Volume of Distribution Calculator

Determines the apparent volume needed to contain the total amount of an administered drug.

You can read more about the volume of distribution of a drug to the tissues in the text below the tool.


The volume of distribution (VD), also known as the apparent volume of distribution is a theoretical value (because the VD is not a physical space but a dilution space) that is calculated and used clinically to determine the loading dose that is required to achieve a desired concentration of a drug in the body at the same concentration as in the plasma. For drugs which accumulate outside the plasma, VD may exceed total plasma volume.

Another clinical use is in the treatment of overdose.


Volume of Distribution Formula

VD = Total amount of drug in the body / Drug blood plasma concentration


Measurement Type
Total amount of drug in the body
Drug blood plasma concentration
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Measurement Type
Amount of drug per Kg
Drug blood plasma concentration
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Volume of distribution explained

The volume of distribution (VD), also known as the apparent volume of distribution is a theoretical value (because the VD is not a physical space but a dilution space) that is calculated and used clinically to determine the loading dose that is required to achieve a desired blood concentration of a drug.

Volume of distribution is the apparent volume into which a drug disperses in order to produce the observed plasma concentration and has the following formula:

VD = Total amount of drug in the body / Drug blood plasma concentration

The above ratio assumes that the distribution of the drug between the tissues and the plasma is at equilibrium. VD is expressed in L or indexed to body mass in L/Kg.

Variation of VD mainly affects the peak plasma concentration of the drug. This is clinically important when peak plasma concentration is essential for the therapeutic effect

Drugs with a volume of distribution of 4L or less are thought to be confined to the plasma. Those with VD between 4 and 7L are thought to be distributed throughout the blood (plasma and red blood cells). For VD larger than 42L, the drug is thought to be distributed to all tissues in the body.

Depending on the timing of the observed plasma concentration, there are several types of volumes of distribution:

  • Vinitial – VD of the central compartment (from the rapid distribution phase);
  • Vextrap – VD of the tissue compartment (from the elimination phase);
  • Varea – VD extrapolated from the AUC of the concentration curve;
  • Vss – VD in a "steady state" model.

VD varies with individual height and weight, as well as accumulation of fat (for obese patients administered lipid-soluble drugs) or accumulation of fluids (in ascites, oedema or pleural effusion).

Main factors which influence the apparent volume of distribution

Category Factors
Measurement and pharmacokinetic modelling of VD Timing of measurements (see above)
Free vs. total drug levels (e.g. highly protein bound drugs)
Properties of the drug Molecule size and charge
pKa
Lipid solubility
Water solubility
Properties of the patient’s body fluids Body water volume
pH
Protein levels
Displacement
Physiology and pathological status Age
Gender
Pregnancy
Oedema
Ascites/ effusions
Effects of apparatus (e.g. dialysis, ECMO) Absorption on to apparatus
Volume expansion
 

References

Guyton AC. Textbook of Medical Physiology (5th ed.). Philadelphia: 1976.

Gibaldi M, McNamara PJ. Apparent volumes of distribution and drug binding to plasma proteins and tissues. European journal of clinical pharmacology 13.5 (1978): 373-378.

Wagner JG. Significance of ratios of different volumes of distribution in pharmacokinetics. Biopharmaceutics & drug disposition 4.3. 1983; 263-270.


Specialty: Pharmacology

Abbreviation: VD

Article By: Denise Nedea

Published On: June 8, 2020

Last Checked: June 8, 2020

Next Review: June 8, 2025