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 (V_D), also known as the apparent volume of distribution is a theoretical value (because the V_D 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, V_D may exceed total plasma volume.

Another clinical use is in the treatment of overdose.

Volume of Distribution Formula

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

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Steps on how to print your input & results:

1. Fill in the calculator/tool with your values and/or your answer choices and press Calculate.

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

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:

V_D = 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. V_D is expressed in L or indexed to body mass in L/Kg.

Variation of V_Dmainly 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 V_D between 4 and 7L are thought to be distributed throughout the blood (plasma and red blood cells). For V_Dlarger 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:

V_initial– V_D of the central compartment (from the rapid distribution phase);
V_extrap – V_D of the tissue compartment (from the elimination phase);
V_area– V_D extrapolated from the AUC of the concentration curve;
V_ss– V_D in a "steady state" model.

V_D 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 V_D	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 · 12:00 AM

Last Checked: June 8, 2020