Volume of distribution

You don't need to be Editor-In-Chief to add or edit content to WikiDoc. You can begin to add to or edit text on this WikiDoc page by clicking on the edit button at the top of this page. Next enter or edit the information that you would like to appear here. Once you are done editing, scroll down and click the Save page button at the bottom of the page.

Jump to: navigation, search

The volume of distribution (VD) , also known as apparent volume of distribution, is a pharmacological term used to quantify the distribution of a medication throughout the body after oral or parenteral dosing. It is defined as the volume in which the amount of drug would need to be uniformly distributed in to produce the observed blood concentration.

Volume of distribution may be increased by renal failure (due to fluid retention) and liver failure (due to altered body fluid and plasma protein binding). Conversely it may be decreased in dehydration.

The initial volume of distribution describes blood concentrations prior to attaining the apparent volume of distribution and uses the same formula.

Equations

The volume of distribution is given by the following equation:

{V_{D}} = \frac{\mathrm{total \ amount \ of \ drug \ in \ the \ body}}{\mathrm{drug \ blood \ concentration}}
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 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 units for Volume of Distribution are typically reported in (ml, liter, or liter)/kg body weight. The fact that VD is a ratio of a theoretical volume to a fixed unit of body weight explains why the VD for children is typically higher than that for adults, even though children are smaller and weigh less. As body composition changes with age, VD decreases.

The VD may also be used to determine how readily a drug will displace into the body tissue compartments relative to the blood:

{V_{D}} = {V_{P}} + {V_{T}} \left(\frac{fu}{fu_{t}}\right)
Where:
  • VP = plasma volume
  • VT = apparent tissue volume
  • fu = fraction unbound in plasma
  • fuT = fraction unbound in tissue

Examples

Drug VD Comments
Warfarin 8L Reflects a high degree of plasma protein binding.
Theophylline, Ethanol 30L Represents distribution in total body water.
Chloroquine 15000L Shows highly lipophilic molecules which sequester into total body fat.
NXY-059 8L Highly-charged hydrophilic molecule.

External links

no:Distribusjonsvolum sv:Distributionsvolym th:ปริมาตรกระจายตัว


Acknowledgement and Attribution Regarding Sources of Content

Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .

Retrieved from "http://en.wikidoc.org/index.php/Volume_of_distribution"
Personal tools
In other languages