The apparent volume of distribution (Vd) of a drug exceeds total body fluid volume, if a drug is:
- The apparent volume of Distribution (Vd) = Dose administered by IV route/Plasma concentration.
- Consider the body as a single compartment in which the drug gets homogenously distributed. So it can be defined as, “The volume that would accommodate all the drug in the body if the concentration throughout was the same as in plasma.”
- In the case of lipid insoluble drugs, drugs do not enter the cells. So their V will be similar to ECF volume. 
- Drugs sequestrated in other tissues may have V much more than total body water or even body mass.
Sequestrated in body tissues
Slowly eliminated from body
Poorly soluble in plasma
Highly bound to plasma proteins