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  • 1
    Electronic Resource
    Electronic Resource
    Methodological Aspects of the Use of a Calibrator in In Vivo Microdialysis–Further Development of the Retrodialysis Method (1998)
    Springer
    Pharmaceutical research 15 (1998), S. 1673-1679 
    Details
    ISSN: 1573-904X
    Keywords: microdialysis ; morphine ; nalorphine ; retrodialysis ; calibrator
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. To investigate the performance of two alternative retrodialysis recovery methods and to describe the influence of different recoveries on the reliability in estimating unbound extracellular concentrations of morphine. Methods. Unbound concentrations of morphine in striatum and in blood were determined by microdialysis after a 10 min i.v. infusion in freely moving rats. In vivo recovery of morphine was determined by morphine itself, retrodialysis by drug, and by the calibrator nalorphine, retrodialysis by calibrator. Results. The low calibrator recovery in striatum (8.6%) resulted in large variability in the estimation of unbound extracellular concentrations when retrodialysis by calibrator was used. In blood, where the recovery was higher (36%), the variability was smaller. Also, when retrodialysis by drug was used, the variability remained low. This difference is caused by the propagation of errors in the way retrodialysis recovery is determined. Therefore, calibrator recovery values ≥ 20% are preferable in concentration estimations using retrodialysis by calibrator. Conclusions. When no time-dependent change in recovery is observed, retrodialysis by drug determined before the systemic administration is the best method. The calibrator is valuable as a quality control during the experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1011992125204
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  • 2
    Electronic Resource
    Electronic Resource
    Drug Equilibration Across the Blood—Brain Barrier-Pharmacokinetic Considerations Based on the Microdialysis Method (1997)
    Springer
    Pharmaceutical research 14 (1997), S. 128-134 
    Details
    ISSN: 1573-904X
    Keywords: microdialysis ; blood-brain barrier transport ; pharmacokinetics ; drug equilibration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. The purpose of the study was to investigate the influence of different rates of transport into and out of the brain, including passive and active transport, on unbound brain concentrations and profile in relation to the blood concentration profile. Special emphasis is put on hydrophilic drugs. Methods. Simulations were performed with a model including one body compartment and one brain compartment, with linear or saturable transport into and out of the brain. Comparisons were made with experimental results from microdialysis (MD) studies. Results. Three features were evident when combining the MD results: 1) equilibration across the blood-brain barrier (BBB) is rapid, 2) half-life is similar in brain and blood for most drugs, and 3) unbound brain concentrations seldom reach the level of unbound blood concentrations. A low concentration ratio brain:blood is not mainly caused by a low influx, but rather by different influx and efflux clearances. Active transport out of the brain can explain the results, but also active transport into the brain under certain conditions. A small volume of distribution in brain vs. that in the rest of the body contributes to a rapid equilibration and similar half-lives. Conclusions. Assumptions of slow equilibration of hydrophilic drugs and similar unbound concentrations across the BBB at steady state are contradicted. The results are more in line with recent findings on the presence of P-glycoprotein and other transport mechanisms at the BBB. Non-passive transport across the BBB seems to be the case for almost all drugs studies with MD so far.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1012080106490
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  • 3
    Electronic Resource
    Electronic Resource
    Blood-Brain Barrier Equilibration of Codeine in Rats Studied with Microdialysis (1998)
    Springer
    Pharmaceutical research 15 (1998), S. 570-575 
    Details
    ISSN: 1573-904X
    Keywords: microdialysis ; codeine ; morphine ; blood-brain barrier ; pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. The purpose of the study was to investigate the distribution of codeine across the blood-brain barrier (BBB) in rats by micro-dialysis (MD). Methods. Rats were administered intravenous infusion of codeine in doses of (1) 10 mg/kg, (2) 20 mg/kg for 10 min, and (3) an exponential infusion for 2 h aiming at a plasma concentration of 2500 ng/ml, in a crossover design (n = 6). Microdialysis was used to determine codeine unbound concentrations in blood and brain extracellular fluid (ECF). Total brain tissue and plasma concentrations were also determined. Nalorphine was used as a calibrator for measurement of in vivo recovery. Results. Relative recovery and retrodialysis loss of codeine and nalorphine were similar both in vitro and in vivo. Codeine was rapidly transported into the brain ECF with identical influx and efflux clearance across the BBB. The AUC ratios of brain to blood were 0.99 ± 0.25 and 0.95 ± 0.16 for Dose 1 and 2, respectively. The Css ratio of brain to blood was 1.06 ± 0.12 for the exponential infusion. The half-lives were 25 ± 4 min, 22 ± 2 min in blood and 27 ± 5 min, 25 ± 5 min in brain for Dose 1 and Dose 2, respectively. Total brain tissue concentrations were 3.6 ± 1.2-fold higher than the unbound concentrations in brain. Codeine was demethylated to morphine with an unbound AUCbIood,morphine/AUCblood,codeine ratio of 7.7 ± 5.1% in blood. No morphine was detected in brain MD, but total concentrations were possible to measure. Conclusions. Codeine rapidly reached a distributional equilibrium with equal unbound concentrations in blood and brain. The brain transport of codeine did not show any dose-dependency.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1011929910782
