Volume of Distribution as a Function of Time

Niazi, Sarfaraz K.

doi:10.1002/jps.2600650339

Cited by 54 publications

(28 citation statements)

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“…MRTA based on equation (24) and estimated by equation (15) was 1.063 and is very similar to MRT" (1.058) based on equation (21) and estimated by equation Table 2 summarizes the MRTs, their equations, and the calculated values.…”

Section: Numerical Examples T O Show Discrepancies In the Calculationsupporting

confidence: 52%

“…Therefore, with a dose of 1000 and a constant volume of distribution of 10, A" versus time is (see Appendix A): (24) A" = 641.31 e-2.2346t + 358.69 e-0.4h54f and is dissimilar to the coefficient and exponent in equation (22). MRTA based on equation (24) and estimated by equation (15) was 1.063 and is very similar to MRT" (1.058) based on equation (21) and estimated by equation Table 2 summarizes the MRTs, their equations, and the calculated values.…”

Section: Numerical Examples T O Show Discrepancies In the Calculationmentioning

confidence: 97%

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Interpretation and estimates of mean residence time with statistical moment theory

Kasuya¹,

Hirayama²,

Kubota³

et al. 1987

Biopharm & Drug Disp

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The definitions of mean residence time of drug molecules in the body (MRT) from the literature are reviewed. A formal definition of MRT, based on excretion of drug molecules and amount of drug, a parameter which is independent of constancy of both clearance and volume of distribution, is introduced and compared to other existing definitions of MRTs, that is, MRT for the two-compartment model, MRT for the stochastic model, and MRT based on amount in the body. The inherent assumptions of the methods for determining the various MRTs are discussed. Published information on coefficients and constants (Collier) which describe a biexponential drug decay in the systemic circulation were utilized to illustrate the similarities and differences in MRTs. MRTs were calculated from theoretical relationships as well as estimated from simulated data based on equivalent conditions. The MRTs based on area under the moment curve/area under the curve (AUMC/AUC) for the two-compartment model and AUC/C(0) for the stochastic model assume a constancy in clearance and in volume of distribution, respectively.

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Section: Numerical Examples T O Show Discrepancies In the Calculationsupporting

confidence: 52%

Section: Numerical Examples T O Show Discrepancies In the Calculationmentioning

confidence: 97%

Interpretation and estimates of mean residence time with statistical moment theory

Kasuya¹,

Hirayama²,

Kubota³

et al. 1987

Biopharm & Drug Disp

View full text Add to dashboard Cite

show abstract

“…(11) was obtained in a similar manner by Niazi, considering intravenous drug injection into multicompartment linear system with central elimination, and plasma concentration given as a sum of exponential terms. 16 The distribution volume A b (t)/C p (t) was considered as a function of time during the whole time course of drug, which eventually becomes time independent at terminal phase.…”

Section: Andmentioning

confidence: 99%

The Connection Between the Steady State (Vss) and Terminal (Vβ) Volumes of Distribution in Linear Pharmacokinetics and The General Proof That Vβ ≥ Vss

Berezhkovskiy

2007

Journal of Pharmaceutical Sciences

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“…It is worth noting that before achieving the equilibrium conditions between the peripheral and central compartments, the relationship between the amount of drug in the body and the measured plasma concentration is not proportional. For these preequilibrium conditions Niazi proposed a variable with time volume term (V t ), relating the drug plasma concentration to the amount of drug in the body at any given point of time (Equation (4)) [11]. In Equation (4), AUC 0!t is the partial area under the plasma concentration-time curve from time zero to t, AUC 0!1 is the area under the plasma concentration-time curve from time zero to infinity and C t is the plasma drug concentration at time t.…”

Section: Introductionmentioning

confidence: 99%

Critical analysis of the discrepancy betweenV? andVss for drugs exhibiting different two-compartment disposition profiles

Sobol¹,

Bialer²

2005

Biopharm. Drug Dispos.

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It is well known that in the two-compartment open body model the values of apparent volume of distribution (V(beta)) and volume of distribution at steady state (V(ss)) are never identical. There are at least two conditions when V(beta) significantly overestimates V(ss). The first is when most of a drug is eliminated relatively rapidly but a small fraction of the dose persists and gives rise to an extremely long half-life. The second is when a drug is rapidly cleared from the central compartment with a short half-life. The primary purpose of the current paper was to investigate how different two-compartment disposition profiles affect the magnitude of difference between V(beta) and V(ss). Novel equations have been developed that relate the V(beta)/V(ss) ratio to f1 (fraction of drug elimination associated with the distributive phase) and to beta/alpha (ratio of the exponential coefficients). This paper demonstrates mathematically that an increasing value of f1 is associated with a greater divergence between V(beta) and V(ss). A similar relationship was also found for the divergence between the terminal half-life (t(1/2beta)) and the mean residence time (MRT). An increase in the beta/alpha ratio results in a substantial decrease of this discrepancy and provides a maximal possible value, or an upper limit to the V(beta)/V(ss) ratio. The newly derived equations along with their graphical presentation may serve as an excellent predictive tool for checking the accuracy of the experimentally obtained values of V(beta) and V(ss).

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Volume of Distribution as a Function of Time

Cited by 54 publications

References 0 publications

Interpretation and estimates of mean residence time with statistical moment theory

Interpretation and estimates of mean residence time with statistical moment theory

The Connection Between the Steady State (Vss) and Terminal (Vβ) Volumes of Distribution in Linear Pharmacokinetics and The General Proof That Vβ ≥ Vss

Critical analysis of the discrepancy betweenV? andVss for drugs exhibiting different two-compartment disposition profiles

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