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  • 1
    ISSN: 1573-904X
    Keywords: pharmacokinetics ; pharmacodynamics ; corticosteroids ; metabolites ; prodrug
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. The pharmacokinetics and pharmacodynamics of deflazacort after oral administration (30 mg) to healthy volunteers were determined and compared with those of 20 mg of methylprednisolone and 25 mg of prednisolone. Methods. Methylprednisolone, prednisolone and the active metabolite of deflazacort, 21-desacetyldeflazacort, were measured in plasma using HPLC. For the assessment of pharmacodynamics, differential white blood cell counts were obtained over 24 hours. An integrated pharmacokinetic-pharmacodynamic (PK-PD) model was applied to link corticosteroid concentrations to the effect on lymphocytes and granulocytes. Results. Deflazacort is an inactive prodrug which is converted rapidly to the active metabolite 21-desacetyldeflazacort. Maximum concentrations of 21-desacetyldeflazacort averaged 116 ng/ml and were observed after 1.3 h. The average area under the curve was 280 ng/ml · h, and the terminal half-life was 1.3 h. 21-Desacetyldeflazacort was cleared significantly faster than both methylprednisolone and prednisolone. The PK-PD-model was suitable to describe time course and magnitude of the observed effects. The results were consistent with reported values for glucocorticoid receptor binding affinities for the investigated compounds. Conclusions. Due to the short pharmacokinetic half-life of its active metabolite, pharmacodynamic effects of deflazacort are of shorter duration than those of methylprednisolone and prednisolone. The PK-PD model allows good prediction of pharmacodynamic effects based on pharmacokinetic and receptor binding data.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-904X
    Keywords: piperacillin ; Escherichia coli ; Emax-model ; PK-PD modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. It was the aim of the present study to investigate the in vitro antimicrobial effects of the β-lactam antibiotic piperacillin on Escherichia coli using concentration-time profiles similar to those encountered in vivo. Methods. An in vitro dilution model was used to expose E. coli to various piperacillin concentration profiles. The antimicrobial effect was evaluated by determination of the number of bacteria over time. Results. A modified Emax-model was found appropriate to describe the pharmacodynamic effect. This model was linked with the respective piperacillin concentrations to provide a suitable pharmaco-kinetic-pharmacodynamic (PK-PD) model. The average growth half-life in absence of piperacillin was 28 min and the maximum kill half-life was 25 min. The EC50 for the various dosing regimens averaged 5.2 µg/mL and was independent of dose. These parameters were used the simulate the bactericidal effects of commonly administered doses or dosing regimens in humans. Conclusions. Based on the in vitro data a more frequent administration of piperacillin will be more efficacious. The proposed PK-PD-model allows a more detailed evaluation of dosing regimens than the use of minimum inhibitory concentrations.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-904X
    Keywords: triamcinolone acetonide ; pulmonary targeting ; liposomes ; glucocorticoid receptors ; sustained release
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. To explore the use of triamcinolone acetonide phosphate liposomes as a pulmonary targeted drug delivery system. Methods. Triamcinolone acetonide phosphate liposomes composed of 1,2-distearoyl phosphatidylcholine and 1,2-distearoyl phosphatidyl glycerol and triamcinolone acetonide 21-phosphate dipotassium salt were prepared by dispersion and extruded through polycarbonate membranes. Encapsulation efficiency and in vitro stability at 37°C were assessed after size exclusion chromatography. TAP liposomes (TAP-lip) or TAP in solution (TAP-sol) were delivered to rats either by intratracheal instillation (IT) or intravenous (IV) administration. Pulmonary targeting was assessed by simultaneous monitoring of glucocorticoid receptor occupancy over time in lung (local organ) and liver (systemic organ) using an ex vivo receptor binding assay as a pharmacodynamic measure of glucocorticoid action. Results. In vitro studies in different fluids over 24 hours, showed that more than 75% of the TAP remained encapsulated in liposomes. Cumulative pulmonary effects after IT administration of TAP-lip were 1.6 times higher than liver receptor occupancy. In contrast, there was no difference in the pulmonary and hepatic receptor occupancy time profiles when TAP was administered intratracheally as a solution. No preferential lung targeting was observed when TAP-lip was administered IV. As indicated by the mean effect times, lung receptor occupancy was sustained only when TAP-lip was administered IT. Conclusions. Intratracheal administration of TAP-lip provided sustained receptor occupancy, and increased pulmonary targeting which was superior to IT administration of TAP-sol or IV administration of TAP-lip. The use of liposomes may represent a valuable approach to optimize sustained delivery of glucocorticoids to the lungs via topical administration.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Pharmaceutical research 16 (1999), S. 176-185 
    ISSN: 1573-904X
