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  • ENERGY PRODUCTION AND CONVERSION  (5)
  • bioequivalence  (3)
  • Electronics and Electrical Engineering  (2)
  • extent of absorption  (2)
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  • 1
    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
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    ISSN: 1573-904X
    Schlagwort(e): absorption rate ; bioequivalence ; Cmax/AUClqc ; Cmax/ AUC ; exposure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Purpose. The goals were to evaluate the usefulness of Cmax/AUClqc, ratio of the maximum plasma drug concentration to the area under the plasma concentration-time curve to the time of the last quantifiable concentration, in bioequivalence testing and to explore the use of exposure as a replacement for the concepts of rate and extent of drug absorption. Methods. The bioequivalence of products differing in both rate (ka) and extent (F) of absorption was assessed under conditions similar to those encountered in a typical trial. A one-compartment model drug with first-order absorption (rate constant = ka) and elimination was used. Variability was introduced in all model parameters using Monte Carlo techniques. The results were expressed in terms of the probability of declaring bioequivalence in a cross-over trial with 24 subjects using Cmax/AUClqc, AUClqc, and Cmax as bioequivalence measures. Results. The outcome of a bioequivalence trial was shown to depend on the measure. Cmax/AUClqc reflected changes in ka, but not in F. AUClqc showed dependence on F, but virtually no dependence on ka. For Cmax, a 3- to 4-fold increase in ka and a concomittant 20% decrease in F, as well as corresponding changes in the opposite directions, resulted in bioequivalent outcomes. Conclusions. It was concluded that use of Cmax/AUClqc should be discouraged and that defining bioequivalence in terms of rate and extent of absorption has major problems. The goal of bioequivalence trials should be to assure that the shape of the concentration-time curve of the test product is sufficiently similar to that of the reference product. To this end, the use of “exposure” rather than “rate and extent of absorption” concepts is encouraged.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    ISSN: 1573-904X
    Schlagwort(e): nitroglycerin ; nitroglycerin metabolites ; bioequivalence ; transdermal drug delivery
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract We recently compared plasma concentrations of nitroglycerin and its two dinitrate metabolites in 16 healthy male subjects after application of two controlled-release transdermal formulations of the drug. Analysis of the resulting plasma concentration–time curves indicated that the two formulations did not produce equivalent concentrations of parent drug or either of the dinitrate metabolites during the initial period of dosing. In addition, both formulations produced concentrations of the two dinitrate metabolites that exceeded the concentration of the parent drug by severalfold. Even if the pharmacologic effect of the dinitrate metabolites is low compared to that of nitroglycerin, these higher concentrations may contribute to the effect of nitroglycerin. Scrutiny of the ratio of 1,2-glyceryl dinitrate to 1,3-glyceryl dinitrate in the 16 subjects confirmed previous observations that preferential formation of the 1,2-glycerol dinitrate metabolite may occur depending on the route of administration. This ratio may thus be indicative of the bioavailability of nitroglycerin following transdermal application. Additional data suggesting racial differences in nitroglycerin absorption after transdermal application are presented.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    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
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    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
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    facet.materialart.
    Unbekannt
    In:  CASI
    Publikationsdatum: 2019-08-17
    Beschreibung: An electrode having higher power output is formed of an open mesh current collector such as expanded nickel covering an electrode film applied to a tube of beta-alumina solid electrolyte (BASE). A plurality of cross-members such as spaced, parallel loops of molybdenum metal wire surround the BASE tube. The loops are electrically connected by a bus wire. As the AMTEC cell is heated, the grid of expanded nickel expands more than the BASE tube and the surrounding loop of wire and become diffusion welded to the electrode film and to the wire loops.
    Schlagwort(e): Electronics and Electrical Engineering
    Format: application/pdf
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    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
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    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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  • 9
    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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  • 10
    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
    Standort Signatur Erwartet Verfügbarkeit
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