# 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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Steps on how to print your input & results:

2. Then you can click on the Print button to open a PDF in a separate window with the inputs and results. You can further save the PDF or print it.

Please note that once you have closed the PDF you need to click on the Calculate button before you try opening it again, otherwise the input and/or results may not appear in the pdf.

## 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 chargepKaLipid solubilityWater solubility Properties of the patient’s body fluids Body water volumepHProtein levelsDisplacement Physiology and pathological status AgeGenderPregnancyOedemaAscites/ effusions Effects of apparatus (e.g. dialysis, ECMO) Absorption on to apparatusVolume 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 · 12:00 AM

Last Checked: June 8, 2020

Next Review: June 8, 2025