    Keywords: pharmacokinetics ; pharmacodynamics ; pharmacology ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Pharmacokinetic/pharmacodynamic (PK/PD)-modeling links dose-concentration relationships (PK) and concentration-effect relationships (PD), thereby facilitating the description and prediction of the time course of drug effects resulting from a certain dosing regimen. PK/PD-modeling approaches can basically be distinguished by four major attributes. The first characterizes the link between measured drug concentration and the response system, direct link versus indirect link. The second considers how the response system relates effect site concentration to the observed outcome, direct versus indirect response. The third regards what clinically or experimentally assessed information is used to establish the link between concentration and effect, hard link versus soft link. And the fourth considers the time dependency of pharmacodynamic model parameters, distinguishing between time-variant versus time-invariant. Application of PK/PD-modeling concepts has been identified as potentially beneficial in all phases of preclinical and clinical drug development. Although today predominantly limited to research, broader application of PK/PD-concepts in clinical therapy will provide a more rational basis for patient-specific dosage individualization and may thus guide applied pharmacotherapy to a higher level of performance.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1573-904X
    Keywords: methylprednisolone phosphate ; methylprednisolone hemisuccinate ; pharmacokinetics ; saliva analysis ; endogenous hydrocortisone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The pharmacokinetics of methylprednisolone and two methylprednisolone esters, the phosphate and the hemisuccinate, were investigated after intravenous administration of the esters to 12 healthy male subjects in two different doses (250 and 1000 mg). Methylprednisolone was formed more rapidly from phosphate than from hemisuccinate. During the first 30 min methylprednisolone levels were three to four times higher after phosphate administration than after hemisuccinate. The mean residence time of the hemisuccinate was significantly longer and the total-body clearance lower than those of the phosphate. Whereas very little of the phosphate (mean, 1.7%) was eliminated unchanged into the urine, there were significant amounts of hemisuccinate (mean, 14.7%) excreted renally and therefore not bioavailable. Methylprednisolone saliva levels paralleled plasma levels; the average saliva/plasma ratio was 0.22. Neither phosphate nor hemisuccinate could be detected in saliva. An average of 7.2% of the administered dose was eliminated in the form of methylprednisolone in urine. Renal clearance was 24 ml/min and not dose or prodrug dependent. For both doses endogenous hydrocortisone levels were lowered after 24 hr. For the 1000-mg dose the depression was still significant after 48 hr. The results indicate that methylprednisolone phosphate results in a faster and more efficient conversion to its active form, methylprednisolone, than methylprednisolone hemisuccinate.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Pharmaceutical research 1 (1984), S. 225-229 
    ISSN: 1573-904X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The time courses of analgesic activity of 4 different tablets containing different amounts of antipyrine were determined in 14 volunteers using electrical tooth pulp stimulation to elicit pain. Drug action was monitored by following somatosensory evoked potentials obtained from electroencephalographic measurements as well as pain rating and pain threshold determination. The results were compared with data obtained after administration of 1000 mg acetaminophen and two different doses of aspirin (500 and 1000 mg). At the same time drug concentration in saliva of the same volunteers was analyzed by quantitative in situ thin-layer-chromatography to investigate the pharmacokinetics. Furthermore, the in vitro drug release from the different tablets was studied with a continuous flow cell model. Antipyrine produced reliable analgesic activity. The onset of action was significantly faster than after administration of the same dose of aspirin, and the effect lasted longer than after intake of the same dose of acetaminophen. Comparison of the drug action and drug level in the body showed an excellent correlation between pharmacodynamics and pharmacokinetics. The study confirms our earlier findings on the value of somatosensory evoked potentials as a method to investigate the pharmacodynamics of weak analgesics in humans. The results also suggest to reconsider the use of antipyrine as an over-the-counter analgesic.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1573-904X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The unanesthetized awake sheep was employed as large animal model for the determination of bioavailability and pharmacokinetics following the pulmonary instillation of the decapeptide detirelix. After intratracheal administration of a 80 µg/kg dose, the average t1/2 of elimination was 9.8 ± 1.3 hours (n = 5) which was similar to the elimination kinetics of a 30 µg/kg i.v. dose (7.2 ± 2.9 hours). Mean residence time (MRT) was prolonged to 10.3 ± 2.0 hours vs. 2.7 ± 0.8 hours i.v., and mean absorption time (MAT) was calculated to be 7.5 ± 1.8 hours. Maximum plasma levels cmax) of 9.2 ng/ml were reached after 2 hours. The average bioavailability was 9.8 ± 3.9% of the dose. The pharmacokinetic profile was found to be similar after aerosol administration. It was concluded that detirelix was absorbed systemically when administered by pulmonary instillation or aerosolization and that the unanesthetized awake sheep is a suitable model to study resulting drug profiles.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1573-904X