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  • 4
    Electronic Resource
    Electronic Resource
    Pharmacokinetic-Pharmacodynamic Modelling of Morphine Transport Across the Blood-Brain Barrier as a Cause of the Antinociceptive Effect Delay in Rats—A Microdialysis Study (2000)
    Springer
    Pharmaceutical research 17 (2000), S. 1220-1227 
    Details
    ISSN: 1573-904X
    Keywords: morphine ; nociceptive effect ; electrical stimulation vocalisation method ; microdialysis ; retrodialysis by drug ; pharmacokinetics ; pharmacodynamics ; modelling ; blood-brain barrier transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. To quantify the contribution of distributional processes across the blood-brain barrier (BBB) to the delay in antinociceptive effect of morphine in rats. Methods. Unbound morphine concentrations were monitored in venous blood and in brain extracellular fluid (ECF) using microdialysis (MD) and in arterial blood by regular sampling. Retrodialysis by drug was used for in vivo calibration of the MD probes. Morphine was infused (10 or 40 mg/kg) over 10 min intravenously. Nociception, measured by the electrical stimulation vocalisation method, and blood gas status were determined. Results. The half-life of unbound morphine in striatum was 44 min compared to 30 min in venous and arterial blood (p 〈 0.05). The BBB equilibration of morphine, expressed as the ratio of areas under the curve between striatum and venous blood, was less than unity (0.28 ± 0.09 and 0.22 ± 0.17 for 10 and 40 mg/kg), respectively, indicating active efflux of morphine across the BBB. The concentration-effect relationship exhibited a clear hysterisis with an effect delay half-life of 32 and 5 min based on arterial blood and brain ECF concentrations, respectively. Conclusions. Eighty five percent of the effect delay was caused by morphine transport across the BBB, indicating possible involvement of rate limiting mechanisms at the receptor level or distributional phenomena for the remaining effect delay of 5 min.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026414713509
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  • 5
    Electronic Resource
    Electronic Resource
    Influence of rate of administration of raclopride on akathisia and prolactin response (1994)
    Springer
    Psychopharmacology 114 (1994), S. 248-256 
    Details
    ISSN: 1432-2072
    Keywords: Akathisia ; Prolactin ; Man ; Raclopride ; Rate of administration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The D2-dopamine receptor antagonist raclopride was administered to eight healthy male subjects, who had previously experienced akathisia following antipsychotic drugs. The influence of administration rate on onset, severity and duration of akathisia and on prolactin response was studied. Raclopride 3,5 or 9 mg or placebo (P) was administered as single IV infusions during 10 min (R10 min/3 mg), 1 h (R1h/5 mg) or 4 h (R4h/9 mg) according to a randomized double-blind design. Despite a 24-fold difference in administration rate a similar peak raclopride concentration of about 350 nmol/l was obtained after all three infusions. Three of the eight subjects experienced akathisia following R10 min/3 mg and R1h/5 mg, respectively. After R4h/9 mg seven subjects experienced akathisia of longer duration but not more severe than after the short infusions. The incidence and duration of akathisia seem to be mainly related to the plasma raclopride concentrations over time, whereas the rate of administration might be more important for the severity. A maximal prolactin response was induced which was not markedly affected by the rate of administration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02244845
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  • 6
    Electronic Resource
    Electronic Resource
    Furosemide pharmacokinetics and pharmacodynamics in health and disease—An update (1989)
    Springer
    Journal of pharmacokinetics and pharmacodynamics 17 (1989), S. 1-46 
    Details
    ISSN: 1573-8744
    Keywords: furosemide ; elderly ; renal failure ; congestive heart failure ; cirrhosis ; nephrotic syndrome, diuretic effects ; acute tolerance ; volume replacement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The literature on furosemide pharmacokinetics and pharmacodynamics is critically reviewed, concentrating on those papers published subsequent to the 1979 reviews of this topic. Intravenous and oral data are presented for healthy volunteers and for patients with various disease states. It is the latter populations about which the majority of the studies have been published since 1979. Inter- and intraindividual variations in bioavailability are discussed, as are data on the metabolism of furosemide to its glucuronide conjugate. Published studies examining the relationship between furosemide pharmacodynamics and pharmacokinetics are also evaluated. The literature is reviewed through June 1988.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01059086
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  • 7
    Electronic Resource
    Electronic Resource
    Potential Use of Microdialysis in Pharmacokinetics: A Protein Binding Study (1992)
    Springer
    Pharmaceutical research 9 (1992), S. 155-158 
    Details
    ISSN: 1573-904X
    Keywords: microdialysis ; protein binding ; aminoglutethimide ; furosemide ; phenytoin ; disopyramide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018960617549
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