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  • 1
    ISSN: 1619-7089
    Keywords: Dopamine D2 receptors ; Solvent extraction ; Single-photon emission tomography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract To establish a quantitative single-photon emission tomography (SPET) procedure for imaging CNS D2 dopamine receptors, measurement of unchanged iodine-123 iodobenzamide (123I-IBZM) (a selective D2 ligand) in human plasma was investigated. There are three possible radioactive components in human plasma: hydrophilic compounds (iodide ion, etc.), lipophilic metabolites, and unchanged IBZM. Based on the difference in lipophilicity of IBZM and its lipophilic metabolites (LM), a new quantitative method of analysis of 123I-IBZM using a simple solvent extraction was developed. The selective extraction was achieved with n-octane/phosphate buffer (0.1 M, pH 7.4). Extraction efficiency was 93.2% ± 0.3% (n=15) for IBZM from plasma, while 99.3% ± 0.2% (n =12) of LM remained in the aqueous plasma fraction. Twenty-one confirmation tests with plasma containing known ratios of IBZM/LM, ranging between 0.39 and 7.60, were performed. The experimental results were very close to the values of the true ratios over the wide range (accuracy ∼ 99%, relative standard error 6.6%). The data from this simplified method are comparable to those obtained by the high-performance liquid chromatography method. This improved method provides an easy and accurate way to quantify unchanged IBZM in human plasma. With appropriate kinetic modeling and in conjunction with a dedicated SPET imaging device for measuring quantitative information, it may be possible to develop a practical method for measuring D2 receptor density in vivo.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Investigational new drugs 1 (1983), S. 47-58 
    ISSN: 1573-0646
    Keywords: dihydro-5-azacytidine ; DHAC ; pharmacokinetics ; clearance ; foxhound
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary An HPLC analytical method was applied to the determination of plasma concentrations of 5,6-dihydro-5-azacytidine (NSC 264880, DHAC) in two foxhounds after a rapid intravenous infusion of 300 mg/kg DHAC. The dose employed is the mouse equivalent LD10 dose which results in mild reversible toxicity in the dog. The decline in DHAC plasma concentrations was greater than three log decades after dosing. The plasma concentration-time data was computer-fitted by NONLIN to a three compartment open model with first-order elimination using the equations for a short intravenous infusion. The half-lives corresponding to the three exponential phases were: t1/2α =5.78 min, t1/2β =1.57 h and t1/2γ =22.0 h in dog 1 and t1/2α =7.41 min, t1/2β =2.25 h and t1/2γ =21.6 h in dog 2. The terminal phase of the plasma concentration time profiles represented a minor contribution (2.2–3.2%) to the total area under the curve. The plasma concentration time data for the first 12 h after dosing was computer fitted to a two compartment open model. The initial and terminal half-lives determined from the two compartment fits were similar to the t1/2α and t1/2β values of the fits to the three compartment open model. Similar total body clearance values were calculated from the areas under the plasma concentration time curves from time zero to infinity for the computer fits to the three and two compartment models, respectively. Thus, for practical purposes, it appears feasible to define adequately the total body clearance of DHAC by analysis of the plasma concentration time data during the time interval in which the plasma concentration is described as a bi-exponential equation. Renal excretion of the parent drug is the principal route of excretion of DHAC from the dog.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-904X
    Keywords: lovastatin ; simvastatin ; sustained-release dosage forms ; 3-hydroxy-3-methylglutaryl–coenzyme A (HMG-CoA) reductase inhibitors ; dog ; humans
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Seven sustained/controlled-release dosage forms were designed for gastrointestinal delivery of lovastatin or simvastatin, two potent HMG-CoA reductase inhibitors for the treatment of hypercholesterolemia. The in vivo performance of these formulations was evaluated in dogs and healthy volunteers in terms of the cholesterol lowering efficacy and/or systemic concentrations of HMG-CoA reductase inhibitors. Results from the present and previous studies suggest that, through the controlled release of HMG-CoA reductase inhibitors, sustained lower plasma concentrations of HMG-CoA reductase inhibitors may result in an equal or better therapeutic efficacy.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of pharmacokinetics and pharmacodynamics 17 (1989), S. 125-130 
