Editing Volume of distribution (section)

==Equations==
The volume of distribution is given by the following equation:

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

Therefore, the dose required to give a certain plasma concentration can be determined if the V<sub>D</sub> for that drug is known. The V<sub>D</sub> 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.  As body composition changes with age, V<sub>D</sub> decreases.

The V<sub>D</sub> 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:

* V<sub>P</sub> = plasma volume
* V<sub>T</sub> = apparent tissue volume
* fu = fraction [[plasma protein binding|unbound in plasma]]
* fu<sub>T</sub> = fraction unbound in tissue