The initial volume of distribution (V
i) is a
pharmacological
Pharmacology is a branch of medicine, biology and pharmaceutical sciences concerned with drug or medication action, where a drug may be defined as any artificial, natural, or endogenous (from within the body) molecule which exerts a biochemica ...
term used to quantify the distribution of a
drug
A drug is any chemical substance that causes a change in an organism's physiology or psychology when consumed. Drugs are typically distinguished from food and substances that provide nutritional support. Consumption of drugs can be via insuffla ...
throughout the body relatively soon after oral or intravenous
dosing
Dosing generally applies to feeding chemicals or medicines when used in small quantities.
For medicines the term '' dose'' is generally used. In the case of inanimate objects the word dosing is typical. The term dose titration, referring to stepw ...
of a drug and prior to the drug reaching a
steady state equilibrium. Following distribution of the drug, measurement of blood levels indicate the
apparent volume of distribution. Calculation of the initial volume of distribution is the same calculation as that for the apparent
volume of distribution
In pharmacology, the volume of distribution (VD, also known as apparent volume of distribution, literally, ''volume of dilution'') is the theoretical volume that would be necessary to contain the total amount of an administered drug at the same c ...
, given by the equation:
:::::::
Therefore the dose required to give a certain plasma concentration can be determined if the V
D for that drug is known. The V
D is not a real volume; it is more a reflection of how a drug will distribute throughout the body depending on several
physicochemical
Physical chemistry is the study of macroscopic and microscopic phenomena in chemical systems in terms of the principles, practices, and concepts of physics such as motion, energy, force, time, thermodynamics, quantum chemistry, statistical mecha ...
properties, e.g. solubility, charge, size, etc. The V
D may also be used to determine how readily a drug will displace into the body tissue compartments relative to the blood:
:::::::
Where:
V
P = plasma volume
V
T = apparent tissue volume
fu = fraction unbound in plasma
fu
T = fraction unbound in tissue
References
{{DEFAULTSORT:Initial Volume Of Distribution
Pharmacokinetics
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