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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of pharmacokinetics and pharmacodynamics 7 (1979), S. 195-206 
    ISSN: 1573-8744
    Keywords: plasma protein binding ; tissue binding ; log plasma concentration-time curves ; apparent volume of distribution ; nonlinear binding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract We have studied by digital computer simulation the effect of concentration-dependent plasma protein and tissue binding on the time course of drug concentrations (both unbound and total) in plasma following rapid injection of a drug whose elimination rate is proportional to either free or total drug concentration in plasma, assuming instantaneous equilibration of the drug between vascular and nonvascular spaces. The following observations were made when elimination rate was assumed to be a function of free drug concentration: (a) when plasma protein binding is nonlinear and there is either no tissue binding or linear tissue binding, log concentration-time plots of free drug are always concave whereas such plots for total (sum of free and bound) drug can be convex, almost linear, or concave (apparently biexponential) depending on the plasma protein binding parameters relative to the initial concentration; (b) linear tissue binding in association with nonlinear plasma protein binding can reduce the concavity or enhance the convexity of log total concentration-time plots. When drug elimination rate was assumed to be a function of total concentration in plasma, nonlinear plasma protein binding in association with linear or no tissue binding yielded convex log total concentration-time plots which could sometimes be described by Michaelis-Menten kinetics. In general, drug concentration-dependent changes in the apparent volume of distribution resulting from nonlinear plasma protein and (where applicable) tissue binding have a pronounced effect on the slope of log total plasma concentration- time plots. It appears that under clinically realistic conditions an otherwise marked curvature of such plots, due to nonlinear plasma protein binding, may in fact be dampened or overcome by linear tissue binding.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of pharmacokinetics and pharmacodynamics 7 (1979), S. 397-405 
    ISSN: 1573-8744
    Keywords: plasma protein binding ; tissue binding ; nonlinear binding ; constantrate infusion ; drug accumulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The purpose of this investigation was to study, by digital computer simulation, the accumulation kinetics of drugs which exhibit concentration-dependent binding to tissues and either linear (constant free fraction) or concentration-dependent (increasing free fraction with increasing drug concentration) binding to plasma proteins. It was assumed that elimination rate is proportional to free drug concentration in plasma and that there occurs instantaneous equilibration of drug between vascular and nonvascular spaces. Nonlinear binding can yield, under certain conditions, apparently biexponential plasma concentrationtime curves which may be misinterpreted as being representative of a linear and biexponential-system. Such misinterpretation would cause the following errors in the prediction of drug accumulation and elimination kinetics during and after constantrate infusion: (a) the time required to reach steady state may be overestimated, and (b) the prominence of the apparent distribution phase after cessation of infusion may be underestimated. Drugs with linear and nonlinear plasma protein binding characteristics differ with respect to the relationship between infusion rate and steadystate concentration. This relationship is linear when plasma protein binding is linear. Steadystate concentration increases less than proportionally with increasing infusion rate if plasma protein binding is drug concentration dependent.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-904X
    Keywords: protein binding ; diabetes ; streptozotocin-treated rats ; glucosylated albumin ; AL01576 ; phenytoin ; diazepam ; propranolol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The extent of serum protein binding of AL01576, phenytoin (DPH), diazepam (DIAZ), and propranolol (PRO) was evaluated in a group of nondiabetic and a group of insulin-dependent diabetic subjects, as well as in streptozotocin-treated rats. Both serum glucose and glucosylated protein levels were elevated in the diabetic patient population (179 and 150% of control values, respectively). The mean free fractions (f p) of AL01576, DPH, and PRO were not statistically different for the two human groups. The DIAZ f p was slightly elevated (P 〈 0.05) in the diabetic patients (mean = 0.016) compared to the control group (mean f p = 0.014). An acute (〈3 days) and chronic (〉20 days) diabetic rodent model was evaluated using Sprague–Dawley rats following streptozotocin administration (60 mg/kg i.p.). Both diabetic rat groups exhibited substantial increases in serum glucose, free fatty acids (FFA), and protein glucosylation compared to controls. The f p of AL01576 was increased in both the acute (mean = 0.248) and the chronic (mean = 0.202) condition compared to controls (mean = 0.163). The f p of DPH was also markedly increased in the acute (mean = 0.348) and the chronic (mean = 0.280) models compared to untreated controls (mean = 0.207). DIAZ and PRO binding was largely unaffected by the streptozotocin treatment. In vitro studies of purified human albumin suggest that a considerable degree of glucosylation would need to be present in diabetic serum before it would effectively alter drug binding. Our data suggest that only minor drug–serum binding changes occur in diabetic patients who are otherwise healthy and whose disease is well controlled.
    Type of Medium: Electronic Resource
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