The physiological significance of the apparent volume of distribution, Vdarea or Vd beta, in pharmacokinetic studies.

The definition and significance of the Vdarea or Vd beta are studied based on the physiological clearance or pharmacolinetic modeling theory. It was found that the Vdarea calculated by dividing the intravenous dose by the beta. AUC. (where beta is the terminal phase exponential rate constant and AUC is the total area under the systemic arterial or venous plasma concentration vs. time curve from time zero to time infinity) can only serve as a proportionality constant to relate the total amount of compound present in the body and its systemic arterial plasma concentration during the terminal phase. Its use with the systemic peripheral venous plasma concentration may result in a significant overestimation of the amount present in the body because of the existence of the potential arterial-venous plasma concentration difference. The above new definition of the V can also be applicable to compounds undergoing the pulmonary first-pass elimination.