WordNet

a relative amount; "mix one volume of the solution with ten volumes of water"
the amount of 3-dimensional space occupied by an object; "the gas expanded to twice its original volume"
the magnitude of sound (usually in a specified direction); "the kids played their music at full volume" (同)loudness, intensity
a publication that is one of a set of several similar publications; "the third volume was missing"; "he asked for the 1989 volume of the Annual Review"
the spatial or geographic property of being scattered about over a range, area, or volume; "worldwide in distribution"; "the distribution of nerve fibers"; "in complementary distribution" (同)dispersion
the act of distributing or spreading or apportioning
the commercial activity of transporting and selling goods from a producer to a consumer
(statistics) an arrangement of values of a variable showing their observed or theoretical frequency of occurrence (同)statistical_distribution
furnished with volumes; "a large room volumed with ancient books"
(often used in combination) consisting of or having a given number or kind of volumes; "the poets volumed works"; "a two-volumed history"; "multi-volumed encyclopedias"; "large-volumed editions"
formed or rising in rounded masses; "gasping with the volumed smoke"

PrepTutorEJDIC

〈C〉(特に分厚い)『本』,書物 / 〈C〉(シリーズものの)『巻』,冊(《略》(単数形で)vol.,(複数形で)vols.) / 〈U〉(…の)『体積』,容積《+of+名》 / 〈U〉〈C〉)…の)『量』,かさ《+of+名》 / 〈U〉(…の)『音量』,音の強さ,ボリューム《+of+名》 / 《複数形で》多量(の…),たくさん(の…)《+of+名》
〈U〉(…への)『配分』,『分配』,配布,配達《+『to』+『名』》 / 〈U〉分布;分布区域 / 〈C〉配分されたもの,配給品 / 〈U〉(商品の)流通[組織,機構]
《所有・所属》…『の』,…のものである,…に属する・《材料・要素》…『でできた』,から成る・《部分》…『の』[『中の』] ・《数量・単位・種類を表す名詞に付いて》…の・《原因・動機》…『で』,のために(because of) ・《主格関係》…『の』,による,によって・《目的格関係》…『を』,の・《同格関係》…『という』・《関係・関連》…『についての』[『の』],の点で・《抽象名詞などと共に》…の[性質をもつ] ・《『It is』+『形』+『of』+『名』+『to』 doの形で,ofの後の名詞を意味上の主語として》・《分離》…『から』・《起原・出所》…『から』[『の』](out of) ・《『名』+『of』+『a』(『an』)+『名』の形で》…のような・《『名』+『of』+『mine』(『yours, his』など独立所有格)の形で》…の…・《時》(1)《副詞句を作って》…に《形容詞句を作って》…の・《時刻》《米》…前(to,《米》before)
OLD French古[代]フランス語

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/01/16 23:29:30」(JST)

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In pharmacology, the volume of distribution (V_D, also known as apparent 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.^[1] It is defined as the distribution of a medication between plasma and the rest of the body after oral or parenteral dosing.^[2]

The V_D of a drug represents the degree to which a drug is distributed in body tissue rather than the plasma. V_D is directly correlated with the amount of drug distributed into tissue; a higher V_D indicates a greater amount of tissue distribution. A V_D greater than the total volume of body water (approximately 42 liters in humans^[3]) is possible, and would indicate that the drug is highly distributed into tissue.

In rough terms, drugs with a high lipid solubility (non-polar drugs), low rates of ionization, or low plasma binding capabilities have higher volumes of distribution than drugs which are more polar, more highly ionized or exhibit high plasma binding in the body's environment. 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:

Therefore the dose required to give a certain plasma concentration can be determined if the V_D for that drug is known. The V_D is not a physiologic 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 liters. As body composition changes with age, V_D decreases.

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

Where:

V_P = plasma volume

V_T = apparent tissue volume

fu = fraction unbound in plasma

fu_T = fraction unbound in tissue

Examples

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 . Mathematically this would be:

But this is generally not what happens. Instead you observe that the drug has distributed out into some other volume (read organs/tissue). So probably the first question you want to ask is: how much of the drug is no longer in the blood stream? The volume of distribution quantifies just that by specifying how big a volume you would need in order to observe the blood concentration actually measured.

A practical example for a simple case (mono-compartmental) would be to administer D=8 mg/kg to a human. A human has a blood volume of around 0.08 l/kg .^[4] This gives a 100 µg/ml if the drug stays in the blood stream only, and thus its volume of distribution is the same as that is 0.08 l/kg. If the drug distributes into all body water the volume of distribution would increase to approximately 0.57 l/kg ^[5]

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 ^[6]

In the simple mono-compartmental case the volume of distribution is defined as: , where the in practice is an extrapolated concentration at time=0 from the first early plasma concentrations after an IV-bolus administration (generally taken around 5min - 30min after giving the drug).

Drug	V_D	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.

Sample values and equations

Characteristic	Description	Example value	Formula
Dose	Amount of drug administered.	500 mg	Design parameter
Dosing interval	Time between drug dose administrations.	24 h	Design parameter
C_max	The peak plasma concentration of a drug after administration.	60.9 mg/L	Direct measurement
t_max	Time to reach C_max.	3.9 h	Direct measurement
C_min	The lowest (trough) concentration that a drug reaches before the next dose is administered.	27.7 mg/L	Direct measurement
Volume of distribution	The apparent volume in which a drug is distributed (i.e., the parameter relating drug concentration to drug amount in the body).	6.0 L
Concentration	Amount of drug in a given volume of plasma.	83.3 mg/L
Elimination half-life	The time required for the concentration of the drug to reach half of its original value.	12 h
Elimination rate constant	The rate at which a drug is removed from the body.	0.0578 h⁻¹
Infusion rate	Rate of infusion required to balance elimination.	50 mg/h
Area under the curve	The integral of the concentration-time curve (after a single dose or in steady state).	1,320 mg/L·h
Area under the curve		1,320 mg/L·h
Clearance	The volume of plasma cleared of the drug per unit time.	0.38 L/h
Bioavailability	The systemically available fraction of a drug.	0.8
Fluctuation	Peak trough fluctuation within one dosing interval at steady state	41.8 %	where
[ v t e ]

References

^ http://sepia.unil.ch/pharmacology/?id=61
^ "vetmed.vt.edu".
^ http://www.anaesthesiamcq.com/FluidBook/fl2_1.php
^ Alberts, Bruce (2005). "Leukocyte functions and percentage breakdown". Molecular Biology of the Cell. NCBI Bookshelf. Retrieved 2007-04-14.
^ Guyton, Arthur C. (1976). Textbook of Medical Physiology (5th ed.). Philadelphia: W.B. Saunders. p. 424. ISBN 0-7216-4393-0.
^ Wetsteyn JC (1995). "The pharmacokinetics of three multiple dose regimens of chloroquine: implications for malaria chemoprophylaxis". Br J Clinical Pharmacology 39 (6): 696–9. PMC 1365086. PMID 7654492.

External links

Tutorial on volume of distribution
Overview at icp.org.nz
Overview at cornell.edu
Overview at stanford.edu
Overview at boomer.org

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