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  • ENERGY PRODUCTION AND CONVERSION  (5)
  • extent of absorption  (2)
  • human  (2)
  • 1
    Digitale Medien
    Digitale Medien
    Evaluation of Bioequivalence of Highly Variable Drugs Using Clinical Trial Simulations. II: Comparison of Single and Multiple-Dose Trials Using AUC and Cmax (1998)
    Springer
    Pharmaceutical research 15 (1998), S. 98-104 
    Details
    ISSN: 1573-904X
    Schlagwort(e): Bioequivalence ; highly variable drugs ; extent of absorption ; rate of absorption ; Monte Carlo simulations ; single-dose ; multiple-dose bioequivalence trial
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Purpose. Evaluating of the effects of high intrasubject variability in clearance (CL) and volume of distribution (V), on 90% confidence intervals (CIs) for AUC (Area Under the concentration Curve) in single and multiple-dose bioequivalence studies. The main methodology was Monte Carlo simulation, and we also used deterministic simulation, and examination of clinical trials. The results are compared with those previously observed for Cmax (maximum concentration.) Methods. The time course of drug concentration in plasma was simulated using a one-compartment model with log-normal statistical distributions of intersubject and intrasubject variabilities in the pharmacokinetic parameters. Both immediate-release and prolonged-release products were simulated using several levels of intrasubject variability in single-dose and multiple-dose studies. Simulations of 2000 clinical bioequivalence trials per condition (138 conditions) with 30 subjects in each crossover trial were carried out. Simulated data were compared with data from actual bioequivalence trials. Results. The current simulations for AUC show similar probabilities of failure for single-dose and multiple-dose bioequivalence studies, even with differences in the rate of absorption or fraction absorbed. AUC values from prolonged-release scenario studies are more sensitive to changes in the first order absorption rate constant ka, and to variability in CL and V than AUC from studies of immediate-release studies. Conclusions. We showed that multiple-dose designs for highly variable drugs do not always reduce intrasubject variability in either AUC or Cmax, although the behavior of AUC differs from Cmax. Single dose AUC to the last quantifiable concentration was more reliable than either single dose AUC extrapolated to infinity, or multiple dose AUC during a steady-state interval. Multiple-dose designs may not be the best solution for assessing bioequivalence of highly variable drugs.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1011961006297
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Bioequivalence of Methylphenidate Immediate-Release Tablets Using a Replicated Study Design to Characterize Intrasubject Variability (2000)
    Springer
    Pharmaceutical research 17 (2000), S. 381-384 
    Details
    ISSN: 1573-904X
    Schlagwort(e): methylphenidate ; average bioequivalence ; individual bioequivalence ; human ; pharmacokinetics ; replicated design
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Purpose. To determine the relative bioavailability of two marketed,immediate-release methylphenidate tablets. The study used a replicatedstudy design to characterize intrasubject variability, and determinebioequivalence using both average and individual bioequivalencecriteria. Methods. A replicated crossover design was employed using 20subjects. Each subject received a single 20 mg dose of the reference tableton two occasions and two doses of the test tablet on two occasions.Blood samples were obtained for 10 hr after dosing, and plasma wasassayed for methylphenidate by GC/MS. Results. The test product was more rapidly dissolved in vitro and morerapidly absorbed in vivo than the reference product. The mean Cmaxand AUC(0 − ∞) differed by 11% and 9%, respectively. Using anaverage bioequivalence criterion, the 90% confidence limits for theLn-transformed Cmax and AUC(0 − ∞), comparing the two replicatesof the test to the reference product, fell within the acceptable range of80–125%. Using an individual bioequivalence criterion the test productfailed to demonstrate equivalence in Cmax to the reference product. Conclusions. The test and reference tablets were bioequivalent usingan average bioequivalence criterion. The intrasubject variability of thegeneric product was greater and the subject-by-formulation interactionvariance was borderline high. For these reasons, the test tablets werenot individually bioequivalent to the reference tablets.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1007560500301
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    The Relative Bioavailability and In Vivo-In Vitro Correlations for Four Marketed Carbamazepine Tablets (1998)
