One-compartment model

In a two-compartment model, /3 is equivalent to k in the one-compartment model. Therefore, the terminal half-life for the elimination of a chemical compound following two-compartment model elimination can be calculated from the equation (i = 0.693/ti/i ... 

Drug elimination may not be first order at high doses due to saturation of the capacity of the elimination processes. When this occurs, a reduction in the slope of the elimination curve is observed since elimination is governed by the relationship Vmax/(Km- -[conc]), where Vmax is the maximal rate of elimination, Km is the concentration at which the process runs at half maximal speed, and [cone] is the concentration of the drug. However, once the concentration falls below saturating levels first-order kinetics prevail. Once the saturating levels of drugs fall to ones eliminated via first-order kinetics, the half time can be measured from the linear portion of the In pt versus time relationship. Most elimination processes can be estimated by a one compartment model. This compartment can... 

The synthetic data have been derived from a theoretical one-compartment model with the following settings of the parameters ... 

Fig. 39.9. Time courses of plasma concentration Cp in a one-compartment model for extravascular administration, with different contingencies of (a) the transfer constant of absorption k p, (b) the transfer constant of elimination kpt and (c) the volume of distribution Vp.

We consider again the pharmacokinetic parameters of the one-compartment model for a single intravenous injection (eq. (39.6)). 

This model is an extension of the one-compartment model for intravenous injection (Section 39.1.1) which is now provided with a peripheral buffering compartment which exchanges with the central plasma compartment. Elimination occurs via the central compartment (Fig. 39.12). The model requires the estimation of the plasma volume of distribution and three transfer constants, namely for... 

A random noise with standard deviation of 0.4 pg 1 has been added to the theoretical values in order to produce a realistic example. The specifications of the model are in part the same as those used for the one-compartment models which have been discussed above. The major distinction between this model and the... 

An important parameter of the one-compartment model is the apparent volume of the body compartment, because it directly determines the relationship between the plasma concentration and the amount of... 

The easiest way to calculate Vd is to use C , the plasma concentration when distribution is complete (assumed to be instantaneous for a one-compartment model) and the entire dose is still in the body. Thus,... 

To predict oral plasma concentration-time profiles, the rate of drug absorption (Eq. (53)) needs to be related to intravenous kinetics. For example, in the case of the one-compartment model with first-order elimination, the rate of plasma concentration change is estimated as... 

Oxidation half-lives predicted by one compartment model t,/2 = 38 h in stream, eutrophic pond or lake and oligotrophic lake based on peroxy radical concentration of 10-9 M (Smith et al. 1978) aquatic fate rate k = 5 x 103 M-1 s-1 with t,/2 = 38 h (Callahan et al. 1979) ... 

This approach assumes that fe is known, the change in CL and k are proportional to CLcr, renal disease does not alter drug metabolism, any metabolites are inactive and nontoxic, the drug obeys first-order (linear) kinetic principles, and the drug is adequately described by a one-compartment model. The kinetic parameter/dosage adjustment factor (Q) can be calculated as ... 

Whether the chemical distributes evenly throughout the body (one-compartment model) or differentially between different compartments (models of two or more compartments). 

The first-order one-compartment model [43,58], which considers the organism as one homogeneous compartment surrounded by a homogeneous medium, provides an acceptable estimation of surfactants bioconcentration, and has been adopted by the OECD and EPA in their guidelines [3-5]. The BCF can be determined as a ratio of the concentrations of the chemical in the organism (Ca) and the medium (Cw) under equilibrium state or as a ratio of the uptake and elimination constants (ki and, respectively). 

Using a simple one-compartment model, the loading dose and the infusion rate required to maintain a constant plasma concentration can be calculated as follows. 

Phillips (1980) andPhillips and Rainbow (1993) have stated that each species of aquatic BMO exhibits unique uptake and elimination kinetics for a particular HOC. The ramification of this statement is revealed in the following simple one-compartment model, which is often used for the determination of steady-state BCFs and Ks s. 

The haif-iife of a drug is the amount of time it takes to reduce concentrations by 50%. With each successive half-life duration, drug concentrations are further reduced until it is no longer present (figure 3.2). In a one-compartment model, a single half-life may be sufficient, but in multiple-compartment models, more than one half-life may need to be calculated. Half-life varies as a function of both the volume of distribu-... 

In serum both forms of vinyldithiins could be detected. The serum concentration time profile of 1,2-vinyldithiin can be characterized by an one-compartment model, whereas a two-compartment model is used as a best fit of the serum concentration of 1,3-vinyldithiin (87). 

The time needed to reach CSS is one of the few instances where the concept of a half-life is useful in anaesthesia. Strictly speaking, the concept of half-life is only applicable to a drug which can be represented by a one-compartment model, when plasma concentrations will decline mono-exponentially. For drugs that... 

The rates of movement of foreign compound into and out of the central compartment are characterized by rate constants kab and kei (Fig. 3.23). When a compound is administered intravenously, the absorption is effectively instantaneous and is not a factor. The situation after a single, intravenous dose, with distribution into one compartment, is the most simple to analyze kinetically, as only distribution and elimination are involved. With a rapidly distributed compound then, this may be simplified further to a consideration of just elimination. When the plasma (blood) concentration is plotted against time, the profile normally encountered is an exponential decline (Fig. 3.24). This is because the rate of removal is proportional to the concentration remaining it is a first-order process, and so a constant fraction of the compound is excreted at any given time. When the plasma concentration is plotted on a logio scale, the profile will be a straight line for this simple, one compartment model (Fig. 3.25). The equation for this line is... 

In the one-compartment model the entire body is considered as one unit (Figure 2.1 A). The drug is administered into the compartment and distributed throughout the compartment (the body) instantaneously.1 Similarly, the drug is eliminated directly from the one compartment at a rate measured by fcel, the elimination rate constant. The time course of the drug, as measured in the... 

Figure 2.1 (A) Schematic representation of a one-compartment model. (B) Log plasma concentration vs. time...

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