One-compartment intravenous injection

Figure 1.18 One-compartment intravenous bolus injection plot using semilogarithmic(S.L.) co-ordinates. K, rate constant ...

FIGURE 5.40 Schematic representation of the concentration of a chemical in the plasma as a function of time after an intravenous injection if the body acts as a one-compartment system and elimination of the chemical obeys first-order kinetics with a rate constant... 

Fig. 39.4. (a) One-compartment open model with single-dose intravenous injection of a dose D. The transfer constant of elimination (excretion and metabolism) is kp - (b) Time course of the plasma concentration Cp and of the contents in the elimination pool Xp. 

Fig. 39.6. (a) Time courses of plasma concentration Cp in the one-compartment open model for intravenous injection, with different contingencies for the transfer constant of elimination kfe and the volume of distribution Vp. (b) Time courses of plasma concentration Cp as in panel (a) on semilogarithmic plots. 

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... 

The administration of a drug by a rapid intravenous injection places the drug in the circulatory system where it is distributed (see section 2.7.1) to all the accessible body compartments and tissues. The one compartment model (Figure 8.3(a)) of drug distribution assumes that the administration and distribution of the drug in the plasma and associated tissues is instantaneous. This does not happen in practice and is one of the possible sources of error when using this model to analyse experimental pharmacokinetic data. 

Intravenous injection or a solution is necessary to be able to compute convolutions and deconvolutions. In some rare cases, only the formulation under interest may be needed if the apparent model is a one-compartment model. 

Hypotension follows the intravenous injection of benzodiazepines, but is usually mild and transient (SED-11, 92) (56), except in neonates who are particularly sensitive to this effect (57). Local reactions to injected diazepam are quite common and can progress to compartment syndrome (SEDA-17, 44). In one study (58), two-thirds of the patients had some problem, and most eventually progressed to thrombophlebitis. Flunitrazepam is similar to diazepam in this regard... 

Figure 10.2 Pharmacokinetics of intravenous T-20 administration. The graphs show the expected changes in plasma concentration vs time after intravenous administration of a single injection (dashed line) or multiple injections (solid line) of intravenous T-20 (lOOmg/dose). The curves are based on the half-life (1.8 h) and volume of distribution (4.7 L) measured in 17 human volunteers [4] using a one-compartment model (see Equation 7-3). Because of its rapid elimination, multiple doses are needed to maintain the peptide level in the effective range.

Following the administration by intravenous injection, if a drug distributes very rapidly in the body, this confers on the body the characteristics of a one-compartment model, and if the drug elimination from the body can be described by a first-order process, then a plot of the logarithm of plasma drug concentration as a function of time yields a straight line, as shown in Figure 9.24. 

The simplest pharmacokinetic model (as we shall see in subsequent chapters, this is an intravenous injection of a one-compartment drug eliminated by a first-order process) is described by a single-term exponential equation ... 

Thus, in the simple case of an open two-compartmental system depicted in Figure 9 which is composed of two mutually interconnected compartments— the central one into which the drug is injected and the peripheral —the decline of drug concentration in plasma forming part of the central compartment is after a rapid instantaneous intravenous injection given by ... 

Figure 39.4a represents schematically the intravenous administration of a dose D into a central compartment from which the amount of drug Xp is eliminated with a transfer constant kp. (The subscript p refers to plasma, which is most often used as the central compartment and which exchanges a substance with all other compartments.) We assume that mixing with blood of the dose D, which is rapidly injected into a vein, is almost instantaneous. By taking blood samples at regular time intervals one can determine the time course of the plasma concentration Cp in the central compartment. This is also illustrated in Fig. 39.4b. The initial concentration Cp(0) at the time of injection can be determined by extrapolation (as will be indicated below). The elimination pool is a hypothetical compartment in which the excreted drug is collected. At any time the amount excreted must be equal to the initial dose D minus the content of the plasma compartment Xp, hence ...

After an intravenous bolus dose, serum concentrations decrease as if the drug were being injected into a central compartment that not only metabolizes and eliminates drug but also distributes drug to one or more other compartments. Of these multicompartment models, the two-compartment model is encountered most commonly (see Fig. 5-5). After an intravenous bolus injection, serum concentrations decrease in two distinct phases described by the equation ... 

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