    ISSN: 1573-8744
    Keywords: apparent metabolite elimination rate constant ; metabolite kinetics ; area function method ; moment analysis ; one-compartment model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A simple method for determination of the apparent elimination rate constant of a metabolite (km) has been developed. This procedure requires calculation of area intervals under the plasma concentration-time curves of the parent drug and its derived metabolite. The method has been evaluated and compared with the Chan moment method using both errorless and errant data. The approach is accurate for various ratios of elimination rate constants of drug and metabolite, allows several values of km to be averaged, but works best using data prior to the metabolite tax.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of pharmacokinetics and pharmacodynamics 24 (1996), S. 389-402 
    ISSN: 1573-8744
    Keywords: volumes of distribution ; mean residence time ; nonlinear protein binding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Based on a generalized model, equations for calculating the mean residence time in the body at single dose (MRT) and at steady state (MRT ss), apparent steady-state volume of distribution ( $$\hat V_{ss}$$ ) and steady-state volume of distribution (V ss) are derived for a drug exhibiting nonlinear protein binding. Interrelationships between $$\hat V_{ss}$$ andV ss as well as betweenMRT andMRT ss are also discussed and illustrated with simulated data. In addition, a method for estimating the central volume of distribution of the bound drug and the sum of the central volume of distribution of the unbound drug and the area under the first moment curve of distribution function for drugs with nonlinear protein binding is proposed and illustrated with both simulated and published data.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of pharmacokinetics and pharmacodynamics 19 (1991), S. 521-536 
    ISSN: 1573-8744
    Keywords: methylprednisolone ; pharmacodynamics ; cell trafficking ; corticosteroids ; glucocorticoid receptors ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A two-compartment closed model was used to characterize the movement of basophils between blood and extravascular sites resulting from methylprednisolone (MP) exposure. This model is consistent with the view that corticosteroids cause a decrease in the recirculation of these cells from peripheral compartments. Methylprednisolone (Solu-Medrol) was given to healthy males at doses of 10, 25, and 40 mg. Blood samples were collected and assayed for MP by HPLC for pharmacokinetic analysis. Whole blood histamine, an index of circulating basophils, was assessed by RIA over 32 hr. Nonlinear least-squares analysis was carried out to solve for the model parameters reflecting cell movement between compartments and sensitivity (IC50)to the steriod. This model quantitates the fall and return pattern of biologic response to corticosteroids with a minimal number of parameters which jointly fit several dose/response curves and yields a mean IC50 value of 8.1 ng/ml similar to receptor binding of MP. Properties of the temporal and integrated response curve and model extrapolations over a wide dose range were explored with simulations. Because corticosteroids exert similar effects on other cells in blood, this model may be applicable to various regulatory and immunosuppressive effects.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1573-904X
    Keywords: montelukast sodium ; Singulair™ ; MK-0476 ; pharmacokinetics ; bioavailability ; gender effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. The safety, tolerability, and pharmacokinetics of intravenous (i.v.) montelukast sodium (Singulair™, MK-0476), and the oral bioavailability of montelukast sodium in healthy males and healthy females were studied. Methods. This was a two-part study. Part I was a four-period study in males of rising i.v. doses of montelukast sodium (3, 9, and 18 mg) administered as 15-minute constant-rate i.v. infusions (Periods 1–3), followed by a 10-mg oral tablet dose of montelukast sodium (Period 4) under fasting conditions. Part II was a four-period study in females of i.v. montelukast sodium (9 mg) infused over 15 and 5 minutes (Periods 5 and 6, respectively) or injected as a bolus over 2 minutes (Period 7), followed