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  • 1
    Electronic Resource
    Electronic Resource
    Mean residence time for drugs subject to enterohepatic cycling (1989)
    Springer
    Journal of pharmacokinetics and pharmacodynamics 17 (1989), S. 327-345 
    Details
    ISSN: 1573-8744
    Keywords: enterohepatic recirculation ; pharmacokinetics ; hepatic extraction ; area under the first moment curve ; model ; bile ; mean residence time ; mean absorption time ; formulations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A physiologically realistic model of enterohepatic cycling (EHC) which includes separate liver and gallbladder compartments, discontinuous gallbladder emptying and first-order absorption from both an oral formulation and secreted bile (ka po and ka b, respectively) has been developed. The effect of EHC on area under the first-moment curve (AUMC) of drug concentration in plasma and on parameters derived from the AUMC was investigated. Unlike AUC, AUMC is dependent on the time and time-course of gallbladder emptying, increasing as the interval between gallbladder emptying increases. Consequently, mean residence time (MRT) is also a time-dependent parameter. Analytical solutions for MRTiv and MRTpo were derived. Mean absorption time (MAT = MRTpo — MRTivj is also time-dependent, contrary to findings previously published for a model of EHC with a continuous time lag. MAT is also dependent on k a po , k a b and the hepatic extraction ratio. The difference between MRT po s two formulations with unequal k a po values may deviate from the difference in the inverse of their absorption rate constants. Implications for design and interpretation of pharmacokinetic studies include (i) MAT values may be dominated by the time-course of recycling rather than the time-course of the initial absorption, depending on the extent of EHC and (ii) the unpredictable nature of the time of gallbladder emptying will contribute to intrasubject variability in derived parameters during crossover studies. Knowledge of the extent of EHC is invaluable in deciding whether modification of the in vitro release characteristics of an oral formulation will have any effect on the overall time-course of absorption in vivo. Techniques to monitor or control gallbladder emptying may be helpful for reducing variability in pharmaco-kinetic studies for compounds which are extensively cycled in bile.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01061900
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  • 2
    Electronic Resource
    Electronic Resource
    Kinetics of drug displacement interactions (1981)
    Springer
    Journal of pharmacokinetics and pharmacodynamics 9 (1981), S. 181-190 
    Details
    ISSN: 1573-8744
    Keywords: drug displacement ; interaction ; kinetics ; simple model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A simple model simulating the kinetics of drug displacement kinetics is investigated. It is demonstrated that for highly bound, lowly cleared drugs, displacement interactions are transitory. Consequently, the kinetics of the interaction have to be considered as well as the in vitrointeraction. It is possible to have a significant in vitrodisplacement interaction with no in vivocounterpart. Methods of moderating drug displacement by adjusting the rate and the timing of administration of the displacing agent are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01068081
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  • 3
    Electronic Resource
    Electronic Resource
    Estimation of area under the curve for drugs subject to enterohepatic cycling (1985)
    Springer
    Journal of pharmacokinetics and pharmacodynamics 13 (1985), S. 589-608 
    Details
    ISSN: 1573-8744
    Keywords: enterohepatic recirculation ; pharmacokinetics ; hepatic extraction ; area under the curve ; model ; bile ; simulated concentration-time curves
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A physiologically realistic model is used to provide insight into the design of sampling protocols for accurate determination of AUC(0– ∞) for drugs subject to enterohepatic cycling. Through simulation of plasma concentration- time curves for such drugs it is found that (1) more than one peak is predicted after oral and intravenous administration of a single dose of drug, (2) the relative magnitude of peaks is dependent on the hepatic extraction ratio for both oral and intravenous drug administration, (3) the percent of the AUC(0– ∞) in later time intervals is also a function of the hepatic extraction ratio, and (4) present methods for the design of sampling protocols may not provide accurate estimates of AUC(0– ∞) (especially for highly extracted drugs), because (a) peaks are only evident at later times after intravenous administration when plasma sampling is less frequent, (b) much of the area occurs at later times, and (c) the amount of drug in the sampling compartment after oral administration is much lower than that after intravenous administration of drug and could be incorrectly interpreted as low bioavailability if sampling is not carried out for a long period of time. The types of oral and intravenous profiles predicted for highly extracted drugs are exemplified by data for naltrexone in the monkey.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01058903
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  • 4
    Electronic Resource
    Electronic Resource
    Pharmacokinetics of lidocaine and its deethylated metabolite: Dose and time dependency studies in man (1982)
    Springer
    Journal of pharmacokinetics and pharmacodynamics 10 (1982), S. 265-281 
    Details
    ISSN: 1573-8744
