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 Volume of distribution - Definition 

The volume of distribution (VD) is a pharmacological term used to quantify the distribution of a drug throughout the body after oral or intravenous dosing. It is defined as the volume in which the amount of drug would need to be uniformly distributed to produce the observed blood concentration. It is given by the equation:


<math>{V_{D}} = \frac{total \ amount \ of \ drug \ in \ the \ body}{drug \ blood \ concentration}<math>


The VD is not a real volume; 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 VD may also be used to determine how readily a drug will displace into the body tissue compartments relative to the blood:

<math>{V_{D}} = {V_{P}} + {V_{T}} \left(\frac{fu}{fu_{t}}\right)<math>

Where:

VP = plasma volume

VT = apparent tissue volume

fu = fraction unbound in plasma

fuT = fraction unbound in tissue


Some examples:

Warfarin VD = 8L Reflects a high degree of plasma protein binding

Theophylline VD = 30L Represents distribution in total body water

Chloroquine VD = 15000L Shows highly lipophilic molecules which sequester into total body fat



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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Volume of distribution".