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  • 1980-1984  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    European journal of clinical pharmacology 23 (1982), S. 445-451 
    ISSN: 1432-1041
    Keywords: mexiletine ; population pharmacokinetics ; NONMEM ; pharmacokinetic analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary A new data analysis approach, NONMEM, proposed by Sheiner and Beal, has been employed to estimate the population pharmacokinetic parameters of oral mexiletine in patients treated for arrhythmias. 452 serum concentration measurements in 58 patients were available for analysis. 27 patients had congestive heart failure and 8 had abnormal liver function tests at the time of the study. The population averages of the pharmacokinetic parameters and their interindividual variability were: oral total body clearance (Cl) 0.38 l/h/kg±43% (C. V.), apparent volume of distribution (Vd) 5.3 l/kg±40%, absorption rate constant 3.1 h−1±205%, absorption time-lag 0.3 h. Congestive heart failure and sex did not show a significant effect on Cl and Vd; the number of patients with severe liver function impairment was too small for a definite conclusion. Normalizing Cl and Vd for body weight significantly decreased their interindividual variability. Based on these results, a dosage regimen is recommended which is expected to produce a “therapeutic” serum concentration (0.8–2 mg/l) in over 60% of patients. Because of its unique features, which allow estimation of pharmacokinetic parameters and their variability from fragmentary patient data, the NONMEM system has great potential applicability to clinical pharmacokinetic studies.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Precipitation of Ca oxalate in the sarcoplasmic reticulum of chemically skinned rabbit psoas fibers caused an increase in light scattering which was proportional to the amount of Ca accumulated per unit fiber volume. The increase in scattering was used to measure net accumulation rates and steady-state Ca capacities of the sarcoplasmic reticulum in single fibers. The data obtained were qualitatively and quantitatively similar to those reported for isolated vesicle preparations. Under conditions in which Ca was not depleted from the medium, Ca accumulation was linear with time over much of its course. Steady-state capacities were independent of the Ca concentration; uptake rates were half-maximal at 0.5 μm Ca++ and saturated above about 1.0 μm. Both rate and capacity varied with the oxalate concentration, being maximal at oxalate concentrations 〉=5mm and decreasing in proportion to one another at lower concentrations, with a threshold near 0.25mm. At the lower loads, electron micrographs showed many sarcoplasmic reticulum elements empty of precipitate alongside others that were full, whereas virtually all were filled in maximally loaded fibers. These data indicate that the Ca oxalate capacity of each fiber varies with the number and volume of elements in which Ca oxalate crystals can form at a given oxalate concentration, and that individual regions of the sarcoplasmic reticulum within each sarcomere differ in their ability to support Ca oxalate precipitation. Our working hypothesis is that this range in ability to form Ca oxalate crystals involves differences in ability to accumulate and retain ionized Ca inside the sarcoplasmic reticulum.
    Type of Medium: Electronic Resource
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