by a 10-mg oral tablet dose of montelukast sodium (Period 8). Plasma samples were collected and analyzed by HPLC. Results. In males (N = 6), as the i.v. dose of montelukast sodium increased from 3 to 18 mg, the area under the plasma concentration-time curve of montelukast sodium from time 0 to infinity (AUC) increased proportionately. The mean values of plasma clearance (CL), steady-state volume of distribution (Vss), plasma terminal half-life (t1/12), and mean residence time in the body (MRTi.v.) of montelukast sodium were 45.5 ml/min, 10.5 1, 5.1 hr, and 3.9 hr, respectively, and remained essentially constant over the i.v. dosage range. Following oral administration of a 10-mg tablet of montelukast sodium, the AUC, maximum plasma concentration (Cmax), time when Cmax occurred (Tmax), apparent t1/12, mean absorption time (MAT), and bioavailability (F) of montelukast sodium averaged 2441 ng · hr/ml, 385 ng/ml, 3.7 hr, 4.9 hr, 3.4 hr, and 66%, respectively. Following i.v. administration of 9 mg of montelukast sodium to females (N = 6), the values of CL, Vss, t1/2, and MRT i.v. averaged 47.6 ml/min, 9.6 1, 4.5 hr, and 3.6 hr, respectively. Following oral administration of a 10-mg tablet to females, the mean AUC, Cmax, Tmax, apparent t1/2, MAT and F were 2270 ng·hr/ml, 350 ng/ml, 3.3 hr, 4.4 hr, 2.6 hr, and 58%, respectively. These parameter values were similar to or slightly smaller than those in healthy males receiving the same i.v. and oral doses. Conclusions. The disposition kinetics of montelukast sodium were linear. Gender had little or no effect on the kinetics of montelukast sodium. Safety results from this study indicate that intravenous doses of montelukast sodium from 3 to 18 mg and a 10-mg oral dose are well tolerated.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1573-904X
    Keywords: intravenous infusion ; volume of distribution ; mean residence time ; reversible metabolism ; pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Equations for the steady-state volumes of distribution (V ss) and the mean residence times in the body (MRT) are derived for a drug and its metabolite subject to reversible metabolism and separately infused intravenously at a constant rate to steady state of both compounds. The V ss and MRT parameters are functions of the integrals of plasma concentrations, plasma concentrations at steady state, and times to reach steady state of both drug and metabolite. In addition, the MRT values are functions of the infusion rates. These equations were validated by computer simulations and comparison with IV bolus dose parameters. These relationships extend the ability to assess the pharmacokinetics of linear reversible metabolic systems.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Pharmaceutical research 6 (1989), S. 133-139 
    ISSN: 1573-904X
    Keywords: apparent zero-order absorption rate constant ; deconvolution ; Wagner–Nelson method ; Loo–Riegelman method ; moment analysis ; nonlinear regression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A noncompartmental approach for determination of the apparent zero-order absorption rate constant (k 0) has been developed. The procedure evolves from the convolution integral and requires individual oral-dose plasma concentration values and calculation of area intervals under the plasma concentration–time curves after intravenous administration. The proposed method was evaluated and compared with the Wagner–Nelson, Loo–Riegelman, deconvolution, nonlinear regression, and moment methods using errorless and errant simulation data for one- or two-compartment models. The area function method is generally equal to the best of these techniques (nonlinear regression) and superior to the weaker methods (moment, deconvolution, Loo–Riegelman), especially for errant two-compartment data. Coupled with a companion procedure for constructing fraction absorbed versus time plots and assessing first-order absorption rate constants, the area function methods offer direct and accurate means of discerning drug absorption kinetics without the need for assignment of a disposition model for drugs with linear elimination kinetics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Pharmaceutical research 6 (1989), S. 258-261 
    ISSN: 1573-904X
    Keywords: mean residence time ; Michaelis–Menten elimination ; first-order elimination ; simultaneous first-order and Michaelis–Menten elimination ; elimination fractions ; compartmental models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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