    Springer
    Pharmaceutical research 15 (1998), S. 1787-1791 
    Details
    ISSN: 1573-904X
    Schlagwort(e): carbamazepine ; human ; bioavailability: gender, dissolution
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Purpose. To determine if three marketed generic carbamazepine tablets were bioequivalent to the innovator formulation, as well as to each other. In addition, to examine in vivo-in vitro relationships among the four formulations. Methods. Each formulation was given as a single dose to 18 healthy male and female subjects using a crossover design. Blood samples were collected for 169 hr. Carbamazepine was assayed by HPLC with UV detection. Results.In vivo fraction absorbed plots indicated that the three generic formulations were absorbed more rapidly than the innovator product, and the mean time of maximum plasma concentration was 6−7 hr sooner for the generic formulations. The mean maximum plasma concentration ranged from 17−19 percent higher for the generic products compared to the innovator, and the 90% confidence limits for Cmax data ranged from 111% to 126%. The mean AUC(0−∞) for the generic products ranged from 101−104% compared to the innovator, and the confidence limits for AUC ranged from 97−108%. Conclusions. The generic products were all more rapidly absorbed than the innovator, but simulations of steady-state concentrations indicated that it would be unlikely that these differences would have any significant clinical effect. An excellent association was seen between the Cmax and the percent of drug dissolved in vitro. The correlation was used to accurately predict the Cmax of four other 200 mg tablets evaluated in an earlier study.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1011929300613
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Bioequivalence: Performance of Several Measures of Extent of Absorption (1994)
    Springer
    Pharmaceutical research 11 (1994), S. 715-722 
    Details
    ISSN: 1573-904X
    Schlagwort(e): pharmacokinetics ; bioequivalence ; extent of absorption ; power analysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The determination of the area under the concentration–time curve (AUC) is the method most commonly used by regulatory agencies to assess extent of drug absorption after single-dose administration of oral products. Using simulations, several approaches toward measuring the actual area, in whole or part, were tested. In addition, the performance of the peak concentration (C max), usually taken as a measure of the rate of absorption was assessed evaluating extent. Model scenarios for drugs with typical mean characteristics and statistical distributions were investigated. Using different kinetic models of disposition, the time course of the drug concentration in plasma was simulated. Intraindividual and interindividual variability and assay error were modeled using Monte Carlo techniques. The accuracy, precision, and ease of use of the various measures of extent were evaluated, and statistical power analyses were performed. Among the measures tested, the most reliable were the AUC computed up to the time of the last quantifiable concentration, without extrapolation, and C max. However, being also sensitive to rate, C max as a measure of extent is of limited potential.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1018932430733
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  • 5
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    Unbekannt
    Reversible thermodynamic cycle for AMTEC power conversion (1992)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The thermodynamic cycle appropriate to an AMTEC (alkali metal thermal-to-electric converter) cell is discussed for both liquid- and vapor-fed modes of operation, under the assumption that all processes can be performed reversibly. In the liquid-fed mode, the reversible efficiency is greater than 89.6 percent of Carnot efficiency for heat input and rejection temperatures (900-1300 K and 400-800 K, respectively) typical of practical devices. Vapor-fed cells can approach the efficiency of liquid-fed cells. Quantitative estimates confirm that the efficiency is insensitive to either the work required to pressurize the sodium liquid or the details of the state changes associated with cooling the low pressure sodium gas to the heat rejection temperature.
    Schlagwort(e): ENERGY PRODUCTION AND CONVERSION
    Materialart: In: IECEC '92; Proceedings of the 27th Intersociety Energy Conversion Engineering Conference, San Diego, CA, Aug. 3-7, 1992. Vol. 3 (A93-25851 09-44); p. 3.123-3.127.
    Format: text
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  • 6
    facet.materialart.
