17AAG was administered by intravenous infusion to 43 patients with refractory, advanced malignancies. Plasma concentrations of 17AAG and 17AG were determined by high-performance liquid chromatography. Plasma concentration vs time data were modeled using NONMEM. Nine covariates (age, sex, performance status, weight, height, body surface area, AST, bilirubin and serum creatinine) were investigated for their influences on individual pharmacokinetic parameters. RESULTS: Plasma concentration vs time data were best described by a two-compartment model for 17AAG and a one-compartment model for 17AG. Volumes of distribution were 24.2 and 89.6 l for 17AAG. Total elimination clearances were 26.7 and 21.3 l/h for 17AAG and 17AG, respectively. Both fixed and random effects pharmacokinetic parameters were well estimated. None of the covariates explained the interindividual variability in 17AAG and 17AG pharmacokinetic parameters or improved the fit of the model based on objective function changes. CONCLUSIONS: A population pharmacokinetic model was developed to describe 17AAG and 17AG population pharmacokinetic parameters and interindividual variabilities. There were substantial interindividual variabilities in 17AAG and 17AG pharmacokinetic parameters despite BSA-normalized dosing.

Adult↗
PubMed2004

Utility of sparse concentration sampling for citalopram in elderly clinical trial subjects.

The objective of this study was to evaluate whether the disposition of the selective serotonin reuptake inhibitor, citalopram, could be robustly captured using 1 to 2 concentration samples per subject in 106 patients participating in 2 clinical trials. Nonlinear mixed-effects modeling was used to evaluate the pharmacokinetic parameters describing citalopram's disposition. Both a prior established 2-compartment model and a de novo 1-compartment pharmacokinetic model were used. Covariates assessed were concomitant medications, race, sex, age (22-93 years), and weight. Covariates affecting disposition were assessed separately and then combined in a stepwise manner. Pharmacokinetic characteristics of citalopram were well captured using this sparse sampling design. Two covariates (age and weight) had a significant effect on the clearance and volume of distribution in both the 1- and 2-compartment pharmacokinetic models. Clearance decreased 0.23 L/h for every year of age and increased 0.14 L/h per kilogram body weight. It was concluded that hyper-sparse sampling designs are adequate to support population pharmacokinetic analysis in clinically treated populations. This is particularly valuable for populations such as the elderly, who are not typically available for pharmacokinetic studies.

Administration, Oral↗
PubMed2003

Impaired 6-hydroxychlorzoxazone elimination in patients with kidney disease: Implication for cytochrome P450 2E1 pharmacogenetic studies.

OBJECTIVE: The purposes of this study were (1) to describe the disposition of chlorzoxazone and 6-hydroxychlorzoxazone in patients with kidney disease, (2) to develop a population pharmacokinetic model including covariates that may influence the pharmacokinetic variability of both compounds, and (3) to examine the effect of covariates on the chlorzoxazone metabolic ratio. METHODS: Twenty-one subjects received a single oral dose of chlorzoxazone, 250 mg, and plasma and urine samples were collected for up to 120 hours. The impact of creatinine clearance (CL(cr)), age, and weight on chlorzoxazone and 6-hydroxychlorzoxazone clearance terms was assessed with NONMEM software (v.5, level 1.1; Globomax LLC, Hanover, Md) by use of a stepwise backward-elimination technique and the likelihood ratio test. RESULTS: A linear model with first-order absorption for chlorzoxazone and first-order formation for 6-hydroxychlorzoxazone simultaneously described the disposition of both compounds. Weight was a significant predictor of 6-hydroxychlorzoxazone formation clearance and other, unaccounted for clearance of chlorzoxazone, whereas CL(cr) was a significant predictor of 6-hydroxychlorzoxazone renal clearance. No relationship between CL(cr) and formation clearance was observed. The 6-hydroxychlorzoxazone area under the plasma concentration-time curve was inversely related to CL(cr), even within the range of normal renal function, resulting in chlorzoxazone metabolic ratio values that were substantially higher in subjects with kidney disease. Both the experimental data and model-based Monte Carlo simulations revealed greatly increased chlorzoxazone metabolic ratio values when CL(cr) was low and weight was high. CONCLUSIONS: Although cytochrome P450 (CYP) 2E1 activity, as estimated by 6-hydroxychlorzoxazone formation clearance, was not affected by kidney disease, the chlorzoxazone metabolic ratio was substantially elevated in these subjects. The results of this study show that the commonly used plasma-based chlorzoxazone metabolic ratio is dependent on renal function and, therefore, does not provide a reliable index of CYP2E1-mediated metabolism.

Adult↗
PubMed2003

Gender differences in the pharmacokinetics and pharmacodynamics of antidepressants.

The paucity of research on gender-specific differences related to antidepressants is a significant public health deficiency and represents an understudied and necessary research area. The current data suggest that the pharmacokinetics of antidepressant drugs can be substantially different between men and women as a result of differences in both the metabolizing enzymes and the expression of P-glycoprotein MDR1. The data suggest that different pharmacodynamic responses are observed between premenopausal women and men. Women are more likely to respond better to an MAOI antidepressant compared to men. In addition, men respond better to TCAs than women in this age group, but differences diminish after menopause. Given the evidence of distinct gender-specific differences, it is critical that these differences be addressed more widely in research evaluating the administration of antidepressants in women.

Antidepressive Agents↗
PubMedDate not supplied

Evaluating the consistency of pharmacotherapy exposure by use of state-of-the-art techniques.

OBJECTIVE: The authors examine the usefulness of population pharmacokinetics coupled with electronic compliance monitoring in evaluating consistency of exposure to pharmacotherapy. Adherence to pharmacotherapy can have a significant impact on drug response, especially in the treatment of schizophrenia and depression. Previous studies evaluating antipsychotics identified schizophrenic individuals with poor pharmacotherapy adherence as having a higher risk of rehospitalization. Other investigators have shown a relationship between pattern of taking selective serotonin-reuptake inhibitors (SSRIs) and probability of a positive outcome. Therefore, it is important to measure adherence patterns in clinical trials evaluating these treatments and to incorporate this information into the research findings. METHODS: Two multisite trials with atypical antipsychotics and antidepressants were simulated to evaluate, by use of population pharmacokinetic methods, the impact of electronic monitoring on measuring consistency of exposure to pharmacotherapy. One of the trials is ongoing and evaluates exposure to atypical antipsychotics, and the other is a proposed trial that examines exposure to an SSRI. RESULTS: Erratic exposure patterns were detected with population pharmacokinetic techniques in the absence of Electronic Medication Event Monitoring (MEMS) data. In our simulations, the use of electronic monitoring improved the identification of atypical exposure by population pharmacokinetics both for the atypical antipsychotics and SSRIs. CONCLUSION: Our simulations demonstrate the potential usefulness of the combination of population pharmacokinetics with electronic monitoring as a robust method for accurately and precisely capturing both magnitude and consistency of pharmacotherapy exposure.

Antidepressive Agents, Second-Generation↗