Use Apparent Vd when you need to estimate volume of distribution as the systemically available dose (administered dose times bioavailability) divided by plasma concentration. Enter Dose, Plasma concentration, and Bioavailability fraction using the definitions and units below so the result can be reproduced.

Dose

Administered dose in milligrams; must be greater than zero.

Plasma concentration

Measured plasma concentration in milligrams per litre; must be greater than zero.

Bioavailability fraction

Bioavailability fraction between zero and one; defaults to complete bioavailability.

The published tool contract uses this rule: Estimate volume of distribution as the systemically available dose (administered dose times bioavailability) divided by plasma concentration.^[1]

Apparent volume of distribution

Apparent volume of distribution in litres.

The output is an estimate tied to the stated model and coefficients; it is not a direct measurement and should retain that label when reported. It is informational and cannot diagnose a condition, select treatment, or replace professional interpretation of the original measurements. Bioavailability fraction must remain between 0 and 1.

Retain the original Dose, Plasma concentration, and Bioavailability fraction values and their units alongside the result. Volume Of Distribution is useful when you instead need to compute the apparent volume of distribution from a dose and plasma concentration. Plasma Volume mL provides another view by helping you compute the plasma volume as blood volume times one minus the hematocrit fraction.

• Volume Of Distribution

  Compute the apparent volume of distribution from a dose and plasma concentration.

• Plasma Volume mL

  Compute the plasma volume as blood volume times one minus the hematocrit fraction.

• Total Blood Volume Estimate

  Estimate total blood volume from body weight using the documented reference value of 70 millilitres per kilogram.