tissue Examples If you administer a dose D of a drug intravenously in one go (IV-bolus), you would naturally expect it to have an immediate blood concentration which directly corresponds to the amount of blood contained in the body . Mathematically this would be: But this is generally not what happens. Instead you observe that the drug has distributed out into some other volume (read organs/tissue). So probably the first question you want to ask is: how much of the drug is no longer in the blood stream? The volume of distribution quantifies just that by specifying how big a volume you would need in order to observe the blood concentration actually measured. An example for a simple case (mono-compartmental) would be to administer D=8 mg/kg to a human. A human has a blood volume of around 0.08 L/kg . This gives a 100 µg/mL if the drug stays in the blood stream only, and thus its volume of distribution is the same as that is 0.08 L/kg. If the drug distributes into all body water the volume of distribution would increase to approximately 0.57 L/kg If the drug readily diffuses into the body fat the volume of distribution may increase dramatically, an example is chloroquine which has a 250-302 L/kg In the simple mono-compartmental case the volume of distribution is defined as: , where the in practice is an extrapolated concentration at time = 0 from the first early plasma concentrations after an IV-bolus administration (generally taken around 5 min - 30 min after giving the drug). Sample values and equations References External links Tutorial on volume of distribution Overview at icp.org.nz Overview at cornell.edu Overview at stanford.edu Overview at boomer.org Pharmacokinetics