Volume of distribution at steady state for a linear pharmacokinetic system with peripheral elimination
β Scribed by Leonid M. Berezhkovskiy
- Publisher
- John Wiley and Sons
- Year
- 2004
- Tongue
- English
- Weight
- 156 KB
- Volume
- 93
- Category
- Article
- ISSN
- 0022-3549
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β¦ Synopsis
The problem of finding the steady-state volume of distribution V ss for a linear pharmacokinetic system with peripheral drug elimination is considered. A commonly used equation V ss ΒΌ (D/AUC)*MRT is applicable only for the systems with central (plasma) drug elimination. The following equation, V ss ΒΌ (D/AUC)*MRT int , was obtained, where AUC is the commonly calculated area under the time curve of the total drug concentration in plasma after intravenous (iv) administration of bolus drug dose, D, and MRT int is the intrinsic mean residence time, which is the average time the drug spends in the body (system) after entering the systemic circulation (plasma). The value of MRT int cannot be found from a drug plasma concentration profile after an iv bolus drug input if a peripheral drug exit occurs. The obtained equation does not contain the assumption of an immediate equilibrium of protein and tissue binding in plasma and organs, and thus incorporates the rates of all possible reactions. If drug exits the system only through central compartment (plasma) and there is an instant equilibrium between bound and unbound drug fractions in plasma, then MRT int becomes equal to MRT ΒΌ AUMC/AUC, which is calculated using the time course of the total drug concentration in plasma after an iv bolus injection. Thus, the obtained equation coincides with the traditional one, V ss ΒΌ (D/AUC)*MRT, if the assumptions for validity of this equation are met. Experimental methods for determining the steady-state volume of distribution and MRT int , as well as the problem of determining whether peripheral drug elimination occurs, are considered. The equation for calculation of the tissue-plasma partition coefficient with the account of peripheral elimination is obtained. The difference between traditionally calculated V ss ΒΌ (D/AUC)*MRT and the true value given by (D/AUC)*MRT int is discussed.
π SIMILAR VOLUMES
The assumption of an instant equilibrium between bound and unbound drug fractions is commonly applied in pharmacokinetic calculations. The equation for the calculation of the steady-state volume of distribution V ss from the time curve of drug concentration in plasma after intravenous bolus dose adm
The volume of distribution at steady state is considered to be one of the primary pharmacokinetic measurements obtained from in vivo experiments. This quantity is quite commonly calculated using moments of the observed concentration curve, the process being referred to as noncompartmental analysis.
The parameters characterizing tissue distribution refer to the tissue/plasma partition coefficients (Kp), which can be used to derive volume of distribution at steady-state (V(ss)). The effort for predicting drug distribution in human has been further expanded to calculation methods using in vitro-b
A consistent account of the assumptions of the well-stirred perfusion limited model leads to the equation for the organ tissue that does not coincide with that often presented in books and papers. The difference in pharmacokinetic profiles calculated by the valid and the commonly used equations coul