    Keywords: lidocaine ; monoethylglycinexylidide ; time and dose dependency ; first pass effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The concentrations of lidocaine and of its deethylated metabolite, MEGX, were measured in blood following the intravenous administration of 50 and 100 mg lidocaine hydrochloride, the oral administration of 100, 300, and 500 mg lidocaine hydrochloride monohydrate, and the oral administration of 300 mg lidocaine hydrochloride monohydrate every 8 h for seven doses, to three healthy volunteers. The range of values for the parameters defining the disposition kinetics of lidocaine were: terminal half-life, 50–231 min; total clearance, 13–17 ml/min/kg; initial dilution space, 0.13–2.5 liters/kg; and volume of distribution at steady state, 0.6–4.5 liters/kg. Lidocaine absorption from solution was rapid, but due to presystemic hepatic metabolism, the availability was low, the range of average values lying between 0.19 and 0.38. No dose or time dependency in lidocaine and monoethylglycinexylidide pharmacokinetics following the single dose studies of lidocaine were noted. Effective hepatic blood flow, based on total clearance and availability measurements, was estimated to be 18–27 ml/min/kg. The concentrations of MEGX were approximately one-third of those of lidocaine following intravenous lidocaine and were comparable following oral lidocaine, but as predicted, the dose normalized area under the MEGX concentration-time curve was constant and independent of the route of administration of lidocaine. In two subjects, the blood concentrations of lidocaine and MEGX following multiple doses of oral lidocaine were those predicted from the single dose studies. In the third subject, the degree of accumulation of lidocaine was greater than predicted. The reasons and mechanism for this difference between subjects on multiple dosing remains unclear.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01059261
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  • 5
    Electronic Resource
    Electronic Resource
    Route of Administration and Sex Differences in the Pharmacokinetics of Aspirin, Administered as Its Lysine Salt (1989)
    Springer
    Pharmaceutical research 6 (1989), S. 660-666 
    Details
    ISSN: 1573-904X
    Keywords: aspirin ; pharmacokinetics ; intramuscular ; sex differences ; rate of absorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract One thousand milligrams of aspirin, as its lysine salt, was administered intravenously, orally, and intramuscularly to nine male and nine female young healthy adult volunteers. After intravenous injection mean (±SD) values of clearance, steady-state volume of distribution, and terminal half-life were 12.2 ± 2.2 ml/min/kg, 0.219 ± 0.042 liter/kg, and 15.4 ± 2.5 min, respectively, with no differences between males and females. Following oral administration aspirin was absorbed more quickly in females than in males (mean absorption times of 16.4 and 21.3 min, respectively) although the bioavailability, 54%, was the same in both groups. In contrast, following intramuscular administration, aspirin was absorbed more slowly in females than males (mean absorption times of 97 and 53 min, respectively) but again the bioavailability, 89%, was the same in both groups. The data suggest that in the female the intramuscular injection is going into fat. Salicylic acid concentration–time profiles showed a less pronounced sex difference and were comparable among the three routes of administration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015978104017
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  • 6
    Electronic Resource
    Electronic Resource
    Efficiency of Drug Targeting: Steady-State Considerations Using a Three-Compartment Model (1989)
    Springer
    Pharmaceutical research 6 (1989), S. 367-372 
    Details
    ISSN: 1573-904X
    Keywords: drug targeting ; site-specific delivery ; steady state ; pharmacokinetics ; pharmacodynamic model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Physiological models have often been used to investigate the processes involved in drug targeting. Such a model is used to investigate some aspects of drug targeting, including the pharmacodynamics of therapeutic and toxic effects. A simple pharmacodynamic model is incorporated in a three-compartment pharmacokinetic model. Conventional administration and drug targeting are compared at steady state for the same degree of therapeutic effect. The efficiency of drug targeting is quantified as the ratio (TA) of the rates of administration of free drug or of a drug–carrier complex required to achieve this effect. Also, the ratios of drug concentrations in the toxicity compartment (DTI) or of the consequent degree of toxic effects (TI) are used to compare conventional administration with drug targeting. The kinetic characteristics of the drug–carrier complex, rate of elimination, and rate of free drug release, influence TA but not DTI or TI. The importance of these characteristics depends on the cost and toxicity of the drug–carrier complex or of the carrier alone. The pharmacodynamics of the free drug in both the target and the toxicity compartments have an important influence on TI but not on TA or DTI. As the pharmacological selectivity of the drug increases, so does TI. However, a drug with good pharmacological selectivity may not be suitable for drug targeting. TI is also very dependent on the shape of the effect–concentration curves, particularly that for toxicity. While TA increases as the rate of elimination of free drug from either central or target compartments increases, TI may actually be reduced if release of free drug is not confined to the target compartment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015971113161
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  • 7
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    Design and analysis of protein binding experiments (1989)
    Elsevier
    Details
    Publication Date: 1989-09-01
    Print ISSN: 0022-5193
    Electronic ISSN: 1095-8541
    Topics: Biology
    Published by Elsevier
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  • 8
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    Enoxacin-warfarin interaction: Pharmacokinetic and stereochemical aspects (1987)
    Wiley
    Details
    Publication Date: 1987-07-01
    Print ISSN: 0009-9236
    Electronic ISSN: 1532-6535
    Topics: Chemistry and Pharmacology , Medicine
    Published by Wiley
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