Volume of distribution


In pharmacology, the volume of distribution is the theoretical volume that would be necessary to contain the total amount of an administered drug at the same concentration that it is observed in the blood plasma.
Roughly speaking, the, as a property of a drug, measures the degree to which it is distributed in body tissue rather than the blood plasma. Drug properties which cause high include high lipid solubility, low rates of ionization, or low plasma protein binding capabilities. Disease states which increase include kidney failure and liver failure. Conversely, dehydration may decrease.
The initial volume of distribution describes blood concentrations prior to attaining the apparent volume of distribution and uses the same formula.

Motivation and equation

Suppose one administers an amount of drug intravascularly, then measures the drug concentration in blood . The volume of distribution is the quotient:
If the drug remains entirely intravascularly, will be identical to the blood volume. However, if a drug diffuses out of the intravascular space into the tissues or interstitium, the measured concentration will be lower-than-expected compared to a hypothetical intravascular-only drug. Therefore,, with a higher value corresponding to a greater tendency for the drug to exit the intravascular space.
One clinical utility is that the dose required to achieve a target plasma concentration can be determined if the for that drug is known.
The is not a physiological value; it is more a reflection of how a drug will distribute throughout the body depending on several physicochemical properties such as solubility, charge, size, etc.
The unit for may be reported extensively in litres, or intensively as litres-per-kilogram.
The may also be used to determine how readily a drug will displace into the body tissue compartments relative to the blood:
Where:
For example, chloroquine has much greater affinity for body fat than blood, resulting in a
compared to.