    Unbekannt
    Performance projections of alternative AMTEC systems and devices (1991)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-08-28
    Beschreibung: The alkali metal thermoelectric converted (AMTEC) converts heat to electrical power without moving parts. Attention is presently given to two AMTEC devices that have been optimized for conversion efficiencies of the order of 30 percent or more at 1100 K, in conjunction with high volumetric power densities. A 'tube-bundle' AMTEC configuration yields a peak power of 426 W/l; a flat-plate AMTEC system yields 2.4 W/l.
    Schlagwort(e): ENERGY PRODUCTION AND CONVERSION
    Materialart: In: Space nuclear power systems; Proceedings of the 8th Symposium, Albuquerque, NM, Jan. 6-10, 1991. Pt. 1 (A93-13751 03-20); p. 472-481.
    Format: text
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    NASA TECHNICAL REPORTS
  • 7
    facet.materialart.
    Unbekannt
    Alkali metal thermoelectric converter (AMTEC) electrode lifetime studies (1987)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: Experimental studies are being conducted at JPL to identify long life, high area power density electrodes for AMTEC. Power versus time measurements are being made in a demountable electrode test cell and, for longer term experiments, a self-contained recirculating cell. The experimental apparatus and procedures are described in detail. The results show that thin film molybdenum electrodes can be designed to produce power near 0.5 W/sq cm for over two hundred hours. Also, platinum/tungsten electrodes exhibit power densities that are stable near 0.5 W/sq cm. If the performance of these electrodes is verified for longer periods (thousands of hours), then practical AMTEC systems will be possible.
    Schlagwort(e): ENERGY PRODUCTION AND CONVERSION
    Materialart: IECEC ''87; Aug 10, 1987 - Aug 14, 1987; Philadelphia, PA; United States
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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    NASA TECHNICAL REPORTS
  • 8
    facet.materialart.
    Unbekannt
    AMTEC system performance studies using the detailed electrode kinetic and transport model (1992)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-08-27
    Beschreibung: A detailed electrochemical model of the alkali metal thermoelectric converter (AMTEC) electrode and current collector grid has been developed recently. Comparative evaluations of the resulting differences in model predictions reveal that the new detailed model predicts up to 50 percent higher electrode power densities at condenser operating temperatures above 600 K. The new model, with experimentally determined parameters, was used to recalculate the projected system performance of previously reported 1- and 100-kWe AMTEC space power systems that had incorporated earlier electrolyte/electrode models. It was found that when the detailed model was used to determine the electrode power densities, enhanced specific power and efficiencies are predicted.
    Schlagwort(e): ENERGY PRODUCTION AND CONVERSION
    Materialart: In: Space nuclear power systems 1989; Proceedings of the 6th Symposium, Albuquerque, NM, Jan. 8-12, 1989. Vol. 2 (A93-20752 06-20); p. 373-378.
    Format: text
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    NASA TECHNICAL REPORTS
  • 9
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    Unbekannt
    AMTEC cell testing, optimization of rhodium/tungsten electrodes, and tests of other components (1991)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-08-27
    Beschreibung: Electrodes, current collectors, ceramic to metal braze seals, and metallic components exposed to the high 'hot side' temperatures and sodium liquid and vapor environment have been tested and evaluated in laboratory cells running for hundreds of hours at 1100-1200 K. Rhodium/tungsten electrodes have been selected as the optimum electrodes based on performance parameters and durability. Current collectors have been evaluated under simulated and actual operating conditions. The microscopic effects of metal migration between electrode and current collector alloys as well as their thermal and electrical properties determined the suitability of current collector and lead materials. Braze seals suitable for long term application to AMTEC devices are being developed.
    Schlagwort(e): ENERGY PRODUCTION AND CONVERSION
    Materialart: In: Space nuclear power systems; Proceedings of the 8th Symposium, Albuquerque, NM, Jan. 6-10, 1991. Pt. 1 (A93-13751 03-20); p. 464-471.
    Format: text
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