    Keywords: triamcinolone acetonide ; lung instillation ; lung targeting ; ex-vivo receptor binding ; corticosteroids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Triamcinolone acetonide (TA, 22 µg) was given to rats by intravenous (IV) injection or intratracheal (IT) instillation. Free glucocorticoid receptors were monitored over time in liver and lung using an ex-vivo receptor binding technique. After IV administration of a TA solution, the reduction of free receptors over time was very similar in lung and liver (AUCLung = 280 ± 47 %*h; AUCLiver = 320 ± 76 %*h). Intratracheal instillation of the same solution produced time profiles which mirrored those of IV injection (AUCLung = 260 ± 41 %*h; AUCLiver = 330 ± 50 %*h). The lack of lung targeting was also reflected in the failure to show any significant difference in the pulmonary targeting factor T (AUCLung/AUCLiver) between IV (T = 0.84 ± 0.18) and IT (T = 0.78 ± 0.03) administration. In contrast, a certain degree of lung specificity was observed after IT instillation of a glucocorticoid suspension (22 µg; AUCLung = 160 ± 135 %*h; AUCLiver = 65 ± 91 %*h, T = 2.3 ± 0.5) as indicated by significant differences in T between IV injection and IT instillation (p = 0.038). The method presented provides a means of simultaneously assessing pulmonary and systemic effects after different forms and routes of administration and might be of value in further studying multiple aspects of inhalation glucocorticoid therapy.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Journal of pharmacokinetics and pharmacodynamics 26 (1998), S. 247-260 
    ISSN: 1573-8744
    Keywords: compartmental analysis ; two-compartment model ; first-order absorption ; vanishing exponential
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract When a pharmacokinetic (PK) two-compartment body model with first-order absorption is fitted to blood levels of a drug, the estimates of the PK parameters may have considerable errors and can cause wrong predictions in other features of the system. The objectives of this report were to illustrate this problem, to provide an easy way to prevent wrong estimation, and to investigate the origin of the mistake. A simple way to prevent wrong interpretation of the calculated PK parameters is to inspect the PK profiles visually. Without observing a clear biphasic profile, one should not apply the two-compartment model if the resulting parameters are to be interpreted and used for further simulations. We investigated the origin of this ambiguity in terms of the relative order of magnitude of microconstants (ka , k12 , k21 , and k10 ) and of hybrid constants (A and B). The observed parameter errors will not be of any relevance if the calculated parameters are used only to predict future blood levels over the same time-span. However, if these parameters are used to predict any other characteristic of the system, erroneous predictions may result.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1573-8744
    Keywords: PK/PD modeling ; corticosteroids ; cortisol suppression ; surrogate marker ; inhalation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The suppression of endogenous cortisol release is one of the major systemic side effects of inhaled corticosteroids in the treatment of asthma. The circadian rhythm of the endogenous cortisol release and the resulting plasma concentrations as well as the release suppression during corticosteroid therapy could previously be described with an integrated PK/PD model. Based on this model, a PK/PD approach was developed to quantify and predict the cumulative cortisol suppression (CCS) as a surrogate marker for the systemic activity of inhaled corticosteroid therapy. The presented method was applied to predict CCS after single doses and during short-term multiple dosing of the inhaled corticosteroids flunisolide (FLU), fluticasone propionate (FP), and triamcinolone acetonide (TCA), and after oral methylprednisolone as systemic reference therapy. Drug-specific PK and PD parameters were obtained from previous single-dose studies and extrapolated to the multiple-dose situation. For single dosing, a similar CCS within the range of 16–21% was predicted for FP 250 μg, FLU 500 μg, and TCA 1000 μg. For multiple dosing, a respective CCS of 28–33% was calculated for FLU 500 μg bid, FP 250 μg, bid, and TCA 1000 μg bid. Higher cortisol suppression compared to these single and multiple dosing regimens of the inhaled corticosteroids was predicted after oral doses of only 1 mg and 2 mg methylprednisolone, respectively. The predictive power of the approach was evaluated by comparing the PK/PD-based simulations with data reported previously in clinical studies. The predicted CCS values were in good correlation with the clinically observed results. Hence, the presented PK/PD approach allows valid predictions of CCS for single and short-term multiple dosing of inhaled corticosteroids and facilitates comparisons between different dosing regimens and steroids.
    Type of Medium: Electronic Resource
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