VD is directly proportional with the amount of drug distributed into tissue; a higher VD indicates a greater amount of tissue distribution.
A VD greater than the total volume of body water (approximately 42 liters in humans[5]) is possible, and would indicate that the drug is highly distributed into tissue.
[6] In rough terms, drugs with a high lipid solubility (non-polar drugs), low rates of ionization, or low plasma protein binding capabilities have higher volumes of distribution than drugs which are more polar, more highly ionized or exhibit high plasma protein binding in the body's environment.
Volume of distribution may be increased by kidney failure (due to fluid retention) and liver failure (due to altered body fluid and plasma protein binding).
The volume of distribution is given by the following equation: Therefore, the dose required to give a certain plasma concentration can be determined if the VD for that drug is known.
The VD is not a physiological value; it is more a reflection of how a drug will distribute throughout the body depending on several physicochemical properties, e.g. solubility, charge, size, etc.
The unit for Volume of Distribution is typically reported in litres.
The VD may also be used to determine how readily a drug will displace into the body tissue compartments relative to the blood: Where: If you administer a dose D of a drug intravenously in one go (IV-bolus), you would naturally expect it to have an immediate blood concentration
which directly corresponds to the amount of blood contained in the body
quantifies just that by specifying how big a volume you would need in order to observe the blood concentration actually measured.
100 μg/mL if the drug stays in the blood stream only, and thus its volume of distribution is the same as
0.57 L/kg [8] If the drug readily diffuses into the body fat the volume of distribution may increase dramatically, an example is chloroquine which has a
250-302 L/kg [9] In the simple mono-compartmental case the volume of distribution is defined as: