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  • intravenous  (2)
  • area under the plasma concentration-time curve  (1)
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  • 1
    ISSN: 1573-8744
    Keywords: quinidine ; pharmacokinetic parameters ; assay methods ; assay specificity ; area under the plasma concentration-time curve ; bioavailability ; clearance ; therapeutic window
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Previously published estimates of pharmacokinetic characteristics of quinidine can be shown to be dependent on whether the investigators have used analytical methods which are specific for quinidine. Areas under the plasma concentration-time curve and peak plasma concentrations after administration of the drug were higher and clearance values consequently lower in studies utilizing nonspecific assays unable to distinguish quinidine from its metabolites. The error introduced is larger after oral administration as a result of marked first-pass metabolism of quinidine. The absolute oral bioavailabilities from pharmaceutical preparations might therefore be estimated higher in studies with assays including metabolites in the determination. Although the pharmacodynamic response to quinidine is related to the plasma concentration, the therapeutic window of drug concentrations has been defined only using nonspecific assays. In light of the availability of newly developed specific assays, redefinition of the range of therapeutic plasma concentrations is opportune.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-8744
    Keywords: theophylline ; absorption ; tablets ; oral solution ; intravenous ; bioavailability criteria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The biovailability of theophylline from alcoholic and aqueous oral solutions was compared to that from an intravenous dose in 12 normal adults. The alcoholic elixir surprisingly gave rise to a significantly greater (114 ±14%, mean±sd amount absorbed than did the intravenous dose. The aqueous solution (99±8%) and intravenous dose were statistically indistinguishable in this respect, and, furthermore, the extent of absorption from a 300-mg dose of the aqueous solution was 99±10% of that from a 500-mg dose, and not statistically different. The aqueous solution was thus employed in three subsequent studies as a standard with which to compare 13 different types of theophylline tablets, all marketed in the United States. Of the 13 tablets, eight showed bioavailability statistically distinguishable from that of the standard. Nevertheless, for only two tablets could it be claimed with 95% confidence that the bioavailability was less than 95%. For none can it be stated at this confidence level that the bioavailability is less than 90%. Bioavailability studies should include criteria of clinical significance in addition to criteria of statistical significance. Contrary to the usual rationale behind choice of a bioavailability standard, nine of the 12 uncoated tablets appeared to allow more rapid absorption of theophylline than did the standard oral solution, an aqueous syrup. Increasing the dose of syrup decreased the rate of theophylline absorption. Orally administered drug solutions may have properties more absorption rate limiting than the disintegration of many brands of tablet.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-8744
    Keywords: quinidine ; pharmacokinetic models ; curve fitting ; bioavalability ; absorption ; humans ; plasma ; intravenous ; oral
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Parameters describing disposition and absolute oral bioavailability of quinidine were determined in ten normal male volunteers using a specific assay. Various models were compared for their ability to describe the experimental data. An intravenous quinidine gluconate and an oral quinidine sulfate solution were administered (3.74 mg/kg quinidine base). In three subjects the intravenous and oral studies were repeated. One-, two-, and three-compartment models with zeroand first-order input were fitted to the plasma concentrations. The selection of the best model was made by the Akaike information criterion and by eye. After intravenous administration, plasma concentrationtime curves could be adequately described by a twocompartment model. Mean disposition constants (±SD) were obtained from individualized fits (V1: 0.398 ±0.336 liter/kg, Vdarea: 2.53±0.72 liter/kg, α: 0.316±0.294 min−1, Β: 0.00204 ± 0.00262 min1, k2: 0.0305 ±0.010 min−1). A clearance of 4.9 ±1.5 ml/min/kg was observed. After oral administration, threecompartment models were needed to describe the observed data in some cases. Absorption was in most cases best described by a zeroorder rather than by a firstorder process. The time to peak concentration varied from 23 to 121 min, the lag time was always less than 3 min, and the mean elimination rate constant was 0.00171 min−1. The mean oral bioavailability of quinidine was 0.70 ±0.17.
    Type of Medium: Electronic Resource
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