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  • 11
    Electronic Resource
    Electronic Resource
    Springer
    Journal of pharmacokinetics and pharmacodynamics 25 (1997), S. 255-260 
    ISSN: 1573-8744
    Keywords: clearance estimation ; bolus injection ; arterial sampling ; initial mixing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In conventional pharmacokinetics monotonic decreasing drug disposition curves are usually assumed after bolus injection. For arterial sampling starting about 1 min after dosing the resulting neglect of the initial concentration peak leads to a relative overestimation of clearance which may be approximated by the percentage of systemic drug extraction. This error can be avoided by administering the drug as a short-term infusion.
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    Springer
    Journal of pharmacokinetics and pharmacodynamics 27 (1999), S. 383-396 
    ISSN: 1573-8744
    Keywords: fractal kinetics ; tissue trapping ; anomalous diffusion ; recirculatory model ; amiodarone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Conventional pharmacokinetic (PK) concepts fail to describe the long-term pharmacokinetics of the extremely cationic amphiphilic drug amiodarone. A nonclassical model based on the phenomenon of trapping at tissue binding sites with very long release times is presented, which implies that a volume of distribution and a steady-state level cannot be defined. In agreement with clinical PK data available in the literature, the model well describes not only single-dose disposition curves but also the persistently increasing plasma concentration–time curve during long-term treatment (up to 5 years) and the washout curve following cessation of therapy. The novel aspect is a long-tailed tissue residence time distribution which is incorporated into a recirculatory model leaving the initial distribution process and the clearance concept unchanged. The underlying theoretical approach, which is known as “strange or anomalous” kinetics in physical sciences, and the fractal scaling property of the model may enhance our understanding of the PK of extremely hydrophobic xenobiotics.
    Type of Medium: Electronic Resource
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  • 13
    Electronic Resource
    Electronic Resource
    Springer
    Journal of pharmacokinetics and pharmacodynamics 23 (1995), S. 635-649 
    ISSN: 1573-8744
    Keywords: mean disposition residence time ; relative dispersion ; model misspecification ; triexponential model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A Monte Carlo simulation study was carried out to examine the accuracy of parameters derived from curve moments. Impulse response (IR) and washout (WO) concentration-time curves, based on a triexponential model, were analyzed by numerical integration and regression analysis. Both designs were tested according to their robustness to measurement error and model misspecification. Performance of the methods was judged using the median error (ME) and the median absolute error (MAE) of 1000 simulations. The WO design provided better estimates of mean disposition residence time and worse estimates of the normalized variance of disposition residence times (CV d 2 ) than its rival. At 20% measurement noise, theMAE ofCV d 2 was less than 13%. The WO design was much more robust to model misspecification. Numerical integration performed as good as, or better than, regression analysis. Both methods are very sensitive to tail-area error, meaning that special attention needs to be paid to this aspect of experimental design. This study demonstrates that it is possible to obtain good estimates of higher moment parameters in a well-designed experiment.
    Type of Medium: Electronic Resource
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  • 14
    ISSN: 1573-904X
    Keywords: pharmacokinetics ; indicator dilution ; permeability ; dispersion ; model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 15
    Electronic Resource
    Electronic Resource
    Springer
    Pharmaceutical research 13 (1996), S. 1547-1553 
    ISSN: 1573-904X
    Keywords: pharmacokinetics ; input model ; bioavailability ; absorption rate ; extended release
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. Flexible parametric models describing the input process after extravascular drug administration are needed for the assessment of absorption rate and the use of population methods in bioavailability and bioequivalence studies. Methods. The oral concentration-time curve modeled as the product of the input and disposition function in the Laplace domain was obtained by numerical inversion methods for parameter estimation. The utility of the inverse Gaussian input density was examined using bioavailability data of an extended-release dosage form. Measures of rate of absorption and the cumulative absorbed amount profile were defined in terms of the estimated model parameters. Results. Accurate estimation of absorption parameters was achieved by simultaneous fitting of the extravascular and intravascular data (describing the latter by a triexponential function). The new input function allowed a direct estimation of both extent of absorption and mean absorption time. Conclusions. The findings suggest that the inverse Gaussian density is a useful input function. Its flexibility may reduce the effect of model misspecification in parameter estimation. All parameters can be readily interpreted in terms of the absorption process.
    Type of Medium: Electronic Resource
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  • 16
    ISSN: 0006-3525
    Keywords: RNA recognition ; RNA binding proteins ; arginine-rich motif ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A ubiquitious class of RNA-binding proteins is distinguished by an arginine-rich motif. Such proteins function in transcription, translation, RNA trafficking, and packaging. Peptide models are derived from viral regulatory proteins, including the virulence factors Tat and Rev of mammalian immunodeficiency viruses. Structures of model peptide-RNA complexes exhibit diverse strategies of recognition based in each case on structural transitions. Induced RNA structures contain noncanonical elements such as purine-purine mismatches, base triples, and flipped bases. Such elements enlarge and extend the RNA major groove to create specific peptide-binding pockets and surfaces. The repertoire of bound peptide structures - β-hairpin, α-helix, and helix-bend-helix - reflects the diversity of induced RNA architectures. This repertoire, reminiscent of primordial exon-encoded peptides, may recapitulate early events in the transition between RNA and protein worlds. Peptide-directed changes in modern RNA structures can provide a mechanism of signaling in higher-order RNA-protein assemblies. © 1999 John Wiley & Sons, Inc. Biopoly 48: 167-180, 1998
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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